You want to tunnel a foreign protocol (such as IPX traffic) through your IP network.
One of the most important applications of tunnels is for passing foreign protocols through a network that only supports IP. A typical example of this would be IPX, although the configuration is similar for other protocols such as AppleTalk:
Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#ipx routing AAAA.BBBB.0001 Router1(config)#interface Tunnel1 Router1(config-if)#ipx network AAA Router1(config-if)#tunnel source 172.25.1.5 Router1(config-if)#tunnel destination 172.25.1.7 Router1(config-if)#end Router1#
Then, on the other router, you must create a tunnel interface with a matching source and destination as well as matching IPX network number:
Router5#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router2(config)#ipx routing AAAA.BBBB.0002 Router5(config)#interface Tunnel3 Router5(config-if)#ipx network AAA Router5(config-if)#tunnel source 172.25.1.7 Router5(config-if)#tunnel destination 172.25.1.5 Router5(config-if)#end Router5#
This recipe is nearly identical to Recipe 12.1, but instead of tunneling IP traffic through an IP network, we use the same kind of tunnel to pass IPX traffic through the same network. Note that of all the supported tunnel modes mentioned in Table 12-1, only the default GRE will transport IPX (although there are several AppleTalk tunnel modes).
This book does not cover IPX, so we won't go into any detail on the IPX-specific commands here. This is merely intended as an example of how to use GRE tunnels for foreign protocols. For more information on IPX, please refer to Designing Large-Scale LANs (O'Reilly).
To enable IPX on both of these routers, you have to first make sure that you are running an IOS release that supports IPX. The various "Desktop" IOS versions support this protocol, as do the "Enterprise" versions. Please consult the Cisco IOS feature matrixes for more details. Assuming, then, that your router supports IPX, you can enable it with the ipx routing command, as shown. Naturally, you need to enable IPX routing on both routers. Then, the only other important detail is to configure both ends of the GRE tunnel with matching IPX network numbers as we have done in the example.
It's important to note that you can configure a GRE tunnel to support more than one protocol by simply specifying appropriate network numbers for each protocol using the tunnel. We could, for example, add IP to this IPX tunnel by simply configuring an IP address on both ends, as we did in Recipe 12.1. The tunnel will then support both protocols simultaneously:
Router1(config)#interface Tunnel1 Router1(config-if)#ip address 192.168.35.6 255.255.255.252 Router1(config-if)#ipx network AAA Router1(config-if)#tunnel source 172.25.1.5 Router1(config-if)#tunnel destination 172.25.1.7 Router1(config-if)#end Router1#
Recipe 12.1; Designing Large-Scale LANs, by Kevin Dooley (O'Reilly)
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