Split horizon, route filtering, and having RIPv2 announce a non-attached route to host...
- by Paul
Routers A, B & C live at 10.1.1.1, 10.1.1.2 and 10.1.1.3 on a /24 metro Ethernet subnet. Each router also has its own private subnet on another interface. Router B's private subnet links thru a firewall to a 10.20.20.0 network at another organization.
Router B redistributes to A and C several static routes for hosts on 10.20.20.0. However, a new host 10.20.20.5/32 must be reached via a different path that goes through router C. I know that C can advertise this host-based route with no problem, but I'd like to keep all my 10.20.20.x static routes in one place.
So, how can B tell A via RIPv2 to send packets for 10.20.20.5/32 to C?
So far it looks like I need no ip split-horizon on router B's 10.1.1.2 interface, perhaps because B has already learned from C other routes with a next hop of 10.1.1.3. But how does RIPv2 split horizon with no auto-summary and network 10.0.0.0 really work? If B learns a route to ANY 10.x.x.x network or host from A or C, is that enough for split horizon to keep it from redistributing ip route 10.20.20.5 255.255.255.255 10.1.1.3?
And if I want to suspend split horizon only for this one new host, how do I filter out the mess of regurgitated routes that B advertises when I try no ip split-horizon?
Thanks much.
