[c-nsp] sup720 ICMP redirects "once per second"

Tóth András diosbejgli at gmail.com
Mon Feb 11 12:42:07 EST 2013

Hi Phil,

As I understand you have disabled the MLS rate-limiter for redirects, so
that should not cause throttling, but you can check with "sh ibc" to see
the rate at which packets arrive to the CPU.

With mls rate-limit redirect disabled, packets will be still subject to
CoPP because they require CPU processing to generate a redirect, so perhaps
your CoPP policy (probably class default) is limiting them? That can also
cause packet loss between those stations if the traffic requires punting.

You could also check the "ip icmp rate-limit unreachable" command, might be
applicable here too.

Best regards,

On Mon, Feb 11, 2013 at 4:22 PM, Phil Mayers <p.mayers at imperial.ac.uk>wrote:

> On 11/02/13 15:18, Tassos Chatzithomaoglou wrote:
>> "show standby redirect" should provide some info.
> Not that I can see:
> Interface    Redirects Unknown   Adv      Holddown
> VlXXX        enabled   enabled   30       180
> Active       Hits  Interface Group Virtual IP            Virtual MAC
> local        0     Vl9       0     x.x.x.1               0000.0c9f.f000
>  Since these redirects are controlled by HSRP (which changes the internal
>> IPs), maybe there is no way to change their
>> interval.
> Maybe. The specific thing I'm interested in is understanding how the
> forwarding happens, and what path the punts take (via CoPP, MLS limits, or
> other); I'm assuming from the lack of CPU problems on this box that the
> PFC/DFC is forwarding the packets, except for the ones it is leaking to the
> CPU, but I can't be sure.
>  There is a command to disable them though.
> Maybe, but I want to understand the problem before I do that, and to do
> that, I need to understand the path the packets take through the box.
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