Huawei AR1200 Series Configuration Guide

1.1 Introduction to GRE
The transmission of packets in a Generic Routing Encapsulation (GRE) tunnel involves two
processes: encapsulation and decapsulation. After receiving a packet of a certain network layer
protocol that needs to be encapsulated and routed, the system adds a GRE header to the packet,
and encapsulates the packet into a packet of another protocol, such as IP.
GRE encapsulates the packets of certain network layer protocols. After encapsulation, these
packets can be transmitted over the network by another network layer protocol, such as IP.
GRE can serve as a Layer 3 tunneling protocol for VPNs. A tunnel is a virtual point-to-point
connection and can be regarded as a virtual interface that supports only point-to-point
connections. This interface provides a path to transmit encapsulated datagrams. GRE
encapsulates and decapsulates datagrams at both ends of the tunnel.
1.2 GRE Features Supported by the AR1200
GRE features supported by the AR1200 include the following: enlargement of the operation
scope of the network running a hop-limited protocol, and working in conjunction with the IP
Security Protocol (IPSec) to compensate for the IPSec flaw in multicast data protection.
Enlarging the Operation Scope of the Network Running a Hop-Limited Protocol
If the hop count between two terminals in Figure 1-1 is more than 15, the two terminals cannot
communicate with each other.
Figure 1-1 Networking diagram of enlarged network operation scope
IP
network
IP
network
IP
network
PC PC
Tunnel
When the tunnel is used in the network, a few hops are hidden. This enlarges the scope of the
network operation.
Working in Combination with IPSec to Compensate for the IPSec Flaw in Multicast
Data Protection
Based on GRE, multicast data can be encapsulated and transmitted in the GRE tunnel. Based on
IPSec, only the unicast data can realize encrypted protection.
Huawei AR1200 Series Enterprise Routers
Configuration Guide - VPN 1 GRE Configuration
Issue 01 (2012-04-20) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
2

Huawei AR1200 Series Specifications

General

Brand	Huawei
Model	AR1200 Series
Category	Network Router
Language	English