Annotation of embedaddon/dnsmasq/man/dnsmasq.8, revision 1.1.1.2
1.1 misho 1: .TH DNSMASQ 8
2: .SH NAME
3: dnsmasq \- A lightweight DHCP and caching DNS server.
4: .SH SYNOPSIS
5: .B dnsmasq
6: .I [OPTION]...
7: .SH "DESCRIPTION"
8: .BR dnsmasq
9: is a lightweight DNS, TFTP, PXE, router advertisement and DHCP server. It is intended to provide
10: coupled DNS and DHCP service to a LAN.
11: .PP
12: Dnsmasq accepts DNS queries and either answers them from a small, local,
13: cache or forwards them to a real, recursive, DNS server. It loads the
14: contents of /etc/hosts so that local hostnames
15: which do not appear in the global DNS can be resolved and also answers
1.1.1.2 ! misho 16: DNS queries for DHCP configured hosts. It can also act as the
! 17: authoritative DNS server for one or more domains, allowing local names
! 18: to appear in the global DNS. It can be configured to do DNSSEC
! 19: validation.
1.1 misho 20: .PP
21: The dnsmasq DHCP server supports static address assignments and multiple
22: networks. It automatically
23: sends a sensible default set of DHCP options, and can be configured to
24: send any desired set of DHCP options, including vendor-encapsulated
25: options. It includes a secure, read-only,
26: TFTP server to allow net/PXE boot of DHCP hosts and also supports BOOTP. The PXE support is full featured, and includes a proxy mode which supplies PXE information to clients whilst DHCP address allocation is done by another server.
27: .PP
28: The dnsmasq DHCPv6 server provides the same set of features as the
29: DHCPv4 server, and in addition, it includes router advertisements and
30: a neat feature which allows nameing for clients which use DHCPv4 and
31: stateless autoconfiguration only for IPv6 configuration. There is support for doing address allocation (both DHCPv6 and RA) from subnets which are dynamically delegated via DHCPv6 prefix delegation.
32: .PP
33: Dnsmasq is coded with small embedded systems in mind. It aims for the smallest possible memory footprint compatible with the supported functions, and allows uneeded functions to be omitted from the compiled binary.
34: .SH OPTIONS
35: Note that in general missing parameters are allowed and switch off
36: functions, for instance "--pid-file" disables writing a PID file. On
37: BSD, unless the GNU getopt library is linked, the long form of the
38: options does not work on the command line; it is still recognised in
39: the configuration file.
40: .TP
41: .B --test
42: Read and syntax check configuration file(s). Exit with code 0 if all
43: is OK, or a non-zero code otherwise. Do not start up dnsmasq.
44: .TP
45: .B \-h, --no-hosts
46: Don't read the hostnames in /etc/hosts.
47: .TP
48: .B \-H, --addn-hosts=<file>
49: Additional hosts file. Read the specified file as well as /etc/hosts. If -h is given, read
50: only the specified file. This option may be repeated for more than one
51: additional hosts file. If a directory is given, then read all the files contained in that directory.
52: .TP
53: .B \-E, --expand-hosts
54: Add the domain to simple names (without a period) in /etc/hosts
55: in the same way as for DHCP-derived names. Note that this does not
56: apply to domain names in cnames, PTR records, TXT records etc.
57: .TP
58: .B \-T, --local-ttl=<time>
59: When replying with information from /etc/hosts or the DHCP leases
60: file dnsmasq by default sets the time-to-live field to zero, meaning
61: that the requester should not itself cache the information. This is
62: the correct thing to do in almost all situations. This option allows a
63: time-to-live (in seconds) to be given for these replies. This will
64: reduce the load on the server at the expense of clients using stale
65: data under some circumstances.
66: .TP
67: .B --neg-ttl=<time>
68: Negative replies from upstream servers normally contain time-to-live
69: information in SOA records which dnsmasq uses for caching. If the
70: replies from upstream servers omit this information, dnsmasq does not
71: cache the reply. This option gives a default value for time-to-live
72: (in seconds) which dnsmasq uses to cache negative replies even in
73: the absence of an SOA record.
74: .TP
75: .B --max-ttl=<time>
76: Set a maximum TTL value that will be handed out to clients. The specified
77: maximum TTL will be given to clients instead of the true TTL value if it is
78: lower. The true TTL value is however kept in the cache to avoid flooding
79: the upstream DNS servers.
80: .TP
81: .B --max-cache-ttl=<time>
82: Set a maximum TTL value for entries in the cache.
83: .TP
84: .B --auth-ttl=<time>
85: Set the TTL value returned in answers from the authoritative server.
86: .TP
87: .B \-k, --keep-in-foreground
88: Do not go into the background at startup but otherwise run as
89: normal. This is intended for use when dnsmasq is run under daemontools
90: or launchd.
91: .TP
92: .B \-d, --no-daemon
93: Debug mode: don't fork to the background, don't write a pid file,
94: don't change user id, generate a complete cache dump on receipt on
95: SIGUSR1, log to stderr as well as syslog, don't fork new processes
96: to handle TCP queries. Note that this option is for use in debugging
97: only, to stop dnsmasq daemonising in production, use
98: .B -k.
99: .TP
100: .B \-q, --log-queries
101: Log the results of DNS queries handled by dnsmasq. Enable a full cache dump on receipt of SIGUSR1.
102: .TP
103: .B \-8, --log-facility=<facility>
104: Set the facility to which dnsmasq will send syslog entries, this
105: defaults to DAEMON, and to LOCAL0 when debug mode is in operation. If
106: the facility given contains at least one '/' character, it is taken to
107: be a filename, and dnsmasq logs to the given file, instead of
108: syslog. If the facility is '-' then dnsmasq logs to stderr.
109: (Errors whilst reading configuration will still go to syslog,
110: but all output from a successful startup, and all output whilst
111: running, will go exclusively to the file.) When logging to a file,
112: dnsmasq will close and reopen the file when it receives SIGUSR2. This
113: allows the log file to be rotated without stopping dnsmasq.
114: .TP
115: .B --log-async[=<lines>]
116: Enable asynchronous logging and optionally set the limit on the
117: number of lines
118: which will be queued by dnsmasq when writing to the syslog is slow.
119: Dnsmasq can log asynchronously: this
120: allows it to continue functioning without being blocked by syslog, and
121: allows syslog to use dnsmasq for DNS queries without risking deadlock.
122: If the queue of log-lines becomes full, dnsmasq will log the
123: overflow, and the number of messages lost. The default queue length is
124: 5, a sane value would be 5-25, and a maximum limit of 100 is imposed.
125: .TP
126: .B \-x, --pid-file=<path>
127: Specify an alternate path for dnsmasq to record its process-id in. Normally /var/run/dnsmasq.pid.
128: .TP
129: .B \-u, --user=<username>
130: Specify the userid to which dnsmasq will change after startup. Dnsmasq must normally be started as root, but it will drop root
131: privileges after startup by changing id to another user. Normally this user is "nobody" but that
132: can be over-ridden with this switch.
133: .TP
134: .B \-g, --group=<groupname>
135: Specify the group which dnsmasq will run
136: as. The defaults to "dip", if available, to facilitate access to
137: /etc/ppp/resolv.conf which is not normally world readable.
138: .TP
139: .B \-v, --version
140: Print the version number.
141: .TP
142: .B \-p, --port=<port>
143: Listen on <port> instead of the standard DNS port (53). Setting this
144: to zero completely disables DNS function, leaving only DHCP and/or TFTP.
145: .TP
146: .B \-P, --edns-packet-max=<size>
147: Specify the largest EDNS.0 UDP packet which is supported by the DNS
148: forwarder. Defaults to 4096, which is the RFC5625-recommended size.
149: .TP
150: .B \-Q, --query-port=<query_port>
151: Send outbound DNS queries from, and listen for their replies on, the
152: specific UDP port <query_port> instead of using random ports. NOTE
153: that using this option will make dnsmasq less secure against DNS
154: spoofing attacks but it may be faster and use less resources. Setting this option
155: to zero makes dnsmasq use a single port allocated to it by the
156: OS: this was the default behaviour in versions prior to 2.43.
157: .TP
158: .B --min-port=<port>
159: Do not use ports less than that given as source for outbound DNS
160: queries. Dnsmasq picks random ports as source for outbound queries:
161: when this option is given, the ports used will always to larger
162: than that specified. Useful for systems behind firewalls.
163: .TP
164: .B \-i, --interface=<interface name>
165: Listen only on the specified interface(s). Dnsmasq automatically adds
166: the loopback (local) interface to the list of interfaces to use when
167: the
168: .B \--interface
169: option is used. If no
170: .B \--interface
171: or
172: .B \--listen-address
173: options are given dnsmasq listens on all available interfaces except any
174: given in
175: .B \--except-interface
176: options. IP alias interfaces (eg "eth1:0") cannot be used with
177: .B --interface
178: or
179: .B --except-interface
180: options, use --listen-address instead. A simple wildcard, consisting
181: of a trailing '*', can be used in
182: .B \--interface
183: and
184: .B \--except-interface
185: options.
186: .TP
187: .B \-I, --except-interface=<interface name>
188: Do not listen on the specified interface. Note that the order of
189: .B \--listen-address
190: .B --interface
191: and
192: .B --except-interface
193: options does not matter and that
194: .B --except-interface
195: options always override the others.
196: .TP
197: .B --auth-server=<domain>,<interface>|<ip-address>
198: Enable DNS authoritative mode for queries arriving at an interface or address. Note that the interface or address
199: need not be mentioned in
200: .B --interface
201: or
202: .B --listen-address
203: configuration, indeed
204: .B --auth-server
1.1.1.2 ! misho 205: will overide these and provide a different DNS service on the
! 206: specified interface. The <domain> is the "glue record". It should
! 207: resolve in the global DNS to a A and/or AAAA record which points to
! 208: the address dnsmasq is listening on. When an interface is specified,
! 209: it may be qualified with "/4" or "/6" to specify only the IPv4 or IPv6
! 210: addresses associated with the interface.
! 211: .TP
! 212: .B --local-service
! 213: Accept DNS queries only from hosts whose address is on a local subnet,
! 214: ie a subnet for which an interface exists on the server. This option
! 215: only has effect is there are no --interface --except-interface,
! 216: --listen-address or --auth-server options. It is intended to be set as
! 217: a default on installation, to allow unconfigured installations to be
! 218: useful but also safe from being used for DNS amplification attacks.
1.1 misho 219: .TP
220: .B \-2, --no-dhcp-interface=<interface name>
221: Do not provide DHCP or TFTP on the specified interface, but do provide DNS service.
222: .TP
223: .B \-a, --listen-address=<ipaddr>
224: Listen on the given IP address(es). Both
225: .B \--interface
226: and
227: .B \--listen-address
228: options may be given, in which case the set of both interfaces and
229: addresses is used. Note that if no
230: .B \--interface
231: option is given, but
232: .B \--listen-address
233: is, dnsmasq will not automatically listen on the loopback
234: interface. To achieve this, its IP address, 127.0.0.1, must be
235: explicitly given as a
236: .B \--listen-address
237: option.
238: .TP
239: .B \-z, --bind-interfaces
240: On systems which support it, dnsmasq binds the wildcard address,
241: even when it is listening on only some interfaces. It then discards
242: requests that it shouldn't reply to. This has the advantage of
243: working even when interfaces come and go and change address. This
244: option forces dnsmasq to really bind only the interfaces it is
245: listening on. About the only time when this is useful is when
246: running another nameserver (or another instance of dnsmasq) on the
247: same machine. Setting this option also enables multiple instances of
248: dnsmasq which provide DHCP service to run in the same machine.
249: .TP
250: .B --bind-dynamic
251: Enable a network mode which is a hybrid between
252: .B --bind-interfaces
253: and the default. Dnsmasq binds the address of individual interfaces,
254: allowing multiple dnsmasq instances, but if new interfaces or
255: addresses appear, it automatically listens on those (subject to any
256: access-control configuration). This makes dynamically created
257: interfaces work in the same way as the default. Implementing this
258: option requires non-standard networking APIs and it is only available
259: under Linux. On other platforms it falls-back to --bind-interfaces mode.
260: .TP
261: .B \-y, --localise-queries
262: Return answers to DNS queries from /etc/hosts which depend on the interface over which the query was
263: received. If a name in /etc/hosts has more than one address associated with
264: it, and at least one of those addresses is on the same subnet as the
265: interface to which the query was sent, then return only the
266: address(es) on that subnet. This allows for a server to have multiple
267: addresses in /etc/hosts corresponding to each of its interfaces, and
268: hosts will get the correct address based on which network they are
269: attached to. Currently this facility is limited to IPv4.
270: .TP
271: .B \-b, --bogus-priv
272: Bogus private reverse lookups. All reverse lookups for private IP ranges (ie 192.168.x.x, etc)
273: which are not found in /etc/hosts or the DHCP leases file are answered
274: with "no such domain" rather than being forwarded upstream.
275: .TP
276: .B \-V, --alias=[<old-ip>]|[<start-ip>-<end-ip>],<new-ip>[,<mask>]
277: Modify IPv4 addresses returned from upstream nameservers; old-ip is
278: replaced by new-ip. If the optional mask is given then any address
279: which matches the masked old-ip will be re-written. So, for instance
280: .B --alias=1.2.3.0,6.7.8.0,255.255.255.0
281: will map 1.2.3.56 to 6.7.8.56 and 1.2.3.67 to 6.7.8.67. This is what
282: Cisco PIX routers call "DNS doctoring". If the old IP is given as
283: range, then only addresses in the range, rather than a whole subnet,
284: are re-written. So
285: .B --alias=192.168.0.10-192.168.0.40,10.0.0.0,255.255.255.0
286: maps 192.168.0.10->192.168.0.40 to 10.0.0.10->10.0.0.40
287: .TP
288: .B \-B, --bogus-nxdomain=<ipaddr>
289: Transform replies which contain the IP address given into "No such
290: domain" replies. This is intended to counteract a devious move made by
291: Verisign in September 2003 when they started returning the address of
292: an advertising web page in response to queries for unregistered names,
293: instead of the correct NXDOMAIN response. This option tells dnsmasq to
294: fake the correct response when it sees this behaviour. As at Sept 2003
295: the IP address being returned by Verisign is 64.94.110.11
296: .TP
297: .B \-f, --filterwin2k
298: Later versions of windows make periodic DNS requests which don't get sensible answers from
299: the public DNS and can cause problems by triggering dial-on-demand links. This flag turns on an option
300: to filter such requests. The requests blocked are for records of types SOA and SRV, and type ANY where the
301: requested name has underscores, to catch LDAP requests.
302: .TP
303: .B \-r, --resolv-file=<file>
304: Read the IP addresses of the upstream nameservers from <file>, instead of
305: /etc/resolv.conf. For the format of this file see
306: .BR resolv.conf (5).
307: The only lines relevant to dnsmasq are nameserver ones. Dnsmasq can
308: be told to poll more than one resolv.conf file, the first file name specified
309: overrides the default, subsequent ones add to the list. This is only
310: allowed when polling; the file with the currently latest modification
311: time is the one used.
312: .TP
313: .B \-R, --no-resolv
314: Don't read /etc/resolv.conf. Get upstream servers only from the command
315: line or the dnsmasq configuration file.
316: .TP
317: .B \-1, --enable-dbus[=<service-name>]
318: Allow dnsmasq configuration to be updated via DBus method calls. The
319: configuration which can be changed is upstream DNS servers (and
320: corresponding domains) and cache clear. Requires that dnsmasq has
321: been built with DBus support. If the service name is given, dnsmasq
322: provides service at that name, rather than the default which is
323: .B uk.org.thekelleys.dnsmasq
324: .TP
325: .B \-o, --strict-order
326: By default, dnsmasq will send queries to any of the upstream servers
327: it knows about and tries to favour servers that are known to
328: be up. Setting this flag forces dnsmasq to try each query with each
329: server strictly in the order they appear in /etc/resolv.conf
330: .TP
331: .B --all-servers
332: By default, when dnsmasq has more than one upstream server available,
333: it will send queries to just one server. Setting this flag forces
334: dnsmasq to send all queries to all available servers. The reply from
335: the server which answers first will be returned to the original requester.
336: .TP
337: .B --stop-dns-rebind
338: Reject (and log) addresses from upstream nameservers which are in the
339: private IP ranges. This blocks an attack where a browser behind a
340: firewall is used to probe machines on the local network.
341: .TP
342: .B --rebind-localhost-ok
343: Exempt 127.0.0.0/8 from rebinding checks. This address range is
344: returned by realtime black hole servers, so blocking it may disable
345: these services.
346: .TP
347: .B --rebind-domain-ok=[<domain>]|[[/<domain>/[<domain>/]
348: Do not detect and block dns-rebind on queries to these domains. The
349: argument may be either a single domain, or multiple domains surrounded
350: by '/', like the --server syntax, eg.
351: .B --rebind-domain-ok=/domain1/domain2/domain3/
352: .TP
353: .B \-n, --no-poll
354: Don't poll /etc/resolv.conf for changes.
355: .TP
356: .B --clear-on-reload
1.1.1.2 ! misho 357: Whenever /etc/resolv.conf is re-read or the upstream servers are set
! 358: via DBus, clear the DNS cache.
1.1 misho 359: This is useful when new nameservers may have different
360: data than that held in cache.
361: .TP
362: .B \-D, --domain-needed
363: Tells dnsmasq to never forward A or AAAA queries for plain names, without dots
364: or domain parts, to upstream nameservers. If the name is not known
365: from /etc/hosts or DHCP then a "not found" answer is returned.
366: .TP
367: .B \-S, --local, --server=[/[<domain>]/[domain/]][<ipaddr>[#<port>][@<source-ip>|<interface>[#<port>]]
368: Specify IP address of upstream servers directly. Setting this flag does
369: not suppress reading of /etc/resolv.conf, use -R to do that. If one or
370: more
371: optional domains are given, that server is used only for those domains
372: and they are queried only using the specified server. This is
373: intended for private nameservers: if you have a nameserver on your
374: network which deals with names of the form
375: xxx.internal.thekelleys.org.uk at 192.168.1.1 then giving the flag
376: .B -S /internal.thekelleys.org.uk/192.168.1.1
377: will send all queries for
378: internal machines to that nameserver, everything else will go to the
379: servers in /etc/resolv.conf. An empty domain specification,
380: .B //
381: has the special meaning of "unqualified names only" ie names without any
382: dots in them. A non-standard port may be specified as
383: part of the IP
384: address using a # character.
385: More than one -S flag is allowed, with
386: repeated domain or ipaddr parts as required.
387:
388: More specific domains take precendence over less specific domains, so:
389: .B --server=/google.com/1.2.3.4
390: .B --server=/www.google.com/2.3.4.5
391: will send queries for *.google.com to 1.2.3.4, except *www.google.com,
392: which will go to 2.3.4.5
393:
394: The special server address '#' means, "use the standard servers", so
395: .B --server=/google.com/1.2.3.4
396: .B --server=/www.google.com/#
397: will send queries for *.google.com to 1.2.3.4, except *www.google.com which will
398: be forwarded as usual.
399:
400: Also permitted is a -S
401: flag which gives a domain but no IP address; this tells dnsmasq that
402: a domain is local and it may answer queries from /etc/hosts or DHCP
403: but should never forward queries on that domain to any upstream
404: servers.
405: .B local
406: is a synonym for
407: .B server
408: to make configuration files clearer in this case.
409:
410: IPv6 addresses may include a %interface scope-id, eg
411: fe80::202:a412:4512:7bbf%eth0.
412:
413: The optional string after the @ character tells
414: dnsmasq how to set the source of the queries to this
415: nameserver. It should be an ip-address, which should belong to the machine on which
416: dnsmasq is running otherwise this server line will be logged and then
417: ignored, or an interface name. If an interface name is given, then
418: queries to the server will be forced via that interface; if an
419: ip-address is given then the source address of the queries will be set
420: to that address.
421: The query-port flag is ignored for any servers which have a
422: source address specified but the port may be specified directly as
423: part of the source address. Forcing queries to an interface is not
424: implemented on all platforms supported by dnsmasq.
425: .TP
1.1.1.2 ! misho 426: .B --rev-server=<ip-address>/<prefix-len>,<ipaddr>[#<port>][@<source-ip>|<interface>[#<port>]]
! 427: This is functionally the same as
! 428: .B --server,
! 429: but provides some syntactic sugar to make specifying address-to-name queries easier. For example
! 430: .B --rev-server=1.2.3.0/24,192.168.0.1
! 431: is exactly equivalent to
! 432: .B --server=/3.2.1.in-addr.arpa/192.168.0.1
! 433: .TP
1.1 misho 434: .B \-A, --address=/<domain>/[domain/]<ipaddr>
435: Specify an IP address to return for any host in the given domains.
436: Queries in the domains are never forwarded and always replied to
437: with the specified IP address which may be IPv4 or IPv6. To give
438: both IPv4 and IPv6 addresses for a domain, use repeated -A flags.
439: Note that /etc/hosts and DHCP leases override this for individual
440: names. A common use of this is to redirect the entire doubleclick.net
441: domain to some friendly local web server to avoid banner ads. The
442: domain specification works in the same was as for --server, with the
443: additional facility that /#/ matches any domain. Thus
444: --address=/#/1.2.3.4 will always return 1.2.3.4 for any query not
445: answered from /etc/hosts or DHCP and not sent to an upstream
446: nameserver by a more specific --server directive.
447: .TP
448: .B --ipset=/<domain>/[domain/]<ipset>[,<ipset>]
449: Places the resolved IP addresses of queries for the specified domains
450: in the specified netfilter ip sets. Domains and subdomains are matched
451: in the same way as --address. These ip sets must already exist. See
452: ipset(8) for more details.
453: .TP
454: .B \-m, --mx-host=<mx name>[[,<hostname>],<preference>]
455: Return an MX record named <mx name> pointing to the given hostname (if
456: given), or
457: the host specified in the --mx-target switch
458: or, if that switch is not given, the host on which dnsmasq
459: is running. The default is useful for directing mail from systems on a LAN
460: to a central server. The preference value is optional, and defaults to
461: 1 if not given. More than one MX record may be given for a host.
462: .TP
463: .B \-t, --mx-target=<hostname>
464: Specify the default target for the MX record returned by dnsmasq. See
465: --mx-host. If --mx-target is given, but not --mx-host, then dnsmasq
466: returns a MX record containing the MX target for MX queries on the
467: hostname of the machine on which dnsmasq is running.
468: .TP
469: .B \-e, --selfmx
470: Return an MX record pointing to itself for each local
471: machine. Local machines are those in /etc/hosts or with DHCP leases.
472: .TP
473: .B \-L, --localmx
474: Return an MX record pointing to the host given by mx-target (or the
475: machine on which dnsmasq is running) for each
476: local machine. Local machines are those in /etc/hosts or with DHCP
477: leases.
478: .TP
479: .B \-W, --srv-host=<_service>.<_prot>.[<domain>],[<target>[,<port>[,<priority>[,<weight>]]]]
480: Return a SRV DNS record. See RFC2782 for details. If not supplied, the
481: domain defaults to that given by
482: .B --domain.
483: The default for the target domain is empty, and the default for port
484: is one and the defaults for
485: weight and priority are zero. Be careful if transposing data from BIND
486: zone files: the port, weight and priority numbers are in a different
487: order. More than one SRV record for a given service/domain is allowed,
488: all that match are returned.
489: .TP
490: .B --host-record=<name>[,<name>....][<IPv4-address>],[<IPv6-address>]
491: Add A, AAAA and PTR records to the DNS. This adds one or more names to
492: the DNS with associated IPv4 (A) and IPv6 (AAAA) records. A name may
493: appear in more than one
494: .B host-record
495: and therefore be assigned more than one address. Only the first
496: address creates a PTR record linking the address to the name. This is
497: the same rule as is used reading hosts-files.
498: .B host-record
499: options are considered to be read before host-files, so a name
500: appearing there inhibits PTR-record creation if it appears in
501: hosts-file also. Unlike hosts-files, names are not expanded, even when
502: .B expand-hosts
503: is in effect. Short and long names may appear in the same
504: .B host-record,
505: eg.
506: .B --host-record=laptop,laptop.thekelleys.org,192.168.0.1,1234::100
507: .TP
508: .B \-Y, --txt-record=<name>[[,<text>],<text>]
509: Return a TXT DNS record. The value of TXT record is a set of strings,
510: so any number may be included, delimited by commas; use quotes to put
511: commas into a string. Note that the maximum length of a single string
512: is 255 characters, longer strings are split into 255 character chunks.
513: .TP
514: .B --ptr-record=<name>[,<target>]
515: Return a PTR DNS record.
516: .TP
517: .B --naptr-record=<name>,<order>,<preference>,<flags>,<service>,<regexp>[,<replacement>]
518: Return an NAPTR DNS record, as specified in RFC3403.
519: .TP
520: .B --cname=<cname>,<target>
521: Return a CNAME record which indicates that <cname> is really
522: <target>. There are significant limitations on the target; it must be a
523: DNS name which is known to dnsmasq from /etc/hosts (or additional
1.1.1.2 ! misho 524: hosts files), from DHCP, from --interface-name or from another
1.1 misho 525: .B --cname.
526: If the target does not satisfy this
527: criteria, the whole cname is ignored. The cname must be unique, but it
528: is permissable to have more than one cname pointing to the same target.
529: .TP
530: .B --dns-rr=<name>,<RR-number>,[<hex data>]
531: Return an arbitrary DNS Resource Record. The number is the type of the
532: record (which is always in the C_IN class). The value of the record is
533: given by the hex data, which may be of the form 01:23:45 or 01 23 45 or
534: 012345 or any mixture of these.
535: .TP
1.1.1.2 ! misho 536: .B --interface-name=<name>,<interface>[/4|/6]
1.1 misho 537: Return a DNS record associating the name with the primary address on
1.1.1.2 ! misho 538: the given interface. This flag specifies an A or AAAA record for the given
1.1 misho 539: name in the same way as an /etc/hosts line, except that the address is
1.1.1.2 ! misho 540: not constant, but taken from the given interface. The interface may be
! 541: followed by "/4" or "/6" to specify that only IPv4 or IPv6 addresses
! 542: of the interface should be used. If the interface is
1.1 misho 543: down, not configured or non-existent, an empty record is returned. The
544: matching PTR record is also created, mapping the interface address to
545: the name. More than one name may be associated with an interface
546: address by repeating the flag; in that case the first instance is used
547: for the reverse address-to-name mapping.
548: .TP
1.1.1.2 ! misho 549: .B --synth-domain=<domain>,<address range>[,<prefix>]
! 550: Create artificial A/AAAA and PTR records for an address range. The
! 551: records use the address, with periods (or colons for IPv6) replaced
! 552: with dashes.
! 553:
! 554: An example should make this clearer.
! 555: .B --synth-domain=thekelleys.org.uk,192.168.0.0/24,internal-
! 556: will result in a query for internal-192-168-0-56.thekelleys.org.uk returning
! 557: 192.168.0.56 and a reverse query vice versa. The same applies to IPv6,
! 558: but IPv6 addresses may start with '::'
! 559: but DNS labels may not start with '-' so in this case if no prefix is
! 560: configured a zero is added in front of the label. ::1 becomes 0--1.
! 561:
! 562: The address range can be of the form
! 563: <ip address>,<ip address> or <ip address>/<netmask>
! 564: .TP
1.1 misho 565: .B --add-mac
566: Add the MAC address of the requestor to DNS queries which are
567: forwarded upstream. This may be used to DNS filtering by the upstream
568: server. The MAC address can only be added if the requestor is on the same
569: subnet as the dnsmasq server. Note that the mechanism used to achieve this (an EDNS0 option)
570: is not yet standardised, so this should be considered
571: experimental. Also note that exposing MAC addresses in this way may
1.1.1.2 ! misho 572: have security and privacy implications. The warning about caching
! 573: given for --add-subnet applies to --add-mac too.
! 574: .TP
! 575: .B --add-subnet[[=<IPv4 prefix length>],<IPv6 prefix length>]
! 576: Add the subnet address of the requestor to the DNS queries which are
! 577: forwarded upstream. The amount of the address forwarded depends on the
! 578: prefix length parameter: 32 (128 for IPv6) forwards the whole address,
! 579: zero forwards none of it but still marks the request so that no
! 580: upstream nameserver will add client address information either. The
! 581: default is zero for both IPv4 and IPv6. Note that upstream nameservers
! 582: may be configured to return different results based on this
! 583: information, but the dnsmasq cache does not take account. If a dnsmasq
! 584: instance is configured such that different results may be encountered,
! 585: caching should be disabled.
1.1 misho 586: .TP
587: .B \-c, --cache-size=<cachesize>
588: Set the size of dnsmasq's cache. The default is 150 names. Setting the cache size to zero disables caching.
589: .TP
590: .B \-N, --no-negcache
591: Disable negative caching. Negative caching allows dnsmasq to remember
592: "no such domain" answers from upstream nameservers and answer
593: identical queries without forwarding them again.
594: .TP
595: .B \-0, --dns-forward-max=<queries>
596: Set the maximum number of concurrent DNS queries. The default value is
597: 150, which should be fine for most setups. The only known situation
598: where this needs to be increased is when using web-server log file
599: resolvers, which can generate large numbers of concurrent queries.
600: .TP
1.1.1.2 ! misho 601: .B --dnssec
! 602: Validate DNS replies and cache DNSSEC data. When forwarding DNS queries, dnsmasq requests the
! 603: DNSSEC records needed to validate the replies. The replies are validated and the result returned as
! 604: the Authenticated Data bit in the DNS packet. In addition the DNSSEC records are stored in the cache, making
! 605: validation by clients more efficient. Note that validation by clients is the most secure DNSSEC mode, but for
! 606: clients unable to do validation, use of the AD bit set by dnsmasq is useful, provided that the network between
! 607: the dnsmasq server and the client is trusted. Dnsmasq must be compiled with HAVE_DNSSEC enabled, and DNSSEC
! 608: trust anchors provided, see
! 609: .B --trust-anchor.
! 610: Because the DNSSEC validation process uses the cache, it is not
! 611: permitted to reduce the cache size below the default when DNSSEC is
! 612: enabled. The nameservers upstream of dnsmasq must be DNSSEC-capable,
! 613: ie capable of returning DNSSEC records with data. If they are not,
! 614: then dnsmasq will not be able to determine the trusted status of
! 615: answers. In the default mode, this menas that all replies will be
! 616: marked as untrusted. If
! 617: .B --dnssec-check-unsigned
! 618: is set and the upstream servers don't support DNSSEC, then DNS service will be entirely broken.
! 619: .TP
! 620: .B --trust-anchor=[<class>],<domain>,<key-tag>,<algorithm>,<digest-type>,<digest>
! 621: Provide DS records to act a trust anchors for DNSSEC
! 622: validation. Typically these will be the DS record(s) for Zone Signing
! 623: key(s) of the root zone,
! 624: but trust anchors for limited domains are also possible. The current
! 625: root-zone trust anchors may be donwloaded from https://data.iana.org/root-anchors/root-anchors.xml
! 626: .TP
! 627: .B --dnssec-check-unsigned
! 628: As a default, dnsmasq does not check that unsigned DNS replies are
! 629: legitimate: they are assumed to be valid and passed on (without the
! 630: "authentic data" bit set, of course). This does not protect against an
! 631: attacker forging unsigned replies for signed DNS zones, but it is
! 632: fast. If this flag is set, dnsmasq will check the zones of unsigned
! 633: replies, to ensure that unsigned replies are allowed in those
! 634: zones. The cost of this is more upstream queries and slower
! 635: performance. See also the warning about upstream servers in the
! 636: section on
! 637: .B --dnssec
! 638: .TP
! 639: .B --dnssec-no-timecheck
! 640: DNSSEC signatures are only valid for specified time windows, and should be rejected outside those windows. This generates an
! 641: interesting chicken-and-egg problem for machines which don't have a hardware real time clock. For these machines to determine the correct
! 642: time typically requires use of NTP and therefore DNS, but validating DNS requires that the correct time is already known. Setting this flag
! 643: removes the time-window checks (but not other DNSSEC validation.) only until the dnsmasq process receives SIGHUP. The intention is
! 644: that dnsmasq should be started with this flag when the platform determines that reliable time is not currently available. As soon as
! 645: reliable time is established, a SIGHUP should be sent to dnsmasq, which enables time checking, and purges the cache of DNS records
! 646: which have not been throughly checked.
! 647: .TP
1.1 misho 648: .B --proxy-dnssec
1.1.1.2 ! misho 649: Copy the DNSSEC Authenticated Data bit from upstream servers to downstream clients and cache it. This is an
! 650: alternative to having dnsmasq validate DNSSEC, but it depends on the security of the network between
! 651: dnsmasq and the upstream servers, and the trustworthiness of the upstream servers.
! 652: .TP
! 653: .B --dnssec-debug
! 654: Set debugging mode for the DNSSEC validation, set the Checking Disabled bit on upstream queries,
! 655: and don't convert replies which do not validate to responses with
! 656: a return code of SERVFAIL. Note that
! 657: setting this may affect DNS behaviour in bad ways, it is not an
! 658: extra-logging flag and should not be set in production.
1.1 misho 659: .TP
1.1.1.2 ! misho 660: .B --auth-zone=<domain>[,<subnet>[/<prefix length>][,<subnet>[/<prefix length>].....]]
1.1 misho 661: Define a DNS zone for which dnsmasq acts as authoritative server. Locally defined DNS records which are in the domain
1.1.1.2 ! misho 662: will be served. If subnet(s) are given, A and AAAA records must be in one of the
! 663: specified subnets.
! 664:
! 665: As alternative to directly specifying the subnets, it's possible to
! 666: give the name of an interface, in which case the subnets implied by
! 667: that interface's configured addresses and netmask/prefix-length are
! 668: used; this is useful when using constructed DHCP ranges as the actual
! 669: address is dynamic and not known when configuring dnsmasq. The
! 670: interface addresses may be confined to only IPv6 addresses using
! 671: <interface>/6 or to only IPv4 using <interface>/4. This is useful when
! 672: an interface has dynamically determined global IPv6 addresses which should
! 673: appear in the zone, but RFC1918 IPv4 addresses which should not.
! 674: Interface-name and address-literal subnet specifications may be used
! 675: freely in the same --auth-zone declaration.
! 676:
! 677: The subnet(s) are also used to define in-addr.arpa and
! 678: ip6.arpa domains which are served for reverse-DNS queries. If not
! 679: specified, the prefix length defaults to 24 for IPv4 and 64 for IPv6.
! 680: For IPv4 subnets, the prefix length should be have the value 8, 16 or 24
! 681: unless you are familiar with RFC 2317 and have arranged the
! 682: in-addr.arpa delegation accordingly. Note that if no subnets are
! 683: specified, then no reverse queries are answered.
1.1 misho 684: .TP
685: .B --auth-soa=<serial>[,<hostmaster>[,<refresh>[,<retry>[,<expiry>]]]]
686: Specify fields in the SOA record associated with authoritative
687: zones. Note that this is optional, all the values are set to sane defaults.
688: .TP
689: .B --auth-sec-servers=<domain>[,<domain>[,<domain>...]]
690: Specify any secondary servers for a zone for which dnsmasq is
691: authoritative. These servers must be configured to get zone data from
692: dnsmasq by zone transfer, and answer queries for the same
693: authoritative zones as dnsmasq.
694: .TP
695: .B --auth-peer=<ip-address>[,<ip-address>[,<ip-address>...]]
696: Specify the addresses of secondary servers which are allowed to
697: initiate zone transfer (AXFR) requests for zones for which dnsmasq is
698: authoritative. If this option is not given, then AXFR requests will be
699: accepted from any secondary.
700: .TP
701: .B --conntrack
702: Read the Linux connection track mark associated with incoming DNS
703: queries and set the same mark value on upstream traffic used to answer
704: those queries. This allows traffic generated by dnsmasq to be
705: associated with the queries which cause it, useful for bandwidth
706: accounting and firewalling. Dnsmasq must have conntrack support
707: compiled in and the kernel must have conntrack support
708: included and configured. This option cannot be combined with
709: --query-port.
710: .TP
711: .B \-F, --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-addr>[,<end-addr>][,<mode>][,<netmask>[,<broadcast>]][,<lease time>]
712: .TP
713: .B \-F, --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-IPv6addr>[,<end-IPv6addr>|constructor:<interface>][,<mode>][,<prefix-len>][,<lease time>]
714:
715: Enable the DHCP server. Addresses will be given out from the range
716: <start-addr> to <end-addr> and from statically defined addresses given
717: in
718: .B dhcp-host
719: options. If the lease time is given, then leases
720: will be given for that length of time. The lease time is in seconds,
721: or minutes (eg 45m) or hours (eg 1h) or "infinite". If not given,
722: the default lease time is one hour. The
723: minimum lease time is two minutes. For IPv6 ranges, the lease time
724: maybe "deprecated"; this sets the preferred lifetime sent in a DHCP
725: lease or router advertisement to zero, which causes clients to use
726: other addresses, if available, for new connections as a prelude to renumbering.
727:
728: This option may be repeated, with different addresses, to enable DHCP
729: service to more than one network. For directly connected networks (ie,
730: networks on which the machine running dnsmasq has an interface) the
731: netmask is optional: dnsmasq will determine it from the interface
732: configuration. For networks which receive DHCP service via a relay
733: agent, dnsmasq cannot determine the netmask itself, so it should be
734: specified, otherwise dnsmasq will have to guess, based on the class (A, B or
735: C) of the network address. The broadcast address is
736: always optional. It is always
737: allowed to have more than one dhcp-range in a single subnet.
738:
739: For IPv6, the parameters are slightly different: instead of netmask
1.1.1.2 ! misho 740: and broadcast address, there is an optional prefix length which must
! 741: be equal to or larger then the prefix length on the local interface. If not
1.1 misho 742: given, this defaults to 64. Unlike the IPv4 case, the prefix length is not
743: automatically derived from the interface configuration. The mimimum
744: size of the prefix length is 64.
745:
746: IPv6 (only) supports another type of range. In this, the start address and optional end address contain only the network part (ie ::1) and they are followed by
747: .B constructor:<interface>.
748: This forms a template which describes how to create ranges, based on the addresses assigned to the interface. For instance
749:
750: .B --dhcp-range=::1,::400,constructor:eth0
751:
1.1.1.2 ! misho 752: will look for addresses on
! 753: eth0 and then create a range from <network>::1 to <network>::400. If
! 754: the interface is assigned more than one network, then the
! 755: corresponding ranges will be automatically created, and then
! 756: deprecated and finally removed again as the address is deprecated and
! 757: then deleted. The interface name may have a final "*" wildcard. Note
! 758: that just any address on eth0 will not do: it must not be an
! 759: autoconfigured or privacy address, or be deprecated.
! 760:
! 761: If a dhcp-range is only being used for stateless DHCP and/or SLAAC,
! 762: then the address can be simply ::
! 763:
! 764: .B --dhcp-range=::,constructor:eth0
! 765:
1.1 misho 766:
767: The optional
768: .B set:<tag>
769: sets an alphanumeric label which marks this network so that
770: dhcp options may be specified on a per-network basis.
771: When it is prefixed with 'tag:' instead, then its meaning changes from setting
772: a tag to matching it. Only one tag may be set, but more than one tag
773: may be matched.
774:
775: The optional <mode> keyword may be
776: .B static
777: which tells dnsmasq to enable DHCP for the network specified, but not
778: to dynamically allocate IP addresses: only hosts which have static
779: addresses given via
780: .B dhcp-host
781: or from /etc/ethers will be served. A static-only subnet with address
782: all zeros may be used as a "catch-all" address to enable replies to all
783: Information-request packets on a subnet which is provided with
784: stateless DHCPv6, ie
1.1.1.2 ! misho 785: .B --dhcp-range=::,static
1.1 misho 786:
787: For IPv4, the <mode> may be
788: .B proxy
789: in which case dnsmasq will provide proxy-DHCP on the specified
790: subnet. (See
791: .B pxe-prompt
792: and
793: .B pxe-service
794: for details.)
795:
796: For IPv6, the mode may be some combination of
797: .B ra-only, slaac, ra-names, ra-stateless.
798:
799: .B ra-only
800: tells dnsmasq to offer Router Advertisement only on this subnet,
801: and not DHCP.
802:
803: .B slaac
804: tells dnsmasq to offer Router Advertisement on this subnet and to set
805: the A bit in the router advertisement, so that the client will use
806: SLAAC addresses. When used with a DHCP range or static DHCP address
807: this results in the client having both a DHCP-assigned and a SLAAC
808: address.
809:
810: .B ra-stateless
811: sends router advertisements with the O and A bits set, and provides a
812: stateless DHCP service. The client will use a SLAAC address, and use
813: DHCP for other configuration information.
814:
815: .B ra-names
816: enables a mode
817: which gives DNS names to dual-stack hosts which do SLAAC for
818: IPv6. Dnsmasq uses the host's IPv4 lease to derive the name, network
819: segment and MAC address and assumes that the host will also have an
820: IPv6 address calculated using the SLAAC algorithm, on the same network
821: segment. The address is pinged, and if a reply is received, an AAAA
822: record is added to the DNS for this IPv6
823: address. Note that this is only happens for directly-connected
824: networks, (not one doing DHCP via a relay) and it will not work
825: if a host is using privacy extensions.
826: .B ra-names
827: can be combined with
828: .B ra-stateless
829: and
830: .B slaac.
831:
832: .TP
833: .B \-G, --dhcp-host=[<hwaddr>][,id:<client_id>|*][,set:<tag>][,<ipaddr>][,<hostname>][,<lease_time>][,ignore]
834: Specify per host parameters for the DHCP server. This allows a machine
835: with a particular hardware address to be always allocated the same
836: hostname, IP address and lease time. A hostname specified like this
837: overrides any supplied by the DHCP client on the machine. It is also
838: allowable to omit the hardware address and include the hostname, in
839: which case the IP address and lease times will apply to any machine
840: claiming that name. For example
841: .B --dhcp-host=00:20:e0:3b:13:af,wap,infinite
842: tells dnsmasq to give
843: the machine with hardware address 00:20:e0:3b:13:af the name wap, and
844: an infinite DHCP lease.
845: .B --dhcp-host=lap,192.168.0.199
846: tells
847: dnsmasq to always allocate the machine lap the IP address
848: 192.168.0.199.
849:
850: Addresses allocated like this are not constrained to be
851: in the range given by the --dhcp-range option, but they must be in
852: the same subnet as some valid dhcp-range. For
853: subnets which don't need a pool of dynamically allocated addresses,
854: use the "static" keyword in the dhcp-range declaration.
855:
1.1.1.2 ! misho 856: It is allowed to use client identifiers (called client
! 857: DUID in IPv6-land rather than
1.1 misho 858: hardware addresses to identify hosts by prefixing with 'id:'. Thus:
859: .B --dhcp-host=id:01:02:03:04,.....
860: refers to the host with client identifier 01:02:03:04. It is also
861: allowed to specify the client ID as text, like this:
862: .B --dhcp-host=id:clientidastext,.....
863:
864: A single
865: .B dhcp-host
866: may contain an IPv4 address or an IPv6 address, or both. IPv6 addresses must be bracketed by square brackets thus:
867: .B --dhcp-host=laptop,[1234::56]
868: IPv6 addresses may contain only the host-identifier part:
869: .B --dhcp-host=laptop,[::56]
870: in which case they act as wildcards in constructed dhcp ranges, with
871: the appropriate network part inserted.
1.1.1.2 ! misho 872: Note that in IPv6 DHCP, the hardware address may not be
! 873: available, though it normally is for direct-connected clients, or
! 874: clients using DHCP relays which support RFC 6939.
1.1 misho 875:
1.1.1.2 ! misho 876:
! 877: For DHCPv4, the special option id:* means "ignore any client-id
1.1 misho 878: and use MAC addresses only." This is useful when a client presents a client-id sometimes
879: but not others.
880:
881: If a name appears in /etc/hosts, the associated address can be
882: allocated to a DHCP lease, but only if a
883: .B --dhcp-host
884: option specifying the name also exists. Only one hostname can be
885: given in a
886: .B dhcp-host
887: option, but aliases are possible by using CNAMEs. (See
888: .B --cname
889: ).
890:
891: The special keyword "ignore"
892: tells dnsmasq to never offer a DHCP lease to a machine. The machine
893: can be specified by hardware address, client ID or hostname, for
894: instance
895: .B --dhcp-host=00:20:e0:3b:13:af,ignore
896: This is
897: useful when there is another DHCP server on the network which should
898: be used by some machines.
899:
1.1.1.2 ! misho 900: The set:<tag> construct sets the tag
1.1 misho 901: whenever this dhcp-host directive is in use. This can be used to
902: selectively send DHCP options just for this host. More than one tag
903: can be set in a dhcp-host directive (but not in other places where
904: "set:<tag>" is allowed). When a host matches any
905: dhcp-host directive (or one implied by /etc/ethers) then the special
906: tag "known" is set. This allows dnsmasq to be configured to
907: ignore requests from unknown machines using
908: .B --dhcp-ignore=tag:!known
909: Ethernet addresses (but not client-ids) may have
910: wildcard bytes, so for example
911: .B --dhcp-host=00:20:e0:3b:13:*,ignore
912: will cause dnsmasq to ignore a range of hardware addresses. Note that
913: the "*" will need to be escaped or quoted on a command line, but not
914: in the configuration file.
915:
916: Hardware addresses normally match any
917: network (ARP) type, but it is possible to restrict them to a single
918: ARP type by preceding them with the ARP-type (in HEX) and "-". so
919: .B --dhcp-host=06-00:20:e0:3b:13:af,1.2.3.4
920: will only match a
921: Token-Ring hardware address, since the ARP-address type for token ring
922: is 6.
923:
924: As a special case, in DHCPv4, it is possible to include more than one
925: hardware address. eg:
926: .B --dhcp-host=11:22:33:44:55:66,12:34:56:78:90:12,192.168.0.2
927: This allows an IP address to be associated with
928: multiple hardware addresses, and gives dnsmasq permission to abandon a
929: DHCP lease to one of the hardware addresses when another one asks for
930: a lease. Beware that this is a dangerous thing to do, it will only
931: work reliably if only one of the hardware addresses is active at any
932: time and there is no way for dnsmasq to enforce this. It is, for instance,
933: useful to allocate a stable IP address to a laptop which
934: has both wired and wireless interfaces.
935: .TP
936: .B --dhcp-hostsfile=<path>
937: Read DHCP host information from the specified file. If a directory
938: is given, then read all the files contained in that directory. The file contains
939: information about one host per line. The format of a line is the same
940: as text to the right of '=' in --dhcp-host. The advantage of storing DHCP host information
941: in this file is that it can be changed without re-starting dnsmasq:
942: the file will be re-read when dnsmasq receives SIGHUP.
943: .TP
944: .B --dhcp-optsfile=<path>
945: Read DHCP option information from the specified file. If a directory
946: is given, then read all the files contained in that directory. The advantage of
947: using this option is the same as for --dhcp-hostsfile: the
948: dhcp-optsfile will be re-read when dnsmasq receives SIGHUP. Note that
949: it is possible to encode the information in a
950: .B --dhcp-boot
951: flag as DHCP options, using the options names bootfile-name,
952: server-ip-address and tftp-server. This allows these to be included
953: in a dhcp-optsfile.
954: .TP
955: .B \-Z, --read-ethers
956: Read /etc/ethers for information about hosts for the DHCP server. The
957: format of /etc/ethers is a hardware address, followed by either a
958: hostname or dotted-quad IP address. When read by dnsmasq these lines
959: have exactly the same effect as
960: .B --dhcp-host
961: options containing the same information. /etc/ethers is re-read when
962: dnsmasq receives SIGHUP. IPv6 addresses are NOT read from /etc/ethers.
963: .TP
964: .B \-O, --dhcp-option=[tag:<tag>,[tag:<tag>,]][encap:<opt>,][vi-encap:<enterprise>,][vendor:[<vendor-class>],][<opt>|option:<opt-name>|option6:<opt>|option6:<opt-name>],[<value>[,<value>]]
965: Specify different or extra options to DHCP clients. By default,
966: dnsmasq sends some standard options to DHCP clients, the netmask and
967: broadcast address are set to the same as the host running dnsmasq, and
968: the DNS server and default route are set to the address of the machine
969: running dnsmasq. (Equivalent rules apply for IPv6.) If the domain name option has been set, that is sent.
970: This configuration allows these defaults to be overridden,
971: or other options specified. The option, to be sent may be given as a
972: decimal number or as "option:<option-name>" The option numbers are
973: specified in RFC2132 and subsequent RFCs. The set of option-names
974: known by dnsmasq can be discovered by running "dnsmasq --help dhcp".
975: For example, to set the default route option to
976: 192.168.4.4, do
977: .B --dhcp-option=3,192.168.4.4
978: or
979: .B --dhcp-option = option:router, 192.168.4.4
980: and to set the time-server address to 192.168.0.4, do
981: .B --dhcp-option = 42,192.168.0.4
982: or
983: .B --dhcp-option = option:ntp-server, 192.168.0.4
1.1.1.2 ! misho 984: The special address 0.0.0.0 is taken to mean "the address of the
! 985: machine running dnsmasq".
! 986:
! 987: Data types allowed are comma separated
! 988: dotted-quad IPv4 addresses, []-wrapped IPv6 addresses, a decimal number, colon-separated hex digits
1.1 misho 989: and a text string. If the optional tags are given then
990: this option is only sent when all the tags are matched.
991:
992: Special processing is done on a text argument for option 119, to
993: conform with RFC 3397. Text or dotted-quad IP addresses as arguments
994: to option 120 are handled as per RFC 3361. Dotted-quad IP addresses
995: which are followed by a slash and then a netmask size are encoded as
996: described in RFC 3442.
997:
998: IPv6 options are specified using the
999: .B option6:
1000: keyword, followed by the option number or option name. The IPv6 option
1001: name space is disjoint from the IPv4 option name space. IPv6 addresses
1002: in options must be bracketed with square brackets, eg.
1003: .B --dhcp-option=option6:ntp-server,[1234::56]
1.1.1.2 ! misho 1004: For IPv6, [::] means "the global address of
! 1005: the machine running dnsmasq", whilst [fd00::] is replaced with the
! 1006: ULA, if it exists, and [fe80::] with the link-local address.
1.1 misho 1007:
1008: Be careful: no checking is done that the correct type of data for the
1009: option number is sent, it is quite possible to
1010: persuade dnsmasq to generate illegal DHCP packets with injudicious use
1011: of this flag. When the value is a decimal number, dnsmasq must determine how
1012: large the data item is. It does this by examining the option number and/or the
1013: value, but can be overridden by appending a single letter flag as follows:
1014: b = one byte, s = two bytes, i = four bytes. This is mainly useful with
1015: encapsulated vendor class options (see below) where dnsmasq cannot
1016: determine data size from the option number. Option data which
1017: consists solely of periods and digits will be interpreted by dnsmasq
1018: as an IP address, and inserted into an option as such. To force a
1019: literal string, use quotes. For instance when using option 66 to send
1020: a literal IP address as TFTP server name, it is necessary to do
1021: .B --dhcp-option=66,"1.2.3.4"
1022:
1023: Encapsulated Vendor-class options may also be specified (IPv4 only) using
1024: --dhcp-option: for instance
1025: .B --dhcp-option=vendor:PXEClient,1,0.0.0.0
1026: sends the encapsulated vendor
1027: class-specific option "mftp-address=0.0.0.0" to any client whose
1028: vendor-class matches "PXEClient". The vendor-class matching is
1029: substring based (see --dhcp-vendorclass for details). If a
1030: vendor-class option (number 60) is sent by dnsmasq, then that is used
1031: for selecting encapsulated options in preference to any sent by the
1032: client. It is
1033: possible to omit the vendorclass completely;
1034: .B --dhcp-option=vendor:,1,0.0.0.0
1035: in which case the encapsulated option is always sent.
1036:
1037: Options may be encapsulated (IPv4 only) within other options: for instance
1038: .B --dhcp-option=encap:175, 190, "iscsi-client0"
1039: will send option 175, within which is the option 190. If multiple
1040: options are given which are encapsulated with the same option number
1041: then they will be correctly combined into one encapsulated option.
1042: encap: and vendor: are may not both be set in the same dhcp-option.
1043:
1044: The final variant on encapsulated options is "Vendor-Identifying
1045: Vendor Options" as specified by RFC3925. These are denoted like this:
1046: .B --dhcp-option=vi-encap:2, 10, "text"
1047: The number in the vi-encap: section is the IANA enterprise number
1048: used to identify this option. This form of encapsulation is supported
1049: in IPv6.
1050:
1051: The address 0.0.0.0 is not treated specially in
1052: encapsulated options.
1053: .TP
1054: .B --dhcp-option-force=[tag:<tag>,[tag:<tag>,]][encap:<opt>,][vi-encap:<enterprise>,][vendor:[<vendor-class>],]<opt>,[<value>[,<value>]]
1055: This works in exactly the same way as
1056: .B --dhcp-option
1057: except that the option will always be sent, even if the client does
1058: not ask for it in the parameter request list. This is sometimes
1059: needed, for example when sending options to PXELinux.
1060: .TP
1061: .B --dhcp-no-override
1062: (IPv4 only) Disable re-use of the DHCP servername and filename fields as extra
1063: option space. If it can, dnsmasq moves the boot server and filename
1064: information (from dhcp-boot) out of their dedicated fields into
1065: DHCP options. This make extra space available in the DHCP packet for
1066: options but can, rarely, confuse old or broken clients. This flag
1067: forces "simple and safe" behaviour to avoid problems in such a case.
1068: .TP
1.1.1.2 ! misho 1069: .B --dhcp-relay=<local address>,<server address>[,<interface]
! 1070: Configure dnsmasq to do DHCP relay. The local address is an address
! 1071: allocated to an interface on the host running dnsmasq. All DHCP
! 1072: requests arriving on that interface will we relayed to a remote DHCP
! 1073: server at the server address. It is possible to relay from a single local
! 1074: address to multiple remote servers by using multiple dhcp-relay
! 1075: configs with the same local address and different server
! 1076: addresses. A server address must be an IP literal address, not a
! 1077: domain name. In the case of DHCPv6, the server address may be the
! 1078: ALL_SERVERS multicast address, ff05::1:3. In this case the interface
! 1079: must be given, not be wildcard, and is used to direct the multicast to the
! 1080: correct interface to reach the DHCP server.
! 1081:
! 1082: Access control for DHCP clients has the same rules as for the DHCP
! 1083: server, see --interface, --except-interface, etc. The optional
! 1084: interface name in the dhcp-relay config has a different function: it
! 1085: controls on which interface DHCP replies from the server will be
! 1086: accepted. This is intended for configurations which have three
! 1087: interfaces: one being relayed from, a second connecting the DHCP
! 1088: server, and a third untrusted network, typically the wider
! 1089: internet. It avoids the possibility of spoof replies arriving via this
! 1090: third interface.
! 1091:
! 1092: It is allowed to have dnsmasq act as a DHCP server on one set of
! 1093: interfaces and relay from a disjoint set of interfaces. Note that
! 1094: whilst it is quite possible to write configurations which appear to
! 1095: act as a server and a relay on the same interface, this is not
! 1096: supported: the relay function will take precedence.
! 1097:
! 1098: Both DHCPv4 and DHCPv6 relay is supported. It's not possible to relay
! 1099: DHCPv4 to a DHCPv6 server or vice-versa.
! 1100: .TP
1.1 misho 1101: .B \-U, --dhcp-vendorclass=set:<tag>,[enterprise:<IANA-enterprise number>,]<vendor-class>
1102: Map from a vendor-class string to a tag. Most DHCP clients provide a
1103: "vendor class" which represents, in some sense, the type of host. This option
1104: maps vendor classes to tags, so that DHCP options may be selectively delivered
1105: to different classes of hosts. For example
1106: .B dhcp-vendorclass=set:printers,Hewlett-Packard JetDirect
1107: will allow options to be set only for HP printers like so:
1108: .B --dhcp-option=tag:printers,3,192.168.4.4
1109: The vendor-class string is
1110: substring matched against the vendor-class supplied by the client, to
1111: allow fuzzy matching. The set: prefix is optional but allowed for
1112: consistency.
1113:
1114: Note that in IPv6 only, vendorclasses are namespaced with an
1115: IANA-allocated enterprise number. This is given with enterprise:
1116: keyword and specifies that only vendorclasses matching the specified
1117: number should be searched.
1118: .TP
1119: .B \-j, --dhcp-userclass=set:<tag>,<user-class>
1120: Map from a user-class string to a tag (with substring
1121: matching, like vendor classes). Most DHCP clients provide a
1122: "user class" which is configurable. This option
1123: maps user classes to tags, so that DHCP options may be selectively delivered
1124: to different classes of hosts. It is possible, for instance to use
1125: this to set a different printer server for hosts in the class
1126: "accounts" than for hosts in the class "engineering".
1127: .TP
1128: .B \-4, --dhcp-mac=set:<tag>,<MAC address>
1.1.1.2 ! misho 1129: Map from a MAC address to a tag. The MAC address may include
1.1 misho 1130: wildcards. For example
1131: .B --dhcp-mac=set:3com,01:34:23:*:*:*
1132: will set the tag "3com" for any host whose MAC address matches the pattern.
1133: .TP
1134: .B --dhcp-circuitid=set:<tag>,<circuit-id>, --dhcp-remoteid=set:<tag>,<remote-id>
1135: Map from RFC3046 relay agent options to tags. This data may
1136: be provided by DHCP relay agents. The circuit-id or remote-id is
1137: normally given as colon-separated hex, but is also allowed to be a
1138: simple string. If an exact match is achieved between the circuit or
1139: agent ID and one provided by a relay agent, the tag is set.
1140:
1141: .B dhcp-remoteid
1142: (but not dhcp-circuitid) is supported in IPv6.
1143: .TP
1144: .B --dhcp-subscrid=set:<tag>,<subscriber-id>
1145: (IPv4 and IPv6) Map from RFC3993 subscriber-id relay agent options to tags.
1146: .TP
1147: .B --dhcp-proxy[=<ip addr>]......
1148: (IPv4 only) A normal DHCP relay agent is only used to forward the initial parts of
1149: a DHCP interaction to the DHCP server. Once a client is configured, it
1150: communicates directly with the server. This is undesirable if the
1.1.1.2 ! misho 1151: relay agent is adding extra information to the DHCP packets, such as
1.1 misho 1152: that used by
1153: .B dhcp-circuitid
1154: and
1155: .B dhcp-remoteid.
1156: A full relay implementation can use the RFC 5107 serverid-override
1157: option to force the DHCP server to use the relay as a full proxy, with all
1158: packets passing through it. This flag provides an alternative method
1159: of doing the same thing, for relays which don't support RFC
1160: 5107. Given alone, it manipulates the server-id for all interactions
1161: via relays. If a list of IP addresses is given, only interactions via
1162: relays at those addresses are affected.
1163: .TP
1164: .B --dhcp-match=set:<tag>,<option number>|option:<option name>|vi-encap:<enterprise>[,<value>]
1165: Without a value, set the tag if the client sends a DHCP
1166: option of the given number or name. When a value is given, set the tag only if
1167: the option is sent and matches the value. The value may be of the form
1.1.1.2 ! misho 1168: "01:ff:*:02" in which case the value must match (apart from wildcards)
1.1 misho 1169: but the option sent may have unmatched data past the end of the
1170: value. The value may also be of the same form as in
1171: .B dhcp-option
1172: in which case the option sent is treated as an array, and one element
1173: must match, so
1174:
1175: --dhcp-match=set:efi-ia32,option:client-arch,6
1176:
1177: will set the tag "efi-ia32" if the the number 6 appears in the list of
1178: architectures sent by the client in option 93. (See RFC 4578 for
1179: details.) If the value is a string, substring matching is used.
1180:
1.1.1.2 ! misho 1181: The special form with vi-encap:<enterprise number> matches against
1.1 misho 1182: vendor-identifying vendor classes for the specified enterprise. Please
1183: see RFC 3925 for more details of these rare and interesting beasts.
1184: .TP
1185: .B --tag-if=set:<tag>[,set:<tag>[,tag:<tag>[,tag:<tag>]]]
1186: Perform boolean operations on tags. Any tag appearing as set:<tag> is set if
1187: all the tags which appear as tag:<tag> are set, (or unset when tag:!<tag> is used)
1188: If no tag:<tag> appears set:<tag> tags are set unconditionally.
1189: Any number of set: and tag: forms may appear, in any order.
1190: Tag-if lines ares executed in order, so if the tag in tag:<tag> is a
1191: tag set by another
1192: .B tag-if,
1193: the line which sets the tag must precede the one which tests it.
1194: .TP
1195: .B \-J, --dhcp-ignore=tag:<tag>[,tag:<tag>]
1196: When all the given tags appear in the tag set ignore the host and do
1197: not allocate it a DHCP lease.
1198: .TP
1199: .B --dhcp-ignore-names[=tag:<tag>[,tag:<tag>]]
1200: When all the given tags appear in the tag set, ignore any hostname
1201: provided by the host. Note that, unlike dhcp-ignore, it is permissible
1202: to supply no tags, in which case DHCP-client supplied hostnames
1203: are always ignored, and DHCP hosts are added to the DNS using only
1204: dhcp-host configuration in dnsmasq and the contents of /etc/hosts and
1205: /etc/ethers.
1206: .TP
1207: .B --dhcp-generate-names=tag:<tag>[,tag:<tag>]
1208: (IPv4 only) Generate a name for DHCP clients which do not otherwise have one,
1.1.1.2 ! misho 1209: using the MAC address expressed in hex, separated by dashes. Note that
1.1 misho 1210: if a host provides a name, it will be used by preference to this,
1211: unless
1212: .B --dhcp-ignore-names
1213: is set.
1214: .TP
1215: .B --dhcp-broadcast[=tag:<tag>[,tag:<tag>]]
1216: (IPv4 only) When all the given tags appear in the tag set, always use broadcast to
1217: communicate with the host when it is unconfigured. It is permissible
1218: to supply no tags, in which case this is unconditional. Most DHCP clients which
1219: need broadcast replies set a flag in their requests so that this
1220: happens automatically, some old BOOTP clients do not.
1221: .TP
1222: .B \-M, --dhcp-boot=[tag:<tag>,]<filename>,[<servername>[,<server address>|<tftp_servername>]]
1223: (IPv4 only) Set BOOTP options to be returned by the DHCP server. Server name and
1224: address are optional: if not provided, the name is left empty, and the
1225: address set to the address of the machine running dnsmasq. If dnsmasq
1226: is providing a TFTP service (see
1227: .B --enable-tftp
1228: ) then only the filename is required here to enable network booting.
1229: If the optional tag(s) are given,
1230: they must match for this configuration to be sent.
1231: Instead of an IP address, the TFTP server address can be given as a domain
1232: name which is looked up in /etc/hosts. This name can be associated in
1233: /etc/hosts with multiple IP addresses, which are used round-robin.
1234: This facility can be used to load balance the tftp load among a set of servers.
1235: .TP
1236: .B --dhcp-sequential-ip
1237: Dnsmasq is designed to choose IP addresses for DHCP clients using a
1238: hash of the client's MAC address. This normally allows a client's
1239: address to remain stable long-term, even if the client sometimes allows its DHCP
1240: lease to expire. In this default mode IP addresses are distributed
1241: pseudo-randomly over the entire available address range. There are
1242: sometimes circumstances (typically server deployment) where it is more
1243: convenient to have IP
1244: addresses allocated sequentially, starting from the lowest available
1245: address, and setting this flag enables this mode. Note that in the
1246: sequential mode, clients which allow a lease to expire are much more
1247: likely to move IP address; for this reason it should not be generally used.
1248: .TP
1249: .B --pxe-service=[tag:<tag>,]<CSA>,<menu text>[,<basename>|<bootservicetype>][,<server address>|<server_name>]
1250: Most uses of PXE boot-ROMS simply allow the PXE
1251: system to obtain an IP address and then download the file specified by
1252: .B dhcp-boot
1253: and execute it. However the PXE system is capable of more complex
1254: functions when supported by a suitable DHCP server.
1255:
1256: This specifies a boot option which may appear in a PXE boot menu. <CSA> is
1257: client system type, only services of the correct type will appear in a
1258: menu. The known types are x86PC, PC98, IA64_EFI, Alpha, Arc_x86,
1259: Intel_Lean_Client, IA32_EFI, BC_EFI, Xscale_EFI and X86-64_EFI; an
1260: integer may be used for other types. The
1261: parameter after the menu text may be a file name, in which case dnsmasq acts as a
1262: boot server and directs the PXE client to download the file by TFTP,
1263: either from itself (
1264: .B enable-tftp
1265: must be set for this to work) or another TFTP server if the final server
1266: address/name is given.
1267: Note that the "layer"
1268: suffix (normally ".0") is supplied by PXE, and should not be added to
1269: the basename. If an integer boot service type, rather than a basename
1270: is given, then the PXE client will search for a
1271: suitable boot service for that type on the network. This search may be done
1272: by broadcast, or direct to a server if its IP address/name is provided.
1273: If no boot service type or filename is provided (or a boot service type of 0 is specified)
1274: then the menu entry will abort the net boot procedure and
1275: continue booting from local media. The server address can be given as a domain
1276: name which is looked up in /etc/hosts. This name can be associated in
1277: /etc/hosts with multiple IP addresses, which are used round-robin.
1278: .TP
1279: .B --pxe-prompt=[tag:<tag>,]<prompt>[,<timeout>]
1280: Setting this provides a prompt to be displayed after PXE boot. If the
1281: timeout is given then after the
1282: timeout has elapsed with no keyboard input, the first available menu
1283: option will be automatically executed. If the timeout is zero then the first available menu
1284: item will be executed immediately. If
1285: .B pxe-prompt
1.1.1.2 ! misho 1286: is omitted the system will wait for user input if there are multiple
1.1 misho 1287: items in the menu, but boot immediately if
1288: there is only one. See
1289: .B pxe-service
1290: for details of menu items.
1291:
1292: Dnsmasq supports PXE "proxy-DHCP", in this case another DHCP server on
1293: the network is responsible for allocating IP addresses, and dnsmasq
1294: simply provides the information given in
1295: .B pxe-prompt
1296: and
1297: .B pxe-service
1298: to allow netbooting. This mode is enabled using the
1299: .B proxy
1300: keyword in
1301: .B dhcp-range.
1302: .TP
1303: .B \-X, --dhcp-lease-max=<number>
1304: Limits dnsmasq to the specified maximum number of DHCP leases. The
1305: default is 1000. This limit is to prevent DoS attacks from hosts which
1306: create thousands of leases and use lots of memory in the dnsmasq
1307: process.
1308: .TP
1309: .B \-K, --dhcp-authoritative
1310: Should be set when dnsmasq is definitely the only DHCP server on a network.
1311: For DHCPv4, it changes the behaviour from strict RFC compliance so that DHCP requests on
1312: unknown leases from unknown hosts are not ignored. This allows new hosts
1313: to get a lease without a tedious timeout under all circumstances. It also
1314: allows dnsmasq to rebuild its lease database without each client needing to
1315: reacquire a lease, if the database is lost. For DHCPv6 it sets the
1316: priority in replies to 255 (the maximum) instead of 0 (the minimum).
1317: .TP
1318: .B --dhcp-alternate-port[=<server port>[,<client port>]]
1319: (IPv4 only) Change the ports used for DHCP from the default. If this option is
1320: given alone, without arguments, it changes the ports used for DHCP
1321: from 67 and 68 to 1067 and 1068. If a single argument is given, that
1322: port number is used for the server and the port number plus one used
1323: for the client. Finally, two port numbers allows arbitrary
1324: specification of both server and client ports for DHCP.
1325: .TP
1326: .B \-3, --bootp-dynamic[=<network-id>[,<network-id>]]
1327: (IPv4 only) Enable dynamic allocation of IP addresses to BOOTP clients. Use this
1328: with care, since each address allocated to a BOOTP client is leased
1329: forever, and therefore becomes permanently unavailable for re-use by
1330: other hosts. if this is given without tags, then it unconditionally
1331: enables dynamic allocation. With tags, only when the tags are all
1332: set. It may be repeated with different tag sets.
1333: .TP
1334: .B \-5, --no-ping
1335: (IPv4 only) By default, the DHCP server will attempt to ensure that an address in
1336: not in use before allocating it to a host. It does this by sending an
1337: ICMP echo request (aka "ping") to the address in question. If it gets
1338: a reply, then the address must already be in use, and another is
1339: tried. This flag disables this check. Use with caution.
1340: .TP
1341: .B --log-dhcp
1342: Extra logging for DHCP: log all the options sent to DHCP clients and
1343: the tags used to determine them.
1344: .TP
1.1.1.2 ! misho 1345: .B --quiet-dhcp, --quiet-dhcp6, --quiet-ra
! 1346: Suppress logging of the routine operation of these protocols. Errors and
! 1347: problems will still be logged. --quiet-dhcp and quiet-dhcp6 are
! 1348: over-ridden by --log-dhcp.
! 1349: .TP
1.1 misho 1350: .B \-l, --dhcp-leasefile=<path>
1351: Use the specified file to store DHCP lease information.
1352: .TP
1353: .B --dhcp-duid=<enterprise-id>,<uid>
1354: (IPv6 only) Specify the server persistent UID which the DHCPv6 server
1355: will use. This option is not normally required as dnsmasq creates a
1356: DUID automatically when it is first needed. When given, this option
1357: provides dnsmasq the data required to create a DUID-EN type DUID. Note
1358: that once set, the DUID is stored in the lease database, so to change between DUID-EN and
1359: automatically created DUIDs or vice-versa, the lease database must be
1360: re-intialised. The enterprise-id is assigned by IANA, and the uid is a
1361: string of hex octets unique to a particular device.
1362: .TP
1363: .B \-6 --dhcp-script=<path>
1364: Whenever a new DHCP lease is created, or an old one destroyed, or a
1365: TFTP file transfer completes, the
1366: executable specified by this option is run. <path>
1367: must be an absolute pathname, no PATH search occurs.
1368: The arguments to the process
1369: are "add", "old" or "del", the MAC
1370: address of the host (or DUID for IPv6) , the IP address, and the hostname,
1371: if known. "add" means a lease has been created, "del" means it has
1372: been destroyed, "old" is a notification of an existing lease when
1373: dnsmasq starts or a change to MAC address or hostname of an existing
1374: lease (also, lease length or expiry and client-id, if leasefile-ro is set).
1375: If the MAC address is from a network type other than ethernet,
1376: it will have the network type prepended, eg "06-01:23:45:67:89:ab" for
1377: token ring. The process is run as root (assuming that dnsmasq was originally run as
1378: root) even if dnsmasq is configured to change UID to an unprivileged user.
1379:
1380: The environment is inherited from the invoker of dnsmasq, with some or
1381: all of the following variables added
1382:
1383: For both IPv4 and IPv6:
1384:
1385: DNSMASQ_DOMAIN if the fully-qualified domain name of the host is
1386: known, this is set to the domain part. (Note that the hostname passed
1387: to the script as an argument is never fully-qualified.)
1388:
1389: If the client provides a hostname, DNSMASQ_SUPPLIED_HOSTNAME
1390:
1391: If the client provides user-classes, DNSMASQ_USER_CLASS0..DNSMASQ_USER_CLASSn
1392:
1393: If dnsmasq was compiled with HAVE_BROKEN_RTC, then
1394: the length of the lease (in seconds) is stored in
1395: DNSMASQ_LEASE_LENGTH, otherwise the time of lease expiry is stored in
1396: DNSMASQ_LEASE_EXPIRES. The number of seconds until lease expiry is
1397: always stored in DNSMASQ_TIME_REMAINING.
1398:
1399: If a lease used to have a hostname, which is
1400: removed, an "old" event is generated with the new state of the lease,
1401: ie no name, and the former name is provided in the environment
1402: variable DNSMASQ_OLD_HOSTNAME.
1403:
1404: DNSMASQ_INTERFACE stores the name of
1405: the interface on which the request arrived; this is not set for "old"
1406: actions when dnsmasq restarts.
1407:
1408: DNSMASQ_RELAY_ADDRESS is set if the client
1409: used a DHCP relay to contact dnsmasq and the IP address of the relay
1410: is known.
1411:
1412: DNSMASQ_TAGS contains all the tags set during the
1413: DHCP transaction, separated by spaces.
1414:
1415: DNSMASQ_LOG_DHCP is set if
1416: .B --log-dhcp
1417: is in effect.
1418:
1419: For IPv4 only:
1420:
1421: DNSMASQ_CLIENT_ID if the host provided a client-id.
1422:
1423: DNSMASQ_CIRCUIT_ID, DNSMASQ_SUBSCRIBER_ID, DNSMASQ_REMOTE_ID if a
1424: DHCP relay-agent added any of these options.
1425:
1426: If the client provides vendor-class, DNSMASQ_VENDOR_CLASS.
1427:
1428: For IPv6 only:
1429:
1430: If the client provides vendor-class, DNSMASQ_VENDOR_CLASS_ID,
1431: containing the IANA enterprise id for the class, and
1432: DNSMASQ_VENDOR_CLASS0..DNSMASQ_VENDOR_CLASSn for the data.
1433:
1434: DNSMASQ_SERVER_DUID containing the DUID of the server: this is the same for
1435: every call to the script.
1436:
1437: DNSMASQ_IAID containing the IAID for the lease. If the lease is a
1438: temporary allocation, this is prefixed to 'T'.
1439:
1.1.1.2 ! misho 1440: DNSMASQ_MAC containing the MAC address of the client, if known.
1.1 misho 1441:
1442: Note that the supplied hostname, vendorclass and userclass data is
1443: only supplied for
1444: "add" actions or "old" actions when a host resumes an existing lease,
1445: since these data are not held in dnsmasq's lease
1446: database.
1447:
1448:
1449:
1450: All file descriptors are
1451: closed except stdin, stdout and stderr which are open to /dev/null
1452: (except in debug mode).
1453:
1454: The script is not invoked concurrently: at most one instance
1455: of the script is ever running (dnsmasq waits for an instance of script to exit
1456: before running the next). Changes to the lease database are which
1457: require the script to be invoked are queued awaiting exit of a running instance.
1458: If this queueing allows multiple state changes occur to a single
1459: lease before the script can be run then
1460: earlier states are discarded and the current state of that lease is
1461: reflected when the script finally runs.
1462:
1463: At dnsmasq startup, the script will be invoked for
1464: all existing leases as they are read from the lease file. Expired
1465: leases will be called with "del" and others with "old". When dnsmasq
1466: receives a HUP signal, the script will be invoked for existing leases
1467: with an "old " event.
1468:
1469:
1470: There are two further actions which may appear as the first argument
1471: to the script, "init" and "tftp". More may be added in the future, so
1472: scripts should be written to ignore unknown actions. "init" is
1473: described below in
1474: .B --leasefile-ro
1475: The "tftp" action is invoked when a TFTP file transfer completes: the
1476: arguments are the file size in bytes, the address to which the file
1477: was sent, and the complete pathname of the file.
1478:
1479: .TP
1480: .B --dhcp-luascript=<path>
1481: Specify a script written in Lua, to be run when leases are created,
1482: destroyed or changed. To use this option, dnsmasq must be compiled
1483: with the correct support. The Lua interpreter is intialised once, when
1484: dnsmasq starts, so that global variables persist between lease
1485: events. The Lua code must define a
1486: .B lease
1487: function, and may provide
1488: .B init
1489: and
1490: .B shutdown
1491: functions, which are called, without arguments when dnsmasq starts up
1492: and terminates. It may also provide a
1493: .B tftp
1494: function.
1495:
1496: The
1497: .B lease
1498: function receives the information detailed in
1499: .B --dhcp-script.
1500: It gets two arguments, firstly the action, which is a string
1501: containing, "add", "old" or "del", and secondly a table of tag value
1502: pairs. The tags mostly correspond to the environment variables
1503: detailed above, for instance the tag "domain" holds the same data as
1504: the environment variable DNSMASQ_DOMAIN. There are a few extra tags
1505: which hold the data supplied as arguments to
1506: .B --dhcp-script.
1507: These are
1508: .B mac_address, ip_address
1509: and
1510: .B hostname
1511: for IPv4, and
1512: .B client_duid, ip_address
1513: and
1514: .B hostname
1515: for IPv6.
1516:
1517: The
1518: .B tftp
1519: function is called in the same way as the lease function, and the
1520: table holds the tags
1521: .B destination_address,
1522: .B file_name
1523: and
1524: .B file_size.
1525: .TP
1526: .B --dhcp-scriptuser
1527: Specify the user as which to run the lease-change script or Lua script. This defaults to root, but can be changed to another user using this flag.
1528: .TP
1529: .B \-9, --leasefile-ro
1530: Completely suppress use of the lease database file. The file will not
1531: be created, read, or written. Change the way the lease-change
1532: script (if one is provided) is called, so that the lease database may
1533: be maintained in external storage by the script. In addition to the
1534: invocations given in
1535: .B --dhcp-script
1536: the lease-change script is called once, at dnsmasq startup, with the
1537: single argument "init". When called like this the script should write
1538: the saved state of the lease database, in dnsmasq leasefile format, to
1539: stdout and exit with zero exit code. Setting this
1540: option also forces the leasechange script to be called on changes
1541: to the client-id and lease length and expiry time.
1542: .TP
1543: .B --bridge-interface=<interface>,<alias>[,<alias>]
1544: Treat DHCP request packets arriving at any of the <alias> interfaces
1545: as if they had arrived at <interface>. This option is necessary when
1546: using "old style" bridging on BSD platforms, since
1547: packets arrive at tap interfaces which don't have an IP address.
1548: .TP
1549: .B \-s, --domain=<domain>[,<address range>[,local]]
1550: Specifies DNS domains for the DHCP server. Domains may be be given
1551: unconditionally (without the IP range) or for limited IP ranges. This has two effects;
1552: firstly it causes the DHCP server to return the domain to any hosts
1553: which request it, and secondly it sets the domain which it is legal
1554: for DHCP-configured hosts to claim. The intention is to constrain
1555: hostnames so that an untrusted host on the LAN cannot advertise
1556: its name via dhcp as e.g. "microsoft.com" and capture traffic not
1557: meant for it. If no domain suffix is specified, then any DHCP
1558: hostname with a domain part (ie with a period) will be disallowed
1559: and logged. If suffix is specified, then hostnames with a domain
1560: part are allowed, provided the domain part matches the suffix. In
1561: addition, when a suffix is set then hostnames without a domain
1562: part have the suffix added as an optional domain part. Eg on my network I can set
1563: .B --domain=thekelleys.org.uk
1564: and have a machine whose DHCP hostname is "laptop". The IP address for that machine is available from
1565: .B dnsmasq
1566: both as "laptop" and "laptop.thekelleys.org.uk". If the domain is
1567: given as "#" then the domain is read from the first "search" directive
1568: in /etc/resolv.conf (or equivalent).
1569:
1570: The address range can be of the form
1571: <ip address>,<ip address> or <ip address>/<netmask> or just a single
1572: <ip address>. See
1573: .B --dhcp-fqdn
1574: which can change the behaviour of dnsmasq with domains.
1575:
1576: If the address range is given as ip-address/network-size, then a
1577: additional flag "local" may be supplied which has the effect of adding
1578: --local declarations for forward and reverse DNS queries. Eg.
1579: .B --domain=thekelleys.org.uk,192.168.0.0/24,local
1580: is identical to
1581: .B --domain=thekelleys.org.uk,192.168.0.0/24
1582: --local=/thekelleys.org.uk/ --local=/0.168.192.in-addr.arpa/
1583: The network size must be 8, 16 or 24 for this to be legal.
1584: .TP
1585: .B --dhcp-fqdn
1586: In the default mode, dnsmasq inserts the unqualified names of
1587: DHCP clients into the DNS. For this reason, the names must be unique,
1588: even if two clients which have the same name are in different
1589: domains. If a second DHCP client appears which has the same name as an
1.1.1.2 ! misho 1590: existing client, the name is transferred to the new client. If
1.1 misho 1591: .B --dhcp-fqdn
1592: is set, this behaviour changes: the unqualified name is no longer
1593: put in the DNS, only the qualified name. Two DHCP clients with the
1594: same name may both keep the name, provided that the domain part is
1595: different (ie the fully qualified names differ.) To ensure that all
1596: names have a domain part, there must be at least
1597: .B --domain
1598: without an address specified when
1599: .B --dhcp-fqdn
1600: is set.
1601: .TP
1602: .B --dhcp-client-update
1603: Normally, when giving a DHCP lease, dnsmasq sets flags in the FQDN
1604: option to tell the client not to attempt a DDNS update with its name
1605: and IP address. This is because the name-IP pair is automatically
1606: added into dnsmasq's DNS view. This flag suppresses that behaviour,
1607: this is useful, for instance, to allow Windows clients to update
1608: Active Directory servers. See RFC 4702 for details.
1609: .TP
1610: .B --enable-ra
1611: Enable dnsmasq's IPv6 Router Advertisement feature. DHCPv6 doesn't
1612: handle complete network configuration in the same way as DHCPv4. Router
1613: discovery and (possibly) prefix discovery for autonomous address
1614: creation are handled by a different protocol. When DHCP is in use,
1615: only a subset of this is needed, and dnsmasq can handle it, using
1616: existing DHCP configuration to provide most data. When RA is enabled,
1617: dnsmasq will advertise a prefix for each dhcp-range, with default
1618: router and recursive DNS server as the relevant link-local address on
1619: the machine running dnsmasq. By default, he "managed address" bits are set, and
1620: the "use SLAAC" bit is reset. This can be changed for individual
1621: subnets with the mode keywords described in
1622: .B --dhcp-range.
1623: RFC6106 DNS parameters are included in the advertisements. By default,
1624: the relevant link-local address of the machine running dnsmasq is sent
1625: as recursive DNS server. If provided, the DHCPv6 options dns-server and
1626: domain-search are used for RDNSS and DNSSL.
1627: .TP
1.1.1.2 ! misho 1628: .B --ra-param=<interface>,[high|low],[[<ra-interval>],<router lifetime>]
! 1629: Set non-default values for router advertisements sent via an
! 1630: interface. The priority field for the router may be altered from the
! 1631: default of medium with eg
! 1632: .B --ra-param=eth0,high.
! 1633: The interval between router advertisements may be set (in seconds) with
! 1634: .B --ra-param=eth0,60.
! 1635: The lifetime of the route may be changed or set to zero, which allows
! 1636: a router to advertise prefixes but not a route via itself.
! 1637: .B --ra-parm=eth0,0,0
! 1638: (A value of zero for the interval means the default value.) All three parameters may be set at once.
! 1639: .B --ra-param=low,60,1200
! 1640: The interface field may include a wildcard.
! 1641: .TP
! 1642: .B --enable-tftp[=<interface>[,<interface>]]
1.1 misho 1643: Enable the TFTP server function. This is deliberately limited to that
1644: needed to net-boot a client. Only reading is allowed; the tsize and
1645: blksize extensions are supported (tsize is only supported in octet
1.1.1.2 ! misho 1646: mode). Without an argument, the TFTP service is provided to the same set of interfaces as DHCP service.
! 1647: If the list of interfaces is provided, that defines which interfaces recieve TFTP service.
1.1 misho 1648: .TP
1649: .B --tftp-root=<directory>[,<interface>]
1650: Look for files to transfer using TFTP relative to the given
1651: directory. When this is set, TFTP paths which include ".." are
1652: rejected, to stop clients getting outside the specified root.
1653: Absolute paths (starting with /) are allowed, but they must be within
1654: the tftp-root. If the optional interface argument is given, the
1655: directory is only used for TFTP requests via that interface.
1656: .TP
1657: .B --tftp-unique-root
1658: Add the IP address of the TFTP client as a path component on the end
1659: of the TFTP-root (in standard dotted-quad format). Only valid if a
1660: tftp-root is set and the directory exists. For instance, if tftp-root is "/tftp" and client
1661: 1.2.3.4 requests file "myfile" then the effective path will be
1662: "/tftp/1.2.3.4/myfile" if /tftp/1.2.3.4 exists or /tftp/myfile otherwise.
1663: .TP
1664: .B --tftp-secure
1665: Enable TFTP secure mode: without this, any file which is readable by
1666: the dnsmasq process under normal unix access-control rules is
1667: available via TFTP. When the --tftp-secure flag is given, only files
1668: owned by the user running the dnsmasq process are accessible. If
1669: dnsmasq is being run as root, different rules apply: --tftp-secure
1670: has no effect, but only files which have the world-readable bit set
1671: are accessible. It is not recommended to run dnsmasq as root with TFTP
1672: enabled, and certainly not without specifying --tftp-root. Doing so
1673: can expose any world-readable file on the server to any host on the net.
1674: .TP
1675: .B --tftp-lowercase
1676: Convert filenames in TFTP requests to all lowercase. This is useful
1677: for requests from Windows machines, which have case-insensitive
1678: filesystems and tend to play fast-and-loose with case in filenames.
1679: Note that dnsmasq's tftp server always converts "\\" to "/" in filenames.
1680: .TP
1681: .B --tftp-max=<connections>
1682: Set the maximum number of concurrent TFTP connections allowed. This
1683: defaults to 50. When serving a large number of TFTP connections,
1684: per-process file descriptor limits may be encountered. Dnsmasq needs
1685: one file descriptor for each concurrent TFTP connection and one
1686: file descriptor per unique file (plus a few others). So serving the
1687: same file simultaneously to n clients will use require about n + 10 file
1688: descriptors, serving different files simultaneously to n clients will
1689: require about (2*n) + 10 descriptors. If
1690: .B --tftp-port-range
1691: is given, that can affect the number of concurrent connections.
1692: .TP
1693: .B --tftp-no-blocksize
1694: Stop the TFTP server from negotiating the "blocksize" option with a
1695: client. Some buggy clients request this option but then behave badly
1696: when it is granted.
1697: .TP
1698: .B --tftp-port-range=<start>,<end>
1699: A TFTP server listens on a well-known port (69) for connection initiation,
1700: but it also uses a dynamically-allocated port for each
1701: connection. Normally these are allocated by the OS, but this option
1702: specifies a range of ports for use by TFTP transfers. This can be
1703: useful when TFTP has to traverse a firewall. The start of the range
1704: cannot be lower than 1025 unless dnsmasq is running as root. The number
1705: of concurrent TFTP connections is limited by the size of the port range.
1706: .TP
1707: .B \-C, --conf-file=<file>
1708: Specify a different configuration file. The conf-file option is also allowed in
1709: configuration files, to include multiple configuration files. A
1710: filename of "-" causes dnsmasq to read configuration from stdin.
1711: .TP
1712: .B \-7, --conf-dir=<directory>[,<file-extension>......]
1713: Read all the files in the given directory as configuration
1714: files. If extension(s) are given, any files which end in those
1715: extensions are skipped. Any files whose names end in ~ or start with . or start and end
1716: with # are always skipped. This flag may be given on the command
1717: line or in a configuration file.
1.1.1.2 ! misho 1718: .TP
! 1719: .B --servers-file=<file>
! 1720: A special case of
! 1721: .B --conf-file
! 1722: which differs in two respects. Firstly, only --server and --rev-server are allowed
! 1723: in the configuration file included. Secondly, the file is re-read and the configuration
! 1724: therein is updated when dnsmasq recieves SIGHUP.
1.1 misho 1725: .SH CONFIG FILE
1726: At startup, dnsmasq reads
1727: .I /etc/dnsmasq.conf,
1728: if it exists. (On
1729: FreeBSD, the file is
1730: .I /usr/local/etc/dnsmasq.conf
1731: ) (but see the
1732: .B \-C
1733: and
1734: .B \-7
1735: options.) The format of this
1736: file consists of one option per line, exactly as the long options detailed
1737: in the OPTIONS section but without the leading "--". Lines starting with # are comments and ignored. For
1738: options which may only be specified once, the configuration file overrides
1739: the command line. Quoting is allowed in a config file:
1740: between " quotes the special meanings of ,:. and # are removed and the
1741: following escapes are allowed: \\\\ \\" \\t \\e \\b \\r and \\n. The later
1742: corresponding to tab, escape, backspace, return and newline.
1743: .SH NOTES
1744: When it receives a SIGHUP,
1745: .B dnsmasq
1746: clears its cache and then re-loads
1747: .I /etc/hosts
1748: and
1749: .I /etc/ethers
1750: and any file given by --dhcp-hostsfile, --dhcp-optsfile or --addn-hosts.
1751: The dhcp lease change script is called for all
1752: existing DHCP leases. If
1753: .B
1754: --no-poll
1755: is set SIGHUP also re-reads
1756: .I /etc/resolv.conf.
1757: SIGHUP
1758: does NOT re-read the configuration file.
1759: .PP
1760: When it receives a SIGUSR1,
1761: .B dnsmasq
1762: writes statistics to the system log. It writes the cache size,
1763: the number of names which have had to removed from the cache before
1764: they expired in order to make room for new names and the total number
1.1.1.2 ! misho 1765: of names that have been inserted into the cache. The number of cache hits and
! 1766: misses and the number of authoritative queries answered are also given. For each upstream
1.1 misho 1767: server it gives the number of queries sent, and the number which
1768: resulted in an error. In
1769: .B --no-daemon
1770: mode or when full logging is enabled (-q), a complete dump of the
1.1.1.2 ! misho 1771: contents of the cache is made.
! 1772:
! 1773: The cache statistics are also available in the DNS as answers to
! 1774: queries of class CHAOS and type TXT in domain bind. The domain names are cachesize.bind, insertions.bind, evictions.bind,
! 1775: misses.bind, hits.bind, auth.bind and servers.bind. An example command to query this, using the
! 1776: .B dig
! 1777: utility would be
! 1778:
! 1779: dig +short chaos txt cachesize.bind
! 1780:
1.1 misho 1781: .PP
1782: When it receives SIGUSR2 and it is logging direct to a file (see
1783: .B --log-facility
1784: )
1785: .B dnsmasq
1786: will close and reopen the log file. Note that during this operation,
1787: dnsmasq will not be running as root. When it first creates the logfile
1788: dnsmasq changes the ownership of the file to the non-root user it will run
1789: as. Logrotate should be configured to create a new log file with
1790: the ownership which matches the existing one before sending SIGUSR2.
1791: If TCP DNS queries are in progress, the old logfile will remain open in
1792: child processes which are handling TCP queries and may continue to be
1793: written. There is a limit of 150 seconds, after which all existing TCP
1794: processes will have expired: for this reason, it is not wise to
1795: configure logfile compression for logfiles which have just been
1796: rotated. Using logrotate, the required options are
1797: .B create
1798: and
1799: .B delaycompress.
1800:
1801:
1802: .PP
1803: Dnsmasq is a DNS query forwarder: it it not capable of recursively
1804: answering arbitrary queries starting from the root servers but
1805: forwards such queries to a fully recursive upstream DNS server which is
1806: typically provided by an ISP. By default, dnsmasq reads
1807: .I /etc/resolv.conf
1808: to discover the IP
1809: addresses of the upstream nameservers it should use, since the
1810: information is typically stored there. Unless
1811: .B --no-poll
1812: is used,
1813: .B dnsmasq
1814: checks the modification time of
1815: .I /etc/resolv.conf
1816: (or equivalent if
1817: .B \--resolv-file
1818: is used) and re-reads it if it changes. This allows the DNS servers to
1819: be set dynamically by PPP or DHCP since both protocols provide the
1820: information.
1821: Absence of
1822: .I /etc/resolv.conf
1823: is not an error
1824: since it may not have been created before a PPP connection exists. Dnsmasq
1825: simply keeps checking in case
1826: .I /etc/resolv.conf
1827: is created at any
1828: time. Dnsmasq can be told to parse more than one resolv.conf
1829: file. This is useful on a laptop, where both PPP and DHCP may be used:
1830: dnsmasq can be set to poll both
1831: .I /etc/ppp/resolv.conf
1832: and
1833: .I /etc/dhcpc/resolv.conf
1834: and will use the contents of whichever changed
1835: last, giving automatic switching between DNS servers.
1836: .PP
1837: Upstream servers may also be specified on the command line or in
1838: the configuration file. These server specifications optionally take a
1839: domain name which tells dnsmasq to use that server only to find names
1840: in that particular domain.
1841: .PP
1842: In order to configure dnsmasq to act as cache for the host on which it is running, put "nameserver 127.0.0.1" in
1843: .I /etc/resolv.conf
1844: to force local processes to send queries to
1845: dnsmasq. Then either specify the upstream servers directly to dnsmasq
1846: using
1847: .B \--server
1848: options or put their addresses real in another file, say
1849: .I /etc/resolv.dnsmasq
1850: and run dnsmasq with the
1851: .B \-r /etc/resolv.dnsmasq
1852: option. This second technique allows for dynamic update of the server
1853: addresses by PPP or DHCP.
1854: .PP
1855: Addresses in /etc/hosts will "shadow" different addresses for the same
1856: names in the upstream DNS, so "mycompany.com 1.2.3.4" in /etc/hosts will ensure that
1857: queries for "mycompany.com" always return 1.2.3.4 even if queries in
1858: the upstream DNS would otherwise return a different address. There is
1859: one exception to this: if the upstream DNS contains a CNAME which
1860: points to a shadowed name, then looking up the CNAME through dnsmasq
1861: will result in the unshadowed address associated with the target of
1862: the CNAME. To work around this, add the CNAME to /etc/hosts so that
1863: the CNAME is shadowed too.
1864:
1865: .PP
1866: The tag system works as follows: For each DHCP request, dnsmasq
1867: collects a set of valid tags from active configuration lines which
1868: include set:<tag>, including one from the
1869: .B dhcp-range
1870: used to allocate the address, one from any matching
1871: .B dhcp-host
1872: (and "known" if a dhcp-host matches)
1873: The tag "bootp" is set for BOOTP requests, and a tag whose name is the
1874: name of the interface on which the request arrived is also set.
1875:
1.1.1.2 ! misho 1876: Any configuration lines which include one or more tag:<tag> constructs
1.1 misho 1877: will only be valid if all that tags are matched in the set derived
1878: above. Typically this is dhcp-option.
1879: .B dhcp-option
1880: which has tags will be used in preference to an untagged
1881: .B dhcp-option,
1882: provided that _all_ the tags match somewhere in the
1883: set collected as described above. The prefix '!' on a tag means 'not'
1.1.1.2 ! misho 1884: so --dhcp-option=tag:!purple,3,1.2.3.4 sends the option when the
1.1 misho 1885: tag purple is not in the set of valid tags. (If using this in a
1886: command line rather than a configuration file, be sure to escape !,
1887: which is a shell metacharacter)
1888:
1889: When selecting dhcp-options, a tag from dhcp-range is second class
1890: relative to other tags, to make it easy to override options for
1891: individual hosts, so
1892: .B dhcp-range=set:interface1,......
1893: .B dhcp-host=set:myhost,.....
1894: .B dhcp-option=tag:interface1,option:nis-domain,"domain1"
1895: .B dhcp-option=tag:myhost,option:nis-domain,"domain2"
1896: will set the NIS-domain to domain1 for hosts in the range, but
1897: override that to domain2 for a particular host.
1898:
1899: .PP
1900: Note that for
1901: .B dhcp-range
1902: both tag:<tag> and set:<tag> are allowed, to both select the range in
1903: use based on (eg) dhcp-host, and to affect the options sent, based on
1904: the range selected.
1905:
1906: This system evolved from an earlier, more limited one and for backward
1907: compatibility "net:" may be used instead of "tag:" and "set:" may be
1908: omitted. (Except in
1909: .B dhcp-host,
1910: where "net:" may be used instead of "set:".) For the same reason, '#'
1911: may be used instead of '!' to indicate NOT.
1912: .PP
1913: The DHCP server in dnsmasq will function as a BOOTP server also,
1914: provided that the MAC address and IP address for clients are given,
1915: either using
1916: .B dhcp-host
1917: configurations or in
1918: .I /etc/ethers
1919: , and a
1920: .B dhcp-range
1921: configuration option is present to activate the DHCP server
1922: on a particular network. (Setting --bootp-dynamic removes the need for
1923: static address mappings.) The filename
1924: parameter in a BOOTP request is used as a tag,
1925: as is the tag "bootp", allowing some control over the options returned to
1926: different classes of hosts.
1927:
1928: .SH AUTHORITATIVE CONFIGURATION
1929: .PP
1930: Configuring dnsmasq to act as an authoritative DNS server is
1931: complicated by the fact that it involves configuration of external DNS
1932: servers to provide delegation. We will walk through three scenarios of
1933: increasing complexity. Prerequisites for all of these scenarios
1934: are a globally accessible IP address, an A or AAAA record pointing to that address,
1935: and an external DNS server capable of doing delegation of the zone in
1936: question. For the first part of this explanation, we will call the A (or AAAA) record
1937: for the globally accessible address server.example.com, and the zone
1938: for which dnsmasq is authoritative our.zone.com.
1939:
1940: The simplest configuration consists of two lines of dnsmasq configuration; something like
1941:
1942: .nf
1943: .B auth-server=server.example.com,eth0
1944: .B auth-zone=our.zone.com,1.2.3.0/24
1945: .fi
1946:
1947: and two records in the external DNS
1948:
1949: .nf
1950: server.example.com A 192.0.43.10
1951: our.zone.com NS server.example.com
1952: .fi
1953:
1954: eth0 is the external network interface on which dnsmasq is listening,
1955: and has (globally accessible) address 192.0.43.10.
1956:
1957: Note that the external IP address may well be dynamic (ie assigned
1958: from an ISP by DHCP or PPP) If so, the A record must be linked to this
1959: dynamic assignment by one of the usual dynamic-DNS systems.
1960:
1961: A more complex, but practically useful configuration has the address
1962: record for the globally accessible IP address residing in the
1963: authoritative zone which dnsmasq is serving, typically at the root. Now
1964: we have
1965:
1966: .nf
1967: .B auth-server=our.zone.com,eth0
1968: .B auth-zone=our.zone.com,1.2.3.0/24
1969: .fi
1970:
1971: .nf
1972: our.zone.com A 1.2.3.4
1973: our.zone.com NS our.zone.com
1974: .fi
1975:
1976: The A record for our.zone.com has now become a glue record, it solves
1977: the chicken-and-egg problem of finding the IP address of the
1978: nameserver for our.zone.com when the A record is within that
1979: zone. Note that this is the only role of this record: as dnsmasq is
1980: now authoritative from our.zone.com it too must provide this
1981: record. If the external address is static, this can be done with an
1982: .B /etc/hosts
1983: entry or
1984: .B --host-record.
1985:
1986: .nf
1987: .B auth-server=our.zone.com,eth0
1988: .B host-record=our.zone.com,1.2.3.4
1989: .B auth-zone=our.zone.com,1.2.3.0/24
1990: .fi
1991:
1992: If the external address is dynamic, the address
1993: associated with our.zone.com must be derived from the address of the
1994: relevant interface. This is done using
1995: .B interface-name
1996: Something like:
1997:
1998: .nf
1999: .B auth-server=our.zone.com,eth0
2000: .B interface-name=our.zone.com,eth0
1.1.1.2 ! misho 2001: .B auth-zone=our.zone.com,1.2.3.0/24,eth0
1.1 misho 2002: .fi
2003:
1.1.1.2 ! misho 2004: (The "eth0" argument in auth-zone adds the subnet containing eth0's
! 2005: dynamic address to the zone, so that the interface-name returns the
! 2006: address in outside queries.)
! 2007:
1.1 misho 2008: Our final configuration builds on that above, but also adds a
2009: secondary DNS server. This is another DNS server which learns the DNS data
2010: for the zone by doing zones transfer, and acts as a backup should
2011: the primary server become inaccessible. The configuration of the
2012: secondary is beyond the scope of this man-page, but the extra
2013: configuration of dnsmasq is simple:
2014:
2015: .nf
2016: .B auth-sec-servers=secondary.myisp.com
2017: .fi
2018:
2019: and
2020:
2021: .nf
2022: our.zone.com NS secondary.myisp.com
2023: .fi
2024:
2025: Adding auth-sec-servers enables zone transfer in dnsmasq, to allow the
2026: secondary to collect the DNS data. If you wish to restrict this data
2027: to particular hosts then
2028:
2029: .nf
2030: .B auth-peer=<IP address of secondary>
2031: .fi
2032:
2033: will do so.
2034:
2035: Dnsmasq acts as an authoritative server for in-addr.arpa and
1.1.1.2 ! misho 2036: ip6.arpa domains associated with the subnets given in auth-zone
1.1 misho 2037: declarations, so reverse (address to name) lookups can be simply
2038: configured with a suitable NS record, for instance in this example,
2039: where we allow 1.2.3.0/24 addresses.
2040:
2041: .nf
2042: 3.2.1.in-addr.arpa NS our.zone.com
2043: .fi
2044:
2045: Note that at present, reverse (in-addr.arpa and ip6.arpa) zones are
2046: not available in zone transfers, so there is no point arranging
2047: secondary servers for reverse lookups.
2048:
2049: .PP
2050: When dnsmasq is configured to act as an authoritative server, the
2051: following data is used to populate the authoritative zone.
2052: .PP
2053: .B --mx-host, --srv-host, --dns-rr, --txt-record, --naptr-record
2054: , as long as the record names are in the authoritative domain.
2055: .PP
2056: .B --cname
2057: as long as the record name is in the authoritative domain. If the
2058: target of the CNAME is unqualified, then it is qualified with the
2059: authoritative zone name.
2060: .PP
2061: IPv4 and IPv6 addresses from /etc/hosts (and
2062: .B --addn-hosts
2063: ) and
2064: .B --host-record
1.1.1.2 ! misho 2065: and
! 2066: .B --interface-name
1.1 misho 2067: provided the address falls into one of the subnets specified in the
2068: .B --auth-zone.
2069: .PP
2070: Addresses of DHCP leases, provided the address falls into one of the subnets specified in the
1.1.1.2 ! misho 2071: .B --auth-zone.
! 2072: (If contructed DHCP ranges are is use, which depend on the address dynamically
! 2073: assigned to an interface, then the form of
1.1 misho 2074: .B --auth-zone
1.1.1.2 ! misho 2075: which defines subnets by the dynamic address of an interface should
! 2076: be used to ensure this condition is met.)
! 2077: .PP
! 2078: In the default mode, where a DHCP lease
1.1 misho 2079: has an unqualified name, and possibly a qualified name constructed
2080: using
2081: .B --domain
2082: then the name in the authoritative zone is constructed from the
2083: unqualified name and the zone's domain. This may or may not equal
2084: that specified by
2085: .B --domain.
2086: If
2087: .B --dhcp-fqdn
2088: is set, then the fully qualified names associated with DHCP leases are
2089: used, and must match the zone's domain.
2090:
2091:
2092:
2093: .SH EXIT CODES
2094: .PP
2095: 0 - Dnsmasq successfully forked into the background, or terminated
2096: normally if backgrounding is not enabled.
2097: .PP
2098: 1 - A problem with configuration was detected.
2099: .PP
2100: 2 - A problem with network access occurred (address in use, attempt
2101: to use privileged ports without permission).
2102: .PP
2103: 3 - A problem occurred with a filesystem operation (missing
2104: file/directory, permissions).
2105: .PP
2106: 4 - Memory allocation failure.
2107: .PP
2108: 5 - Other miscellaneous problem.
2109: .PP
2110: 11 or greater - a non zero return code was received from the
2111: lease-script process "init" call. The exit code from dnsmasq is the
2112: script's exit code with 10 added.
2113:
2114: .SH LIMITS
2115: The default values for resource limits in dnsmasq are generally
2116: conservative, and appropriate for embedded router type devices with
2117: slow processors and limited memory. On more capable hardware, it is
2118: possible to increase the limits, and handle many more clients. The
2119: following applies to dnsmasq-2.37: earlier versions did not scale as well.
2120:
2121: .PP
2122: Dnsmasq is capable of handling DNS and DHCP for at least a thousand
2123: clients. The DHCP lease times should not be very short (less than one hour). The
2124: value of
2125: .B --dns-forward-max
2126: can be increased: start with it equal to
2127: the number of clients and increase if DNS seems slow. Note that DNS
2128: performance depends too on the performance of the upstream
2129: nameservers. The size of the DNS cache may be increased: the hard
2130: limit is 10000 names and the default (150) is very low. Sending
2131: SIGUSR1 to dnsmasq makes it log information which is useful for tuning
2132: the cache size. See the
2133: .B NOTES
2134: section for details.
2135:
2136: .PP
2137: The built-in TFTP server is capable of many simultaneous file
2138: transfers: the absolute limit is related to the number of file-handles
2139: allowed to a process and the ability of the select() system call to
2140: cope with large numbers of file handles. If the limit is set too high
2141: using
2142: .B --tftp-max
2143: it will be scaled down and the actual limit logged at
2144: start-up. Note that more transfers are possible when the same file is
2145: being sent than when each transfer sends a different file.
2146:
2147: .PP
2148: It is possible to use dnsmasq to block Web advertising by using a list
2149: of known banner-ad servers, all resolving to 127.0.0.1 or 0.0.0.0, in
2150: .B /etc/hosts
2151: or an additional hosts file. The list can be very long,
2152: dnsmasq has been tested successfully with one million names. That size
2153: file needs a 1GHz processor and about 60Mb of RAM.
2154:
2155: .SH INTERNATIONALISATION
2156: Dnsmasq can be compiled to support internationalisation. To do this,
2157: the make targets "all-i18n" and "install-i18n" should be used instead of
2158: the standard targets "all" and "install". When internationalisation
2159: is compiled in, dnsmasq will produce log messages in the local
2160: language and support internationalised domain names (IDN). Domain
2161: names in /etc/hosts, /etc/ethers and /etc/dnsmasq.conf which contain
2162: non-ASCII characters will be translated to the DNS-internal punycode
2163: representation. Note that
2164: dnsmasq determines both the language for messages and the assumed
2165: charset for configuration
2166: files from the LANG environment variable. This should be set to the system
2167: default value by the script which is responsible for starting
2168: dnsmasq. When editing the configuration files, be careful to do so
2169: using only the system-default locale and not user-specific one, since
2170: dnsmasq has no direct way of determining the charset in use, and must
2171: assume that it is the system default.
2172:
2173: .SH FILES
2174: .IR /etc/dnsmasq.conf
2175:
2176: .IR /usr/local/etc/dnsmasq.conf
2177:
2178: .IR /etc/resolv.conf
2179: .IR /var/run/dnsmasq/resolv.conf
2180: .IR /etc/ppp/resolv.conf
2181: .IR /etc/dhcpc/resolv.conf
2182:
2183: .IR /etc/hosts
2184:
2185: .IR /etc/ethers
2186:
2187: .IR /var/lib/misc/dnsmasq.leases
2188:
2189: .IR /var/db/dnsmasq.leases
2190:
2191: .IR /var/run/dnsmasq.pid
2192: .SH SEE ALSO
2193: .BR hosts (5),
2194: .BR resolver (5)
2195: .SH AUTHOR
2196: This manual page was written by Simon Kelley <simon@thekelleys.org.uk>.
2197:
2198:
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