[c-nsp] ISR detects interface status with delay

[Łukasz Bromirski]

> On 06 Feb 2015, at 10:36, Martin T <m4rtntns at gmail.com> wrote:
> 
> In order to illustrate this behavior I made a short video where IOS
> detects that interface Fa0/0 went down with almost 13 seconds delay.
> Usually this delay is around 5 to 8 seconds, but sometimes up to 15
> seconds. Video can be seen here:
> https://www.dropbox.com/s/yb9o379935s3hou/20150206_110347.mp4 PHY chip
> should detect this within micro- or milliseconds and as seen from the
> video, LED's indicating the link status went off immediately when I
> removed the cable, but why does it take so long for IOS to detect
> this?

First of all, carrier-delay on ISRs is not supported. The command is for
that hardware platforms, that have more extensive instrumentation
on the edge between hardware and software.

Second, ISR polls interface controllers for up/down, so your
better bet would be to use BFD, despite it being CPU-intensive,
to detect link up/down event.

-- 
"There's no sense in being precise when |               Łukasz Bromirski
 you don't know what you're talking     |      jid:lbromirski at jabber.org
 about."               John von Neumann |    http://lukasz.bromirski.net