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