GRE Configuration ON Cisco Router

It is assumed that you know the basics of GRE. If you have no idea about GRE then Click Here to study about Generic Routing Encapsulation (GRE). This blog goes only with the configuration of GRE.

Lab Scenario

IOS version used is c7200-adventerprisek9-mz.15.2-4.s4.image
R1 is the Headquarter Router and R2 is the Remote site router.
PC1 is connected to R1 on interface fa 0/1 and PC2 is connected to R2 on interface fa 0/1
Tunnel interfaces network used is 192.168.0.0/24

Goal: The Goal of this Lab is to configure a GRE tunnel between R1 and R2 so that we can have such connection that R1 and R2 looks like they are connected through a point to point connection.


Configuration On R1 (Headquarter Router)

when you are at the enable mode enter the below commands
!..............................start of configuration..................................
config t
interface tunnel 0
ip address 192.168.0.1 255.255.255.0
       !this is tunnel interface's ip address
tunnel source 51.10.1.1
        !you can use interface as well
tunnel destination 51.10.2.2
end
write
show ip interface brief
!.................................end of configuration..............................
with the show commad you will see that the tunnel 0 interface is create and its up

Configuration on R2 (Remote site router)
when you are at the enable mode then enter these commands
!...............................start of configuration..................................
config t
interface tunnel 0
ip address 192.168.0.2 255.255.255.0
tunnel source fa 0/0
tunnel destination 51.10.1.1
end
write
show ip interface brief
!...............................end of configuration...................................

Verification of GRE Tunnel

Run any IGP (RIP, OSPF,EIGRP) on both ends of the tunnel and then check these routers routing table. you will see IGP routes in the routing table
show ip route

Note: GRE provides a sateless (non secure) virtual point to point connection. For security IPSEC is laid over GRE