What is a GRE tunnel?

Generic Routing Encapsulation (GRE) is a tunneling protocol that lets you run a routing protocol between endpoints.

This example will create a GRE tunnel between two routers and will run EIGRP between the two.

Topology Summary:

• 192.168.13.0/24 will be the Tunnel Network IP block
•  Router-1
  • lo0 10.1.1.0/24
  • e0/0 192.1.12.2
• Router-2
  • lo0 10.2.2.0/24
  • e0/0 192.1.23.2

Router-1

• interface tunnel1
  • ip address 192.168.13.1 255.255.255.0
  • tunnel source 192.1.12.1
  • tunnel destination 192.1.23.3
• router eigrp 100
  • no auto-summ
  • net 192.168.13.0
  • net 10.0.0.0

Router-2

• interface tunnel1
  • ip address 192.168.13.3 255.255.255.0
  • tunnel source eth0/0
  • tunnel destination 192.1.12.1
• router eigrp 100
  • no auto-summ
  • net 192.168.13.0
  • net 10.0.0.0