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David Parrish 32e5db5906 Small typo fixes from Paul Lampron
2004-04-16 02:33:32 +00:00

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<TITLE>L2TPNS Manual</TITLE>
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<H1>L2TPNS Manual</H1>
<OL>
<LI>Overview</LI>
<LI>Installation</LI>
<LI>Configuration</LI>
<LI>Controlling the process</LI>
<LI>Command-Line Interface</LI>
<LI>Throttling</LI>
<LI>Interception</LI>
<LI>Authentication</LI>
<LI>Plugins</LI>
<LI>Walled Garden</LI>
<LI>Clustering</LI>
<LI>Performance</LI>
</OL>
<H2>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>Installation</H2>
<H3>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 1.5 or greater.<BR>You can get this from <A
HREF="http://sourceforge.net/projects/libcli">http://sourceforge.net/projects/libcli</A></LI>
<LI>The iproute2 user-space tools. These are used for throttling,
so if you don't want to throttle then this is not required.<BR>You
may also need to patch tc and the kernel to include HTB
support. You can find the relevant patches and instructions at <A
HREF="http://luxik.cdi.cz/~devik/qos/htb/">http://luxik.cdi.cz/~devik/qos/htb/</A>.</LI>
</OL>
<H3>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>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 file before you start.
See the Configuration section for more information.<P>
You should also create the appropriate iptables chains if you want to use
throttling or walled garden.
<PRE>
# Create the walled garden stuff
iptables -t nat -N l2tpns
iptables -t nat -F l2tpns
iptables -t nat -A PREROUTING -j l2tpns
iptables -t nat -A l2tpns -j garden_users
# Create the throttling stuff
iptables -t mangle -N l2tpns
iptables -t mangle -F l2tpns
iptables -t mangle -N throttle
iptables -t mangle -F throttle
iptables -t mangle -A PREROUTING -j l2tpns
iptables -t mangle -A l2tpns -j throttle
</PRE>
<H3>Running it</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>Configuration</H2>
All configuration of the software is done from the files installed into
/etc/l2tpns.
<H3>l2tpns.cfg</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 # 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>
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)<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.<BR>
This sets the first DNS entry that will be sent.
<P>
</LI>
<LI><B>secondary_dns</B> (ip address)<BR>
See <EM>primary_dns</EM>.
<P>
</LI>
<LI><B>snoop_host</B> (ip address)<BR>
Whenever a user is intercepted, a copy of their traffic will be sent to this
IP address, using the port specified by <EM>snoop_port</EM>. Each packet
will be sent as UDP.
<P>
</LI>
<LI><B>snoop_port</B> (int)<BR>
See <EM>snoop_host</EM>.
<P>
</LI>
<LI><B>primary_radius</B> (ip address)<BR>
This sets the primary radius server used for both authentication and
accounting. If this server does not respond, then the secondary radius
server will be used.
<P>
</LI>
<LI><B>secondary_radius</B> (ip address)<BR>
See <EM>primary_radius</EM>.
<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.<BR>
If an address is given here, then packets containing user traffic should be
routed via this address, otherwise the primary address of the machine.<BR>
This is set automatically by the cluster master when taking over a failed
machine.
<P>
</LI>
<LI><B>cluster_master</B> (ip address)<BR>
This sets the address of the cluster master. See the <EM>Clustering</EM>
section for more information on configuring a cluster.
<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>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>setuid</B> (int)<BR>
After starting up and binding the interface, change UID to this. This
doesn't work properly.
<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. 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>save_state</B> (boolean)<BR>
If set to true, a state file will be dumped to disk when the process dies.
This will be restored on startup, loading all active tunnels and sessions.
<P>
</LI>
</UL>
<H3>l2tpns.users</H3>
This file's sole purpose is to manage access to the command-line
interface. If this file doesn't exist, then anyone who can get to port
23 will be allowed access without a username / password.<P>
If this is not what you want, then create this file and put in it a list of
username / password pairs, separated by a <B>:</B>. e.g.:<P>
<PRE>
user.1:randompassword
fred:bhPe4rD1ME8.s
bob:SP2RHKl3Q3qo6
</PRE>
Keep in mind that the password should be in clear-text. There is no user
privilege distinction, so anyone on this list will have full control of the
system.<P>
<H3>l2tpns.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 IP mask
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.
<H2>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>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 l2tpns.users 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.<P>
After you have connected to the telnet port (and perhaps logged in), you
will be presented with a prompt <PRE>l2tpns&gt;</PRE><P>
You can type <EM>help</EM> to get a list of all possible commands, but this
list could be quite long. 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 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>write memory</B><BR>
This will write the current running configuration to the config file
l2tpns.cfg, which will be run on a restart.
<P>
</LI>
<LI><B>snoop</B><BR>
You must specify a username, which will be intercepted for the current
session. Specify <EM>no snoop username</EM> to disable interception for the
current session.<P>
If you want interception to be permanent, you will have to modify the radius
response for the user. See <EM>Interception</EM>.
<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 <EM>Throttling</EM>.
<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>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 quotes (").
<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>
</UL>
<H3>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.<BR>
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>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<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>
This is really useful when doing an upgrade, as the code can change without
dropping any users. However, if the internal structures such as
<EM>sessiont</EM> or <EM>tunnelt</EM> change, then this saved state file
will not reload, and none of the sessions will be recreated. This is bad.<P>
If these structures do change, you should kill the server with SIGQUIT,
which won't dump the state.</LI>
<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>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>
Throttling is actually performed using a combination of iptables and tc.<BR>
First, a HTB bucket is created using tc (unless one is already created and
unused).<BR>
Secondly, an iptables rule is inserted into the throttle chanin in the
mangle table so all packets destined for the user's IP address go into the
HTB.<P>
You can check the packets being throttled using the tc command. Find the HTB
handle by doing <EM>show session id</EM> in the CLI, next to the Filter
Bucket tag. Then at the shell prompt, you can run:
<PRE>
tc -s class ls dev tun0 | grep -A3 <EM>1:870</EM>
class htb 1:870 root prio 0 rate 28Kbit ceil 28Kbit burst 15Kb cburst 1634b
Sent 27042557 bytes 41464 pkts (dropped 1876, overlimits 0)
lended: 41471 borrowed: 0 giants: 0
tokens: 3490743 ctokens: 353601
</PRE>
<H2>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>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>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>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 need to create
2 iptables chains on the nat table - <B>garden</B> and <B>garden_users</B>.
<PRE>
iptables -t nat -N garden
iptables -t nat -F garden
iptables -t nat -N garden_users
iptables -t nat -F garden_users
</PRE>
You should add rules to the <B>garden</B> chain 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 firewall startup script:
<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>Clustering</H2>
Clustering is currently broken. But here's how it's supposed to work.<P>
<H2>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+Documentation">david@dparrish.com</A>
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