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Hack 90 NoCatSplash and Cheshire

If you need a simple "splash
screen" for your wireless users, try either of these
simple captive portals.

Some people find that Perl is too heavy
of a requirement for their gateway hardware, making it impractical to
use NoCatAuth. If you are only looking for a "click
here to continue" sort of splash page (without the
full authentication mechanism), you may be interested in NoCatSplash.
It is a port of NoCatAuth entirely rewritten in C. Its requirements
are quite small, but it supports only simple open mode portal
functionality. The current version works under Linux, and portability
to BSD and other systems is planned for the near future.

To install NoCatSplash, download the current CVS tree or just grab
the archive available at http://nocat.net/download/NoCatSplash/.
Unpack the archive, navigate to
NoCatSplash-nightly/, and install it with a
simple:

rob@florian:~/NoCatSplash-nightly$ ./configure; make; make install

This installs splashd to
/usr/local/sbin/, and puts the
nocat.conf configuration file in
/usr/local/etc/. Edit the
nocat.conf file to your tastes, taking note to
set the ExternalDevice, InternalDevice, LocalNetwork, and DNSAddr
options to fit your network layout. See the comments in the
configuration file for details.

Start the portal by running splashd as root:

root@florian:~# /usr/local/sbin/splashd &

NoCatSplash uses the same firewall scripts as NoCatAuth to do the
actual firewall manipulation. It installs these scripts to
/usr/local/libexec/nocat/, making it simple to
customize your firewall rules if you need to. With
splashd running, any users whose traffic
originates on InternalDevice will be captured and shown the splash
page defined in nocat.conf. The default
html files for the splash page are kept in
/usr/local/share/nocat/htdocs/, but can be kept
wherever you like by setting the DocumentRoot in
nocat.conf.

Another possible alternative to
NoCatAuth is Cheshire,
a captive portal written completely in shell script. It is available
at http://nocat.net/download/cheshire/. The goal
of Cheshire is to provide the smallest possible captive portal,
suitable for use with very tiny Linux installations. Without decent
networking functions of its own, Cheshire needs a couple of helper
apps to do the dirty work of actual networking. Notably, it needs the
getpeername utility from NetPipes (http://freshmeat.net/projects/netpipes/). It
also needs the faucet utility from the same package, or it
can use the system's
inetd if you have one installed.

Apart from this, standard system tools such as sed, awk, and cron are
all you need. Cheshire works fine under the very lightweight ash
shell. If you want to serve graphics on your splash page, and your
gateway has a slow CPU, you will probably be happiest with a
"real" web server rather than using
Cheshire itself. I find that
khttpd (the Kernel space
http server available in Linux 2.4) works very well for this job, and
is very tiny.

To install Cheshire, extract the archive into /usr/local/cheshire/. Edit the
cheshire.conf file in this directory to your
liking, and launch the script using faucet like this:

root@gateway:~# faucet 5280 --in --out --daemon /usr/local/cheshire/bin/grin

If you would rather not use faucet, you can run Cheshire out of your
inetd. Add the port as a service in /etc/services by appending a line like this:

cheshire                5280/tcp

Add Cheshire itself to your /etc/inetd.conf
with this line:

cheshire  stream  tcp  nowait  root  /usr/local/cheshire/bin/grin

Finally, you will probably want to boot your users out ever so often,
to force them to see the splash page again. Use the system cron to
accomplish this. I run it once a day at 4:00 in the morning. Put a
line like this in the crontab for root:

0 4 * * *       /usr/local/cheshire/bin/grin -R

While Cheshire and NoCatSplash might not be as feature rich as
NoCatAuth, their requirements are very simple. They can be ideal for
situations where you simply want to give people an idea of whose
network they are using, especially if the capabilities of your
wireless gateway are limited.