Administration of the Avaya G350 Media Gateway - Avaya Support

Configuring GRE tunnelingGRE tunnel application exampleThis section provides an example of a GRE tunnel application and its configuration.Figure 13: Simple GRE tunneling application example10.0.0.110.0.0.210.0.0.310.0.0.4Host 1RouterInterfaceRouter 111.0.0.10TunnelInterface11.0.0.1 12.0.0.1InternetGRE TunnelTunnelInterfaceRouter 211.0.0.20RouterInterfaceHost 28.0.0.18.0.0.28.0.0.38.0.0.410.0.0.18.0.0.2DataMAC HeaderSource IP AddressDestination IP Address11.0.0.1011.0.0.2010.0.0.18.0.0.2DataMAC HeaderSource IP AddressDestination IP AddressGRE HeaderSource IP AddressDestination IP Address10.0.0.18.0.0.2DataMAC HeaderSource IP AddressDestination IP AddressIn the example shown in Figure 13, Host 1 and Host 2 are private networks using a GRE tunnelto connect them via the Internet. 11.0.0.10 are public IP addresses used by the GRE tunnel forthe 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. Sincethe destination IP address is a private IP address, the packet cannot be routed as is over theInternet. Instead, Router 1 receives the packet from host 1, looks up the packet’s destinationaddress in its routing table, and determines that the next hop to the destination address is theremote end of the GRE tunnel.Router 1 encapsulates the packet with a GRE header and a new IP header that assigns the IPaddress 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 endpoint of the GRE tunnel, Router 2 removes the outer IP header and the GRE header and sendsthe packet to its original destination at IP address (8.0.0.2).Issue 3 January 2005 175