I've a question on the PQ egress in a c3750...I read that when you enable PQ on the egress, the scheduler will service the PQ (Q1) until it is empty. Once the PQ has been completely serviced then Q2-4 will be serviced.
The question I have is, if Q1 is a VoIP traffic queue and the call is active for 30mins, then how will Q2-4 get sevice for the past 30mins??
Your understanding is correct. On 3750, once you put q1 in priority queue, it will be strict priority queue. Scheduler will transmit packets in Q1 until is empty. But that won't cause issue by normal voice traffic, because the bandwidth used for voice traffic is really low. What need to be consider is some PC might send packet marked with EF, which couldstarve other queues.
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As also confirmed by Lei, Q1 configured to use PQ can starve other queues of all their bandwidth.
One way to help avoid this from happening, is to police (ingress) "PQ" marketed traffic and/or validate "PQ" marked traffic is what's expected. (I.e. on the latter, TCP traffic with something like DSCP EF or IPPrec 5, might be an invalid marking (assuming DSCP EF and/or IPPrec 5 are directed to PQ).
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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