Gre Tunnel Application Example - Avaya G250 Administration

Use the tunnel TTL command in the context of the GRE tunnel interface to assign a TTL
●
value to packets traveling through the tunnel. The TTL value is placed in the packet's
Carrier IP header. You can assign a TTL value between 1 and 255. The default tunnel TTL
value is 255.
Use the show interface tunnel command to show interface configuration and
●
statistics for a particular tunnel or all GRE tunnels.
Note:
If the tunnel interface is down, the show interface tunnel command
Note:
displays the MTU value as not available.

GRE tunnel application example

This section provides an example of a GRE tunnel application and its configuration.
Figure 35: Simple GRE tunneling application example
Host 1
10.0.0.1
10.0.0.2
10.0.0.3
10.0.0.4
10.0.0.1
8.0.0.2
Data
In the example shown in
to connect them via the Internet. 11.0.0.10 are public IP addresses used by the GRE tunnel for
the tunnel encapsulation.
A packet originating from 10.0.0.1 on Host 1 is sent to the destination 8.0.0.2 on Host 2. Since
the destination IP address is a private IP address, the packet cannot be routed as is over the
Internet. Instead, Router 1 receives the packet from host 1, looks up the packet's destination
address in its routing table, and determines that the next hop to the destination address is the
remote end of the GRE tunnel.
Router 1 encapsulates the packet with a GRE header and a new IP header that assigns the IP
address of Router 2 (12.0.0.20) as the destination IP address and the IP address of Router 1
(11.0.0.10) as the source IP address. When the packet arrives at Router 2, which is the end
point of the GRE tunnel, Router 2 removes the outer IP header and the GRE header and sends
the packet to its original destination at IP address (8.0.0.2).
11.0.0.1
Router 1
11.0.0.10
GRE Tunnel
Router Tunnel
Interface
Interface
MAC Header 11.0.0.10
Source IP Address 11.0.0.20
Destination IP Address
10.0.0.1
8.0.0.2
Data
Figure 35, Host 1 and Host 2 are private networks using a GRE tunnel
12.0.0.1
Internet
Router 2
11.0.0.20
Tunnel
Interface
MAC Header
Source IP Address
Destination IP Address
GRE Header
Source IP Address
Destination IP Address
Configuring GRE tunneling
Host 2
8.0.0.1
8.0.0.2
8.0.0.3
Router
8.0.0.4
Interface
MAC Header
10.0.0.1 Source IP Address
8.0.0.2
Destination IP Address
Data
Issue 1.1 June 2005 329