GRE Tunnel

[kjanakiraman]

I saw a GRE Tunnel configuration and i would like some advice. There is loopback interface loopbacko configured. There is a tunnel0 interface configured with ip address in different subnet and tunnel source pointing towards loopback0. How GRE Tunnel Works. Is there any good documentation where i can get all the information?

Thanks in Advance

[Richard Burts]

The essential concept of GRE tunnels is that the router takes some packet (it might be IP or might be some other protocol) and re-encapsulates it producing a new IP packet with the original packet as the payload of the new packet. The source address of the GRE packet is some interface on the originating router and the destination address is some address on the receiving router.

There is no rule about which interface to choose as the GRE source (or destination). Many times the loopback is chosen as the GRE source/destination address. This is particularly advantageous when there are multiple paths to the other router and multiple interfaces over which the GRE packet might be sent. But there are also situations where it is advantageous to choose a physical interface as the GRE source/destination address.

This link should give you some information to get started in becoming more familiar with GRE tunnels:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080087093.html#1012601

HTH

Rick

[kjanakiraman]

Thanks a lot for your information. I will go through the doucmentation link that you have provided and will get back if i have any queries.