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  25 <H1>L2TPNS Manual</H1>
  26 <OL>
  27     <LI><A HREF="#Overview">Overview</A></LI>
  28     <LI><A HREF="#Installation">Installation</A>
  29         <OL>
  30             <LI><A HREF="#Requirements">Requirements</A></LI>
  31             <LI><A HREF="#Compile">Compile</A></LI>
  32             <LI><A HREF="#Install">Install</A></LI>
  33             <LI><A HREF="#Running">Running</A></LI>
  34         </OL>
  35     </LI>
  36     <LI><A HREF="#Configuration">Configuration</A>
  37         <OL>
  38             <LI><A HREF="#startup-config">startup-config</A></LI>
  39             <LI><A HREF="#users">users</A></LI>
  40             <LI><A HREF="#ip-pool">ip_pool</A></LI>
  41             <LI><A HREF="#build-garden">build-garden</A></LI>
  42         </OL>
  43     </LI>
  44     <LI><A HREF="#ControllingtheProcess">Controlling the Process</A>
  45         <OL>
  46             <LI><A HREF="#Command-LineInterface">Command-Line Interface</A></LI>
  47             <LI><A HREF="#nsctl">nsctl</A></LI>
  48             <LI><A HREF="#Signals">Signals</A></LI>
  49         </OL>
  50     </LI>
  51     <LI><A HREF="#Throttling">Throttling</A></LI>
  52     <LI><A HREF="#Interception">Interception</A></LI>
  53     <LI><A HREF="#Authentication">Authentication</A></LI>
  54     <LI><A HREF="#Plugins">Plugins</A></LI>
  55     <LI><A HREF="#WalledGarden">Walled Garden</A></LI>
  56     <LI><A HREF="#Filtering">Filtering</A></LI>
  57     <LI><A HREF="#Clustering">Clustering</A></LI>
  58     <LI><A HREF="#Routing">Routing</A></LI>
  59     <LI><A HREF="#AvoidingFragmentation">Avoiding Fragmentation</A></LI>
  60     <LI><A HREF="#Performance">Performance</A></LI>
  61 </OL>
  62
  63 <H2 ID="Overview">Overview</H2>
  64 l2tpns is half of a complete L2TP implementation.  It supports only the
  65 LNS side of the connection.<P>
  66
  67 L2TP (Layer 2 Tunneling Protocol) is designed to allow any layer 2
  68 protocol (e.g. Ethernet, PPP) to be tunneled over an IP connection.  l2tpns
  69 implements PPP over L2TP only.<P>
  70
  71 There are a couple of other L2TP implementations, of which <A
  72 HREF="http://sourceforge.net/projects/l2tpd">l2tpd</A> is probably the
  73 most popular.  l2tpd also will handle being either end of a tunnel, and
  74 is a lot more configurable than l2tpns.  However, due to the way it works,
  75 it is nowhere near as scalable.<P>
  76
  77 l2tpns uses the TUN/TAP interface provided by the Linux kernel to receive
  78 and send packets.  Using some packet manipulation it doesn't require a
  79 single interface per connection, as l2tpd does.<P>
  80
  81 This allows it to scale extremely well to very high loads and very high
  82 numbers of connections.<P>
  83
  84 It also has a plugin architecture which allows custom code to be run
  85 during processing.  An example of this is in the walled garden module
  86 included.<P>
  87
  88 <BR>
  89 <EM>Documentation is not my best skill.  If you find any problems
  90 with this document, or if you wish to contribute, please email <A
  91 HREF="mailto:l2tpns-users@lists.sourceforge.net?subject=L2TPNS+Documentation">the mailing list</A>.</EM><P>
  92
  93 <H2 ID="Installation">Installation</H2>
  94 <H3 ID="Requirements">Requirements</H3>
  95
  96 <OL>
  97 <LI>Linux kernel version 2.4 or above, with the Tun/Tap interface either
  98 compiled in, or as a module.</LI>
  99
 100 <LI>libcli 1.8.0 or greater.<BR>You can get this from <A
 101 HREF="http://sourceforge.net/projects/libcli">http://sourceforge.net/projects/libcli</A></LI>
 102 </OL>
 103
 104 <H3 ID="Compile">Compile</H3>
 105
 106 You can generally get away with just running <B>make</B> from the source
 107 directory.  This will compile the daemon, associated tools and any modules
 108 shipped with the distribution.<P>
 109
 110 <H3 ID="Install">Install</H3>
 111
 112 After you have successfully compiled everything, run <B>make
 113 install</B> to install it.  By default, the binaries are installed into
 114 <EM>/usr/sbin</EM>, the configuration into <EM>/etc/l2tpns</EM>, and the
 115 modules into <EM>/usr/lib/l2tpns</EM>.<P>
 116
 117 You will definately need to edit the configuration files before you
 118 start.  See the <A HREF="#Configuration">Configuration</A> section for
 119 more information.<P>
 120
 121 <H3 ID="Running">Running</H3>
 122
 123 You only need to run <B>/usr/sbin/l2tpns</B> as root to start it.  It does
 124 not detach to a daemon process, so you should perhaps run it from init.<P>
 125
 126 By default there is no log destination set, so all log messages will go to
 127 stdout.<P>
 128
 129 <H2 ID="Configuration">Configuration</H2>
 130
 131 All configuration of the software is done from the files installed into
 132 /etc/l2tpns.
 133
 134 <H3 ID="startup-config">startup-config</H3>
 135
 136 This is the main configuration file for l2tpns.  The format of the file is a
 137 list of commands that can be run through the command-line interface.  This
 138 file can also be written directly by the l2tpns process if a user runs the
 139 <EM>write memory</EM> command, so any comments will be lost.  However if your
 140 policy is not to write the config by the program, then feel free to comment
 141 the file with a # or ! at the beginning of the line.<P>
 142
 143 A list of the possible configuration directives follows.  Each of these
 144 should be set by a line like:<P>
 145 <PRE>
 146 set configstring "value"
 147 set ipaddress 192.168.1.1
 148 set boolean true
 149 </PRE>
 150
 151 <P>
 152 <UL>
 153 <LI><B>debug</B> (int)<BR>
 154 Sets the level of messages that will be written to the log file.  The value
 155 should be between 0 and 5, with 0 being no debugging, and 5 being the
 156 highest.  A rough description of the levels is:
 157         <OL>
 158         <LI VALUE=0>Critical Errors - Things are probably broken</LI>
 159         <LI>Errors - Things might have gone wrong, but probably will recover</LI>
 160         <LI>Warnings - Just in case you care what is not quite perfect</LI>
 161         <LI>Information - Parameters of control packets</LI>
 162         <LI>Calls - For tracing the execution of the code</LI>
 163         <LI>Packets - Everything, including a hex dump of all packets processed...  probably twice</LI>
 164         </OL><P>
 165 Note that the higher you set the debugging level, the slower the program
 166 will run.  Also, at level 5 a LOT of information will be logged.  This should
 167 only ever be used for working out why it doesn't work at all.
 168 </LI>
 169
 170 <LI><B>log_file</B> (string)<BR>
 171 This will be where all logging and debugging information is written
 172 to.  This may be either a filename, such as <EM>/var/log/l2tpns</EM>, or
 173 the special magic string <EM>syslog:facility</EM>, where <EM>facility</EM>
 174 is any one of the syslog logging facilities, such as local5.
 175 </LI>
 176
 177 <LI><B>pid_file</B> (string)<BR>
 178 If set, the process id will be written to the specified file.  The
 179 value must be an absolute path.
 180 </LI>
 181
 182 <LI><B>l2tp_secret</B> (string)<BR>
 183 The secret used by l2tpns for authenticating tunnel request.  Must be
 184 the same as the LAC, or authentication will fail.  Only actually be
 185 used if the LAC requests authentication.
 186 </LI>
 187
 188 <LI><B>l2tp_mtu</B> (int)<BR>
 189 MTU of interface for L2TP traffic (default: 1500).  Used to set link
 190 MRU and adjust TCP MSS.
 191 </LI>
 192
 193 <LI><B>ppp_restart_time</B> (int)<BR>
 194 <B>ppp_max_configure</B> (int)<BR>
 195 <B>ppp_max_failure</B> (int)<BR>
 196 PPP counter and timer values, as described in &sect;4.1 of
 197 <a href="ftp://ftp.rfc-editor.org/in-notes/rfc1661.txt">RFC1661</a>.
 198 </LI>
 199
 200 <LI><B>primary_dns</B> (ip address)
 201 <LI><B>secondary_dns</B> (ip address)<BR>
 202 Whenever a PPP connection is established, DNS servers will be sent to the
 203 user, both a primary and a secondary.  If either is set to 0.0.0.0, then that
 204 one will not be sent.
 205 </LI>
 206
 207 <LI><B>primary_radius</B> (ip address)
 208 <LI><B>secondary_radius</B> (ip address)<BR>
 209 Sets the RADIUS servers used for both authentication and accounting.
 210 If the primary server does not respond, then the secondary RADIUS
 211 server will be tried.<br>
 212 <strong>Note:</strong> in addition to the source IP address and
 213 identifier, the RADIUS server <strong>must</strong> include the source
 214 port when detecting duplicates to supress (in order to cope with a
 215 large number of sessions comming on-line simultaneously l2tpns uses a
 216 set of udp sockets, each with a seperate identifier).
 217 </LI>
 218
 219 <LI><B>primary_radius_port</B> (short)
 220 <LI><B>secondary_radius_port</B> (short)<BR>
 221 Sets the authentication ports for the primary and secondary RADIUS
 222 servers.  The accounting port is one more than the authentication
 223 port.  If no RADIUS ports are given, the authentication port defaults
 224 to 1645, and the accounting port to 1646.
 225 </LI>
 226
 227 <LI><B>radius_accounting</B> (boolean)<BR>
 228 If set to true, then RADIUS accounting packets will be sent.  This
 229 means that a Start record will be sent when the session is
 230 successfully authenticated, and a Stop record will be sent when the
 231 session is closed.
 232 </LI>
 233
 234 <LI><B>radius_secret</B> (string)<BR>
 235 This secret will be used in all RADIUS queries.  If this is not set then
 236 RADIUS queries will fail.
 237 </LI>
 238
 239 <LI><B>radius_authtypes</B> (string)</BR>
 240 A comma separated list of supported RADIUS authentication methods
 241 (<B>pap</B> or <B>chap</B>), in order of preference (default <B>pap</B>).
 242 </LI>
 243
 244 <LI><B>radius_dae_port</B> (short)<BR>
 245 Port for DAE RADIUS (Packet of Death/Disconnect, Change of Authorization)
 246 requests (default: <B>3799</B>).
 247 </LI>
 248
 249 <LI><B>allow_duplicate_users</B> (boolean)</BR>
 250 Allow multiple logins with the same username.  If false (the default),
 251 any prior session with the same username will be dropped when a new
 252 session is established.
 253 </LI>
 254
 255 <LI><B>bind_address</B> (ip address)<BR>
 256 When the tun interface is created, it is assigned the address
 257 specified here.  If no address is given, 1.1.1.1 is used.  Packets
 258 containing user traffic should be routed via this address if given,
 259 otherwise the primary address of the machine.
 260 </LI>
 261
 262 <LI><B>peer_address</B> (ip address)<BR>
 263 Address to send to clients as the default gateway.
 264 </L1>
 265
 266 <LI><B>send_garp</B> (boolean)<BR>
 267 Determines whether or not to send a gratuitous ARP for the
 268 bind_address when the server is ready to handle traffic (default:
 269 true).<BR>
 270 This value is ignored if BGP is configured.
 271 </LI>
 272
 273 <LI><B>throttle_speed</B> (int)<BR>
 274 Sets the default speed (in kbits/s) which sessions will be limited to.
 275 If this is set to 0, then throttling will not be used at all.  Note:
 276 You can set this by the CLI, but changes will not affect currently
 277 connected users.
 278 </LI>
 279
 280 <LI><B>throttle_buckets</B> (int)<BR>
 281 Number of token buckets to allocate for throttling.  Each throttled
 282 session requires two buckets (in and out).
 283 </LI>
 284
 285 <LI><B>accounting_dir</B> (string)<BR>
 286 If set to a directory, then every 5 minutes the current usage for
 287 every connected use will be dumped to a file in this directory.  Each
 288 file dumped begins with a header, where each line is prefixed by #.
 289 Following the header is a single line for every connected user, fields
 290 separated by a space.<BR> The fields are username, ip, qos,
 291 uptxoctets, downrxoctets.  The qos field is 1 if a standard user, and
 292 2 if the user is throttled.
 293 </LI>
 294
 295 <LI><B>setuid</B> (int)<BR>
 296 After starting up and binding the interface, change UID to this.  This
 297 doesn't work properly.
 298 </LI>
 299
 300 <LI><B>dump_speed</B> (boolean)<BR>
 301 If set to true, then the current bandwidth utilization will be logged every
 302 second.  Even if this is disabled, you can see this information by running
 303 the <EM>uptime</EM> command on the CLI.
 304 </LI>
 305
 306 <LI><B>multi_read_count</B> (int)<BR>
 307 Number of packets to read off each of the UDP and TUN fds when
 308 returned as readable by select (default:  10).  Avoids incurring the
 309 unnecessary system call overhead of select on busy servers.
 310 </LI>
 311
 312 <LI><B>scheduler_fifo</B> (boolean)<BR>
 313 Sets the scheduling policy for the l2tpns process to SCHED_FIFO.  This
 314 causes the kernel to immediately preempt any currently running SCHED_OTHER
 315 (normal) process in favour of l2tpns when it becomes runnable.
 316 Ignored on uniprocessor systems.
 317 </LI>
 318
 319 <LI><B>lock_pages</B> (boolean)<BR>
 320 Keep all pages mapped by the l2tpns process in memory.
 321 </LI>
 322
 323 <LI><B>icmp_rate</B> (int)<BR>
 324 Maximum number of host unreachable ICMP packets to send per second.
 325 </LI>
 326
 327 <LI><B>packet_limit</B> (int><BR>
 328 Maximum number of packets of downstream traffic to be handled each
 329 tenth of a second per session.  If zero, no limit is applied (default:
 330 0).  Intended as a DoS prevention mechanism and not a general
 331 throttling control (packets are dropped, not queued).
 332 </LI>
 333
 334 <LI><B>cluster_address</B> (ip address)<BR>
 335 Multicast cluster address (default:  239.192.13.13).  See the section
 336 on <A HREF="#Clustering">Clustering</A> for more information.
 337 </LI>
 338
 339 <LI><B>cluster_interface</B> (string)<BR>
 340 Interface for cluster packets (default: eth0).
 341 </LI>
 342
 343 <LI><B>cluster_mcast_ttl</B> (int)<BR>
 344 TTL for multicast packets (default: 1).
 345 </LI>
 346
 347 <LI><B>cluster_hb_interval</B> (int)<BR>
 348 Interval in tenths of a second between cluster heartbeat/pings.
 349 </LI>
 350
 351 <LI><B>cluster_hb_timeout</B> (int)<BR>
 352 Cluster heartbeat timeout in tenths of a second.  A new master will be
 353 elected when this interval has been passed without seeing a heartbeat
 354 from the master.
 355 </LI>
 356
 357 <LI><B>cluster_master_min_adv</B> (int)<BR>
 358 Determines the minumum number of up to date slaves required before the
 359 master will drop routes (default: 1).
 360 </LI>
 361 </UL>
 362
 363 <P>BGP routing configuration is entered by the command:
 364 The routing configuration section is entered by the command
 365 <DL><DD><B>router bgp</B> <I>as</I></DL>
 366 where <I>as</I> specifies the local AS number.
 367
 368 <P>Subsequent lines prefixed with
 369 <DL><DD><B>neighbour</B> <I>peer</I></DL>
 370 define the attributes of BGP neighhbours.  Valid commands are:
 371 <DL>
 372   <DD><B>neighbour</B> <I>peer</I> <B>remote-as</B> <I>as</I>
 373   <DD><B>neighbout</B> <I>peer</I> <B>timers</B> <I>keepalive hold</I>
 374 </DL>
 375
 376 Where <I>peer</I> specifies the BGP neighbour as either a hostname or
 377 IP address, <I>as</I> is the remote AS number and <I>keepalive</I>,
 378 <I>hold</I> are the timer values in seconds.
 379
 380 <P>Named access-lists are configured using one of the commands:
 381 <DL>
 382   <DD><B>ip access-list standard</B> <I>name</I>
 383   <DD><B>ip access-list extended</B> <I>name</I>
 384 </DL>
 385
 386 <P>Subsequent lines prefixed with <B>permit</B> or <B>deny</B>
 387 define the body of the access-list.  Standard access-list syntax:
 388 <DL>
 389   <DD>{<B>permit</B>|<B>deny</B>}
 390     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 391     [{<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}]
 392 </DL>
 393
 394 Extended access-lists:
 395
 396 <DIV STYLE="margin-left: 4em; text-indent: -2em">
 397   <P>{<B>permit</B>|<B>deny</B>} <B>ip</B>
 398     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 399     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>} [<B>fragments</B>]
 400   <P>{<B>permit</B>|<B>deny</B>} <B>udp</B>
 401     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 402         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 403     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}
 404         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 405         [<B>fragments</B>]
 406   <P>{<B>permit</B>|<B>deny</B>} <B>tcp</B>
 407     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 408         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 409     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}
 410         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 411         [{<B>established</B>|{<B>match-any</B>|<B>match-all</B>}
 412             {<B>+</B>|<B>-</B>}{<B>fin</B>|<B>syn</B>|<B>rst</B>|<B>psh</B>|<B>ack</B>|<B>urg</B>}
 413             ...|<B>fragments</B>]
 414 </DIV>
 415
 416 <H3 ID="users">users</H3>
 417
 418 Usernames and passwords for the command-line interface are stored in
 419 this file.  The format is <I>username</I><B>:</B><I>password</I> where
 420 <I>password</I> may either by plain text, an MD5 digest (prefixed by
 421 <B>$1</B><I>salt</I><B>$</B>) or a DES password, distinguished from
 422 plain text by the prefix <B>{crypt}</B>.<P>
 423
 424 The username <B>enable</B> has a special meaning and is used to set
 425 the enable password.<P>
 426
 427 <B>Note:</B> If this file doesn't exist, then anyone who can get to
 428 port 23 will be allowed access without a username / password.<P>
 429
 430 <H3 ID="ip-pool">ip_pool</H3>
 431
 432 This file is used to configure the IP address pool which user
 433 addresses are assigned from.  This file should contain either an IP
 434 address or a CIDR network per line.  e.g.:<P>
 435
 436 <PRE>
 437     192.168.1.1
 438     192.168.1.2
 439     192.168.1.3
 440     192.168.4.0/24
 441     172.16.0.0/16
 442     10.0.0.0/8
 443 </PRE>
 444
 445 Keep in mind that l2tpns can only handle 65535 connections per
 446 process, so don't put more than 65535 IP addresses in the
 447 configuration file.  They will be wasted.
 448
 449 <H3 ID="build-garden">build-garden</H3>
 450
 451 The garden plugin on startup creates a NAT table called "garden" then
 452 sources the <B>build-garden</B> script to populate that table.  All
 453 packets from gardened users will be sent through this table.  Example:
 454
 455 <PRE>
 456     iptables -t nat -A garden -p tcp -m tcp --dport 25 -j DNAT --to 192.168.1.1
 457     iptables -t nat -A garden -p udp -m udp --dport 53 -j DNAT --to 192.168.1.1
 458     iptables -t nat -A garden -p tcp -m tcp --dport 53 -j DNAT --to 192.168.1.1
 459     iptables -t nat -A garden -p tcp -m tcp --dport 80 -j DNAT --to 192.168.1.1
 460     iptables -t nat -A garden -p tcp -m tcp --dport 110 -j DNAT --to 192.168.1.1
 461     iptables -t nat -A garden -p tcp -m tcp --dport 443 -j DNAT --to 192.168.1.1
 462     iptables -t nat -A garden -p icmp -m icmp --icmp-type echo-request -j DNAT --to 192.168.1.1
 463     iptables -t nat -A garden -p icmp -j ACCEPT
 464     iptables -t nat -A garden -j DROP
 465 </PRE>
 466
 467 <H2 ID="ControllingtheProcess">Controlling the Process</H2>
 468
 469 A running l2tpns process can be controlled in a number of ways.  The primary
 470 method of control is by the Command-Line Interface (CLI).<P>
 471
 472 You can also remotely send commands to modules via the nsctl client
 473 provided.<P>
 474
 475 Also, there are a number of signals that l2tpns understands and takes action
 476 when it receives them.
 477
 478 <H3 ID="Command-LineInterface">Command-Line Interface</H3>
 479
 480 You can access the command line interface by telnet'ing to port 23.
 481 There is no IP address restriction, so it's a good idea to firewall
 482 this port off from anyone who doesn't need access to it.  See
 483 <A HREF="#users">users</A> for information on restricting access based
 484 on a username and password.<P>
 485
 486 The CLI gives you real-time control over almost everything in
 487 the process.  The interface is designed to look like a Cisco
 488 device, and supports things like command history, line editing and
 489 context sensitive help.  This is provided by linking with the
 490 <A HREF="http://sourceforge.net/projects/libcli">libcli</A>
 491 library.  Some general documentation of the interface is
 492 <A HREF="http://sourceforge.net/docman/display_doc.php?docid=20501&group_id=79019">
 493 here</A>.<P>
 494
 495 After you have connected to the telnet port (and perhaps logged in), you
 496 will be presented with a <I>hostname</I><B>&gt;</B> prompt.<P>
 497
 498 Enter <EM>help</EM> to get a list of possible commands.  A brief
 499 overview of the more important commands follows:
 500
 501 <UL>
 502 <LI><B>show session</B><BR>
 503 Without specifying a session ID, this will list all tunnels currently
 504 connected.  If you specify a session ID, you will be given all
 505 information on a single tunnel.  Note that the full session list can
 506 be around 185 columns wide, so you should probably use a wide terminal
 507 to see the list properly.<P>
 508 The columns listed in the overview are:
 509 <TABLE>
 510         <TR><TD><B>SID</B></TD><TD>Session ID</TD></TR>
 511         <TR><TD><B>TID</B></TD><TD>Tunnel ID - Use with <EM>show tunnel tid</EM></TD></TR>
 512         <TR><TD><B>Username</B></TD><TD>The username given in the PPP
 513         authentication.  If this is *, then LCP authentication has not
 514         completed.</TD></TR>
 515         <TR><TD><B>IP</B></TD><TD>The IP address given to the session.  If
 516         this is 0.0.0.0, LCP negotiation has not completed.</TD></TR>
 517         <TR><TD><B>I</B></TD><TD>Intercept - Y or N depending on whether the
 518         session is being snooped.  See <EM>snoop</EM>.</TD></TR>
 519         <TR><TD><B>T</B></TD><TD>Throttled - Y or N if the session is
 520         currently throttled.  See <EM>throttle</EM>.</TD></TR>
 521         <TR><TD><B>G</B></TD><TD>Walled Garden - Y or N if the user is
 522         trapped in the walled garden.  This field is present even if the
 523         garden module is not loaded.</TD></TR>
 524         <TR><TD><B>opened</B></TD><TD>The number of seconds since the
 525         session started</TD></TR>
 526         <TR><TD><B>downloaded</B></TD><TD>Number of bytes downloaded by the user</TD></TR>
 527         <TR><TD><B>uploaded</B></TD><TD>Number of bytes uploaded by the user</TD></TR>
 528         <TR><TD><B>idle</B></TD><TD>The number of seconds since traffic was
 529         detected on the session</TD></TR>
 530         <TR><TD><B>LAC</B></TD><TD>The IP address of the LAC the session is
 531         connected to.</TD></TR>
 532         <TR><TD><B>CLI</B></TD><TD>The Calling-Line-Identification field
 533         provided during the session setup.  This field is generated by the
 534         LAC.</TD></TR>
 535 </TABLE>
 536 <P>
 537 </LI>
 538
 539 <LI><B>show users</B><BR>
 540 With no arguments, display a list of currently connected users.  If an
 541 argument is given, the session details for the given username are
 542 displayed.
 543 </LI>
 544
 545 <LI><B>show tunnel</B><BR>
 546 This will show all the open tunnels in a summary, or detail on a single
 547 tunnel if you give a tunnel id.<P>
 548 The columns listed in the overview are:
 549 <TABLE>
 550         <TR><TD><B>TID</B></TD><TD>Tunnel ID</TD></TR>
 551         <TR><TD><B>Hostname</B></TD><TD>The hostname for the tunnel as
 552         provided by the LAC.  This has no relation to DNS, it is just
 553         a text field.</TD></TR>
 554         <TR><TD><B>IP</B></TD><TD>The IP address of the LAC</TD></TR>
 555         <TR><TD><B>State</B></TD><TD>Tunnel state - Free, Open, Dieing,
 556         Opening</TD></TR>
 557         <TR><TD><B>Sessions</B></TD><TD>The number of open sessions on the
 558         tunnel</TD></TR>
 559 </TABLE>
 560 <P>
 561 </LI>
 562
 563 <LI><B>show pool</B><BR>
 564 Displays the current IP address pool allocation.  This will only display
 565 addresses that are in use, or are reserved for re-allocation to a
 566 disconnected user.<P>
 567 If an address is not currently in use, but has been used, then in the User
 568 column the username will be shown in square brackets, followed by the time
 569 since the address was used:
 570 <PRE>
 571 IP Address      Used  Session User
 572 192.168.100.6     N           [joe.user] 1548s
 573 </PRE>
 574 <P>
 575 </LI>
 576
 577 <LI><B>show radius</B><BR>
 578 Show a summary of the in-use RADIUS sessions.  This list should not be very
 579 long, as RADIUS sessions should be cleaned up as soon as they are used.  The
 580 columns listed are:
 581 <TABLE>
 582         <TR><TD><B>Radius</B></TD><TD>The ID of the RADIUS request.  This is
 583         sent in the packet to the RADIUS server for identification.</TD></TR>
 584         <TR><TD><B>State</B></TD><TD>The state of the request - WAIT, CHAP,
 585         AUTH, IPCP, START, STOP, NULL.</TD></TR>
 586         <TR><TD><B>Session</B></TD><TD>The session ID that this RADIUS
 587         request is associated with</TD></TR>
 588         <TR><TD><B>Retry</B></TD><TD>If a response does not appear to the
 589         request, it will retry at this time.  This is a unix timestamp.</TD></TR>
 590         <TR><TD><B>Try</B></TD><TD>Retry count.  The RADIUS request is
 591         discarded after 3 retries.</TD></TR>
 592 </TABLE>
 593 <P>
 594 </LI>
 595
 596 <LI><B>show running-config</B><BR>
 597 This will list the current running configuration.  This is in a format that
 598 can either be pasted into the configuration file, or run directly at the
 599 command line.
 600 <P>
 601 </LI>
 602
 603 <LI><B>show counters</B><BR>
 604 Internally, counters are kept of key values, such as bytes and packets
 605 transferred, as well as function call counters.  This function displays all
 606 these counters, and is probably only useful for debugging.<P>
 607 You can reset these counters by running <EM>clear counters</EM>.
 608 <P>
 609 </LI>
 610
 611 <LI><B>show cluster</B><BR>
 612 Show cluster status.  Shows the cluster state for this server
 613 (Master/Slave), information about known peers and (for slaves) the
 614 master IP address, last packet seen and up-to-date status.<P>
 615 See <A HREF="#Clustering">Clustering</A> for more information.
 616 <P>
 617 </LI>
 618
 619 <LI><B>write memory</B><BR>
 620 This will write the current running configuration to the config file
 621 <B>startup-config</B>, which will be run on a restart.
 622 <P>
 623 </LI>
 624
 625 <LI><B>snoop</B><BR>
 626 You must specify a username, IP address and port.  All packets for the
 627 current session for that username will be forwarded to the given
 628 host/port.  Specify <EM>no snoop username</EM> to disable interception
 629 for the session.<P>
 630
 631 If you want interception to be permanent, you will have to modify the RADIUS
 632 response for the user.  See <A HREF="#Interception">Interception</A>.
 633 <P>
 634 </LI>
 635
 636 <LI><B>throttle</B><BR>
 637 You must specify a username, which will be throttled for the current
 638 session.  Specify <EM>no throttle username</EM> to disable throttling
 639 for the current session.<P>
 640
 641 If you want throttling to be permanent, you will have to modify the
 642 RADIUS response for the user.  See <A HREF="#Throttling">Throttling</A>.
 643 <P>
 644 </LI>
 645
 646 <LI><B>drop session</B><BR>
 647 This will cleanly disconnect a session.  You must specify a session id, which
 648 you can get from <EM>show session</EM>.  This will send a disconnect message
 649 to the remote end.
 650 <P>
 651 </LI>
 652
 653 <LI><B>drop tunnel</B><BR>
 654 This will cleanly disconnect a tunnel, as well as all sessions on that
 655 tunnel.  It will send a disconnect message for each session individually, and
 656 after 10 seconds it will send a tunnel disconnect message.
 657 <P>
 658 </LI>
 659
 660 <LI><B>uptime</B><BR>
 661 This will show how long the l2tpns process has been running, and the current
 662 bandwidth utilization:
 663 <PRE>
 664 17:10:35 up 8 days, 2212 users, load average: 0.21, 0.17, 0.16
 665 Bandwidth: UDP-ETH:6/6  ETH-UDP:13/13  TOTAL:37.6   IN:3033 OUT:2569
 666 </PRE>
 667 The bandwidth line contains 4 sets of values.<BR>
 668 UDP-ETH is the current bandwidth going from the LAC to the ethernet
 669 (user uploads), in mbits/sec.<BR>
 670 ETH-UDP is the current bandwidth going from ethernet to the LAC (user
 671 downloads).<BR>
 672 TOTAL is the total aggregate bandwidth in mbits/s.<BR>
 673 IN and OUT are packets/per-second going between UDP-ETH and ETH-UDP.
 674 <P>
 675 These counters are updated every second.
 676 <P>
 677 </LI>
 678
 679 <LI><B>configure terminal</B><BR>
 680 Enter configuration mode.  Use <EM>exit</EM> or ^Z to exit this mode.
 681 The following commands are valid in this mode:<P>
 682 </LI>
 683
 684 <LI><B>load plugin</B><BR>
 685 Load a plugin.  You must specify the plugin name, and it will search in
 686 /usr/lib/l2tpns for <EM>plugin</EM>.so.  You can unload a loaded plugin with
 687 <EM>remove plugin</EM>.
 688 <P>
 689 </LI>
 690
 691 <LI><B>set</B><BR>
 692 Set a configuration variable.  You must specify the variable name, and
 693 the value.  If the value contains any spaces, you should quote the
 694 value with double (") or single (') quotes.<P>
 695
 696 You can set any <A HREF="#startup-config">startup-config</A> value in
 697 this way, although some may require a restart to take effect.<P>
 698 </LI>
 699 </UL>
 700
 701 <H3 ID="nsctl">nsctl</H3>
 702
 703 nsctl allows messages to be passed to plugins.<P>
 704
 705 Arguments are <EM>command</EM> and optional <EM>args</EM>.  See
 706 <STRONG>nsctl</STRONG>(8) for more details.<P>
 707
 708 Built-in command are <EM>load_plugin</EM>, <EM>unload_plugin</EM> and
 709 <EM>help</EM>.  Any other commands are passed to plugins for processing.
 710
 711 <H3 ID="Signals">Signals</H3>
 712
 713 While the process is running, you can send it a few different signals, using
 714 the kill command.
 715 <PRE>
 716 killall -HUP l2tpns
 717 </PRE>
 718
 719 The signals understood are:
 720 <DL>
 721 <DT>SIGHUP</DT><DD>Reload the config from disk and re-open log file.</DD>
 722 <DT>SIGTERM, SIGINT</DT><DD>Stop process.  Tunnels and sessions are not
 723 terminated.  This signal should be used to stop l2tpns on a
 724 <A HREF="#Clustering">cluster node</A> where there are other machines to
 725 continue handling traffic.</DD>
 726 <DT>SIGQUIT</DT><DD>Shut down tunnels and sessions, exit process when
 727 complete.</DD>
 728 </DL>
 729
 730 <H2 ID="Throttling">Throttling</H2>
 731
 732 l2tpns contains support for slowing down user sessions to whatever speed you
 733 desire.  You must first enable the global setting <EM>throttle_speed</EM>
 734 before this will be activated.<P>
 735
 736 If you wish a session to be throttled permanently, you should set the
 737 Vendor-Specific RADIUS value <B>Cisco-Avpair="throttle=yes"</B>, which
 738 will be handled by the <EM>autothrottle</EM> module.<P>
 739
 740 Otherwise, you can enable and disable throttling an active session using
 741 the <EM>throttle</EM> CLI command.<P>
 742
 743 <H2 ID="Interception">Interception</H2>
 744
 745 You may have to deal with legal requirements to be able to intercept a
 746 user's traffic at any time.  l2tpns allows you to begin and end interception
 747 on the fly, as well as at authentication time.<P>
 748
 749 When a user is being intercepted, a copy of every packet they send and
 750 receive will be sent wrapped in a UDP packet to the IP address and port set
 751 in the <EM>snoop_host</EM> and <EM>snoop_port</EM> configuration
 752 variables.<P>
 753
 754 The UDP packet contains just the raw IP frame, with no extra headers.<P>
 755
 756 To enable interception on a connected user, use the <EM>snoop username</EM>
 757 and <EM>no snoop username</EM> CLI commands.  These will enable interception
 758 immediately.<P>
 759
 760 If you wish the user to be intercepted whenever they reconnect, you will
 761 need to modify the RADIUS response to include the Vendor-Specific value
 762 <B>Cisco-Avpair="intercept=yes"</B>.  For this feature to be enabled,
 763 you need to have the <EM>autosnoop</EM> module loaded.<P>
 764
 765 <H2 ID="Authentication">Authentication</H2>
 766
 767 Whenever a session connects, it is not fully set up until authentication is
 768 completed.  The remote end must send a PPP CHAP or PPP PAP authentication
 769 request to l2tpns.<P>
 770
 771 This request is sent to the RADIUS server, which will hopefully respond with
 772 Auth-Accept or Auth-Reject.<P>
 773
 774 If Auth-Accept is received, the session is set up and an IP address is
 775 assigned.  The RADIUS server can include a Framed-IP-Address field in the
 776 reply, and that address will be assigned to the client.  It can also include
 777 specific DNS servers, and a Framed-Route if that is required.<P>
 778
 779 If Auth-Reject is received, then the client is sent a PPP AUTHNAK packet,
 780 at which point they should disconnect.  The exception to this is when the
 781 walled garden module is loaded, in which case the user still receives the
 782 PPP AUTHACK, but their session is flagged as being a garden'd user, and they
 783 should not receive any service.<P>
 784
 785 The RADIUS reply can also contain a Vendor-Specific attribute called
 786 Cisco-Avpair.  This field is a freeform text field that most Cisco
 787 devices understand to contain configuration instructions for the session.  In
 788 the case of l2tpns it is expected to be of the form
 789 <PRE>
 790 key=value,key2=value2,key3=value3,key<EM>n</EM>=<EM>value</EM>
 791 </PRE>
 792
 793 Each key-value pair is separated and passed to any modules loaded.  The
 794 <EM>autosnoop</EM> and <EM>autothrottle</EM> understand the keys
 795 <EM>intercept</EM> and <EM>throttle</EM> respectively.  For example, to have
 796 a user who is to be throttled and intercepted, the Cisco-Avpair value should
 797 contain:
 798 <PRE>
 799 intercept=yes,throttle=yes
 800 </PRE>
 801
 802 <H2 ID="Plugins">Plugins</H2>
 803
 804 So as to make l2tpns as flexible as possible (I know the core code is pretty
 805 difficult to understand), it includes a plugin API, which you can use to
 806 hook into certain events.<P>
 807
 808 There are a few example modules included - autosnoop, autothrottle and
 809 garden.<P>
 810
 811 When an event happens that has a hook, l2tpns looks for a predefined
 812 function name in every loaded module, and runs them in the order the modules
 813 were loaded.<P>
 814
 815 The function should return <B>PLUGIN_RET_OK</B> if it is all OK.  If it returns
 816 <B>PLUGIN_RET_STOP</B>, then it is assumed to have worked, but that no further
 817 modules should be run for this event.<P>
 818 A return of <B>PLUGIN_RET_ERROR</B> means that this module failed, and
 819 no further processing should be done for this event.  <EM>Use this with care.</EM>
 820
 821 Every event function called takes a specific structure named
 822 param_<EM>event</EM>, which varies in content with each event.  The
 823 function name for each event will be <B>plugin_<EM>event</EM></B>,
 824 so for the event <EM>timer</EM>, the function declaration should look like:
 825 <PRE>
 826 int plugin_timer(struct param_timer *data);
 827 </PRE>
 828
 829 A list of the available events follows, with a list of all the fields in the
 830 supplied structure:
 831 <TABLE CELLSPACING=0 CELLPADDING=0><TR BGCOLOR=LIGHTGREEN><TD>
 832 <TABLE CELLSPACING=1 CELLPADDING=3>
 833         <TR BGCOLOR=LIGHTGREEN><TH><B>Event</B></TH><TH><B>Description</B></TH><TH><B>Parameters</B></TH></TR>
 834         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>pre_auth</B></TD>
 835                 <TD>This is called after a RADIUS response has been
 836                 received, but before it has been processed by the
 837                 code.  This will allow you to modify the response in
 838                 some way.
 839                 </TD>
 840                 <TD>
 841                 <DL>
 842                         <DT>t<DD>Tunnel
 843                         <DT>s<DD>Session
 844                         <DT>username
 845                         <DT>password
 846                         <DT>protocol<DD>0xC023 for PAP, 0xC223 for CHAP
 847                         <DT>continue_auth<DD>Set to 0 to stop processing authentication modules
 848                 </DL>
 849                 </TD>
 850         </TR>
 851         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>post_auth</B></TD>
 852                 <TD>This is called after a RADIUS response has been
 853                 received, and the basic checks have been performed.  This
 854                 is what the garden module uses to force authentication
 855                 to be accepted.
 856                 </TD>
 857                 <TD>
 858                 <DL>
 859                         <DT>t<DD>Tunnel
 860                         <DT>s<DD>Session
 861                         <DT>username
 862                         <DT>auth_allowed<DD>This is already set to true or
 863                         false depending on whether authentication has been
 864                         allowed so far.  You can set this to 1 or 0 to force
 865                         allow or disallow authentication
 866                         <DT>protocol<DD>0xC023 for PAP, 0xC223 for CHAP
 867                 </DL>
 868                 </TD>
 869         </TR>
 870         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_rx</B></TD>
 871                 <TD>This is called whenever a session receives a
 872                 packet.  <FONT COLOR=RED>Use this sparingly, as this will
 873                 seriously slow down the system.</FONT>
 874                 </TD>
 875                 <TD>
 876                 <DL>
 877                         <DT>t<DD>Tunnel
 878                         <DT>s<DD>Session
 879                         <DT>buf<DD>The raw packet data
 880                         <DT>len<DD>The length of buf
 881                 </DL>
 882                 </TD>
 883         </TR>
 884         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_tx</B></TD>
 885                 <TD>This is called whenever a session sends a
 886                 packet.  <FONT COLOR=RED>Use this sparingly, as this will
 887                 seriously slow down the system.</FONT>
 888                 </TD>
 889                 <TD>
 890                 <DL>
 891                         <DT>t<DD>Tunnel
 892                         <DT>s<DD>Session
 893                         <DT>buf<DD>The raw packet data
 894                         <DT>len<DD>The length of buf
 895                 </DL>
 896                 </TD>
 897         </TR>
 898         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>timer</B></TD>
 899                 <TD>This is run every second, no matter what is happening.
 900                 This is called from a signal handler, so make sure anything
 901                 you do is reentrant.
 902                 </TD>
 903                 <TD>
 904                 <DL>
 905                         <DT>time_now<DD>The current unix timestamp
 906                 </DL>
 907                 </TD>
 908         </TR>
 909         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>new_session</B></TD>
 910                 <TD>This is called after a session is fully set up.  The
 911                 session is now ready to handle traffic.
 912                 </TD>
 913                 <TD>
 914                 <DL>
 915                         <DT>t<DD>Tunnel
 916                         <DT>s<DD>Session
 917                 </DL>
 918                 </TD>
 919         </TR>
 920         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>kill_session</B></TD>
 921                 <TD>This is called when a session is about to be shut down.
 922                 This may be called multiple times for the same session.
 923                 </TD>
 924                 <TD>
 925                 <DL>
 926                         <DT>t<DD>Tunnel
 927                         <DT>s<DD>Session
 928                 </DL>
 929                 </TD>
 930         </TR>
 931         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>radius_response</B></TD>
 932                 <TD>This is called whenever a RADIUS response includes a
 933                 Cisco-Avpair value.  The value is split up into
 934                 <EM>key=value</EM> pairs, and each is processed through all
 935                 modules.
 936                 </TD>
 937                 <TD>
 938                 <DL>
 939                         <DT>t<DD>Tunnel
 940                         <DT>s<DD>Session
 941                         <DT>key
 942                         <DT>value
 943                 </DL>
 944                 </TD>
 945         </TR>
 946         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>radius_reset</B></TD>
 947                 <TD>This is called whenever a RADIUS CoA request is
 948                 received to reset any options to default values before
 949                 the new values are applied.
 950                 </TD>
 951                 <TD>
 952                 <DL>
 953                         <DT>t<DD>Tunnel
 954                         <DT>s<DD>Session
 955                 </DL>
 956                 </TD>
 957         </TR>
 958         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>control</B></TD>
 959                 <TD>This is called in whenever a nsctl packet is received.
 960                 This should handle the packet and form a response if
 961                 required.
 962                 </TD>
 963                 <TD>
 964                 <DL>
 965                         <DT>iam_master<DD>Cluster master status
 966                         <DT>argc<DD>The number of arguments
 967                         <DT>argv<DD>Arguments
 968                         <DT>response<DD>Return value: NSCTL_RES_OK or NSCTL_RES_ERR
 969                         <DT>additional<DD>Extended response text
 970                 </DL>
 971                 </TD>
 972         </TR>
 973 </TABLE>
 974 </TD></TR></TABLE>
 975
 976 <H2 ID="WalledGarden">Walled Garden</H2>
 977
 978 Walled Garden is implemented so that you can provide perhaps limited service
 979 to sessions that incorrectly authenticate.<P>
 980
 981 Whenever a session provides incorrect authentication, and the
 982 RADIUS server responds with Auth-Reject, the walled garden module
 983 (if loaded) will force authentication to succeed, but set the flag
 984 <EM>garden</EM> in the session structure, and adds an iptables rule to
 985 the <B>garden_users</B> chain to force all packets for the session's IP
 986 address to traverse the <B>garden</B> chain.<P>
 987
 988 This doesn't <EM>just work</EM>.  To set this all up, you will to
 989 setup the <B>garden</B> nat table with the
 990 <A HREF="#build-garden">build-garden</A> script with rules to limit
 991 user's traffic.  For example, to force all traffic except DNS to be
 992 forwarded to 192.168.1.1, add these entries to your
 993 <EM>build-garden</EM>:
 994 <PRE>
 995 iptables -t nat -A garden -p tcp --dport ! 53 -j DNAT --to 192.168.1.1
 996 iptables -t nat -A garden -p udp --dport ! 53 -j DNAT --to 192.168.1.1
 997 </PRE>
 998
 999 l2tpns will add entries to the garden_users chain as appropriate.<P>
1000
1001 You can check the amount of traffic being captured using the following
1002 command:
1003 <PRE>
1004 iptables -t nat -L garden -nvx
1005 </PRE>
1006
1007 <H2 ID="Filtering">Filtering</H2>
1008
1009 Sessions may be filtered by specifying <B>Filter-Id</B> attributes in
1010 the RADIUS reply.  <I>filter</I>.<B>in</B> specifies that the named
1011 access-list <I>filter</I> should be applied to traffic from the
1012 customer, <I>filter</I>.<B>out</B> specifies a list for traffic to the
1013 customer.
1014
1015 <H2 ID="Clustering">Clustering</H2>
1016
1017 An l2tpns cluster consists of of one* or more servers configured with
1018 the same configuration, notably the multicast <B>cluster_address</B>.<P>
1019
1020 *A stand-alone server is simply a degraded cluster.<P>
1021
1022 Initially servers come up as cluster slaves, and periodically (every
1023 <B>cluster_hb_interval</B>/10 seconds) send out ping packets
1024 containing the start time of the process to the multicast
1025 <B>cluster_address</B>.<P>
1026
1027 A cluster master sends heartbeat rather than ping packets, which
1028 contain those session and tunnel changes since the last heartbeat.<P>
1029
1030 When a slave has not seen a heartbeat within
1031 <B>cluster_hb_timeout</B>/10 seconds it "elects" a new master by
1032 examining the list of peers it has seen pings from and determines
1033 which of these and itself is the "best" candidate to be master.
1034 "Best" in this context means the server with the highest uptime (the
1035 highest IP address is used as a tie-breaker in the case of equal
1036 uptimes).<P>
1037
1038 After discovering a master, and determining that it is up-to-date (has
1039 seen an update for all in-use sessions and tunnels from heartbeat
1040 packets) will raise a route (see <A HREF="#Routing">Routing</A>) for
1041 the <B>bind_address</B> and for all addresses/networks in
1042 <B>ip_pool</B>.  Any packets recieved by the slave which would alter
1043 the session state, as well as packets for throttled or gardened
1044 sessions are forwarded to the master for handling.  In addition, byte
1045 counters for session traffic are periodically forwarded.<P>
1046
1047 A master, when determining that it has at least one up-to-date slave
1048 will drop all routes (raising them again if all slaves disappear) and
1049 subsequently handle only packets forwarded to it by the slaves.<P>
1050
1051 <H2 ID="Routing">Routing</H2>
1052 If you are running a single instance, you may simply statically route
1053 the IP pools to the <B>bind_address</B> (l2tpns will send a gratuitous
1054 arp).<P>
1055
1056 For a cluster, configure the members as BGP neighbours on your router
1057 and configure multi-path load-balancing.  Cisco uses "maximum-paths
1058 ibgp" for IBGP.  If this is not supported by your IOS revision, you
1059 can use "maximum-paths" (which works for EBGP) and set
1060 <B>as_number</B> to a private value such as 64512.<P>
1061
1062 <H2 ID="AvoidingFragmentation">Avoiding Fragmentation</H2>
1063
1064 Fragmentation of encapsulated return packets to the LAC may be avoided
1065 for TCP sessions by adding a firewall rule to clamps the MSS on
1066 outgoing SYN packets.
1067
1068 The following is appropriate for interfaces with a typical MTU of
1069 1500:
1070
1071 <pre>
1072 iptables -A FORWARD -i tun+ -o eth0     \
1073     -p tcp --tcp-flags SYN,RST SYN      \
1074     -m tcpmss --mss 1413:1600           \
1075     -j TCPMSS --set-mss 1412
1076 </pre>
1077
1078 <H2 ID="Performance">Performance</H2>
1079
1080 Performance is great.<P>
1081
1082 I'd like to include some pretty graphs here that show a linear performance
1083 increase, with no impact by number of connected sessions.<P>
1084
1085 That's really what it looks like.<P>
1086
1087 <BR>
1088 David Parrish<BR>
1089 <A HREF="mailto:l2tpns-users@lists.sourceforge.net?subject=L2TPNS%20Documentation">l2tpns-users@lists.sourceforge.net</A>
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