QOS drops in LLQ/CBWFQ queues

May 05, 2006 2 Replies
O

We've configured LLQ on one of our Point to Point circuits. We uses LLQ to protect the following traffic on our network. Voice (Priority Queue) Voice control Citrix and IPCC



During high traffic volumes (>40%) we see drops in the citrix and/or IPCC queue even though there is plenty enough bandwidth on the circuit. Please see the example below;



pen-router1#sh policy-map int ser 0/0 Serial0/0



Service-policy output: VoiceFirst



Class-map: VOICE-media (match-all)



12982 packets, 830848 bytes
30 second offered rate 87000 bps, drop rate 0 bps Match: ip precedence 5 Queueing Strict Priority Output Queue: Conversation 264 Bandwidth 500 (kbps) Burst 12500 (Bytes) (pkts matched/bytes matched) 5101/326464 (total drops/bytes drops) 0/0

Class-map: VOICE-sig (match-all)



966 packets, 70016 bytes
30 second offered rate 8000 bps, drop rate 0 bps Match: ip precedence 3 Queueing Output Queue: Conversation 265 Bandwidth remaining 10 (%) Max Threshold 64 (packets) (pkts matched/bytes matched) 559/45246 (depth/total drops/no-buffer drops) 0/0/0

Class-map: CITRIX (match-any)



24578 packets, 5580021 bytes
30 second offered rate 752000 bps, drop rate 20000 bps Match: protocol citrix
0 packets, 0 bytes
30 second rate 0 bps Match: access-group 101
24578 packets, 5580021 bytes
30 second rate 752000 bps Queueing Output Queue: Conversation 266 Bandwidth remaining 70 (%) Max Threshold 64 (packets) (pkts matched/bytes matched) 13781/4892001 (depth/total drops/no-buffer drops) 0/267/0

Class-map: IPCC-traffic (match-all)



126 packets, 7480 bytes
30 second offered rate 0 bps, drop rate 0 bps Match: access-group 100 Queueing Output Queue: Conversation 267 Bandwidth remaining 20 (%) Max Threshold 64 (packets) (pkts matched/bytes matched) 72/4158 (depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)



1068 packets, 218716 bytes
30 second offered rate 23000 bps, drop rate 0 bps Match: any pen-router1#

As you can see the drop rate on the citrix queue is 20000. However, only around



50-60% of the T1 is currently being using. So, in my opinion, there should be no reason for drop packets in this queue. Am I correct?
Vote
Twitter Facebook LinkedIn
J

If you see 50-60% usuage, it is at 30 sec averages (do you have 'load-inteval 30' on the inteface?)

This is saying that Citrix is cetainly bursting above 70% of the CBFWQ bandwidth (75%reservation by default, less any LLQ reservation) and the link is certainly peaking at access speed at millisecond intervals. Notice how its less than 1% of packets ? this is nothing to worry about..

If you ran a SNMP get of ifOctects at the 10 secs intervals, you would probably sees peaks of 75% utilisation on the T1. If ran it at one second interfals, you would probably see T1 usuage peaks at 90% utilisilation. If the ran a sub-second intervals (when I dont think the SNMP engine update that quick), you would see the 100% peaks... you get the picture.

So a) your really getting T1 peaks at 100%, which is normal - and that what QoS is for b) you probably dont realise that is not simply 70% of the T1 reserved

- less voice, and CBFWQ max-reserved Bandwidth.

Search for Corvil at Cisco.com.. you can get sub-millisecond visibility to how bursty the traffic is, without SNMP polling info out of the rotuer every second. Requires 12.3T/12.4 though.

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required