[c-nsp] Question about CBWFQ and PING times

[Peter Rathlev]

Hi Andy,

On Wed, 2009-03-25 at 11:15 +1100, Andy Saykao wrote: 
> 1/ We have a 200mb link between two POPS that is being congested in the
> evening. Congestion is happening on the outbound direction from POP2 to
> POP1, so from a user's perspective in GROUP1 it would be impacting their
> download.
...
> interface GigabitEthernet4/0/2
>  service-policy output POP2-POP1-QOS-POLICY
> 
> I can see matches for this when doing a show policy-map interface. Is it
> as simple as this to ensure that users in GROUP1 will be assured of
> bandwidth to access our hosted services?

If you have a 200mbps connection going out from GigabitEthernet-link
your prioritising won't take effect, since buffers will never saturate.
Heirarchical QoS (as discussed thoroughly many times recently on this
list) with a parent shaper could solve this, but it is uncertain if your
platform can do this. What hardware and IOS version are you using?

Another possibility would be to police some of the traffic that causes
the congestion, which even the least feature rich switches with L3
features can do.

If you have some SRR-device (Catalyst 3560, 3750, some 6500 modules) you
could do some crude shaping, but the number of queues available often
makes this an interesting task and traffic limited this way could be an
unpleasant experience for the users.

> 2/ If I wanted to prioritze ping times between POP1 to POP2, how would
> this be done?

On a side note: Giving priority to ICMP Echo is in my eyes a bad
strategy. This is almost by definition not important business traffic,
so the main reason to give it higher priority would be to avoid
problematic questions from incompetent users who only know how to
measure latency and loss this way. It will not give them a better
experience in using the network connection itself and might instead hide
certain symptoms that could be helpful in troubleshooting one day.

Regards,
Peter