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-<H1>L2TPNS Manual</H1>
-<OL>
- <LI><A HREF="#Overview">Overview</A></LI>
- <LI><A HREF="#Installation">Installation</A>
- <OL>
- <LI><A HREF="#Requirements">Requirements</A></LI>
- <LI><A HREF="#Compile">Compile</A></LI>
- <LI><A HREF="#Install">Install</A></LI>
- <LI><A HREF="#Running">Running</A></LI>
- </OL>
- </LI>
- <LI><A HREF="#Configuration">Configuration</A>
- <OL>
- <LI><A HREF="#startup-config">startup-config</A></LI>
- <LI><A HREF="#users">users</A></LI>
- <LI><A HREF="#ip-pool">ip_pool</A></LI>
- <LI><A HREF="#build-garden">build-garden</A></LI>
- </OL>
- </LI>
- <LI><A HREF="#ControllingtheProcess">Controlling the Process</A>
- <OL>
- <LI><A HREF="#Command-LineInterface">Command-Line Interface</A></LI>
- <LI><A HREF="#nsctl">nsctl</A></LI>
- <LI><A HREF="#Signals">Signals</A></LI>
- </OL>
- </LI>
- <LI><A HREF="#Throttling">Throttling</A></LI>
- <LI><A HREF="#Interception">Interception</A></LI>
- <LI><A HREF="#Authentication">Authentication</A></LI>
- <LI><A HREF="#Plugins">Plugins</A></LI>
- <LI><A HREF="#Walled Garden">Walled Garden</A></LI>
- <LI><A HREF="#Clustering">Clustering</A></LI>
- <LI><A HREF="#Routing">Routing</A></LI>
- <LI><A HREF="#Performance">Performance</A></LI>
-</OL>
-
-<H2 ID="Overview">Overview</H2>
-l2tpns is half of a complete L2TP implementation. It supports only the
-LNS side of the connection.<P>
-
-L2TP (Layer 2 Tunneling Protocol) is designed to allow any layer 2
-protocol (e.g. Ethernet, PPP) to be tunneled over an IP connection. l2tpns
-implements PPP over L2TP only.<P>
-
-There are a couple of other L2TP imlementations, of which <A
-HREF="http://sourceforge.net/projects/l2tpd">l2tpd</A> is probably the
-most popular. l2tpd also will handle being either end of a tunnel, and
-is a lot more configurable than l2tpns. However, due to the way it works,
-it is nowhere near as scalable.<P>
-
-l2tpns uses the TUN/TAP interface provided by the Linux kernel to receive
-and send packets. Using some packet manipulation it doesn't require a
-single interface per connection, as l2tpd does.<P>
-
-This allows it to scale extremely well to very high loads and very high
-numbers of connections.<P>
-
-It also has a plugin architecture which allows custom code to be run
-during processing. An example of this is in the walled garden module
-included.<P>
-
-<BR>
-<EM>Documentation is not my best skill. If you find any problems
-with this document, or if you wish to contribute, please email <A
-HREF="mailto:david@dparrish.com?subject=L2TPNS+Documentation">david@dparrish.com</A>.</EM><P>
-
-<H2 ID="Installation">Installation</H2>
-<H3 ID="Requirements">Requirements</H3>
-
-<OL>
-<LI>Linux kernel version 2.4 or above, with the Tun/Tap interface either
-compiled in, or as a module.</LI>
-
-<LI>libcli 1.8.0 or greater.<BR>You can get this from <A
-HREF="http://sourceforge.net/projects/libcli">http://sourceforge.net/projects/libcli</A></LI>
-</OL>
-
-<H3 ID="Compile">Compile</H3>
-
-You can generally get away with just running <B>make</B> from the source
-directory. This will compile the daemon, associated tools and any modules
-shipped with the distribution.<P>
-
-<H3 ID="Install">Install</H3>
-
-After you have successfully compiled everything, run <B>make
-install</B> to install it. By default, the binaries are installed into
-<EM>/usr/sbin</EM>, the configuration into <EM>/etc/l2tpns</EM>, and the
-modules into <EM>/usr/lib/l2tpns</EM>.<P>
-
-You will definately need to edit the configuration files before you
-start. See the <A HREF="#Configuration">Configuration</A> section for
-more information.<P>
-
-<H3 ID="Running">Running</H3>
-
-You only need to run <B>/usr/sbin/l2tpns</B> as root to start it. It does
-not detach to a daemon process, so you should perhaps run it from init.<P>
-
-By default there is no log destination set, so all log messages will go to
-stdout.<P>
-
-<H2 ID="Configuration">Configuration</H2>
-
-All configuration of the software is done from the files installed into
-/etc/l2tpns.
-
-<H3 ID="startup-config">startup-config</H3>
-
-This is the main configuration file for l2tpns. The format of the file is a
-list of commands that can be run through the command-line interface. This
-file can also be written directly by the l2tpns process if a user runs the
-<EM>write memory</EM> command, so any comments will be lost. However if your
-policy is not to write the config by the program, then feel free to comment
-the file with a # or ! at the beginning of the line.<P>
-
-A list of the possible configuration directives follows. Each of these
-should be set by a line like:<P>
-<PRE>
-set configstring "value"
-set ipaddress 192.168.1.1
-set boolean true
-</PRE>
-
-<UL>
-<LI><B>debug</B> (int)<BR>
-Sets the level of messages that will be written to the log file. The value
-should be between 0 and 5, with 0 being no debugging, and 5 being the
-highest. A rough description of the levels is:
- <OL>
- <LI VALUE=0>Critical Errors - Things are probably broken</LI>
- <LI>Errors - Things might have gone wrong, but probably will recover</LI>
- <LI>Warnings - Just in case you care what is not quite perfect</LI>
- <LI>Information - Parameters of control packets</LI>
- <LI>Calls - For tracing the execution of the code</LI>
- <LI>Packets - Everything, including a hex dump of all packets processed... probably twice</LI>
- </OL><P>
-Note that the higher you set the debugging level, the slower the program
-will run. Also, at level 5 a LOT of information will be logged. This should
-only ever be used for working out why it doesn't work at all.
-<P>
-</LI>
-
-<LI><B>log_file</B> (string)<BR>
-This will be where all logging and debugging information is written
-to. This can be either a filename, such as <EM>/var/log/l2tpns</EM>, or
-the special magic string <EM>syslog:facility</EM>, where <EM>facility</EM>
-is any one of the syslog logging facilities, such as local5.
-<P>
-</LI>
-
-<LI><B>l2tp_secret</B> (string)<BR>
-This sets the string that l2tpns will use for authenticating tunnel request.
-This must be the same as the LAC, or authentication will fail. This will
-only actually be used if the LAC requests authentication.
-<P>
-</LI>
-
-<LI><B>primary_dns</B> (ip address)
-<LI><B>secondary_dns</B> (ip address)<BR>
-Whenever a PPP connection is established, DNS servers will be sent to the
-user, both a primary and a secondary. If either is set to 0.0.0.0, then that
-one will not be sent.
-<P>
-</LI>
-
-<LI><B>save_state</B> (boolean)<BR>
-When l2tpns receives a STGTERM it will write out its current
-ip_address_pool, session and tunnel tables to disk prior to exiting to
-be re-loaded at startup. The validity of this data is obviously quite
-short and the intent is to allow an sessions to be retained over a
-software upgrade.
-<P>
-</LI>
-
-<LI><B>primary_radius</B> (ip address)
-<LI><B>secondary_radius</B> (ip address)<BR>
-This sets the radius servers used for both authentication and
-accounting. If the primary server does not respond, then the
-secondary radius server will be tried.
-<P>
-</LI>
-
-<LI><B>radius_accounting</B> (boolean)<BR>
-If set to true, then radius accounting packets will be sent. This
-means that a Start record will be sent when the session is
-successfully authenticated, and a Stop record will be sent when the
-session is closed.
-<P>
-</LI>
-
-<LI><B>radius_secret</B> (string)<BR>
-This secret will be used in all radius queries. If this is not set then
-radius queries will fail.
-<P>
-</LI>
-
-<LI><B>bind_address</B> (ip address)<BR>
-When the tun interface is created, it is assigned the address
-specified here. If no address is given, 1.1.1.1 is used. Packets
-containing user traffic should be routed via this address if given,
-otherwise the primary address of the machine.
-<P>
-</LI>
-
-<LI><B>send_garp</B> (boolean)<BR>
-Determines whether or not to send a gratuitous ARP for the
-bind_address when the server is ready to handle traffic (default:
-true).<BR>
-This value is ignored if BGP is configured.
-<P>
-</LI>
-
-<LI><B>throttle_speed</B> (int)<BR>
-Sets the speed (in kbits/s) which sessions will be limited to. If this is
-set to 0, then throttling will not be used at all. Note: You can set this by
-the CLI, but changes will not affect currently connected users.
-<P>
-</LI>
-
-<LI><B>accounting_dir</B> (string)<BR>
-If set to a directory, then every 5 minutes the current usage for
-every connected use will be dumped to a file in this directory. Each
-file dumped begins with a header, where each line is prefixed by #.
-Following the header is a single line for every connected user, fields
-separated by a space.<BR> The fields are username, ip, qos,
-uptxoctets, downrxoctets. The qos field is 1 if a standard user, and
-2 if the user is throttled.
-<P>
-</LI>
-
-<LI><B>setuid</B> (int)<BR>
-After starting up and binding the interface, change UID to this. This
-doesn't work properly.
-<P>
-</LI>
-
-<LI><B>dump_speed</B> (boolean)<BR>
-If set to true, then the current bandwidth utilization will be logged every
-second. Even if this is disabled, you can see this information by running
-the <EM>uptime</EM> command on the CLI.
-<P>
-</LI>
-
-<LI><B>cleanup_interval</B> (int)<BR>
-Interval between regular cleanups (in seconds).
-<P>
-</LI>
-
-<LI><B>multi_read_count</B> (int)<BR>
-Number of packets to read off each of the UDP and TUN fds when
-returned as readable by select (default: 10). Avoids incurring the
-unnecessary system call overhead of select on busy servers.
-<P>
-</LI>
-
-<LI><B>scheduler_fifo</B> (boolean)<BR>
-Sets the scheduling policy for the l2tpns process to SCHED_FIFO. This
-causes the kernel to immediately preempt any currently SCHED_OTHER
-(normal) process in favour of l2tpns when it becomes runnable.
-Ignored on uniprocessor systems.
-<P>
-</LI>
-
-<LI><B>lock_pages</B> (boolean)<BR>
-Keep all pages mapped by the l2tpns process in memory.
-<P>
-</LI>
-
-<LI><B>icmp_rate</B> (int)<BR>
-Maximum number of host unreachable icmp packets to send per second.
-<P>
-</LI>
-
-<LI><B>cluster_address</B> (ip address)<BR>
-Multicast cluster address (default: 239.192.13.13). See the section
-on <A HREF="#Clustering">Clustering</A> for more information.
-<P>
-</LI>
-
-<LI><B>cluster_interface</B> (string)<BR>
-Interface for cluster packets (default: eth0).
-<P>
-</LI>
-
-<LI><B>cluster_hb_interval</B> (int)<BR>
-Interval in tenths of a second between cluster heartbeat/pings.
-<P>
-</LI>
-
-<LI><B>cluster_hb_timeout</B> (int)<BR>
-Cluster heartbeat timeout in tenths of a second. A new master will be
-elected when this interval has been passed without seeing a heartbeat
-from the master.
-<P>
-</LI>
-
-<LI><B>as_number</B> (int)<BR>
-Defines the local AS number for BGP (see <A HREF="#Routing">Routing</A>).
-<P>
-</LI>
-
-<LI><B>bgp_peer1</B> (string)
-<LI><B>bgp_peer1_as</B> (int)
-<LI><B>bgp_peer2</B> (string)
-<LI><B>bgp_peer2_as</B> (int)<BR>
-<P>
-DNS name (or IP) and AS number of BGP peers.
-</LI>
-</UL>
-
-<H3 ID="users">users</H3>
-
-Usernames and passwords for the command-line interface are stored in
-this file. The format is <I>username</I><B>:</B><I>password</I> where
-<I>password</I> may either by plain text, an MD5 digest (prefixed by
-<B>$1</B><I>salt</I><B>$</B>) or a DES password, distinguished from
-plain text by the prefix <B>{crypt}</B>.<P>
-
-The username <B>enable</B> has a special meaning and is used to set
-the enable password.<P>
-
-<B>Note:</B> If this file doesn't exist, then anyone who can get to
-port 23 will be allowed access without a username / password.<P>
-
-<H3 ID="ip-pool">ip_pool</H3>
-
-This file is used to configure the IP address pool which user
-addresses are assigned from. This file should contain either an IP
-address or a CIDR network per line. e.g.:<P>
-
-<PRE>
- 192.168.1.1
- 192.168.1.2
- 192.168.1.3
- 192.168.4.0/24
- 172.16.0.0/16
- 10.0.0.0/8
-</PRE>
-
-Keep in mind that l2tpns can only handle 65535 connections per
-process, so don't put more than 65535 IP addresses in the
-configuration file. They will be wasted.
-
-<H3 ID="build-garden">build-garden</H3>
-
-The garden plugin on startup creates a NAT table called "garden" then
-sources the <B>build-garden</B> script to populate that table. All
-packets from gardened users will be sent through this table. Example:
-
-<PRE>
- iptables -t nat -A garden -p tcp -m tcp --dport 25 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p udp -m udp --dport 53 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p tcp -m tcp --dport 53 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p tcp -m tcp --dport 80 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p tcp -m tcp --dport 110 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p tcp -m tcp --dport 443 -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p icmp -m icmp --icmp-type echo-request -j DNAT --to 192.168.1.1
- iptables -t nat -A garden -p icmp -j ACCEPT
- iptables -t nat -A garden -j DROP
-</PRE>
-
-<H2 ID="ControllingtheProcess">Controlling the Process</H2>
-
-A running l2tpns process can be controlled in a number of ways. The primary
-method of control is by the Command-Line Interface (CLI).<P>
-
-You can also remotely send commands to modules via the nsctl client
-provided. This currently only works with the walled garden module, but
-modification is trivial to support other modules.<P>
-
-Also, there are a number of signals that l2tpns understands and takes action
-when it receives them.
-
-<H3 ID="Command-LineInterface">Command-Line Interface</H3>
-
-You can access the command line interface by telnet'ing to port 23.
-There is no IP address restriction, so it's a good idea to firewall
-this port off from anyone who doesn't need access to it. See
-<A HREF="#users">users</A> for information on restricting access based
-on a username and password.<P>
-
-The CLI gives you real-time control over almost everything in
-the process. The interface is designed to look like a Cisco
-device, and supports things like command history, line editing and
-context sensitive help. This is provided by linking with the
-<A HREF="http://sourceforge.net/projects/libcli">libcli</A>
-library. Some general documentation of the interface is
-<A HREF="http://sourceforge.net/docman/display_doc.php?docid=20501&group_id=79019">
-here</A>.<P>
-
-After you have connected to the telnet port (and perhaps logged in), you
-will be presented with a <I>hostname</I><B>></B> prompt.<P>
-
-Enter <EM>help</EM> to get a list of possible commands. A brief
-overview of the more important commands follows:
-
-<UL>
-<LI><B>show session</B><BR>
-Without specifying a session ID, this will list all tunnels currently
-connected. If you specify a session ID, you will be given all
-information on a single tunnel. Note that the full session list can
-be around 185 columns wide, so you should probably use a wide terminal
-to see the list properly.<P>
-The columns listed in the overview are:
-<TABLE>
- <TR><TD><B>SID</B></TD><TD>Session ID</TD></TR>
- <TR><TD><B>TID</B></TD><TD>Tunnel ID - Use with <EM>show tunnel tid</EM></TD></TR>
- <TR><TD><B>Username</B></TD><TD>The username given in the PPP
- authentication. If this is *, then LCP authentication has not
- completed.</TD></TR>
- <TR><TD><B>IP</B></TD><TD>The IP address given to the session. If
- this is 0.0.0.0, LCP negotiation has not completed.</TD></TR>
- <TR><TD><B>I</B></TD><TD>Intercept - Y or N depending on whether the
- session is being snooped. See <EM>snoop</EM>.</TD></TR>
- <TR><TD><B>T</B></TD><TD>Throttled - Y or N if the session is
- currently throttled. See <EM>throttle</EM>.</TD></TR>
- <TR><TD><B>G</B></TD><TD>Walled Garden - Y or N if the user is
- trapped in the walled garden. This field is present even if the
- garden module is not loaded.</TD></TR>
- <TR><TD><B>opened</B></TD><TD>The number of seconds since the
- session started</TD></TR>
- <TR><TD><B>downloaded</B></TD><TD>Number of bytes downloaded by the user</TD></TR>
- <TR><TD><B>uploaded</B></TD><TD>Number of bytes uploaded by the user</TD></TR>
- <TR><TD><B>idle</B></TD><TD>The number of seconds since traffic was
- detected on the session</TD></TR>
- <TR><TD><B>LAC</B></TD><TD>The IP address of the LAC the session is
- connected to.</TD></TR>
- <TR><TD><B>CLI</B></TD><TD>The Calling-Line-Identification field
- provided during the session setup. This field is generated by the
- LAC.</TD></TR>
-</TABLE>
-<P>
-</LI>
-
-<LI><B>show users</B><BR>
-With no arguments, display a list of currently connected users. If an
-argument is given, the session details for the given username are
-displayed.
-</LI>
-
-<LI><B>show tunnel</B><BR>
-This will show all the open tunnels in a summary, or detail on a single
-tunnel if you give a tunnel id.<P>
-The columns listed in the overview are:
-<TABLE>
- <TR><TD><B>TID</B></TD><TD>Tunnel ID</TD></TR>
- <TR><TD><B>Hostname</B></TD><TD>The hostname for the tunnel as
- provided by the LAC. This has no relation to DNS, it is just
- a text field.</TD></TR>
- <TR><TD><B>IP</B></TD><TD>The IP address of the LAC</TD></TR>
- <TR><TD><B>State</B></TD><TD>Tunnel state - Free, Open, Dieing,
- Opening</TD></TR>
- <TR><TD><B>Sessions</B></TD><TD>The number of open sessions on the
- tunnel</TD></TR>
-</TABLE>
-<P>
-</LI>
-
-<LI><B>show pool</B><BR>
-Displays the current IP address pool allocation. This will only display
-addresses that are in use, or are reserved for re-allocation to a
-disconnected user.<P>
-If an address is not currently in use, but has been used, then in the User
-column the username will be shown in square brackets, followed by the time
-since the address was used:
-<PRE>
-IP Address Used Session User
-192.168.100.6 N [joe.user] 1548s
-</PRE>
-<P>
-</LI>
-
-<LI><B>show radius</B><BR>
-Show a summary of the in-use radius sessions. This list should not be very
-long, as radius sessions should be cleaned up as soon as they are used. The
-columns listed are:
-<TABLE>
- <TR><TD><B>Radius</B></TD><TD>The ID of the radius request. This is
- sent in the packet to the radius server for identification.</TD></TR>
- <TR><TD><B>State</B></TD><TD>The state of the request - WAIT, CHAP,
- AUTH, IPCP, START, STOP, NULL.</TD></TR>
- <TR><TD><B>Session</B></TD><TD>The session ID that this radius
- request is associated with</TD></TR>
- <TR><TD><B>Retry</B></TD><TD>If a response does not appear to the
- request, it will retry at this time. This is a unix timestamp.</TD></TR>
- <TR><TD><B>Try</B></TD><TD>Retry count. The radius request is
- discarded after 3 retries.</TD></TR>
-</TABLE>
-<P>
-</LI>
-
-<LI><B>show running-config</B><BR>
-This will list the current running configuration. This is in a format that
-can either be pasted into the configuration file, or run directly at the
-command line.
-<P>
-</LI>
-
-<LI><B>show counters</B><BR>
-Internally, counters are kept of key values, such as bytes and packets
-transferred, as well as function call counters. This function displays all
-these counters, and is probably only useful for debugging.<P>
-You can reset these counters by running <EM>clear counters</EM>.
-<P>
-</LI>
-
-<LI><B>show cluster</B><BR>
-Show cluster status. Shows the cluster state for this server
-(Master/Slave), information about known peers and (for slaves) the
-master IP address, last packet seen and up-to-date status.<P>
-See <A HREF="#Clustering">Clustering</A> for more information.
-<P>
-</LI>
-
-<LI><B>write memory</B><BR>
-This will write the current running configuration to the config file
-<B>startup-config</B>, which will be run on a restart.
-<P>
-</LI>
-
-<LI><B>snoop</B><BR>
-You must specify a username, IP address and port. All packets for the
-current session for that username will be forwarded to the given
-host/port. Specify <EM>no snoop username</EM> to disable interception
-for the session.<P>
-
-If you want interception to be permanent, you will have to modify the radius
-response for the user. See <A HREF="#Interception">Interception</A>.
-<P>
-</LI>
-
-<LI><B>throttle</B><BR>
-You must specify a username, which will be throttled for the current
-session. Specify <EM>no throttle username</EM> to disable throttling
-for the current session.<P>
-
-If you want throttling to be permanent, you will have to modify the
-radius response for the user. See <A HREF="#THrottling">Throttling</A>.
-<P>
-</LI>
-
-<LI><B>drop session</B><BR>
-This will cleanly disconnect a session. You must specify a session id, which
-you can get from <EM>show session</EM>. This will send a disconnect message
-to the remote end.
-<P>
-</LI>
-
-<LI><B>drop tunnel</B><BR>
-This will cleanly disconnect a tunnel, as well as all sessions on that
-tunnel. It will send a disconnect message for each session individually, and
-after 10 seconds it will send a tunnel disconnect message.
-<P>
-</LI>
-
-<LI><B>uptime</B><BR>
-This will show how long the l2tpns process has been running, and the current
-bandwidth utilization:
-<PRE>
-17:10:35 up 8 days, 2212 users, load average: 0.21, 0.17, 0.16
-Bandwidth: UDP-ETH:6/6 ETH-UDP:13/13 TOTAL:37.6 IN:3033 OUT:2569
-</PRE>
-The bandwidth line contains 4 sets of values.<BR>
-UDP-ETH is the current bandwidth going from the LAC to the ethernet
-(user uploads), in mbits/sec.<BR>
-ETH-UDP is the current bandwidth going from ethernet to the LAC (user
-downloads).<BR>
-TOTAL is the total aggregate bandwidth in mbits/s.<BR>
-IN and OUT are packets/per-second going between UDP-ETH and ETH-UDP.
-<P>
-These counters are updated every second.
-<P>
-</LI>
-
-<LI><B>configure terminal</B><BR>
-Enter configuration mode. Use <EM>exit</EM> or ^Z to exit this mode.
-The following commands are valid in this mode:<P>
-</LI>
-
-<LI><B>load plugin</B><BR>
-Load a plugin. You must specify the plugin name, and it will search in
-/usr/lib/l2tpns for <EM>plugin</EM>.so. You can unload a loaded plugin with
-<EM>remove plugin</EM>.
-<P>
-</LI>
-
-<LI><B>set</B><BR>
-Set a configuration variable. You must specify the variable name, and
-the value. If the value contains any spaces, you should quote the
-value with double (") or single (') quotes.<P>
-
-You can set any <A HREF="#startup-config">startup-config</A> value in
-this way, although some may require a restart to take effect.<P>
-</LI>
-</UL>
-
-<H3 ID="nsctl">nsctl</H3>
-
-nsctl was implemented (badly) to allow messages to be passed to modules.<P>
-
-You must pass at least 2 parameters: <EM>host</EM> and <EM>command</EM>. The
-host is the address of the l2tpns server which you want to send the message
-to.<P>
-
-Command can currently be either <EM>garden</EM> or <EM>ungarden</EM>. With
-both of these commands, you must give a session ID as the 3rd parameter.
-This will activate or deactivate the walled garden for a session
-temporarily.
-
-<H3 ID="Signals">Signals</H3>
-
-While the process is running, you can send it a few different signals, using
-the kill command.
-<PRE>
-killall -HUP l2tpns
-</PRE>
-
-The signals understood are:
-<UL>
-<LI>SIGHUP - Reload the config from disk and re-open log file<P></LI>
-<LI>SIGTERM / SIGINT - Shut down for a restart. This will dump the current
-state to disk (if <EM>save_state</EM> is set to true). Upon restart, the
-process will read this saved state to resume active sessions.<P>
-<LI>SIGQUIT - Shut down cleanly. This will send a disconnect message for
-every active session and tunnel before shutting down. This is a good idea
-when upgrading the code, as no sessions will be left with the remote end
-thinking they are open.</LI>
-</UL>
-
-<H2 ID="Throttling">Throttling</H2>
-
-l2tpns contains support for slowing down user sessions to whatever speed you
-desire. You must first enable the global setting <EM>throttle_speed</EM>
-before this will be activated.<P>
-
-If you wish a session to be throttled permanently, you should set the
-Vendor-Specific radius value <B>Cisco-Avpair="throttle=yes"</B>, which
-will be handled by the <EM>autothrottle</EM> module.<P>
-
-Otherwise, you can enable and disable throttling an active session using
-the <EM>throttle</EM> CLI command.<P>
-
-<H2 ID="Interception">Interception</H2>
-
-You may have to deal with legal requirements to be able to intercept a
-user's traffic at any time. l2tpns allows you to begin and end interception
-on the fly, as well as at authentication time.<P>
-
-When a user is being intercepted, a copy of every packet they send and
-receive will be sent wrapped in a UDP packet to the IP address and port set
-in the <EM>snoop_host</EM> and <EM>snoop_port</EM> configuration
-variables.<P>
-
-The UDP packet contains just the raw IP frame, with no extra headers.<P>
-
-To enable interception on a connected user, use the <EM>snoop username</EM>
-and <EM>no snoop username</EM> CLI commands. These will enable interception
-immediately.<P>
-
-If you wish the user to be intercepted whenever they reconnect, you will
-need to modify the radius response to include the Vendor-Specific value
-<B>Cisco-Avpair="intercept=yes"</B>. For this feature to be enabled,
-you need to have the <EM>autosnoop</EM> module loaded.<P>
-
-<H2 ID="Authentication">Authentication</H2>
-
-Whenever a session connects, it is not fully set up until authentication is
-completed. The remote end must send a PPP CHAP or PPP PAP authentication
-request to l2tpns.<P>
-
-This request is sent to the radius server, which will hopefully respond with
-Auth-Accept or Auth-Reject.<P>
-
-If Auth-Accept is received, the session is set up and an IP address is
-assigned. The radius server can include a Framed-IP-Address field in the
-reply, and that address will be assigned to the client. It can also include
-specific DNS servers, and a Framed-Route if that is required.<P>
-
-If Auth-Reject is received, then the client is sent a PPP AUTHNAK packet,
-at which point they should disconnect. The exception to this is when the
-walled garden module is loaded, in which case the user still receives the
-PPP AUTHACK, but their session is flagged as being a garden'd user, and they
-should not receive any service.<P>
-
-The radius reply can also contain a Vendor-Specific attribute called
-Cisco-Avpair. This field is a freeform text field that most Cisco
-devices understand to contain configuration instructions for the session. In
-the case of l2tpns it is expected to be of the form
-<PRE>
-key=value,key2=value2,key3=value3,key<EM>n</EM>=<EM>value</EM>
-</PRE>
-
-Each key-value pair is separated and passed to any modules loaded. The
-<EM>autosnoop</EM> and <EM>autothrottle</EM> understand the keys
-<EM>intercept</EM> and <EM>throttle</EM> respectively. For example, to have
-a user who is to be throttled and intercepted, the Cisco-Avpair value should
-contain:
-<PRE>
-intercept=yes,throttle=yes
-</PRE>
-
-<H2 ID="Plugins">Plugins</H2>
-
-So as to make l2tpns as flexible as possible (I know the core code is pretty
-difficult to understand), it includes a plugin API, which you can use to
-hook into certain events.<P>
-
-There are a few example modules included - autosnoop, autothrottle and
-garden.<P>
-
-When an event happens that has a hook, l2tpns looks for a predefined
-function name in every loaded module, and runs them in the order the modules
-were loaded.<P>
-
-The function should return <B>PLUGIN_RET_OK</B> if it is all OK. If it returns
-<B>PLUGIN_RET_STOP</B>, then it is assumed to have worked, but that no further
-modules should be run for this event.<P>
-A return of <B>PLUGIN_RET_ERROR</B> means that this module failed, and
-no further processing should be done for this event. <EM>Use this with care.</EM>
-
-Every event function called takes a specific structure named
-param_<EM>event</EM>, which varies in content with each event. The
-function name for each event will be <B>plugin_<EM>event</EM></B>,
-so for the event <EM>timer</EM>, the function declaration should look like:
-<PRE>
-int plugin_timer(struct param_timer *data);
-</PRE>
-
-A list of the available events follows, with a list of all the fields in the
-supplied structure:
-<TABLE CELLSPACING=0 CELLPADDING=0><TR BGCOLOR=LIGHTGREEN><TD>
-<TABLE CELLSPACING=1 CELLPADDING=3>
- <TR BGCOLOR=LIGHTGREEN><TH><B>Event</B></TH><TH><B>Description</B></TH><TH><B>Parameters</B></TH></TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>pre_auth</B></TD>
- <TD>This is called after a radius response has been
- received, but before it has been processed by the
- code. This will allow you to modify the response in
- some way.
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- <LI>username</LI>
- <LI>password</LI>
- <LI>protocol (0xC023 for PAP, 0xC223 for CHAP)</LI>
- <LI>continue_auth - Set to 0 to stop processing authentication modules</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>post_auth</B></TD>
- <TD>This is called after a radius response has been
- received, and the basic checks have been performed. This
- is what the garden module uses to force authentication
- to be accepted.
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- <LI>username</LI>
- <LI>auth_allowed - This is already set to true or
- false depending on whether authentication has been
- allowed so far. You can set this to 1 or 0 to force
- allow or disallow authentication</LI>
- <LI>protocol (0xC023 for PAP, 0xC223 for CHAP)</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_rx</B></TD>
- <TD>This is called whenever a session receives a
- packet. <FONT COLOR=RED>Use this sparingly, as this will
- seriously slow down the system.</FONT>
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- <LI>buf - The raw packet data</LI>
- <LI>len - The length of buf</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>packet_tx</B></TD>
- <TD>This is called whenever a session sends a
- packet. <FONT COLOR=RED>Use this sparingly, as this will
- seriously slow down the system.</FONT>
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- <LI>buf - The raw packet data</LI>
- <LI>len - The length of buf</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>timer</B></TD>
- <TD>This is run every second, no matter what is happening.
- This is called from a signal handler, so make sure anything
- you do is reentrant.
- </TD>
- <TD>
- <UL>
- <LI>time_now - The current unix timestamp</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>new_session</B></TD>
- <TD>This is called after a session is fully set up. The
- session is now ready to handle traffic.
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>kill_session</B></TD>
- <TD>This is called when a session is about to be shut down.
- This may be called multiple times for the same session.
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>radius_response</B></TD>
- <TD>This is called whenever a radius response includes a
- Cisco-Avpair value. The value is split up into
- <EM>key=value</EM> pairs, and each is processed through all
- modules.
- </TD>
- <TD>
- <UL>
- <LI>t - Tunnel ID</LI>
- <LI>s - Session ID</LI>
- <LI>key</LI>
- <LI>value</LI>
- </UL>
- </TD>
- </TR>
- <TR VALIGN=TOP BGCOLOR=WHITE><TD><B>control</B></TD>
- <TD>This is called in whenever a nsctl packet is received.
- This should handle the packet and form a response if
- required.
- </TD>
- <TD>
- <UL>
- <LI>buf - The raw packet data</LI>
- <LI>l - The raw packet data length</LI>
- <LI>source_ip - Where the request came from</LI>
- <LI>source_port - Where the request came from</LI>
- <LI>response - Allocate a buffer and put your response in here</LI>
- <LI>response_length - Length of response</LI>
- <LI>send_response - true or false whether a response
- should be sent. If you set this to true, you must
- allocate a response buffer.</LI>
- <LI>type - Type of request (see nsctl.c)</LI>
- <LI>id - ID of request</LI>
- <LI>data - I'm really not sure</LI>
- <LI>data_length - Length of data</LI>
- </UL>
- </TD>
- </TR>
-</TABLE>
-</TD></TR></TABLE>
-
-<H2 ID="WalledGarden">Walled Garden</H2>
-
-Walled Garden is implemented so that you can provide perhaps limited service
-to sessions that incorrectly authenticate.<P>
-
-Whenever a session provides incorrect authentication, and the
-radius server responds with Auth-Reject, the walled garden module
-(if loaded) will force authentication to succeed, but set the flag
-<EM>garden</EM> in the session structure, and adds an iptables rule to
-the <B>garden_users</B> chain to force all packets for the session's IP
-address to traverse the <B>garden</B> chain.<P>
-
-This doesn't <EM>just work</EM>. To set this all up, you will to
-setup the <B>garden</B> nat table with the
-<A HREF="#build-garden">build-garden</A> script with rules to limit
-user's traffic. For example, to force all traffic except DNS to be
-forwarded to 192.168.1.1, add these entries to your
-<EM>build-garden</EM>:
-<PRE>
-iptables -t nat -A garden -p tcp --dport ! 53 -j DNAT --to 192.168.1.1
-iptables -t nat -A garden -p udp --dport ! 53 -j DNAT --to 192.168.1.1
-</PRE>
-
-l2tpns will add entries to the garden_users chain as appropriate.<P>
-
-You can check the amount of traffic being captured using the following
-command:
-<PRE>
-iptables -t nat -L garden -nvx
-</PRE>
-
-<H2 ID="Clustering">Clustering</H2>
-
-An l2tpns cluster consists of of one* or more servers configured with
-the same configuration, notably the multicast <B>cluster_address</B>.<P>
-
-*A stand-alone server is simply a degraded cluster.<P>
-
-Initially servers come up as cluster slaves, and periodically (every
-<B>cluster_hb_interval</B>/10 seconds) send out ping packets
-containing the start time of the process to the multicast
-<B>cluster_address</B>.<P>
-
-A cluster master sends heartbeat rather than ping packets, which
-contain those session and tunnel changes since the last heartbeat.<P>
-
-When a slave has not seen a heartbeat within
-<B>cluster_hb_timeout</B>/10 seconds it "elects" a new master by
-examining the list of peers it has seen pings from and determines
-which of these and itself is the "best" candidate to be master.
-"Best" in this context means the server with the highest uptime (the
-highest IP address is used as a tie-breaker in the case of equal
-uptimes).<P>
-
-After discovering a master, and determining that it is up-to-date (has
-seen an update for all in-use sessions and tunnels from heartbeat
-packets) will raise a route (see <A HREF="#Routing">Routing</A>) for
-the <B>bind_address</B> and for all addresses/networks in
-<B>ip_pool</B>. Any packets recieved by the slave which would alter
-the session state, as well as packets for throttled or gardened
-sessions are forwarded to the master for handling. In addition, byte
-counters for session traffic are periodically forwarded.<P>
-
-A master, when determining that it has at least one up-to-date slave
-will drop all routes (raising them again if all slaves disappear) and
-subsequently handle only packets forwarded to it by the slaves.<P>
-
-<H2 ID="Routing">Routing</H2>
-If you are running a single instance, you may simply statically route
-the IP pools to the <B>bind_address</B> (l2tpns will send a gratuitous
-arp).<P>
-
-For a cluster, configure the members as BGP neighbours on your router
-and configure multi-path load-balancing. Cisco uses "maximum-paths
-ibgp" for IBGP. If this is not supported by your IOS revision, you
-can use "maximum-paths" (which works for EBGP) and set
-<B>as_number</B> to a private value such as 64512.<P>
-
-<H2 ID="Performance">Performance</H2>
-
-Performance is great.<P>
-
-I'd like to include some pretty graphs here that show a linear performance
-increase, with no impact by number of connected sessions.<P>
-
-That's really what it looks like.<P>
-
-<BR>
-David Parrish<BR>
-<A HREF="mailto:david@dparrish.com?subject=L2TPNS%20Documentation">david@dparrish.com</A>
-</BODY>
-</HTML>
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