Simple shaping at hub site

jdevoll · ‎08-30-2007

I have a hub site with a DS-3, and many spoke sites with T1's. I want to shape traffic sources from the hub site to each spoke site to stop the hub from slamming the remote site. This is a pretty typical request. My question is related to the specific thresholds. Being that each hub has a full T1, is it reasonable to set the CIR to the full line speed? (being that the CIR is...well the full line speed.) I feel a bit silly asking this question, but I could use a sanity check on this one.

policy-map SpokeT1Sites

class class-default

fair-queue

random-detect

shape average 1536000 15360 0

For my simple situation, is my WRED config going to work for me?

mohammedmahmoud · ‎08-30-2007

Hi,

As a best practice avoid setting the shaper at the access rate. Otherwise, you may see output queues building up and causing big delays in CBWFQ classes. The reason is that the shape rate does not take into account the overhead, so shaping at line rate is actually oversubscribing and will cause interface congestion. There really is no reason to shape at the access rate. You should always traffic shape at 95 percent of the access rate or, more generally, the aggregate shaped rate should always be 95 percent below the access rate.

HTH,

Mohammed Mahmoud.

jdevoll · ‎08-30-2007

Doesn't setting the bandwidth to 1536000 rather then 1540000 take into account the overhead?

mohammedmahmoud · ‎08-30-2007

Hi,

No, i meant the layer 2 overhead, by doing it at 1536 you have just taken the robbed bits into account.

HTH,

Mohammed Mahmoud.

jdevoll · ‎08-30-2007

ah right...thanks