3com 3031 Instruccion De Instalación

C

HAPTER

 64: C

ONFIGURATION

 

OF

 GRE

.

Figure 221   GRE-IPSec tunnel application 

As illustrated in the above figure, GRE can encapsulate the multicast data and 
transmit the data through the GRE tunnel. As stipulated in the protocol, IPSec can 
only protect the unicast data by encryption. Therefore, in case that multicast data 
such as routing protocol, voice and image needs transmitting in the IPSec tunnel, 
users can implement the transmission by establishing GRE tunnel. You can 
encapsulate the multicast data with GRE and then encrypt the encapsulated data 
with IPSec, thus realizing the encrypted transmission of multicast data in the IPSec 
tunnel.

In addition, GRE also supports the users to select and record identification key 
word of tunnel interface, and supports the end-to-end check of encapsulated 
message.

Due to the influence of such factors as encapsulation and de-encapsulation 
between GRE forwarder and receiver, data increase caused by encapsulation, and 
so on, data forwarding efficiency of routers may decrease to some extent on using 
GRE.

Among all the configuration tasks, virtual Tunnel interface must be created first 
before configuring other function features on the virtual Tunnel interface. After 
the virtual Tunnel interface is deleted, all configurations on the interface will be 
deleted subsequently.

GRE configuration includes:

■

Create virtual Tunnel interface (required)

■

Set the encapsulation mode of Tunnel interface packet (optional)

■

Specify the source end of Tunnel (required)

■

Specify the destination end of Tunnel (required)

■

Assign network address for Tunnel interface (required)

■

Configure the end to end authentication on both ends of Tunnel (optional)

■

Set identification keyword of Tunnel interface (optional)

■

Configure routing via Tunnel (optional)

Virtual Tunnel interface should be created so that other parameters of GRE can be 
configured on the interface. These configurations are required to be performed on 
both ends of Tunnel.

Internet

IPSec Tunnel

GRE Tunnel

Remote

office

network

Corporate

intranet

Router A

Router B