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