[c-nsp] Question about CBWFQ and PING times

Peter Rathlev peter at rathlev.dk
Wed Mar 25 08:46:56 EDT 2009

On Wed, 2009-03-25 at 13:17 +1100, Andy Saykao wrote:
> POP1 = Cisco 7204VXR (NPE-G1) GigE Interface running 12.2(31)SB13
> POP2 = Cisco 7606 with 4-subslot SPA Interface (7600-SIP-400) running
> 12.2(33)SRB3
> 1/ "If you have a 200mbps connection going out from GigabitEthernet-link
> your prioritising won't take effect, since buffers will never saturate."
> So if we were to prioritize something like Voice, we would need to
> implement some Heirarchical QoS solution on the Cisco 7606???

Generally speaking: Yes. When the scheduler needs to figure out if there
is bandwidth enough for non-priority traffic it needs to know how much
bandwidth is available. You need to tell the router that it only has 200
mbps and not the full 1 Gbps. Otherwise it will allocate ~50 mbps (your
5%) for priority traffic and ~950 mbps for class-default.

AFAIK both the SIP-400 and the G1 should be able to shape an interface
this way, but I could be wrong. :-)

> 2/ I understand your arguments exactly about not prioritizing ICMP
> traffic, but I was told to look into this. I guess based on 1/ above,
> some form of Heirarchical QoS solution is needed for this also.

Yes, you just need to wrap a shaping parent policy around your existing
"POP2-POP1-QOS-POLICY" policy.


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