Cisco Support Community
Community Member

Configuring IPSec with EIGRP and IPX Using GRE Tunneling

After using "Configuring IPSec with EIGRP and IPX Using GRE Tunneling.pdf" as a guide, I ran my config by the VPN group at TAC. Both the fellow I worked with and his lead agreed that it is unnecessary to use the loopback interface as the IKE peer, tunnel source and tunnel destination.

Who wrote this doc and why is the loopback used? Which is the preferred method?

Note: The tunnel mask in the Network Drawing has a typo. Should be /30.

Cisco Employee

Re: Configuring IPSec with EIGRP and IPX Using GRE Tunneling


1. When you create a Tunnel Interface, you also define a Tunnel Source and Tunnel Destination which are basically routable ip addresses. It is not a must to have the Tunnel source as the loopback address but this procedure is usually followed due to the simple fact that the loopback interface is a logical interface and also this helps when you have a backup connection.

For example, if you have a connection to the internet via a Serial Interace and also have an ISDN connection as a backup, then using the Loopback interface as the Tunnel source will come very handy cos when the serial fails your tunnel will kick in via the ISDN.

The same analogy can be applied to the IKE Peer as well.

I hope you are looking at this URL:

I see that the diagram has the tunnel interface has mask /30.

Please do let me know if there is any other URL or typo, so that I can file a bug on this Doc and have it corrected.



CreatePlease to create content