1: .\" dhcrelay.8
2: .\"
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26: .\" by Ted Lemon in cooperation with Vixie Enterprises.
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31: .\" $Id: dhcrelay.8,v 1.1 2012/02/21 22:30:18 misho Exp $
32: .\"
33: .TH dhcrelay 8
34: .SH NAME
35: dhcrelay - Dynamic Host Configuration Protocol Relay Agent
36: .SH SYNOPSIS
37: .B dhcrelay
38: [
39: .B -4
40: ]
41: [
42: .B -dqaD
43: ]
44: [
45: .B -p
46: .I port
47: ]
48: [
49: .B -c
50: .I count
51: ]
52: [
53: .B -A
54: .I length
55: ]
56: [
57: .B -pf
58: .I pid-file
59: ]
60: [
61: .B --no-pid
62: ]
63: [
64: .B -m
65: .I append
66: |
67: .I replace
68: |
69: .I forward
70: |
71: .I discard
72: ]
73: [
74: .B -i
75: .I interface0
76: [
77: .B ...
78: .B -i
79: .I interfaceN
80: ]
81: ]
82: .I server0
83: [
84: .I ...serverN
85: ]
86: .PP
87: .B dhcrelay -6
88: [
89: .B -dqI
90: ]
91: [
92: .B -p
93: .I port
94: ]
95: [
96: .B -c
97: .I count
98: ]
99: [
100: .B -pf
101: .I pid-file
102: ]
103: [
104: .B --no-pid
105: ]
106: .B -l
107: .I lower0
108: [
109: .B ...
110: .B -l
111: .I lowerN
112: ]
113: .B -u
114: .I upper0
115: [
116: .B ...
117: .B -u
118: .I upperN
119: ]
120: .SH DESCRIPTION
121: The Internet Systems Consortium DHCP Relay Agent, dhcrelay, provides a
122: means for relaying DHCP and BOOTP requests from a subnet to which
123: no DHCP server is directly connected to one or more DHCP servers on
124: other subnets. It supports both DHCPv4/BOOTP and DHCPv6 protocols.
125: .SH OPERATION
126: .PP
127: The DHCP Relay Agent listens for DHCPv4 or DHCPv6 queries from clients or
128: other relay agents on one or more interfaces, passing them along to
129: ``upstream'' servers or relay agents as specified on the command line.
130: When a reply is received from upstream, it is multicast or unicast back
131: downstream to the source of the original request.
132: .SH COMMAND LINE
133: .PP
134: \fIProtocol selection options:\fR
135: .TP
136: -6
137: Run dhcrelay as a DHCPv6 relay agent. Incompatible with the \fB-4\fR
138: option.
139: .TP
140: -4
141: Run dhcrelay as a DHCPv4/BOOTP relay agent. This is the default mode of
142: operation, so the argument is not necessary, but may be specified for
143: clarity. Incompatible with \fB-6\fR.
144: .PP
145: \fISpecifying DHCPv4/BOOTP servers\fR
146: .PP
147: In DHCPv4 mode, a list of one or more server addresses must be specified on
148: the command line, to which DHCP/BOOTP queries should be relayed.
149: .PP
150: \fIOptions available for both DHCPv4 and DHCPv6:\fR
151: .TP
152: -c COUNT
153: Maximum hop count. When forwarding packets, dhcrelay discards packets
154: which have reached a hop count of COUNT. Default is 10. Maximum is 255.
155: .TP
156: -d
157: Force dhcrelay to run as a foreground process. Useful when running
158: dhcrelay under a debugger, or running out of inittab on System V systems.
159: .TP
160: -p PORT
161: Listen and transmit on port PORT. This is mostly useful for debugging
162: purposes. Default is port 67 for DHCPv4/BOOTP, or port 547 for DHCPv6.
163: .TP
164: -q
165: Quiet mode. Prevents dhcrelay6 from printing its network configuration
166: on startup.
167: .TP
168: -pf pid-file
169: Path to alternate pid file.
170: .TP
171: --no-pid
172: Option to disable writing pid files. By default the program
173: will write a pid file.
174: .PP
175: \fIOptions available in DHCPv4 mode only:\fR
176: .TP
177: -a
178: Append an agent option field to each request before forwarding it to
179: the server. Agent option fields in responses sent from servers to
180: clients will be stripped before forwarding such responses back to the
181: client. The agent option field will contain two agent options: the Circuit
182: ID suboption and the Remote ID suboption. Currently, the Circuit ID will
183: be the printable name of the interface on which the client request was
184: received. The client supports inclusion of a Remote ID suboption as well,
185: but this is not used by default.
186: .TP
187: -A LENGTH
188: Specify the maximum packet size to send to a DHCPv4/BOOTP server. This
189: might be done to allow sufficient space for addition of relay agent
190: options while still fitting into the Ethernet MTU size.
191: .TP
192: -D
193: Drop packets from upstream servers if they contain Relay Agent
194: Information options that indicate they were generated in response to
195: a query that came via a different relay agent. If this option is not
196: specified, such packets will be relayed anyway.
197: .TP
198: -i \fIifname\fR
199: Listen for DHCPv4/BOOTP queries on interface \fIifname\fR. Multiple
200: interfaces may be specified by using more than one \fB-i\fR option. If
201: no interfaces are specified on the command line, dhcrelay will identify
202: all network interfaces, eliminating non-broadcast interfaces if possible,
203: and attempt to listen on all of them.
204: .TP
205: -m \fIappend\fR|\fIreplace\fR|\fIforward\fR|\fIdiscard\fR
206: Control the handling of incoming DHCPv4 packets which already contain
207: relay agent options. If such a packet does not have \fIgiaddr\fR set in
208: its header, the DHCP standard requires that the packet be discarded.
209: However, if \fIgiaddr\fR is set, the relay agent may handle the situation
210: in four ways: It may \fIappend\fR its own set of relay options to the
211: packet, leaving the supplied option field intact; it may \fIreplace\fR the
212: existing agent option field; it may \fIforward\fR the packet unchanged; or,
213: it may \fIdiscard\fR it.
214: .PP
215: \fIOptions available in DHCPv6 mode only:\fR
216: .TP
217: -I
218: Force use of the DHCPv6 Interface-ID option. This option is
219: automatically sent when there are two or more downstream interfaces
220: in use, to disambiguate between them. The \fB-I\fR option causes
221: dhcrelay to send the option even if there is only one downstream
222: interface.
223: .TP
224: -l [\fIaddress%\fR]\fIifname\fR[\fI#index\fR]
225: Specifies the ``lower'' network interface for DHCPv6 relay mode: the
226: interface on which queries will be received from clients or from other
227: relay agents. At least one \fB-l\fR option must be included in the command
228: line when running in DHCPv6 mode. The interface name \fIifname\fR is a
229: mandatory parameter. The link address can be specified by \fIaddress%\fR;
230: if it isn't, dhcrelay will use the first non-link-local address configured
231: on the interface. The optional \fI#index\fR parameter specifies the
232: interface index.
233: .TP
234: -u [\fIaddress%\fR]\fIifname\fR
235: Specifies the ``upper'' network interface for DHCPv6 relay mode: the
236: interface to which queries from clients and other relay agents should be
237: forwarded. At least one \fB-u\fR option must be included in the command
238: line when running in DHCPv6 mode. The interface name \fIifname\fR is a
239: mandatory parameter. The destination unicast or multicast address can be
240: specified by \fIaddress%\fR; if not specified, the relay agent will forward
241: to the DHCPv6 \fIAll_DHCP_Relay_Agents_and_Servers\fR multicast address.
242: .PP
243: It is possible to specify the same interface with different addresses
244: more than once, and even, when the system supports it, to use the same
245: interface as both upper and lower interfaces.
246: .SH SEE ALSO
247: dhclient(8), dhcpd(8), RFC3315, RFC2132, RFC2131.
248: .SH BUGS
249: .PP
250: Using the same interface on both upper and lower sides may cause
251: loops, so when running this way, the maximum hop count should be set
252: to a low value.
253: .PP
254: The loopback interface is not (yet) recognized as a valid interface.
255: .SH AUTHOR
256: .B dhcrelay(8)
257: To learn more about Internet Systems Consortium, see
258: .B https://www.isc.org
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