Network Warrior, 2nd Edition

GRE Tunnels and Routing Protocols

The introduction of a routing protocol across a GRE tunnel can cause some interesting problems. Take, for example, our network, now altered as shown in Figure 12-3. This time, we have the links between the routers updating routes using RIPv2. The other interfaces on Router A and Router D are included in RIP using the redistribute connected command. EIGRP is running on all interfaces on Routers A and D with the exception of the serial links, which are running RIPv2.

While this may look a bit odd, consider the possibility that the Routers B and C are owned and operated by a service provider. We cannot control them, and they only run RIPv2. We run EIGRP on our routers (A and D) and want to route between them using EIGRP.

Figure 12-3. Recursive routing example

Here are the pertinent configurations for Router A and Router D (remember, in this scenario, Routers B and C are beyond our control):

Router A:

interface Loopback0 ip address 10.100.100.100 255.255.255.255 ! interface Tunnel0 ip address 172.16.0.1 255.255.255.0 tunnel source Loopback0 tunnel destination 10.200.200.200 ! interface Ethernet0/0 ip address 10.10.10.1 255.255.255.0 ! interface Serial0/1 ip address 192.168.1.1 255.255.255.0 router eigrp 100 network 10.10.10.0 0.0.0.255 network 10.100.100.0 0.0.0.255 network 172.16.0.0 0.0.0.255 no auto-summary ! router rip version 2 redistribute connected ...