Chapter 1 1 Configuring Gre Tunnels; Configuring Gre Tunnels - Cisco NCS 5500 Series Configuration Manual

Configuring GRE Tunnels

Generic Routing Encapsulation (GRE) is a tunneling protocol that provides a simple generic approach to
transport packets of one protocol over another protocol by means of encapsulation. This module provides
information about how to configure a GRE tunnel.
•
•
Configuring GRE Tunnels
Tunneling provides a mechanism to transport packets of one protocol within another protocol. Generic Routing
Encapsulation (GRE) is a tunneling protocol that provides a simple generic approach to transport packets of
one protocol over another protocol by means of encapsulation. GRE encapsulates a payload, that is, an inner
packet that needs to be delivered to a destination network inside an outer IP packet. The GRE tunnel behave
as virtual point-to-point link that have two endpoints identified by the tunnel source and tunnel destination
address. The tunnel endpoints send payloads through GRE tunnels by routing encapsulated packets through
intervening IP networks. Other IP routers along the way do not parse the payload (the inner packet); they only
parse the outer IP packet as they forward it towards the GRE tunnel endpoint. Upon reaching the tunnel
endpoint, GRE encapsulation is removed and the payload is forwarded to the packet's ultimate destination.
Restrictions for Configuring GRE Tunnels
The following restrictions apply while configuring GRE tunnels:
• NCS5500 Series Routers support up to 500 GRE tunnels.
• Only up to 16 unique source IP addresses are supported for the tunnel source.
Configuration Example
Configuring a GRE tunnel involves creating a tunnel interface and defining the tunnel source and destination.
This example shows how to configure a GRE tunnel between Router1 and Router2. You need to configure
tunnel interfaces on both the routers. Tunnel source IP address on Router1 will be configured as the tunnel
destination IP address on Router2. Tunnel destination IP address on Router1 will be configured as the tunnel
Configuring GRE Tunnels, page 155
IP-in-IP De-capsulation, page 156
Interface and Hardware Component Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.1.x
11
C H A P T E R
155