Recursive routing

Publication Date:  2016-07-11 Views:  327 Downloads:  0
Issue Description
This is GRE tunnel setup between two router. The public IP of router A is 1.1.1.1, public IP of router B is 2.2.2.2. Customer wants to connect two site through tunnel. All traffic from router B will first go to router A and then either access to internet or private network. Customer finds that after configuring router A and B, tunnel is down in state. Below is the configuration of router A and B.

Configuration of router A:

Int tunnel 0/0/1 
Tunnel-protocol gre
Ip address 192.168.0.1 255.255.255.252
Source 1.1.1.1
Destination 2.2.2.2

Int vlan 1
Ip address 10.1.1.1 255.255.255.0

Ip route 0.0.0.0 0.0.0.0 1.1.1.100
Ip route 10.2.2.0 255.255.255.0 tunnel 0/0/1


Configuration of router B:

Int tunnel 0/0/1 
Tunnel-protocol gre
Ip address 192.168.0.2 255.255.255.252
Source 2.2.2.2
Destination 1.1.1.1

Int vlan 1
Ip address 10.2.2.2. 255.255.255.0

Ip route 0.0.0.0 0.0.0.0 2.2.2.100
Ip route 0.0.0.0 0.0.0.0.0 tunnel 0/0/1

After checking the configuration, it was found that in router B, tunnel can’t find its destination end because it choose its own default route which results in recursive routing.

Solution
Change the default route in router B to be static:

Ip route 0.0.0.0 0.0.0.0 2.2.2.100
Changes to
Ip route 1.1.1.1 255.255.255.255 2.2.2.100

Tunnel then change to up in state and the problem is solved.

END