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GRE Protocol Overview 637
GRE Services GRE can fulfill the following services:
1 Implement the LAN protocol communication in WAN by encapsulating all kinds of
LAN protocols into a WAN protocol.
Figure 201 Multi-protocol local network transmitting via single-protocol backbone
network
In Figure 201, Group1 and Group2 are the local networks running the Novell IPX
protocol. Term1 and Term2 is the local network running the IP protocol. The tunnel
encapsulated by the GRE protocol is created between Router A and Router B. Thus
Group1 and Group2 can communicate without affecting each other, as can Term1
and Term2.
2 Enlarge the operating range of the hop-limited network, such as IPX.
Figure 202 Enlarge network operating range
When using RIP, if the hop count between two terminals in Figure 202 is more
than 15, the two terminals cannot communicate with each other. If tunneling is
used in the network, hop counts will not be incremented inside the tunnel, that is,
hops can be hidden, which enlarges the operating range of the network.
3 Connect some discontinuous sub-networks to establish a VPN.
Figure 203 Tunnel connecting discontinuous sub-networks
Internet
Novell IPX
Group1
IP
Term 1
Novell IPX
Group2
IP
Term 2
Tunnel
Router B
Router A
Router
r
r
Tunnel
Router
Router
Router
IP network
IP network
PC
PC
IP network
Tunnel
group2
novel
l
Router
Router
group 1
novell
IP network
VLAN