QOS :LLQ clarification

chintan.shah · ‎10-14-2008

Hi,

I have one doubt on LLQ. Say for example I have LLQ with 60% BW and remaining 40% is assigned to 4 CBWFQ.

If LLQ is not utilizining it ful bandwdith say 60% then the remaining one will be part fo CBWFQ queue ??.

i.e LLQ is using 40% then remaining 20 % will be divided among the other CBWFQ classes on proportionate basis ????

Chintan

Joseph W. Doherty · ‎10-14-2008

My understanding has been any class bandwidth not being used by any class, including LLQ, is made available to other classes that want more than their minimal bandwidth guarantees. Futher, my understanding has been the excess available bandwidth is given to the other classes in proportion of their class bandwidths but I recently came across information on the Cisco web site that noted the excess bandwidth was equally proportioned to other demanding classes. Personally I suspect the former because when you look at queued packets, queued weights don't appear to change.

Giuseppe Larosa · ‎10-14-2008

Hello Joseph,

I agree I made some performance tests on CBWFQ on cisco 7500 some years ago using a SMARTBITS traffic generator: we were able to generate traffic patterns at 101% of link bandwidth and when using less then LLQ BW the available space was used by other classes.

The first class to have some of its packets dropped was the one with the lower BW settings as could be expected.

Hope to help

Giuseppe