User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform Chapter 3
Configuration of GRE
3-3
Router
r
r
r
r r
Tunnel Router
Router Router Router
Figure VPN-3-4 Enlarge network operating range
When using RIP, if the hop count between two terminals in the above figure is more
than 15, the two terminals can not communicate with each other. When the tunnel is
used in the network, a part of hops can be hidden, enlarging the operating range of the
network.
3) Connect some discontinuous sub-networks to establish VPN.
Tunnel
group2
novell
RouterA
RouterB
Router
Router
group 1
novell
Figure VPN-3-5 Tunnel connects discontinuous sub-networks
The two sub-networks group1 and group2 running Novell IPX protocol are in diff erent
cities. With the tunnel available, the trans-WAN Virtual Private Network can be
established.
In addition, GRE also supports the users to select and record identification key word of
tunnel interface, supports the check of encapsulated mess age, and supports the use of
synchronous serial numbers to ensure channel safety and correctness of transmission
data.
Because of encapsulation and de-encapsulation on GRE receiving side and
transmitting side and data volume increase caused by encapsulation, GRE will
decrease the forwarding rate of router data to some extent.
3.2 Configuring GRE

3.2.1 GRE Configuration Task List

GRE configuration task list is as follows:
z Create virtual tunnel interface.
z Set the source address of tunnel interface.
z Set the destination address of tunnel interface.
z Set the network address of tunnel interface.