IPtables and RIP

Hello All,

I encountered a little problem on a friend's server, maybe one of you 
can help me out?

He wants to use RIP for more efficient routing, so I had to patch my 
firewall script which is running on his server. So far not a problem. 
RIP works and all. But to make it work I had to accept ICMP redirect 
(type 5) packets, because RIP uses it for rerouting packets. Now this 
I'm not happy about because ICMP type 5 messages can be easily abused 
for hacking/DOS purposes.

Is there a way I can check with IPtables if an ICMP redirect message is 
legitimate? I did see in the log that there is extra information about 
the original RIP packet which caused the redirect.... Is there a way I 
can use that information? Can I let the connection tracker handle it? If 
so, how? (accepting "related" messages didn't seem to work)

I looked on the Net for information as well as in my firewall books, but 
they just say don't enable it :(

Anyone who can help me out?

He's using iptables-1.2.5-3 and a 2.4.18-24.7.xcustom kernel, just in 
case someone needs that info.

Tnx,
Eric.