Edge Router GRE Tunnel Interfaces

Each CNA USTAT module needs to be associated with a different tunnel interface on the Cisco router, so you will need to create three tunnels. Since we have three USTAT modules and only two edge routers, two of the tunnels--Tunnel1 and Tunnel2--will be created on the one edge router, while the third tunnel--Tunnel3--will be created by itself on the other edge router.

Set up the first GRE tunnel interface on your Cisco edge router by inserting the following commands into your router’s configuration:

interface Tunnel1
 
description GRE to provider_1
 
ip address 172.25.5.129 255.255.255.252
 
ip policy route-map provider_1
 
tunnel source 172.16.6.1
 
tunnel destination 172.16.6.6
 

 

Cisco IOS defines a tunnel interface incrementally, rather than the single command-line entry used by the CNA system.

In addition, we’ve added a line of descriptive text and we’ve identified a route-map to be used for policy based routing on this tunnel (the route map will be defined a bit later).

Specifically, here’s what the Cisco commands did:

• the interface command identifies the tunnel to be created--Tunnel1
• the description command adds the text “GRE to provider_1” to the tunnel configuration (“provider_1” will be the name of a route map defined later)
• the ip address command identifies the tunnel IP address as 172.25.5.129 255.255.255.252; this address should be in the same network as the tunnel IP address specified on the CNA configuration--172.25.5.130 255.255.255.252
• the ip policy command identifies the route map to be used, which we have called provider_1 (not yet created); the route map will ensure that traffic from a given USTAT will be directed to the correct ISP link
• the tunnel source command designates the address of the physical interface on the edge router--172.16.6.1 (Cisco IOS syntax requires you to specify it explicitly; CNA syntax has no such requirement--the address is implicitly set to the eth0 interface address of the USTAT module)
• the tunnel destination command should identify the physical address on the USTAT module

Repeat these commands for each GRE tunnel (one for each USTAT module).