GRE Tunnels

GRE stands for "Generic Routing Encapsulation". GRE is now industry tunneling method used to create a logical "TUNNEL" interface. It is designed to work with logical protocols, only GRE is completely non-secure as we have no concept of crypto-map. This makes a seperate network over the network, but now they add an IP header in the GRE header so makes it secure and provides a perfect tunneling. I will talk about GRE tunneling here, lets look at the configurations of GRE.



Run EIGRP on both sides

ReedWood(config) # router eigrp 1
ReedWood(config-router) # network 10.0.0.0
ReedWood(config-router) # network 41.0.0.0

PineWood(config) # router eigrp 1
PineWood(config-router) # network 10.0.0.0
PineWood(config-router) # network 41.0.0.0

Now to create tunnel on both side lets look at the configurations

ReedWood(config) # interface tunnel 0
# ip address 10.5.1.2 255.255.255.0
# tunnel source 0/0
# tunnel destination 41.95.110.2
# tunnel mode gre ip

PineWood(config) # interface tunnel 0
# ip address 10.5.1.1 255.255.255.0
# tunnel source 0/0
# tunnel destination 41.95.110.1
# tunnel mode gre ip

At this point for simplicty define static route on Router-A and check the connectivity

Router-A (config) # ip route 0.0.0.0 0.0.0.0

PineWood # show ip eigrp neighbor

It will shows you that the route is learned via Tunnel.

I Hope this will be informative for You !

Cheers :)