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Unknown Protocol Drops

I've seen this one a few times and it is always momentarily confusing: on an interface on a Cisco router there is a rather high number of "unknown protocol drops". What protocol could that be?! Is it some type of hack attempt? Ambitious if they are shaping there own raw packets onto the wire. But, no, the explanation is the much less exciting, and typical, lazy ape kind of error.

no ip domain-lookup

One of the most annoying features of Cisco's IOS is the assuming that anything you type which is not a command is a hostname. So...

Translating "dev"...domain server (
Translating "dev"...domain server (

... and when you are configuring a router which either (a) does not have DNS, (b) is on a network that is down, or (c) is on the workbench and not actually connected to a network - you get to enjoy the long pause of a DNS timeout.


Simple NAT With Cisco IOS

Performing NAT with any variety of a LINUX box is possibly one of the most redundantly documented applications on the Web. Attempting to do the same with a Cisco IOS router is not documented in so straight-forward a way.

This little snippet shows the configuration for an IOS router where vLAN 13 is a public network and vLAN 12 is a private network. The router has a public IP address of A.B.C.D [netmask: E.F.G.H] and the gateway address is A.B.C.I. The private network is a with multiple /24 segments which all route to this NAT gateway.

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