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  25 <H1>L2TPNS Manual</H1>
  26 <OL>
  27     <LI><A HREF="#Overview">Overview</A></LI>
  28     <LI><A HREF="#Installation">Installation</A>
  29         <OL>
  30             <LI><A HREF="#Requirements">Requirements</A></LI>
  31             <LI><A HREF="#Compile">Compile</A></LI>
  32             <LI><A HREF="#Install">Install</A></LI>
  33             <LI><A HREF="#Running">Running</A></LI>
  34         </OL>
  35     </LI>
  36     <LI><A HREF="#Configuration">Configuration</A>
  37         <OL>
  38             <LI><A HREF="#startup-config">startup-config</A></LI>
  39             <LI><A HREF="#users">users</A></LI>
  40             <LI><A HREF="#ip-pool">ip_pool</A></LI>
  41             <LI><A HREF="#build-garden">build-garden</A></LI>
  42         </OL>
  43     </LI>
  44     <LI><A HREF="#ControllingtheProcess">Controlling the Process</A>
  45         <OL>
  46             <LI><A HREF="#Command-LineInterface">Command-Line Interface</A></LI>
  47             <LI><A HREF="#nsctl">nsctl</A></LI>
  48             <LI><A HREF="#Signals">Signals</A></LI>
  49         </OL>
  50     </LI>
  51     <LI><A HREF="#Throttling">Throttling</A></LI>
  52     <LI><A HREF="#Interception">Interception</A></LI>
  53     <LI><A HREF="#Authentication">Authentication</A></LI>
  54     <LI><A HREF="#Plugins">Plugins</A></LI>
  55     <LI><A HREF="#WalledGarden">Walled Garden</A></LI>
  56     <LI><A HREF="#Filtering">Filtering</A></LI>
  57     <LI><A HREF="#Clustering">Clustering</A></LI>
  58     <LI><A HREF="#Routing">Routing</A></LI>
  59     <LI><A HREF="#AvoidingFragmentation">Avoiding Fragmentation</A></LI>
  60     <LI><A HREF="#Performance">Performance</A></LI>
  61 </OL>
  62
  63 <H2 ID="Overview">Overview</H2>
  64 l2tpns is half of a complete L2TP implementation.  It supports only the
  65 LNS side of the connection.<P>
  66
  67 L2TP (Layer 2 Tunneling Protocol) is designed to allow any layer 2
  68 protocol (e.g. Ethernet, PPP) to be tunneled over an IP connection.  l2tpns
  69 implements PPP over L2TP only.<P>
  70
  71 There are a couple of other L2TP implementations, of which <A
  72 HREF="http://sourceforge.net/projects/l2tpd">l2tpd</A> is probably the
  73 most popular.  l2tpd also will handle being either end of a tunnel, and
  74 is a lot more configurable than l2tpns.  However, due to the way it works,
  75 it is nowhere near as scalable.<P>
  76
  77 l2tpns uses the TUN/TAP interface provided by the Linux kernel to receive
  78 and send packets.  Using some packet manipulation it doesn't require a
  79 single interface per connection, as l2tpd does.<P>
  80
  81 This allows it to scale extremely well to very high loads and very high
  82 numbers of connections.<P>
  83
  84 It also has a plugin architecture which allows custom code to be run
  85 during processing.  An example of this is in the walled garden module
  86 included.<P>
  87
  88 <BR>
  89 <EM>Documentation is not my best skill.  If you find any problems
  90 with this document, or if you wish to contribute, please email <A
  91 HREF="mailto:l2tpns-users@lists.sourceforge.net?subject=L2TPNS+Documentation">the mailing list</A>.</EM><P>
  92
  93 <H2 ID="Installation">Installation</H2>
  94 <H3 ID="Requirements">Requirements</H3>
  95
  96 <OL>
  97 <LI>Linux kernel version 2.4 or above, with the Tun/Tap interface either
  98 compiled in, or as a module.</LI>
  99
 100 <LI>libcli 1.8.0 or greater.<BR>You can get this from <A
 101 HREF="http://sourceforge.net/projects/libcli">http://sourceforge.net/projects/libcli</A></LI>
 102 </OL>
 103
 104 <H3 ID="Compile">Compile</H3>
 105
 106 You can generally get away with just running <B>make</B> from the source
 107 directory.  This will compile the daemon, associated tools and any modules
 108 shipped with the distribution.<P>
 109
 110 <H3 ID="Install">Install</H3>
 111
 112 After you have successfully compiled everything, run <B>make
 113 install</B> to install it.  By default, the binaries are installed into
 114 <EM>/usr/sbin</EM>, the configuration into <EM>/etc/l2tpns</EM>, and the
 115 modules into <EM>/usr/lib/l2tpns</EM>.<P>
 116
 117 You will definately need to edit the configuration files before you
 118 start.  See the <A HREF="#Configuration">Configuration</A> section for
 119 more information.<P>
 120
 121 <H3 ID="Running">Running</H3>
 122
 123 You only need to run <B>/usr/sbin/l2tpns</B> as root to start it.  It does
 124 not detach to a daemon process, so you should perhaps run it from init.<P>
 125
 126 By default there is no log destination set, so all log messages will go to
 127 stdout.<P>
 128
 129 <H2 ID="Configuration">Configuration</H2>
 130
 131 All configuration of the software is done from the files installed into
 132 /etc/l2tpns.
 133
 134 <H3 ID="startup-config">startup-config</H3>
 135
 136 This is the main configuration file for l2tpns.  The format of the file is a
 137 list of commands that can be run through the command-line interface.  This
 138 file can also be written directly by the l2tpns process if a user runs the
 139 <EM>write memory</EM> command, so any comments will be lost.  However if your
 140 policy is not to write the config by the program, then feel free to comment
 141 the file with a # or ! at the beginning of the line.<P>
 142
 143 A list of the possible configuration directives follows.  Each of these
 144 should be set by a line like:<P>
 145 <PRE>
 146 set configstring "value"
 147 set ipaddress 192.168.1.1
 148 set boolean true
 149 </PRE>
 150
 151 <P>
 152 <UL>
 153 <LI><B>debug</B> (int)<BR>
 154 Sets the level of messages that will be written to the log file.  The value
 155 should be between 0 and 5, with 0 being no debugging, and 5 being the
 156 highest.  A rough description of the levels is:
 157         <OL>
 158         <LI VALUE=0>Critical Errors - Things are probably broken</LI>
 159         <LI>Errors - Things might have gone wrong, but probably will recover</LI>
 160         <LI>Warnings - Just in case you care what is not quite perfect</LI>
 161         <LI>Information - Parameters of control packets</LI>
 162         <LI>Calls - For tracing the execution of the code</LI>
 163         <LI>Packets - Everything, including a hex dump of all packets processed...  probably twice</LI>
 164         </OL><P>
 165 Note that the higher you set the debugging level, the slower the program
 166 will run.  Also, at level 5 a LOT of information will be logged.  This should
 167 only ever be used for working out why it doesn't work at all.
 168 </LI>
 169
 170 <LI><B>log_file</B> (string)<BR>
 171 This will be where all logging and debugging information is written
 172 to.  This may be either a filename, such as <EM>/var/log/l2tpns</EM>, or
 173 the special magic string <EM>syslog:facility</EM>, where <EM>facility</EM>
 174 is any one of the syslog logging facilities, such as local5.
 175 </LI>
 176
 177 <LI><B>pid_file</B> (string)<BR>
 178 If set, the process id will be written to the specified file.  The
 179 value must be an absolute path.
 180 </LI>
 181
 182 <LI><B>l2tp_secret</B> (string)<BR>
 183 The secret used by l2tpns for authenticating tunnel request.  Must be
 184 the same as the LAC, or authentication will fail.  Only actually be
 185 used if the LAC requests authentication.
 186 </LI>
 187
 188 <LI><B>ppp_restart_time</B> (int)<BR>
 189 <B>ppp_max_configure</B> (int)<BR>
 190 <B>ppp_max_failure</B> (int)<BR>
 191 PPP counter and timer values, as described in &sect;4.1 of
 192 <a href="ftp://ftp.rfc-editor.org/in-notes/rfc1661.txt">RFC1661</a>.
 193 </LI>
 194
 195 <LI><B>ppp_mru</B> (int)<BR>
 196 PPP link MRU (default: 1452).
 197 </LI>
 198
 199 <LI><B>primary_dns</B> (ip address)
 200 <LI><B>secondary_dns</B> (ip address)<BR>
 201 Whenever a PPP connection is established, DNS servers will be sent to the
 202 user, both a primary and a secondary.  If either is set to 0.0.0.0, then that
 203 one will not be sent.
 204 </LI>
 205
 206 <LI><B>primary_radius</B> (ip address)
 207 <LI><B>secondary_radius</B> (ip address)<BR>
 208 Sets the RADIUS servers used for both authentication and accounting.
 209 If the primary server does not respond, then the secondary RADIUS
 210 server will be tried.<br>
 211 <strong>Note:</strong> in addition to the source IP address and
 212 identifier, the RADIUS server <strong>must</strong> include the source
 213 port when detecting duplicates to supress (in order to cope with a
 214 large number of sessions comming on-line simultaneously l2tpns uses a
 215 set of udp sockets, each with a seperate identifier).
 216 </LI>
 217
 218 <LI><B>primary_radius_port</B> (short)
 219 <LI><B>secondary_radius_port</B> (short)<BR>
 220 Sets the authentication ports for the primary and secondary RADIUS
 221 servers.  The accounting port is one more than the authentication
 222 port.  If no RADIUS ports are given, the authentication port defaults
 223 to 1645, and the accounting port to 1646.
 224 </LI>
 225
 226 <LI><B>radius_accounting</B> (boolean)<BR>
 227 If set to true, then RADIUS accounting packets will be sent.  This
 228 means that a Start record will be sent when the session is
 229 successfully authenticated, and a Stop record will be sent when the
 230 session is closed.
 231 </LI>
 232
 233 <LI><B>radius_secret</B> (string)<BR>
 234 This secret will be used in all RADIUS queries.  If this is not set then
 235 RADIUS queries will fail.
 236 </LI>
 237
 238 <LI><B>radius_authtypes</B> (string)</BR>
 239 A comma separated list of supported RADIUS authentication methods
 240 (<B>pap</B> or <B>chap</B>), in order of preference (default <B>pap</B>).
 241 </LI>
 242
 243 <LI><B>radius_dae_port</B> (short)<BR>
 244 Port for DAE RADIUS (Packet of Death/Disconnect, Change of Authorization)
 245 requests (default: <B>3799</B>).
 246 </LI>
 247
 248 <LI><B>allow_duplicate_users</B> (boolean)</BR>
 249 Allow multiple logins with the same username.  If false (the default),
 250 any prior session with the same username will be dropped when a new
 251 session is established.
 252 </LI>
 253
 254 <LI><B>bind_address</B> (ip address)<BR>
 255 When the tun interface is created, it is assigned the address
 256 specified here.  If no address is given, 1.1.1.1 is used.  Packets
 257 containing user traffic should be routed via this address if given,
 258 otherwise the primary address of the machine.
 259 </LI>
 260
 261 <LI><B>peer_address</B> (ip address)<BR>
 262 Address to send to clients as the default gateway.
 263 </L1>
 264
 265 <LI><B>send_garp</B> (boolean)<BR>
 266 Determines whether or not to send a gratuitous ARP for the
 267 bind_address when the server is ready to handle traffic (default:
 268 true).<BR>
 269 This value is ignored if BGP is configured.
 270 </LI>
 271
 272 <LI><B>throttle_speed</B> (int)<BR>
 273 Sets the default speed (in kbits/s) which sessions will be limited to.
 274 If this is set to 0, then throttling will not be used at all.  Note:
 275 You can set this by the CLI, but changes will not affect currently
 276 connected users.
 277 </LI>
 278
 279 <LI><B>throttle_buckets</B> (int)<BR>
 280 Number of token buckets to allocate for throttling.  Each throttled
 281 session requires two buckets (in and out).
 282 </LI>
 283
 284 <LI><B>accounting_dir</B> (string)<BR>
 285 If set to a directory, then every 5 minutes the current usage for
 286 every connected use will be dumped to a file in this directory.  Each
 287 file dumped begins with a header, where each line is prefixed by #.
 288 Following the header is a single line for every connected user, fields
 289 separated by a space.<BR> The fields are username, ip, qos,
 290 uptxoctets, downrxoctets.  The qos field is 1 if a standard user, and
 291 2 if the user is throttled.
 292 </LI>
 293
 294 <LI><B>setuid</B> (int)<BR>
 295 After starting up and binding the interface, change UID to this.  This
 296 doesn't work properly.
 297 </LI>
 298
 299 <LI><B>dump_speed</B> (boolean)<BR>
 300 If set to true, then the current bandwidth utilization will be logged every
 301 second.  Even if this is disabled, you can see this information by running
 302 the <EM>uptime</EM> command on the CLI.
 303 </LI>
 304
 305 <LI><B>multi_read_count</B> (int)<BR>
 306 Number of packets to read off each of the UDP and TUN fds when
 307 returned as readable by select (default:  10).  Avoids incurring the
 308 unnecessary system call overhead of select on busy servers.
 309 </LI>
 310
 311 <LI><B>scheduler_fifo</B> (boolean)<BR>
 312 Sets the scheduling policy for the l2tpns process to SCHED_FIFO.  This
 313 causes the kernel to immediately preempt any currently running SCHED_OTHER
 314 (normal) process in favour of l2tpns when it becomes runnable.
 315 Ignored on uniprocessor systems.
 316 </LI>
 317
 318 <LI><B>lock_pages</B> (boolean)<BR>
 319 Keep all pages mapped by the l2tpns process in memory.
 320 </LI>
 321
 322 <LI><B>icmp_rate</B> (int)<BR>
 323 Maximum number of host unreachable ICMP packets to send per second.
 324 </LI>
 325
 326 <LI><B>packet_limit</B> (int><BR>
 327 Maximum number of packets of downstream traffic to be handled each
 328 tenth of a second per session.  If zero, no limit is applied (default:
 329 0).  Intended as a DoS prevention mechanism and not a general
 330 throttling control (packets are dropped, not queued).
 331 </LI>
 332
 333 <LI><B>cluster_address</B> (ip address)<BR>
 334 Multicast cluster address (default:  239.192.13.13).  See the section
 335 on <A HREF="#Clustering">Clustering</A> for more information.
 336 </LI>
 337
 338 <LI><B>cluster_interface</B> (string)<BR>
 339 Interface for cluster packets (default: eth0).
 340 </LI>
 341
 342 <LI><B>cluster_mcast_ttl</B> (int)<BR>
 343 TTL for multicast packets (default: 1).
 344 </LI>
 345
 346 <LI><B>cluster_hb_interval</B> (int)<BR>
 347 Interval in tenths of a second between cluster heartbeat/pings.
 348 </LI>
 349
 350 <LI><B>cluster_hb_timeout</B> (int)<BR>
 351 Cluster heartbeat timeout in tenths of a second.  A new master will be
 352 elected when this interval has been passed without seeing a heartbeat
 353 from the master.
 354 </LI>
 355
 356 <LI><B>cluster_master_min_adv</B> (int)<BR>
 357 Determines the minumum number of up to date slaves required before the
 358 master will drop routes (default: 1).
 359 </LI>
 360 </UL>
 361
 362 <P>BGP routing configuration is entered by the command:
 363 The routing configuration section is entered by the command
 364 <DL><DD><B>router bgp</B> <I>as</I></DL>
 365 where <I>as</I> specifies the local AS number.
 366
 367 <P>Subsequent lines prefixed with
 368 <DL><DD><B>neighbour</B> <I>peer</I></DL>
 369 define the attributes of BGP neighhbours.  Valid commands are:
 370 <DL>
 371   <DD><B>neighbour</B> <I>peer</I> <B>remote-as</B> <I>as</I>
 372   <DD><B>neighbout</B> <I>peer</I> <B>timers</B> <I>keepalive hold</I>
 373 </DL>
 374
 375 Where <I>peer</I> specifies the BGP neighbour as either a hostname or
 376 IP address, <I>as</I> is the remote AS number and <I>keepalive</I>,
 377 <I>hold</I> are the timer values in seconds.
 378
 379 <P>Named access-lists are configured using one of the commands:
 380 <DL>
 381   <DD><B>ip access-list standard</B> <I>name</I>
 382   <DD><B>ip access-list extended</B> <I>name</I>
 383 </DL>
 384
 385 <P>Subsequent lines prefixed with <B>permit</B> or <B>deny</B>
 386 define the body of the access-list.  Standard access-list syntax:
 387 <DL>
 388   <DD>{<B>permit</B>|<B>deny</B>}
 389     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 390     [{<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}]
 391 </DL>
 392
 393 Extended access-lists:
 394
 395 <DIV STYLE="margin-left: 4em; text-indent: -2em">
 396   <P>{<B>permit</B>|<B>deny</B>} <B>ip</B>
 397     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 398     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>} [<B>fragments</B>]
 399   <P>{<B>permit</B>|<B>deny</B>} <B>udp</B>
 400     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 401         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 402     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}
 403         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 404         [<B>fragments</B>]
 405   <P>{<B>permit</B>|<B>deny</B>} <B>tcp</B>
 406     {<I>host</I>|<I>source source-wildcard</I>|<B>any</B>}
 407         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 408     {<I>host</I>|<I>destination destination-wildcard</I>|<B>any</B>}
 409         [{<B>eq</B>|<B>neq</B>|<B>gt</B>|<B>lt</B>} <I>port</I>|<B>range</B> <I>from</I> <I>to</I>]
 410         [{<B>established</B>|{<B>match-any</B>|<B>match-all</B>}
 411             {<B>+</B>|<B>-</B>}{<B>fin</B>|<B>syn</B>|<B>rst</B>|<B>psh</B>|<B>ack</B>|<B>urg</B>}
 412             ...|<B>fragments</B>]
 413 </DIV>
 414
 415 <H3 ID="users">users</H3>
 416
 417 Usernames and passwords for the command-line interface are stored in
 418 this file.  The format is <I>username</I><B>:</B><I>password</I> where
 419 <I>password</I> may either by plain text, an MD5 digest (prefixed by
 420 <B>$1</B><I>salt</I><B>$</B>) or a DES password, distinguished from
 421 plain text by the prefix <B>{crypt}</B>.<P>
 422
 423 The username <B>enable</B> has a special meaning and is used to set
 424 the enable password.<P>
 425
 426 <B>Note:</B> If this file doesn't exist, then anyone who can get to
 427 port 23 will be allowed access without a username / password.<P>
 428
 429 <H3 ID="ip-pool">ip_pool</H3>
 430
 431 This file is used to configure the IP address pool which user
 432 addresses are assigned from.  This file should contain either an IP
 433 address or a CIDR network per line.  e.g.:<P>
 434
 435 <PRE>
 436     192.168.1.1
 437     192.168.1.2
 438     192.168.1.3
 439     192.168.4.0/24
 440     172.16.0.0/16
 441     10.0.0.0/8
 442 </PRE>
 443
 444 Keep in mind that l2tpns can only handle 65535 connections per
 445 process, so don't put more than 65535 IP addresses in the
 446 configuration file.  They will be wasted.
 447
 448 <H3 ID="build-garden">build-garden</H3>
 449
 450 The garden plugin on startup creates a NAT table called "garden" then
 451 sources the <B>build-garden</B> script to populate that table.  All
 452 packets from gardened users will be sent through this table.  Example:
 453
 454 <PRE>
 455     iptables -t nat -A garden -p tcp -m tcp --dport 25 -j DNAT --to 192.168.1.1
 456     iptables -t nat -A garden -p udp -m udp --dport 53 -j DNAT --to 192.168.1.1
 457     iptables -t nat -A garden -p tcp -m tcp --dport 53 -j DNAT --to 192.168.1.1
 458     iptables -t nat -A garden -p tcp -m tcp --dport 80 -j DNAT --to 192.168.1.1
 459     iptables -t nat -A garden -p tcp -m tcp --dport 110 -j DNAT --to 192.168.1.1
 460     iptables -t nat -A garden -p tcp -m tcp --dport 443 -j DNAT --to 192.168.1.1
 461     iptables -t nat -A garden -p icmp -m icmp --icmp-type echo-request -j DNAT --to 192.168.1.1
 462     iptables -t nat -A garden -p icmp -j ACCEPT
 463     iptables -t nat -A garden -j DROP
 464 </PRE>
 465
 466 <H2 ID="ControllingtheProcess">Controlling the Process</H2>
 467
 468 A running l2tpns process can be controlled in a number of ways.  The primary
 469 method of control is by the Command-Line Interface (CLI).<P>
 470
 471 You can also remotely send commands to modules via the nsctl client
 472 provided.<P>
 473
 474 Also, there are a number of signals that l2tpns understands and takes action
 475 when it receives them.
 476
 477 <H3 ID="Command-LineInterface">Command-Line Interface</H3>
 478
 479 You can access the command line interface by telnet'ing to port 23.
 480 There is no IP address restriction, so it's a good idea to firewall
 481 this port off from anyone who doesn't need access to it.  See
 482 <A HREF="#users">users</A> for information on restricting access based
 483 on a username and password.<P>
 484
 485 The CLI gives you real-time control over almost everything in
 486 the process.  The interface is designed to look like a Cisco
 487 device, and supports things like command history, line editing and
 488 context sensitive help.  This is provided by linking with the
 489 <A HREF="http://sourceforge.net/projects/libcli">libcli</A>
 490 library.  Some general documentation of the interface is
 491 <A HREF="http://sourceforge.net/docman/display_doc.php?docid=20501&group_id=79019">
 492 here</A>.<P>
 493
 494 After you have connected to the telnet port (and perhaps logged in), you
 495 will be presented with a <I>hostname</I><B>&gt;</B> prompt.<P>
 496
 497 Enter <EM>help</EM> to get a list of possible commands.  A brief
 498 overview of the more important commands follows:
 499
 500 <UL>
 501 <LI><B>show session</B><BR>
 502 Without specifying a session ID, this will list all tunnels currently
 503 connected.  If you specify a session ID, you will be given all
 504 information on a single tunnel.  Note that the full session list can
 505 be around 185 columns wide, so you should probably use a wide terminal
 506 to see the list properly.<P>
 507 The columns listed in the overview are:
 508 <TABLE>
 509         <TR><TD><B>SID</B></TD><TD>Session ID</TD></TR>
 510         <TR><TD><B>TID</B></TD><TD>Tunnel ID - Use with <EM>show tunnel tid</EM></TD></TR>
 511         <TR><TD><B>Username</B></TD><TD>The username given in the PPP
 512         authentication.  If this is *, then LCP authentication has not
 513         completed.</TD></TR>
 514         <TR><TD><B>IP</B></TD><TD>The IP address given to the session.  If
 515         this is 0.0.0.0, LCP negotiation has not completed.</TD></TR>
 516         <TR><TD><B>I</B></TD><TD>Intercept - Y or N depending on whether the
 517         session is being snooped.  See <EM>snoop</EM>.</TD></TR>
 518         <TR><TD><B>T</B></TD><TD>Throttled - Y or N if the session is
 519         currently throttled.  See <EM>throttle</EM>.</TD></TR>
 520         <TR><TD><B>G</B></TD><TD>Walled Garden - Y or N if the user is
 521         trapped in the walled garden.  This field is present even if the
 522         garden module is not loaded.</TD></TR>
 523         <TR><TD><B>opened</B></TD><TD>The number of seconds since the
 524         session started</TD></TR>
 525         <TR><TD><B>downloaded</B></TD><TD>Number of bytes downloaded by the user</TD></TR>
 526         <TR><TD><B>uploaded</B></TD><TD>Number of bytes uploaded by the user</TD></TR>
 527         <TR><TD><B>idle</B></TD><TD>The number of seconds since traffic was
 528         detected on the session</TD></TR>
 529         <TR><TD><B>LAC</B></TD><TD>The IP address of the LAC the session is
 530         connected to.</TD></TR>
 531         <TR><TD><B>CLI</B></TD><TD>The Calling-Line-Identification field
 532         provided during the session setup.  This field is generated by the
 533         LAC.</TD></TR>
 534 </TABLE>
 535 <P>
 536 </LI>
 537
 538 <LI><B>show users</B><BR>
 539 With no arguments, display a list of currently connected users.  If an
 540 argument is given, the session details for the given username are
 541 displayed.
 542 </LI>
 543
 544 <LI><B>show tunnel</B><BR>
 545 This will show all the open tunnels in a summary, or detail on a single
 546 tunnel if you give a tunnel id.<P>
 547 The columns listed in the overview are:
 548 <TABLE>
 549         <TR><TD><B>TID</B></TD><TD>Tunnel ID</TD></TR>
 550         <TR><TD><B>Hostname</B></TD><TD>The hostname for the tunnel as
 551         provided by the LAC.  This has no relation to DNS, it is just
 552         a text field.</TD></TR>
 553         <TR><TD><B>IP</B></TD><TD>The IP address of the LAC</TD></TR>
 554         <TR><TD><B>State</B></TD><TD>Tunnel state - Free, Open, Dieing,
 555         Opening</TD></TR>
 556         <TR><TD><B>Sessions</B></TD><TD>The number of open sessions on the
 557         tunnel</TD></TR>
 558 </TABLE>
 559 <P>
 560 </LI>
 561
 562 <LI><B>show pool</B><BR>
 563 Displays the current IP address pool allocation.  This will only display
 564 addresses that are in use, or are reserved for re-allocation to a
 565 disconnected user.<P>
 566 If an address is not currently in use, but has been used, then in the User
 567 column the username will be shown in square brackets, followed by the time
 568 since the address was used:
 569 <PRE>
 570 IP Address      Used  Session User
 571 192.168.100.6     N           [joe.user] 1548s
 572 </PRE>
 573 <P>
 574 </LI>
 575
 576 <LI><B>show radius</B><BR>
 577 Show a summary of the in-use RADIUS sessions.  This list should not be very
 578 long, as RADIUS sessions should be cleaned up as soon as they are used.  The
 579 columns listed are:
 580 <TABLE>
 581         <TR><TD><B>Radius</B></TD><TD>The ID of the RADIUS request.  This is
 582         sent in the packet to the RADIUS server for identification.</TD></TR>
 583         <TR><TD><B>State</B></TD><TD>The state of the request - WAIT, CHAP,
 584         AUTH, IPCP, START, STOP, NULL.</TD></TR>
 585         <TR><TD><B>Session</B></TD><TD>The session ID that this RADIUS
 586         request is associated with</TD></TR>
 587         <TR><TD><B>Retry</B></TD><TD>If a response does not appear to the
 588         request, it will retry at this time.  This is a unix timestamp.</TD></TR>
 589         <TR><TD><B>Try</B></TD><TD>Retry count.  The RADIUS request is
 590         discarded after 3 retries.</TD></TR>
 591 </TABLE>
 592 <P>
 593 </LI>
 594
 595 <LI><B>show running-config</B><BR>
 596 This will list the current running configuration.  This is in a format that
 597 can either be pasted into the configuration file, or run directly at the
 598 command line.
 599 <P>
 600 </LI>
 601
 602 <LI><B>show counters</B><BR>
 603 Internally, counters are kept of key values, such as bytes and packets
 604 transferred, as well as function call counters.  This function displays all
 605 these counters, and is probably only useful for debugging.<P>
 606 You can reset these counters by running <EM>clear counters</EM>.
 607 <P>
 608 </LI>
 609
 610 <LI><B>show cluster</B><BR>
 611 Show cluster status.  Shows the cluster state for this server
 612 (Master/Slave), information about known peers and (for slaves) the
 613 master IP address, last packet seen and up-to-date status.<P>
 614 See <A HREF="#Clustering">Clustering</A> for more information.
 615 <P>
 616 </LI>
 617
 618 <LI><B>write memory</B><BR>
 619 This will write the current running configuration to the config file
 620 <B>startup-config</B>, which will be run on a restart.
 621 <P>
 622 </LI>
 623
 624 <LI><B>snoop</B><BR>
 625 You must specify a username, IP address and port.  All packets for the
 626 current session for that username will be forwarded to the given
 627 host/port.  Specify <EM>no snoop username</EM> to disable interception
 628 for the session.<P>
 629
 630 If you want interception to be permanent, you will have to modify the RADIUS
 631 response for the user.  See <A HREF="#Interception">Interception</A>.
 632 <P>
 633 </LI>
 634
 635 <LI><B>throttle</B><BR>
 636 You must specify a username, which will be throttled for the current
 637 session.  Specify <EM>no throttle username</EM> to disable throttling
 638 for the current session.<P>
 639
 640 If you want throttling to be permanent, you will have to modify the
 641 RADIUS response for the user.  See <A HREF="#Throttling">Throttling</A>.
 642 <P>
 643 </LI>
 644
 645 <LI><B>drop session</B><BR>
 646 This will cleanly disconnect a session.  You must specify a session id, which
 647 you can get from <EM>show session</EM>.  This will send a disconnect message
 648 to the remote end.
 649 <P>
 650 </LI>
 651
 652 <LI><B>drop tunnel</B><BR>
 653 This will cleanly disconnect a tunnel, as well as all sessions on that
 654 tunnel.  It will send a disconnect message for each session individually, and
 655 after 10 seconds it will send a tunnel disconnect message.
 656 <P>
 657 </LI>
 658
 659 <LI><B>uptime</B><BR>
 660 This will show how long the l2tpns process has been running, and the current
 661 bandwidth utilization:
 662 <PRE>
 663 17:10:35 up 8 days, 2212 users, load average: 0.21, 0.17, 0.16
 664 Bandwidth: UDP-ETH:6/6  ETH-UDP:13/13  TOTAL:37.6   IN:3033 OUT:2569
 665 </PRE>
 666 The bandwidth line contains 4 sets of values.<BR>
 667 UDP-ETH is the current bandwidth going from the LAC to the ethernet
 668 (user uploads), in mbits/sec.<BR>
 669 ETH-UDP is the current bandwidth going from ethernet to the LAC (user
 670 downloads).<BR>
 671 TOTAL is the total aggregate bandwidth in mbits/s.<BR>
 672 IN and OUT are packets/per-second going between UDP-ETH and ETH-UDP.
 673 <P>
 674 These counters are updated every second.
 675 <P>
 676 </LI>
 677
 678 <LI><B>configure terminal</B><BR>
 679 Enter configuration mode.  Use <EM>exit</EM> or ^Z to exit this mode.
 680 The following commands are valid in this mode:<P>
 681 </LI>
 682
 683 <LI><B>load plugin</B><BR>
 684 Load a plugin.  You must specify the plugin name, and it will search in
 685 /usr/lib/l2tpns for <EM>plugin</EM>.so.  You can unload a loaded plugin with
 686 <EM>remove plugin</EM>.
 687 <P>
 688 </LI>
 689
 690 <LI><B>set</B><BR>
 691 Set a configuration variable.  You must specify the variable name, and
 692 the value.  If the value contains any spaces, you should quote the
 693 value with double (") or single (') quotes.<P>
 694
 695 You can set any <A HREF="#startup-config">startup-config</A> value in
 696 this way, although some may require a restart to take effect.<P>
 697 </LI>
 698 </UL>
 699
 700 <H3 ID="nsctl">nsctl</H3>
 701
 702 nsctl allows messages to be passed to plugins.<P>
 703
 704 Arguments are <EM>command</EM> and optional <EM>args</EM>.  See
 705 <STRONG>nsctl</STRONG>(8) for more details.<P>
 706
 707 Built-in command are <EM>load_plugin</EM>, <EM>unload_plugin</EM> and
 708 <EM>help</EM>.  Any other commands are passed to plugins for processing.
 709
 710 <H3 ID="Signals">Signals</H3>
 711
 712 While the process is running, you can send it a few different signals, using
 713 the kill command.
 714 <PRE>
 715 killall -HUP l2tpns
 716 </PRE>
 717
 718 The signals understood are:
 719 <DL>
 720 <DT>SIGHUP</DT><DD>Reload the config from disk and re-open log file.</DD>
 721 <DT>SIGTERM, SIGINT</DT><DD>Stop process.  Tunnels and sessions are not
 722 terminated.  This signal should be used to stop l2tpns on a
 723 <A HREF="#Clustering">cluster node</A> where there are other machines to
 724 continue handling traffic.</DD>
 725 <DT>SIGQUIT</DT><DD>Shut down tunnels and sessions, exit process when
 726 complete.</DD>
 727 </DL>
 728
 729 <H2 ID="Throttling">Throttling</H2>
 730
 731 l2tpns contains support for slowing down user sessions to whatever speed you
 732 desire.  You must first enable the global setting <EM>throttle_speed</EM>
 733 before this will be activated.<P>
 734
 735 If you wish a session to be throttled permanently, you should set the
 736 Vendor-Specific RADIUS value <B>Cisco-Avpair="throttle=yes"</B>, which
 737 will be handled by the <EM>autothrottle</EM> module.<P>
 738
 739 Otherwise, you can enable and disable throttling an active session using
 740 the <EM>throttle</EM> CLI command.<P>
 741
 742 <H2 ID="Interception">Interception</H2>
 743
 744 You may have to deal with legal requirements to be able to intercept a
 745 user's traffic at any time.  l2tpns allows you to begin and end interception
 746 on the fly, as well as at authentication time.<P>
 747
 748 When a user is being intercepted, a copy of every packet they send and
 749 receive will be sent wrapped in a UDP packet to the IP address and port set
 750 in the <EM>snoop_host</EM> and <EM>snoop_port</EM> configuration
 751 variables.<P>
 752
 753 The UDP packet contains just the raw IP frame, with no extra headers.<P>
 754
 755 To enable interception on a connected user, use the <EM>snoop username</EM>
 756 and <EM>no snoop username</EM> CLI commands.  These will enable interception
 757 immediately.<P>
 758
 759 If you wish the user to be intercepted whenever they reconnect, you will
 760 need to modify the RADIUS response to include the Vendor-Specific value
 761 <B>Cisco-Avpair="intercept=yes"</B>.  For this feature to be enabled,
 762 you need to have the <EM>autosnoop</EM> module loaded.<P>
 763
 764 <H2 ID="Authentication">Authentication</H2>
 765
 766 Whenever a session connects, it is not fully set up until authentication is
 767 completed.  The remote end must send a PPP CHAP or PPP PAP authentication
 768 request to l2tpns.<P>
 769
 770 This request is sent to the RADIUS server, which will hopefully respond with
 771 Auth-Accept or Auth-Reject.<P>
 772
 773 If Auth-Accept is received, the session is set up and an IP address is
 774 assigned.  The RADIUS server can include a Framed-IP-Address field in the
 775 reply, and that address will be assigned to the client.  It can also include
 776 specific DNS servers, and a Framed-Route if that is required.<P>
 777
 778 If Auth-Reject is received, then the client is sent a PPP AUTHNAK packet,
 779 at which point they should disconnect.  The exception to this is when the
 780 walled garden module is loaded, in which case the user still receives the
 781 PPP AUTHACK, but their session is flagged as being a garden'd user, and they
 782 should not receive any service.<P>
 783
 784 The RADIUS reply can also contain a Vendor-Specific attribute called
 785 Cisco-Avpair.  This field is a freeform text field that most Cisco
 786 devices understand to contain configuration instructions for the session.  In
 787 the case of l2tpns it is expected to be of the form
 788 <PRE>
 789 key=value,key2=value2,key3=value3,key<EM>n</EM>=<EM>value</EM>
 790 </PRE>
 791
 792 Each key-value pair is separated and passed to any modules loaded.  The
 793 <EM>autosnoop</EM> and <EM>autothrottle</EM> understand the keys
 794 <EM>intercept</EM> and <EM>throttle</EM> respectively.  For example, to have
 795 a user who is to be throttled and intercepted, the Cisco-Avpair value should
 796 contain:
 797 <PRE>
 798 intercept=yes,throttle=yes
 799 </PRE>
 800
 801 <H2 ID="Plugins">Plugins</H2>
 802
 803 So as to make l2tpns as flexible as possible (I know the core code is pretty
 804 difficult to understand), it includes a plugin API, which you can use to
 805 hook into certain events.<P>
 806
 807 There are a few example modules included - autosnoop, autothrottle and
 808 garden.<P>
 809
 810 When an event happens that has a hook, l2tpns looks for a predefined
 811 function name in every loaded module, and runs them in the order the modules
 812 were loaded.<P>
 813
 814 The function should return <B>PLUGIN_RET_OK</B> if it is all OK.  If it returns
 815 <B>PLUGIN_RET_STOP</B>, then it is assumed to have worked, but that no further
 816 modules should be run for this event.<P>
 817 A return of <B>PLUGIN_RET_ERROR</B> means that this module failed, and
 818 no further processing should be done for this event.  <EM>Use this with care.</EM>
 819
 820 Every event function called takes a specific structure named
 821 param_<EM>event</EM>, which varies in content with each event.  The
 822 function name for each event will be <B>plugin_<EM>event</EM></B>,
 823 so for the event <EM>timer</EM>, the function declaration should look like:
 824 <PRE>
 825 int plugin_timer(struct param_timer *data);
 826 </PRE>
 827
 828 A list of the available events follows, with a list of all the fields in the
 829 supplied structure:
 830 <TABLE CELLSPACING=0 CELLPADDING=0><TR BGCOLOR=LIGHTGREEN><TD>
 831 <TABLE CELLSPACING=1 CELLPADDING=3>
 832         <TR BGCOLOR=LIGHTGREEN><TH><B>Event</B></TH><TH><B>Description</B></TH><TH><B>Parameters</B></TH></TR>
 833         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>pre_auth</B></TD>
 834                 <TD>This is called after a RADIUS response has been
 835                 received, but before it has been processed by the
 836                 code.  This will allow you to modify the response in
 837                 some way.
 838                 </TD>
 839                 <TD>
 840                 <DL>
 841                         <DT>t<DD>Tunnel
 842                         <DT>s<DD>Session
 843                         <DT>username
 844                         <DT>password
 845                         <DT>protocol<DD>0xC023 for PAP, 0xC223 for CHAP
 846                         <DT>continue_auth<DD>Set to 0 to stop processing authentication modules
 847                 </DL>
 848                 </TD>
 849         </TR>
 850         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>post_auth</B></TD>
 851                 <TD>This is called after a RADIUS response has been
 852                 received, and the basic checks have been performed.  This
 853                 is what the garden module uses to force authentication
 854                 to be accepted.
 855                 </TD>
 856                 <TD>
 857                 <DL>
 858                         <DT>t<DD>Tunnel
 859                         <DT>s<DD>Session
 860                         <DT>username
 861                         <DT>auth_allowed<DD>This is already set to true or
 862                         false depending on whether authentication has been
 863                         allowed so far.  You can set this to 1 or 0 to force
 864                         allow or disallow authentication
 865                         <DT>protocol<DD>0xC023 for PAP, 0xC223 for CHAP
 866                 </DL>
 867                 </TD>
 868         </TR>
 869         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_rx</B></TD>
 870                 <TD>This is called whenever a session receives a
 871                 packet.  <FONT COLOR=RED>Use this sparingly, as this will
 872                 seriously slow down the system.</FONT>
 873                 </TD>
 874                 <TD>
 875                 <DL>
 876                         <DT>t<DD>Tunnel
 877                         <DT>s<DD>Session
 878                         <DT>buf<DD>The raw packet data
 879                         <DT>len<DD>The length of buf
 880                 </DL>
 881                 </TD>
 882         </TR>
 883         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_tx</B></TD>
 884                 <TD>This is called whenever a session sends a
 885                 packet.  <FONT COLOR=RED>Use this sparingly, as this will
 886                 seriously slow down the system.</FONT>
 887                 </TD>
 888                 <TD>
 889                 <DL>
 890                         <DT>t<DD>Tunnel
 891                         <DT>s<DD>Session
 892                         <DT>buf<DD>The raw packet data
 893                         <DT>len<DD>The length of buf
 894                 </DL>
 895                 </TD>
 896         </TR>
 897         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>timer</B></TD>
 898                 <TD>This is run every second, no matter what is happening.
 899                 This is called from a signal handler, so make sure anything
 900                 you do is reentrant.
 901                 </TD>
 902                 <TD>
 903                 <DL>
 904                         <DT>time_now<DD>The current unix timestamp
 905                 </DL>
 906                 </TD>
 907         </TR>
 908         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>new_session</B></TD>
 909                 <TD>This is called after a session is fully set up.  The
 910                 session is now ready to handle traffic.
 911                 </TD>
 912                 <TD>
 913                 <DL>
 914                         <DT>t<DD>Tunnel
 915                         <DT>s<DD>Session
 916                 </DL>
 917                 </TD>
 918         </TR>
 919         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>kill_session</B></TD>
 920                 <TD>This is called when a session is about to be shut down.
 921                 This may be called multiple times for the same session.
 922                 </TD>
 923                 <TD>
 924                 <DL>
 925                         <DT>t<DD>Tunnel
 926                         <DT>s<DD>Session
 927                 </DL>
 928                 </TD>
 929         </TR>
 930         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>radius_response</B></TD>
 931                 <TD>This is called whenever a RADIUS response includes a
 932                 Cisco-Avpair value.  The value is split up into
 933                 <EM>key=value</EM> pairs, and each is processed through all
 934                 modules.
 935                 </TD>
 936                 <TD>
 937                 <DL>
 938                         <DT>t<DD>Tunnel
 939                         <DT>s<DD>Session
 940                         <DT>key
 941                         <DT>value
 942                 </DL>
 943                 </TD>
 944         </TR>
 945         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>radius_reset</B></TD>
 946                 <TD>This is called whenever a RADIUS CoA request is
 947                 received to reset any options to default values before
 948                 the new values are applied.
 949                 </TD>
 950                 <TD>
 951                 <DL>
 952                         <DT>t<DD>Tunnel
 953                         <DT>s<DD>Session
 954                 </DL>
 955                 </TD>
 956         </TR>
 957         <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>control</B></TD>
 958                 <TD>This is called in whenever a nsctl packet is received.
 959                 This should handle the packet and form a response if
 960                 required.
 961                 </TD>
 962                 <TD>
 963                 <DL>
 964                         <DT>iam_master<DD>Cluster master status
 965                         <DT>argc<DD>The number of arguments
 966                         <DT>argv<DD>Arguments
 967                         <DT>response<DD>Return value: NSCTL_RES_OK or NSCTL_RES_ERR
 968                         <DT>additional<DD>Extended response text
 969                 </DL>
 970                 </TD>
 971         </TR>
 972 </TABLE>
 973 </TD></TR></TABLE>
 974
 975 <H2 ID="WalledGarden">Walled Garden</H2>
 976
 977 Walled Garden is implemented so that you can provide perhaps limited service
 978 to sessions that incorrectly authenticate.<P>
 979
 980 Whenever a session provides incorrect authentication, and the
 981 RADIUS server responds with Auth-Reject, the walled garden module
 982 (if loaded) will force authentication to succeed, but set the flag
 983 <EM>garden</EM> in the session structure, and adds an iptables rule to
 984 the <B>garden_users</B> chain to force all packets for the session's IP
 985 address to traverse the <B>garden</B> chain.<P>
 986
 987 This doesn't <EM>just work</EM>.  To set this all up, you will to
 988 setup the <B>garden</B> nat table with the
 989 <A HREF="#build-garden">build-garden</A> script with rules to limit
 990 user's traffic.  For example, to force all traffic except DNS to be
 991 forwarded to 192.168.1.1, add these entries to your
 992 <EM>build-garden</EM>:
 993 <PRE>
 994 iptables -t nat -A garden -p tcp --dport ! 53 -j DNAT --to 192.168.1.1
 995 iptables -t nat -A garden -p udp --dport ! 53 -j DNAT --to 192.168.1.1
 996 </PRE>
 997
 998 l2tpns will add entries to the garden_users chain as appropriate.<P>
 999
1000 You can check the amount of traffic being captured using the following
1001 command:
1002 <PRE>
1003 iptables -t nat -L garden -nvx
1004 </PRE>
1005
1006 <H2 ID="Filtering">Filtering</H2>
1007
1008 Sessions may be filtered by specifying <B>Filter-Id</B> attributes in
1009 the RADIUS reply.  <I>filter</I>.<B>in</B> specifies that the named
1010 access-list <I>filter</I> should be applied to traffic from the
1011 customer, <I>filter</I>.<B>out</B> specifies a list for traffic to the
1012 customer.
1013
1014 <H2 ID="Clustering">Clustering</H2>
1015
1016 An l2tpns cluster consists of of one* or more servers configured with
1017 the same configuration, notably the multicast <B>cluster_address</B>.<P>
1018
1019 *A stand-alone server is simply a degraded cluster.<P>
1020
1021 Initially servers come up as cluster slaves, and periodically (every
1022 <B>cluster_hb_interval</B>/10 seconds) send out ping packets
1023 containing the start time of the process to the multicast
1024 <B>cluster_address</B>.<P>
1025
1026 A cluster master sends heartbeat rather than ping packets, which
1027 contain those session and tunnel changes since the last heartbeat.<P>
1028
1029 When a slave has not seen a heartbeat within
1030 <B>cluster_hb_timeout</B>/10 seconds it "elects" a new master by
1031 examining the list of peers it has seen pings from and determines
1032 which of these and itself is the "best" candidate to be master.
1033 "Best" in this context means the server with the highest uptime (the
1034 highest IP address is used as a tie-breaker in the case of equal
1035 uptimes).<P>
1036
1037 After discovering a master, and determining that it is up-to-date (has
1038 seen an update for all in-use sessions and tunnels from heartbeat
1039 packets) will raise a route (see <A HREF="#Routing">Routing</A>) for
1040 the <B>bind_address</B> and for all addresses/networks in
1041 <B>ip_pool</B>.  Any packets recieved by the slave which would alter
1042 the session state, as well as packets for throttled or gardened
1043 sessions are forwarded to the master for handling.  In addition, byte
1044 counters for session traffic are periodically forwarded.<P>
1045
1046 A master, when determining that it has at least one up-to-date slave
1047 will drop all routes (raising them again if all slaves disappear) and
1048 subsequently handle only packets forwarded to it by the slaves.<P>
1049
1050 <H2 ID="Routing">Routing</H2>
1051 If you are running a single instance, you may simply statically route
1052 the IP pools to the <B>bind_address</B> (l2tpns will send a gratuitous
1053 arp).<P>
1054
1055 For a cluster, configure the members as BGP neighbours on your router
1056 and configure multi-path load-balancing.  Cisco uses "maximum-paths
1057 ibgp" for IBGP.  If this is not supported by your IOS revision, you
1058 can use "maximum-paths" (which works for EBGP) and set
1059 <B>as_number</B> to a private value such as 64512.<P>
1060
1061 <H2 ID="AvoidingFragmentation">Avoiding Fragmentation</H2>
1062
1063 Fragmentation of encapsulated return packets to the LAC may be avoided
1064 for TCP sessions by adding a firewall rule to clamps the MSS on
1065 outgoing SYN packets.
1066
1067 The following is appropriate for interfaces with a typical MTU of
1068 1500:
1069
1070 <pre>
1071 iptables -A FORWARD -i tun+ -o eth0     \
1072     -p tcp --tcp-flags SYN,RST SYN      \
1073     -m tcpmss --mss 1413:1600           \
1074     -j TCPMSS --set-mss 1412
1075 </pre>
1076
1077 <H2 ID="Performance">Performance</H2>
1078
1079 Performance is great.<P>
1080
1081 I'd like to include some pretty graphs here that show a linear performance
1082 increase, with no impact by number of connected sessions.<P>
1083
1084 That's really what it looks like.<P>
1085
1086 <BR>
1087 David Parrish<BR>
1088 <A HREF="mailto:l2tpns-users@lists.sourceforge.net?subject=L2TPNS%20Documentation">l2tpns-users@lists.sourceforge.net</A>
1089 </BODY>
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