Distributing traffic across multiple GRE tunnels between two routers

[moyhajjat]

Hi,

I have a GRE tunnel between a pair of vrfs on two routers. Can I create a second tunnel between the pair of vrfs using the same source tunnel IP given that I use a distinct destination tunnel IPs on the second router? I would like to ECMP traffic across the two tunnels.

Thanks!

[Vinit Jain]

Yes, you can have two seperate tunnels between two routers (even if its in VRF). the only thing to point out here is even if you have two ECMP paths, the load-balancing will happen based on flow and not based on packet. thus, you can still have one tunnel having more traffic over the other.

Note: You can have tunnels between same source and same destination and also between same source and distinct destination.

Hope this helps.

Regards

Vinit

[moyhajjat]

Thanks Vinit! Yes load balancing based on flow is fine. If I run BGP inside the GRE tunnel, would that cause it to always go through the same tunnel?

Also, I'm assuming the same subnet can be used for both tunnels?

[Vinit Jain]

You will have to use two different subnets for both the tunnels. It cannot have same subnets unless you are using ip unnumbered.

If you are forming BGP session on the tunnel IP's then the BGP will always form on those IP's and take the same tunnel, but if you are forming BGP on loopbacks, it can take any of the two interfaces. You can check which interface the router is taking using the "show ip cef exact-route <source> <destination>" command.

[moyhajjat]

Thanks Vinit! I've trying to read more about IP Unnumbered but I wasn't sure how this can be used in my case. Can you please provide a simple example or a pointer? Thanks!

[Vinit Jain]

Do you have any further questions related to this thread. If all your queries have been answered, Please mark teh quesiton as answered as it help others who might have similar questions.

Regards

Vinit