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ospf to run on gre tunnel

How do I run ospf on gre tunnel , now the tunnel comes up and goes down stating the problem of recursive routing .

I have got two routers which are connected back to back , 1751 both , the serial interfaces have not been advertised through ospf , the tunnel ip address have been advertised through ospf , the tunnel ip address are in area 0 , the lan ip address are in area 1 , & the lan ip address of the router 2 is area 2, the gre tunnels are starting up from loopback ip address from router 1 to router 2 loopback ip address , the loopback are in area 0 , why the tunnel is not coming up.


Re: ospf to run on gre tunnel

The answer to your question is the error your getting "recursive routing".

the problem is that the router is learning the network of the other router's loopback address

through the loopback with ospf.and the loopback network learned is the tunnel endpoint. so the logic of the problem is a router cannot get to a tunnel destination endpoint through the tunnel itself

so I advise you to make a filter on each router so they will not learn the loopback address of the other router through ospf on the loopback(you can always not advertise the loopback to ospf but if you have other routers in your network they will not learn the route)

so make an access-list that denies the loopback network and permits all others

then under "router ospf"

do a "distribute-list 1 in loopback 0"

where 1 is the access-list number and 0 is the loopback number .

Cisco Employee

Re: ospf to run on gre tunnel

there is a sample config for this on CCO, might help;

below example is with EIGRP, but you can replace EIGRP with OSPF, rest would remain same.

below example is with OSPF but might not fit your setup, since the IPSec is b/w 2 PIXs and GRE is b/w 2 routers