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

[Saku Ytti]

On (2013-01-05 15:14 +0330), h bagade wrote:

> I was wondering how Cisco routers could detect the directly connected
> interface at the other end is shutdown!

If it is truly directly connected, it should go down in both ends at RTT/2
delay.
Maybe you've disabled autonegotiation which may break this?

Interestingly enough, ethernet standard allows autonegotiation to send type
of 'dying gasp' when operationally shutdown. I.e. far-end device could
differentiate link-loss due to link-cut/HW issue and link-loss due to
intentional shutdown of remote end.
Someone I know checked specs of particular common broadcom chip and this
feature is supported in HW. For some reason router vendors are not
supporting it in software. I personally would love to see in syslog special
line if we detected linkdown due to remote end shutdown.

-- 
  ++ytti