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