[c-nsp] cisco interface shutdown detection, how is possible?

[Sander Steffann]

Hi,

> I was wondering how Cisco routers could detect the directly connected
> interface at the other end is shutdown!
> 
> there are two general possibility on my point of view:
> 1- the other device is sending special information before shutting down the
> interface.
> 2- there are some method of polling which is done periodically and based on
> the answer, the router detect the interface is up or no!

Neither. The router just sees the power or light disappear on the interface...
Sander