You probably want to look at DD-WRT or OpenWRT.
Those guys have done so much in the way of open source routers - back since the WRT54g / early buffalo routers...

By default the router shows this for routing in Lan Setup *native firmware*:

# RIP Direction: RIP (Routing Information Protocol, RFC1058 and RFC1389) allows a router to exchange routing information with other routers. The RIP Direction selection controls how the router sends and receives RIP packets. None is the default.

* When set to Both or Out Only, the router will broadcast its routing table periodically.
* When set to Both or In Only, it will incorporate the RIP information that it receives.
* When set to None, it will not send any RIP packets and will ignore any RIP packets received. None is the default.

# RIP Version: This controls the format and the broadcasting method of the RIP packets that the router sends. (It recognizes both formats when receiving.) By default, this is set for Disabled.

* RIP-1 is universally supported. RIP-1 is probably adequate for most networks, unless you have an unusual network setup.
* RIP-2 carries more information. Both RIP-2B and RIP-2M send the routing data in RIP-2 format.
o RIP-2B uses subnet broadcasting.
o RIP-2M uses multicasting