GRE Tunnel Key

This topic is to discuss the following lesson:

Hi Rene
How to change it to use second key instead the first key

Hello Lam

The choice of GRE key depends on the routing configured in each router.

There are two GRE tunnels between R1 and R2 with specific IP addresses. The default route within R1 and R2 indicates which should be the next-hop IP. This next-hop IP is also what specifies which tunnel should be used.

R1 has a default route to 172.16.12.2 and R2 has a default route to 172.16.12.1 so for all communication in both directions, Tunnel 1 should be used since tunnel 1 is on the 172.16.12.0/24 subnet.

Without the GRE key, as you see in the lesson, either tunnel will be used. By putting in the GRE key, only tunnel 1 is used.

Now if you want to use Tunnel 2, you simply change the routing so that the default route of R1 points to 172.16.21.2 and the default route of R2 points to 172.16.21.1. Then traffic will use the other tunnel.

I hope this has been helpful!

Laz

HI Laz

Thank, I now has clearer understanding.

Regards

Tan lam soon

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