Re: Static ARP firewall advice

["Greg Dickinson" <gdickinson () indiansprings org>]

Thank you all for your advice.

Yes, the new proxy server that I install will use authentication (ident
for when they are using lab machines, and LDAP against eDirectory for
dorm machines.)

We had also realized that this would only be a stopgap measure against
the brighter students - but we had to do something to maintain the
integrity of the internet access :-) while not making it overly
difficult for all involved.

I hadn't thought about using PPPoE for dorm access.  I may look into
that when I upgrade the firewall to the latest version of OBSD.

Thanks again.


> > > Chuck Swiger <chuck () codefab com> 04/09/04 8:51 AM >>>
Greg Dickinson wrote:
[ ... ]
> I am currently in the process of reloading the proxy server to get it
> off RH9, but in the interim I was wondering if there is an
> easy/recommended way to accomplish this: I had the idea of adding
static
> ARP entries in the firewall so that only the specified Layer 3
addresses
> that match the specified Layer 2 addresses can get through the
firewall.
>  However (as you can imagine) this is a nightmare to maintain, as well
> as difficult for the local administrator to add static ARP entries (he
> has to add the addresses to /etc/rc.local and reboot the firewall
> everytime [yes, I know a reboot is not required...but it's simpler...
> :-> ])

On most systems, you should be adding IP-to-MAC mappings via
/etc/ethers, and 
disabling ARP on that particular network interface.  While you can
accomplish 
what you've asked for and it will work to some extent, you'll discover
that 
clever students can also change their MAC addresses, too.

Better approaches be to switch to using authenticating proxy servers for

traffic (ie, squid for HTTP/HTTPS), or to require students to use PPPoE
in 
order to get a connection (which will use an authentication mechanism
that's 
not trivial to spoof).

-- 
-Chuck
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