6500 Port Input Scheduling (Receive Priority Queue)

[kfarrington]

Guys,

Reading the Cat QoS book, and on page 258 (or approx) it seems to indicate that if you have a line card that supports ports that have a priority receive queue, you can only put frames into this queue if it comes in on a trunk (isl or dot1q), if if not, it will use a default CoS setting and thus be placed into the normal queue.

Can someone confirm this is the case and to use the strict priority receive queue, it has to be received on a trunk, that has a CoS field (user field - isl or dot1q frame) available in the ethernet frame?

Kindest regards,

Ken

[johansens]

I can't verify either way, but I just thought about this for a second, and then read up on some doc's.

It's logical that it uses CoS to classify which queue it should enter, and CoS can only be introduced in ISL/802.1Q frames (and then implied internally in the switch of course). This logic is deducted from this being in fact done in hardware at the outer point of the switch, and the queue is there specifically enable the switch to receive packets and process them before forwarding.

The only thing you can do is set a default CoS value for the access-port. Then every packet could be put in the priority-queue.. but that wouldn't give you any more advantage..

So in conclusion: To use the different queues, you need differing CoS fields. To achieve different CoS fields, you need a trunk-port (and it to be set as "trusted").