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naming of serial interfaces on 1721

I noticed a funny thing on my 1721 running 12.2(13) today. I was troubleshooting a suspect WIC when I decided to move it from the WIC0 slot to the WIC1 slot. I moved it and the router recognized it but it still saw it as serial0 even though it was now in the WIC1 slot. I thought it would be named serial1. I believe that I remember seeing the 2600 routers rename the interfaces as they were moved to different slots. Is it not the same with the 1700s?




Re: naming of serial interfaces on 1721

The 2600's work the same way and this is confusing but once you're aware of how it works hopefully it won't trip you up that much.

What is happening is there is the potential to have a WIC that isn't a serial interface. If you plug a Serial WIC in WIC0 then that will be Serial0. If you add another serial WIC in WIC1 that will be serial1.

Now if you remove WIC in WIC0 the WIC in WIC1 (serial1) becomes serial0 since it is the first serial interface the router sees. The config is for the previous WIC in WIC0 now.

I guess they could have done interface WIC0, interface WIC1, etc but that wouldn't be as much fun. :)

Re: naming of serial interfaces on 1721

You findings are surprising.

I thought that the numbering convention for WIC-slots was to use

slot / interface. Following this convention, your WIC should have been called serial 0/0 and after the move I would expect it to become serial 1/0.

A numbering convention like this is required to use modules like the WIC-2T which have more than one interface on a module.

Could you please check again and provide some more details?

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