So here is a simple scenario where all you need to do is setup NAT (Network Address Translation) – very simple indeed. Sometimes, however, the most simple networking setup could still give us some headache. And usually, it will be something extremely simple … so simple, that it would even cross your mind.
See below the network diagram I’ll be working on.
The Host is actually a Cisco router on which I have disabled IP routing and, set it up with a default gateway of 192.168.1.254 using the ip default-gateway command. The router, acting as the gateway for the network, is a Cisco 1700 series router running IOS v12.4(23).
You can see below my configuration (I have left only the relevant commands):
Ok … so this should work – to confirm, I’ve also enabled NAT debugging on the NAT router:
There is also no debug output on the router’s console!
So what is wrong? Can you spot it?
That’s right – if you remove the “log” keyword, NAT suddenly starts working – see snippet below:
However, the log keyword can be very useful indeed when troubleshooting. What I found is that the statement above is true, depending on the platform and IOS version in use.
Despite the lab above running on GNS3, I have recently seen this behaviour on live environment, on Cisco 3900 series routers.