I think the things work this way (for 3560!): - when there's no PQ, you have normal distribution over 4 queues and BW is divided between all 4 of them according to the srr-queue BW command
- when there is a PQ, it is always the first queue, and it is serviced as long there is traffic inside it; srr-queue BW command regarding the first queue is ignored, and the BW is divided between other three queues (based on your config i.e. numbers entered on the command) Keep in mind that other three queues will be serviced according to your config only while there's no data in PQ. During PQ servicing there's no way other queues will get there BW, so in overall your BW config will not be accurate (could not be anyway) because of this. Also, 3550 is different and you should pay attention on the exam. For instance, PQ is queue number 4... And some initial cos-dscp mappings (regarding voice - EF markings) are not correct... Best Regards, Bojan Zivancevic Network Engineer From: Ryan Jensen [mailto:[email protected]] Sent: Thursday, October 21, 2010 3:00 To: Di Bias, Steve; [email protected] Subject: Re: [OSL | CCIE_RS] 3560 Queueing and srr-queue bandwidth Thanks everyone for your help. I appreciate it. I'm making steady progress towards the written exam and the queueing along with scheduling and shaping are one of my weak spots. Sent from my Verizon Wireless BlackBerry ________________________________ From: "Di Bias, Steve" <[email protected]> Date: Wed, 20 Oct 2010 17:03:19 -0400 To: Ryan Jensen<[email protected]>; [email protected]<[email protected]> Subject: RE: [OSL | CCIE_RS] 3560 Queueing and srr-queue bandwidth I can see why you would be confused because by default queue 1 is not acting as the priority queue, and needs to be enabled manually with the "priority-queue out" command Just to verify Cat1(config)#do show mls qos int gig0/1 que GigabitEthernet0/1 Egress Priority Queue : disabled Shaped queue weights (absolute) : 25 0 0 0 Shared queue weights : 25 25 25 25 The port bandwidth limit : 100 (Operational Bandwidth:100.0) The port is mapped to qset : 1 Now let's enable to priority queue Cat1(config-if)#int gig0/1 Cat1(config-if)#priority-queue out This time it should show as "enabled" Cat1(config-if)#do show mls qos int gig0/1 que GigabitEthernet0/1 Egress Priority Queue : enabled Shaped queue weights (absolute) : 25 0 0 0 Shared queue weights : 25 25 25 25 The port bandwidth limit : 100 (Operational Bandwidth:100.0) The port is mapped to qset : 1 Here is a blog on 3560 QoS that may help as well http://blog.ipexpert.com/2010/05/26/introduction-to-catalyst-3560-qos/ Steve Di Bias ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Ryan Jensen Sent: Wednesday, October 20, 2010 1:22 PM To: [email protected] Subject: Re: [OSL | CCIE_RS] 3560 Queueing and srr-queue bandwidth I found my answer in Cisco's documentation. http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_50_se/configuration/guide/swqos.html#wp1284809 All four queues participate in the SRR unless the expedite queue is enabled, in which case the first bandwidth weight is ignored and is 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. You enable the expedite queue by using the priority-queue out interface configuration command. On Wed, Oct 20, 2010 at 3:12 PM, Ryan Jensen <[email protected]<mailto:[email protected]>> wrote: Hi all, I have some confusion when it comes to egress queueing on the 3560. Reading through the study guide, the command format is: srr-queue bandwidth {share|shape} weight1 weight2 weight3 weight4 I understand that the weightX values are relative, but i have some confusion. My reading (CCIE Routing and switching Exam Certification Guide 4th Ed) says "When you configure the priority queue, the switch ignores any bandwidth values assigned to the priority queue in the share or shape commands." And leaves it at that. Could I theoretically configure somthing that has weight 0 for Queue 1? Like: srr-queue bandwidth shape 0 20 40 20 under an interface? How does the switch know how much weight to assign to the PQ on egress? Is this determined by the queue-set configuration? (mls qos queue-set output 1 buffers 40 20 30 10).What happens if I don't assign a queue-set to an interface? Unfortunately I don't have any 3560s available to test this with. Can anyone help? Thanks in advance. UHS Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution of this information is prohibited, and may be punishable by law. If this was sent to you in error, please notify the sender by reply e-mail and destroy all copies of the original message.
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