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1: <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> 2: <HTML> 3: <HEAD> 4: <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> 5: <TITLE>Link layer</TITLE> 6: </HEAD> 7: <BODY text="#000000" bgcolor="#ffffff"> 8: 9: <A HREF="mpd.html">Mpd 5.9 User Manual</A> 10: : <A HREF="mpd17.html">Configuring Mpd</A> 11: : Link layer  12: Previous: <A HREF="mpd19.html">Mpd Layers</A>  13: Next: <A HREF="mpd21.html">EAP</A> 14: 15: 16: <HR NOSHADE> 17: <H2><A NAME="20"></A>4.3. Link layer<A NAME="links"></A></H2> 18: This chapter describes commands that configure the link layer. 19: All of these commands apply to the currently active link, i.e., 20: the link shown at the command line prompt. 21:  22: <dl> 23: 24: <dt><code>set link action (bundle|forward) name [ regexp ]</code><dd> 25: <dt><code>set link action drop [ regexp ]</code><dd> 26: List of such command describes how incoming calls should be processed. 27: "bundle" means that connection should be processed locally with 28: specified bundle. "forward" means that connection should be forwarded 29: using repeater to the specified link. "drop" means that connection 30: should be dropped. Optional "regexp" parameter defines regular 31: expression which will be checked against peer auth name. 32: Actions from list are checked in order of definition until regexp 33: match will be found. Actions processed at three points. First time 34: they are checked just after connection acception, second time just 35: after receiving peer's auth during LCP negotiation and third time 36: when link is authenticated. As during first check there is no peer 37: auth name known yet, check will be skipped if there are more then 38: one action specified for link or if action has regexp specified. 39: 40: <dt><code>set link action clear</code><dd> 41: Clears link actions list. 42: 43: <dt><code>set link latency microseconds</code><dd> 44: <dt><code>set link bandwidth bits-per-second</code><dd> 45: These commands are relevant when multi-link PPP is active. They 46: affect the way in which packets are chopped up into fragments 47: before being sent over the various links that make up the bundle. 48: To motivate the idea, imagine a bundle that had a modem link and 49: a 1.5Mbps T1 link. If mpd sent each packet in two equal sized 50: fragments over these links, then by the time the modem got around 51: to transmitting the first byte of its fragment, the T1 link would 52: have probably already sent the whole other fragment. Clearly this 53: is not very good. By factoring in the latency and bandwidth parameters 54: for each link, mpd can distribute the fragments in a more intelligent 55: way. 56: Mpd attempts to distribute bytes over the links so that (if the 57: configured parameters are accurate) the last byte of each fragment 58: arrives at the peer at the same time on each link. This minimizes 59: latency. However, if you only care about maximizing throughput, 60: simply set all of the latency values to zero. 61: If all of your links are of the same type and speed (which is often 62: the case), then they should be configured with the same values (or 63: just not configured at all, since all links default to the same 64: values anyway). Then mpd will distribute packets in equal sized 65: fragments over the links. 66: 67: <dt><code>set link mtu numbytes</code><dd> 68: <dt><code>set link mru numbytes</code><dd> 69: <dt><code>set link mrru numbytes</code><dd> 70: The <code>set link mtu</code> command sets the maximum transmit unit 71: (MTU) value for the link. This is the size of the largest single 72: PPP frame (minus PPP header) that this link will transmit, unless 73: the peer requests an even lower value. The default value is 1500 bytes. 74: The <code>set link mru</code> command sets maximum receive unit (MRU) 75: value for the link, which is the size of the largest single PPP frame 76: (minus PPP header) that this link is capable of receiving. The default 77: value is 1500 bytes. 78: If PPP multilink is negotiated on a link, then these values are 79: less important, because multilink allows PPP frames themselves to 80: be fragmented, so a PPP frame up to MRRU bytes can always pass 81: through no matter how small the MTU is in a particular direction. 82: Otherwise, mpd is responsible for making sure that the MTU configured 83: on the system networking interface is low enough so that the largest 84: transmitted IP packet does not exceed the peer's negotiated MRU after 85: it becomes a PPP frame. This includes e.g. PPP encryption and/or 86: compression overhead. 87: However, mpd does not account for overhead that occurs ``outside'' 88: of the PPP frame. For example, when using link types such as PPTP 89: that encapsulate PPP frames within IP packets, a large outgoing 90: ``inner'' IP packet can result in a fragmented ``outer'' IP packet, 91: resulting in suboptimal performance. In this situation it may be 92: useful to set the link MTU to a lower value to avoid fragmentation. 93: 94: <dt><code>set link accmap value</code><dd>This sets the desired asynchronous control-character map for the 95: link at the local end. This option is only relevant for the 96: asynchronous link types (i.e., modem and tcp). 97: It determines which control characters need to be escaped. 98: The <code>value</code> is expressed as a 32-bit hex 99: value; the default is <code>0x000a0000</code>, which escapes the 100: Control-S and Control-Q characters. 101: 102: <dt><code>set link ident string</code><dd>This enables the sending of an identification string to the peer 103: via the LCP Ident code. The Ident string is sent when the link is 104: brought up. This is useful for debugging, etc. and is meant to be 105: human-readable. However, it confuses some broken PPP implementations. 106: Setting an empty string disables this feature; this is the default. 107: 108: <dt><code>set link fsm-timeout seconds</code><dd>This command is analogous to the same command at the bundle layer, 109: but it applies to link-layer FSM's such as Link Control Protocol (LCP). 110: The default is two seconds; normally this value should not be changed. 111: 112: <dt><code>set link keep-alive seconds max</code><dd>This command enables the sending of LCP echo packets on the link. 113: The first echo packet is sent after <code>seconds</code> 114: seconds of quiet time (i.e., no frames received from the peer on 115: that link). After <code>seconds</code> more seconds, another 116: echo request is sent. If after <code>max</code> seconds of 117: doing this no echo reply has been received yet, the link is brought 118: down. 119: If <code>seconds</code> is zero, echo packets are disabled. 120: The default values are five second intervals with a maximum no-reply 121: time of forty. 122: This feature is especially useful with modems when the carrier 123: detect signal is unreliable. However, in situations where lines are 124: noisy and modems spend a lot of time retraining, the <code>max</code> 125: value may need to be bumped up to a more generous value. 126: 127: <dt><code>set link max-redial num</code><dd>When a link fails to connect, mpd automatically retries the connection. 128: This command limits the number of consecutive retries. 129: After <code>num</code> attempts, mpd will give up. 130: When there is another open event, new dial-on-demand traffic, etc. 131: mpd will try again, starting over at zero. 132: If <code>max-redial</code> is set to -1, then mpd will never redial. 133: This setting should be used with links that are dedicated for dial-in. 134: If <code>max-redial</code> is set to 0, then mpd will redial infinitely. 135: The default value is -1. 136: 137: <dt><code>set link redial-delay seconds</code><dd>This command defines time between connection retries. 138: The default value is 1. 139: 140: <dt><code>set link max-children num</code><dd>This template option specifies maximum number of links, created using 141: this template, that could exist at the same time. Value 0 disables template. 142: The default value is 10000. 143: 144: <dt><code>set link accept option ... </code><dd> 145: <dt><code>set link deny option ... </code><dd> 146: <dt><code>set link enable option ... </code><dd> 147: <dt><code>set link disable option ... </code><dd> 148: <dt><code>set link yes option ... </code><dd> 149: <dt><code>set link no option ... </code><dd> 150: These commands configure various link options. Most options 151: are bi-directional in that they can be independently 152: enabled and disabled in each direction. 153: The <code>enable</code> and <code>disable</code> commands determine 154: whether we want the corresponding option. 155: The <code>accept</code> and <code>deny</code> commands determine 156: whether we will allow the peer to request the corresponding option. 157: Note that when talking about the authentication options PAP and CHAP, 158: when you <code>enable</code> an option you're saying you are going 159: to require a login and password from the peer. 160: When you <code>accept</code> an option you're saying you will 161: allow the peer to require a login and password from us. 162: 163: The <code>yes</code> command is the same as 164: <code>enable</code> and <code>accept</code>. 165: The <code>no</code> command is the same as 166: <code>disable</code> and <code>deny</code>. 167: 168: </dl> 169:  170: 171: The options available at the link layer are: 172:  173: <dl> 174: 175: <dt><code>pap</code><dd>PAP style authentication. Note that this style of authentication 176: is insecure, since the password crosses the link in plaintext. 177: Default <code>disable</code> and <code>accept</code>. 178: 179: <dt><code>chap</code><dd>CHAP style authentication. This style of authentication is safer 180: than PAP, because only a hash of the password is passed over the 181: link. Mpd supports MD5 style CHAP and Microsoft style CHAP versions 182: 1 and 2. Mpd will prefer Microsoft CHAP over MD5 CHAP to get 183: encryption keys. 184: This option is an alias for <code>chap-md5</code> <code>chap-msv1</code> <code>chap-msv2</code> 185: 186: <dt><code>chap-md5</code><dd>Traditional CHAP MD5 style authentication. 187: Default <code>disable</code> and <code>accept</code>. 188: 189: <dt><code>chap-msv1</code><dd>Microsoft CHAP style authentication. 190: Default <code>disable</code> and <code>deny</code>. 191: 192: <dt><code>chap-msv2</code><dd>Microsoft CHAP style authentication Version 2. 193: Default <code>disable</code> and <code>accept</code>. 194: 195: <dt><code>eap</code><dd>Extensible Authentication Protocol. For details see 196: <A HREF="mpd21.html#eap">the EAP chapter</A>. 197: Default <code>disable</code> and <code>accept</code>. 198: 199: <dt><code>incoming</code><dd>This option enables the acceptance of incoming connections. 200: If this option is disabled, mpd will not accept incoming connections 201: using this link. To avoid races it is advised to enable it after 202: all other link options are configured. 203: The default is <code>disable</code>. 204: 205: <dt><code>multilink</code><dd>This command enables multi-link PPP on the link. This option is required 206: in both directions if there is more than one link in the bundle. However, 207: multi-link PPP is sometimes useful on single links when the link MTU is 208: low; multi-link PPP allows arbitrarily long packets to go over a link 209: in fragments. 210: The default is <code>disable</code> (i.e., normal non-multilink PPP). 211: 212: <dt><code>shortseq</code><dd>This option is only meaningful if multi-link PPP is negotiated. 213: It proscribes shorter multi-link fragment headers, 214: saving two bytes on every frame. 215: The default is <code>enable</code> and <code>accept</code>. 216: 217: <dt><code>acfcomp</code><dd>Address and control field compression. This option only applies 218: to asynchronous link types. It saves two bytes per frame. 219: The default is <code>enable</code> and <code>accept</code>. 220: 221: <dt><code>protocomp</code><dd>Protocol field compression. This option saves one byte per frame 222: for most frames. 223: The default is <code>enable</code> and <code>accept</code>. 224: 225: <dt><code>magicnum</code><dd> 226: <dt><code>check-magic</code><dd>The <code>magicnum</code> option enables using a magic number for the 227: local end of the PPP link. This causes a unique number to be 228: included in each LCP packet we send, which helps detect loopback 229: conditions. 230: The <code>check-magic</code> option causes mpd to verify that the peer's 231: magic number is correct in all received LCP frames. 232: Some old broken PPP implementations do not handle magic numbers correctly, 233: so these options need to be disabled in these cases. 234: Default for both options is <code>enable</code>. 235: Note that the two most common reasons for seeing ``loopback condition 236: detected'' on a modem link are: 237: <ul> 238: <li> The modem is in command mode and is echoing back all of our frames.</li> 239: <li> The PPP server is not in PPP mode, but is giving a shell prompt 240: or somesuch and echoing back all of our frames.</li> 241: </ul> 242:  243: 244: <dt><code>passive</code><dd>Enables passive mode for this link. This is useful on some full time 245: connections. See RFC 1661 for more information about this option. 246: Default <code>disable</code>. 247: 248: <dt><code>callback</code><dd>Enables PPP callback request. If the remote peer can/wants to, it will 249: hangup immediately after connecting and call us back. 250: Default <code>disable</code>. 251: 252: <dt><code>no-orig-auth</code><dd>Normally, if PAP or CHAP is enabled, we require the peer to 253: authenticate to us at the beginning of each connection. This option 254: temporarily disables this requirement if we are the one who originated 255: the connection and the peer rejects our request for a login. 256: This is useful when the same link is used for both dial-in and dial-out. 257: Default <code>disable</code>. 258: 259: <dt><code>keep-ms-domain</code><dd>Normally, if using MS-CHAP, the MS-Domain is stripped and only the plain 260: username is used. Under certain circumstances the MS-Domain should be kept, 261: for instance if IAS is used as RADIUS server. 262: Default <code>disable</code>. 263: 264: <dt><code>time-remain</code><dd>Send Time-Remaining LCP packet to the peer if AAA returned session timeout. 265: Default <code>disable</code>. 266: 267: <dt><code>peer-as-calling</code><dd>Forces mpd to send remote tunnel address in Calling-Station-Id 268: instead of address supplied by remote peer via tunnel (for PPTP and L2TP). 269: Can be enabled for untrusted peers. 270: Default is <code>disable</code>. 271: 272: <dt><code>report-mac</code><dd>Forces mpd to send peer MAC address and interface in Calling-Station-Id. 273: Default <code>disable</code>. 274: 275: </dl> 276:  277: 278: <H3>4.3.1. <A HREF="mpd21.html#21">EAP</A></H3> 279: <HR NOSHADE> 280: <A HREF="mpd.html">Mpd 5.9 User Manual</A> 281: : <A HREF="mpd17.html">Configuring Mpd</A> 282: : Link layer  283: Previous: <A HREF="mpd19.html">Mpd Layers</A>  284: Next: <A HREF="mpd21.html">EAP</A> 285: 286: 287: 288: </BODY> 289: </HTML>