Hide a Token Ring router

my current frame relay switch is a Token Ring router (see My current lab English). Once a frame relay switch is configured there is no need to reach it any more. But what about messages on the main syslog server from the frame relay switch and the correct time on the this switch. Not so easy for a Token Ring router in an Ethernet router environment.

The solution is easy (it is always easy when you are writing a blog post about a problem that you already solved). My frame relay switch is a Cisco 2521 and this is, you will guess it, a Token Ring router. I also use a Cisco 2501 router in my lab. Both routers have an AUX port and so I connect both routers together using a (so called) rollover English cable. For the configuration that enables routing on both AUX ports see Using the AUX port to connect two routers English.

On the Token Ring router (aka frame relay switch aka 2521) we need two static routes.

ip route Async4
ip route

The first route is a static route to my Ethernet network and the second a static route to the default gateway of this network. (The IP address belongs to my DSL router.)

On the other router (aka 2501) we need three extra lines to hide the Token Ring router.

interface Ethernet0
 ip nat outside
interface Async1
 description from aux to aux r2521a
 ip address
 ip nat inside
ip nat inside source static

Yes, it is only a simple “static nat insde” line. But this line does the trick! With this trick the Token Ring router is hiding behind an IP address that belongs to my Ethernet IP address range.

Bye, Tore

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