srr-queue bandwidth limit question 3560

Unanswered Question
Oct 29th, 2009


srr-queue bandwidth limit weight 10 should limit a gigabit interface to 100 mbps per the example given.

Unfortunately, limiting to 10 seems to only allow @5mbps on various speed tests; bumping srr-queue to 30 will allow up to @30 mbps. So, is srr-queue actually based on negotiated port speed then? and if that is the case, shouldn't a bandwidth limit of 10 give results closer to 10mbps?

Thus srr-queue is based on negotiated speed then and not port speed?

Also, this is ingress only, don't even get me started on the lack of egress control!

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Joseph W. Doherty Thu, 10/29/2009 - 09:37

Could Cisco's Usage Guideline note, in your reference, "These values are not exact because the hardware adjusts the line rate in increments of six. ", account for the results you noticed?

"Thus srr-queue is based on negotiated speed then and not port speed?" How do you get these to differ? I mean, if I set port speed to 100, if it comes up, it's 100, but if I set it to auto, it's whatever it negotiated.

"Also, this is ingress only, don't even get me started on the lack of egress control!"

Ingress only? I thought this was an egress control. I.e. (also from your reference) "Use the srr-queue bandwidth limit interface configuration command to limit the maximum output on a port. Use the no form of this command to return to the default setting. "

ericgarnel Thu, 10/29/2009 - 09:50

So, based on what you & I are sort of agreeing upon, a gigabit ethernet port set to auto, the bandwidth would be @10mpbs for a 100mbps client and 100mbps for a 1000mbps client.

Unfortunately, this is in a guest environment and we have no control over the end devices. auto/auto works best for us in regards to mitigating client negotiation issues.

from what I have found on the web, the 3560s & 3570s perform ingress queuing only as compared to the old 3550s which perform both.

a snippet from trying to apply a policy-map..

lounge-sw(config-if)#service-policy output Police-8M

police command is not supported for this interface

Configuration failed!

Warning: Assigning a policy map to the output side of an interface not supported

Joseph W. Doherty Thu, 10/29/2009 - 10:00

Yes, I think we agree if what you're trying to do is limit bandwidth to 5 Mbps regardless of port speed. If so, although also true you can't use a service policy on a 3560/3750, you can police (I recall at least on port egress). Configuration guide for your IOS ver. would have more details. (NB: you might also look at queue shaping, but that too might not be absolute values.)


This Discussion