[c-nsp] Question about CBWFQ and PING times

[Peter Rathlev]

On Fri, 2009-03-27 at 13:34 +1100, Andy Saykao wrote:
> How misleading is that then. When you issue the "show policy-map"
> command, it calculates the bandwidth % using what's set with the
> bandwidth interface command. I'll make a note to disregard this piece of
> cosmetic from cisco when using the "show policy-map" command.

Well, the "bandwidth" command does have it's uses, just not very much in
doing QoS. People running e.g. EIGRP would use it a lot. :-)

> 1/ There's an "offered rate" for each class - is this the amount of
> bandwidth the router is currently reserving for each class?

The "30 second offered rate" tells you how much this class has been used
in the past 30 seconds. It you reserve 64kbps for a specific class but
no traffic in this class arrives at the router the offered rate would be
0. If you have a very smooth stream of relevant traffic the offered rate
would be very close to the reserved rate.

> 2/ One odd thing I've found is that when I permit additional icmp's to
> the ACL, the "offered rate" rapidly decreases until the "offered rate"
> is ZERO. 
...
> The throughput on the interface is still as expected.
...
> Why does adding the extra icmp lines in the ACL cause the "offered rate"
> to be zero in both classes???

A little strange, but the simplest explanation would be that no incoming
traffic falls in this specific class. If you're running a known standard
load through the router where you are certain there is traffic of this
class it is strange indeed. If this is just "normal" traffic then you
might just not receive any interesting traffic.

Regards,
Peter