Home / server / Questions / 99984
In Process
Paul
Asked: 2010-01-07 03:20:21 +0800 CST

Split horizon, route filtering, and having RIPv2 announce a non-attached route to host

  • 772

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.

networking

2 Answers

  1. Maybe post the relevant parts of your config? I believe redistribute static on router should distribute the static routes that are on the router with that config. Do you not see the route on the routers when you run show ip route?

    Also, I am a bit confused by what you mean with 'the routers share the same subnet'.... Wouldn't the hosts all then be on the same subnet, so the traffic will just go through the switches? I think you need to de-abstract your question a little, for example, paste IP address and subnets.

    Keep in mind that redistribute static will redistribute all the static routes, use a route map to limit which static routes get redistributed. This cisco page says how.

    • 0

  2. You are going to need a static route on router 'C' for the /32 host. You can also have a static on router 'B' for the same host pointing to router 'C' as the next hop, which you can then redistributed through RIP.

    router B>
ip route 10.20.20.5 255.255.255.255 10.1.1.3

router rip
 version 2
 redistribute static

router C>
ip route 10.20.20.5 255.255.255.255 10.30.30.1

    Are the networks behind the 'B' and 'C' router the same network? If yes, then you will probably have some asymmetric routing unless they also do some work on their routers.

    • 0