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