How to Build Tunnels on Cisco Routers

Cisco routers can create a tunnel to transport non-IP traffic across networks.

A tunnel on a Cisco router can transfer information that is not IP based. For example, a Netbios connection, that is a network that uses only the computer name, and not an IP address, could not traverse a network because that would require an IP address and a subnet mask. The tunnel provides that. Another example of the need for a tunnel is for video or audio streaming. In those cases, an IP address does not exist in the packets, but they packets still must travel from source to destination. Again, a tunnel can provide the mechanism to do this.

Instructions

1. Type "Enable" to start the router configuration command. The router-configuration editor will automatically launch. It looks like a command line editor. Cisco commands operate at a command-like prompt. This is the router privilege mode. To actually configure the router you must enter global configuration mode. That is the next step.

2. Type "Config T" to start the global configuration mode. Now you must type "Interface Tunnel0" as the first tunnel configuration step. Follow this with the IP address, the tunnel source, and the tunnel destination. For example, type "IP address 110.50.30.2 255.255.255.252 tunnel source 217.126.86.98 tunnel destination 217.106.31.242 ." (Ignore the last period.) The tunnel source is the beginning of the tunnel, and the tunnel destination is the end. This just leaves us with one last operation, to configure the IP route, which will take you to the location that you want to get to after you have gone through the tunnel. For example, type "IP route 217.116.11.242 255.255.255.255 217.126.86.97 ." (Ignore the last period.) The first IP number (217.116 etc) is the destination you want to get to. But in order to get there you must go through a gateway, (217.126 etc.). The last step is to configure the tunnel interface for the second router.

3. Type "enable" followed by "Config T" to begin the configuration of the second router. The procedure to configure the tunnel is similar to step 2. So type "Interface Tunnel0 IP address 110.50.30.1 255.255.255.252 tunnel source 217.106.31.242 tunnel destination 217.126.86.98 ." (Ignore the last period.)The last step here is to configure the IP route, just like in step 2. So, type "IP route 217.126.86.98 255.255.255.255 217.116.11.241 ." (Ignore the last period.) So now, with the two routers configured and the source and destination tunnel IP address identified, you have created a tunnel on a Cisco router.

References

• He: Tunneling with Cisco Routers
• Mailman: Tunnel in cisco router