Administration of the Avaya G350 Media Gateway - Avaya Support

Configuring GRE tunnelingGRE tunneling overviewGeneric Routing Encapsulation (GRE) is a multi-carrier protocol that encapsulates packets withan IP header and enables them to pass through the Internet via a GRE tunnel. A GRE tunnel isa virtual interface in which two routers serve as endpoints. The first router encapsulates thepacket and sends it over the Internet to a router at the far end of the GRE tunnel. The secondrouter removes the encapsulation and sends the packet towards its destination.A GRE tunnel is set up as an IP interface, which allows you to use the GRE tunnel as a routingdestination. A GRE tunnel can transport multicast packets, which allows it to work with routingprotocols such as RIP and OSPF.To set up a GRE tunnel, you must create the interface and assign it the following: an IP address,a tunnel source address, and a tunnel destination address. GRE tunnels can be configured asnext hops on static routes and policy-based routing next hop lists. Packets can also be routed toGRE tunnels dynamically.Note:Note: There may be cases in which the GRE tunnel is not used for routing. In suchcases, it may not be necessary to assign an IP address to the tunnel.The main application for GRE tunneling is to allow packets that use protocols not supported onthe Internet, or packets that use private IP addresses that cannot be routed on the Internet, totravel across the Internet. The following are examples of situations in which this can be useful:●●●Providing multiprotocol local networks over a single-protocol backboneProviding workarounds for networks containing protocols that have limited hop counts,such as AppleTalkConnecting discontinuous subnetworks● Enabling virtual private networks (VPNs) over a WANYou can also configure a GRE tunnel to serve as a backup interface. For information onconfiguring backup interfaces, see Backup interfaces on page 97.For an example of a GRE tunneling application, see GRE tunnel application example onpage 175.Issue 3 January 2005 167