GRE - Recursive routing error - filtering solution

One of the solutions to the GRE - Recursive routing error is to prevent the advertising of the tunnel destination IP address on the tunnel interface. Refer to the following diagram:

recursive-routing-gre-topology.png

Based on this topology, the following configurations would resolve the issue assuming we are using RIP:

R1 Configuration:

interface Loopback0
 ip address 1.1.1.1 255.255.255.255

interface FastEthernet0/0
 ip address 192.168.12.1 255.255.255.0

interface Tunnel0
 ip address 192.168.13.1 255.255.255.0
 tunnel source 1.1.1.1
 tunnel destination 3.3.3.3

router rip
 version 2
 network 1.1.1.1
 network 192.168.12.0
 network 192.168.13.0
 no auto-summary
 distribute-list 101 out Tunnel0

access-list 101 deny   ip host 3.3.3.3 any
access-list 101 permit ip any any

R3 Configuration:

interface Loopback0
 ip address 3.3.3.3 255.255.255.255

interface FastEthernet0/0
 ip address 192.168.23.3 255.255.255.0

interface Tunnel0
 ip address 192.168.13.3 255.255.255.0
 tunnel source 3.3.3.3
 tunnel destination 1.1.1.1

router rip
 version 2
 network 3.3.3.3
 network 192.168.23.0
 network 192.168.13.0
 no auto-summary
 distribute-list 102 out Tunnel0

access-list 102 deny   ip host 1.1.1.1 any
access-list 102 permit ip any any

With this setup:

  1. The distribute-list on R1 prevents the tunnel destination (3.3.3.3) from being advertised out on the Tunnel0 interface. Similarly, on R3, it prevents the tunnel destination (1.1.1.1) from being advertised out the Tunnel0 interface.
  2. Since the default administrative distance for RIP is 120, routes learned via the GRE tunnel will inherently have a distance of 120. Routes learned directly through the FastEthernet interfaces will also have a distance of 120, but the RIP updates for the tunnel endpoints (1.1.1.1 and 3.3.3.3) are not advertised through the tunnel, hence recursive routing through the tunnel should be avoided.

Links:

https://forum.networklessons.com/t/gre-tunnel-recursive-routing-error/998/58?u=lagapides

https://networklessons.com/cisco/ccie-routing-switching/gre-tunnel-recursive-routing-error

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