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3560 egress PQ limiting

Hi all,

I'm trying to understand the behaviour of egress PQ in 3560. Some credible sources claim that such a queue ignores shaping/sharing and can starve other queues.

Is it possible to limit egress PQ?

It seems that this topic is matter of debates as explanations differ from publication to publication.

Cheers.

Everyone's tags (4)
2 REPLIES
Green

3560 egress PQ limiting

Oleg,

Your friends are correct.

whem you apply priority-queue out to an interface the expediate Q (Q1 in a 3560) is emptied before

processing the othe 3 Qs.

Please see this link

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst3560/software/release/12.2_55_se/command/reference/cli1.html#wp11909150

Usage Guidelines

When you configure the priority-queue out command, the shaped round robin (SRR) weight ratios are affected because there is one fewer queue participating in SRR. This means that weight1 in the srr-queue bandwidth shape or the srr-queue bandwidth shape interface configuration command is ignored (not used in the ratio calculation). The expedite queue is a priority queue, and it is serviced until empty before the other queues are serviced.

Also look at the QOS section in the 3560 config guide.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_55_se/configuration/guide/swqos.html

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.
Super Bronze

3560 egress PQ limiting

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Posting

Ditto to what Alex posted, but do realize different devices have different features, so perhaps what you were reading wasn't all specific to the 3560.  That noted, you might somewhat mimic a router LLQ, on a 3560, using something like:

interface x

srr-queue bandwidth shape 3 0 0 0

srr-queue bandwidth share 255 1 1 1
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