Avaya G430 Manual page 442

The router
Figure 14: Simple GRE tunneling application example
In the example shown in this figure, Host 1 and Host 2 are private networks using a GRE tunnel
to connect them via the Internet. 11.0.0.10 and 12.0.0.20 are public IP addresses used by the
GRE tunnel for the tunnel encapsulation.
A packet originating from 10.0.0.1 on Host 1 is sent to the destination 8.0.0.2 on Host 2. Since
the destination IP address is a private IP address, the packet cannot be routed as is over the
Internet. Instead, Router 1 receives the packet from host 1, looks up the packet's destination
address in its routing table, and determines that the next hop to the destination address is the
remote end of the GRE tunnel.
Router 1 encapsulates the packet with a GRE header and a new IP header that assigns the
IP address of Router 2 (12.0.0.20) as the destination IP address and the IP address of Router
1 (11.0.0.10) as the source IP address. When the packet arrives at Router 2, which is the end
point of the GRE tunnel, Router 2 removes the outer IP header and the GRE header and sends
the packet to its original destination at IP address (8.0.0.2).
You can use the following commands to configure GRE tunneling (with OSPF) in this example:
Example
Router 1 configuration
Gxxx-001(super)# interface fastethernet 10/3
Gxxx-001(super-if:FastEthernet 10/3)# ip address 11.0.0.10 255.255.255.0
Gxxx-001(super-if:FastEthernet 10/3)# exit
Gxxx-001(super)# interface tunnel 1
Gxxx-001(super-if:Tunnel 1)# keepalive 10 3
Done!
Gxxx-001(super-if:Tunnel 1)# tunnel source 11.0.0.10
Done!
Gxxx-001(super-if:Tunnel 1)# tunnel destination 12.0.0.20
Done!
Gxxx-001(super-if:Tunnel 1)# ip address 1.1.1.1 255.255.255.0
Done!
Gxxx-001(super-if:Tunnel 1)# exit
Gxxx-001(super)# ip route 12.0.0.0 255.255.255.0 11.0.0.1 1 high
Gxxx-001(super)# router ospf
Gxxx-001(super router:ospf)# network 1.1.1.0 0.0.0.255 area 0.0.0.0
Done!
442 Administering Avaya G430 Branch Gateway
Comments? infodev@avaya.com
October 2013