OSPF GRE Tunnel

[Mr. Andrew]

We are currently moving over from EIGRP to OSPF on our network.  We have multiple P2P OSPF networks with a centralized Core node with encryption devices inbetween. EIGRP works fine with the tunnel source and destination set as the layer 3 interfaces connecting to the encryption devices on both sides and a gateway of last resort set to the encrpyiton devices IP on the distant end. However when we turn on OSPF and turn off EIGRP recursive routing occurs and the tunnel flaps. The only way to fix it is to put a static route pointing to the layer 3 interface on the core node and set a gateway of last resort to the core nodes loopback address. 

I have done some research and found the tunnel uses itself to establish it.

Is that not how it is set up now with EIGRP since the tunnel is a connected link in the routing table and will always take precedence over any static route, so why the need to add one for OSPF?

My other questions is why does it only work with EIGRP and not OSPF why do we have to edit these small details for it to work properly?

[Georg Pauwen]

Hello,

post the running configuration of the tunnel routers (tunnel endpoints)...

[David Ruess]

Hello,

EIGRP will be the preferred method for tunnels because OSPF will have caveats that EIGRP does not have due to its hierarchical structure. Its true that you cannot learn the route of the tunnel destination through the tunnel itself..so you would need something else (like a static route) to provide underlying connectivity.

As @Georg Pauwen  said running configs will help but with the limitations that may be your only course.

-David

[MHM Cisco World]

ip ospf network point-to-multipoint <- do you config this in tunnel of Core?

can I see the config of tunnel or tunnels in Core?
can I see the config of OSPF Core and Site ?

note:-Also I need to know are all Site run in same OSPF Area or different Area?

[Richard Burts]

I am surprised at the description of this issue. If a dynamic routing protocol like EIGRP causes recursive routing problems, then I would expect that it would have been a problem with OSPF also. Perhaps there is something in the OSPF config that addresses this? Perhaps posting the configurations might help us to understand what is going on here?