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Hi,

a few answers please:

1) why SG have assigned queue 3 as default queue?

2) why SG matchs VoIP packets using 'lt' operator, and not using a regular access-list ?

3) from the byte-count standpoint everything looks as it was specified at the task - ratio between flows. But when we take into account that packets are of unequal size, we would encounter that:

ICMP packets will be serviced one at a time

VoIP packets will be serviced 320/64=5 at a round

and WWW transactions receives 640/160=4 packets at a time

It is obvious that packets proportion is 4:5:1

Why authors choose byte-count approach instead of packet-count ? Thank you for your feedback.

Hi,

a few answers please:

1) why SG have assigned queue 3 as default queue?

2) why SG matchs VoIP packets using 'lt' operator, and not using a regular access-list ?

3) from the byte-count standpoint everything looks as it was specified at the task - ratio between flows. But when we take into account that packets are of unequal size, we would encounter that:

ICMP packets will be serviced one at a time

VoIP packets will be serviced 320/64=5 at a round

and WWW transactions receives 640/160=4 packets at a time

It is obvious that packets proportion is 4:5:1

 

Why authors choose byte-count approach instead of packet-count ? Thank you for your feedback.

 

 

 

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First, I assume you have read the blog post on the topic (at least there is your comment there ;)

http://blog.internetworkexpert.com/2008/08/12/understanding-custom-queuing/

Next for the questions. First, queue 3 is chosen the default to make sure that no other packets use queue 1. Second you can use any operation that makes sense to match VoIP packets, just ACLs are more flexible. Using the "lt" operator is just another option, which may work as well. In the lab exam, you should either be given a direct hint or ask the proctor for clarification. As for the byte-counting. This procedure is explained in the blog post. However, since some IOS version (I think it's 12.1 or 12.2) they implement deficit round robin, so the procedure remains fair even for packets of unequal sizes. 

http://en.wikipedia.org/wiki/Deficit_weighted_round_robin

I read every blog entry as soon as you post it.

I defineately knew about this CQ's "feature" of not providing fairness between packet counts, just forgot it and spent at least 30 mins trying to solve this task. Now it's burned for me.

This is a big fear for me - to not implement what I've already learnt/read.

Brian, Petr, thank you for your answers, it is clear now.

"First, queue 3 is chosen the default to make sure that no other packets use queue 1"

Petr - why we have not put remaining other traffic into differnet queue number like 4or 5....

If I place default queue in queue number 4 (or another queue nunber) what will happen?

This means all other traffic + ICMP traffic should share the same byte count number 104? why? in question it did not mention that ALL other traffic + ICMP should place under same queue

Another thing If I choose ACL to match rtp traffic instead of "lt 65" then is it still requre the default queue 3?