QoS ME 3400 : prioritization

[Hishigi]

Hi everyone,

this is my first post so I hope it was placed appropriately.

My english isn't good and I will do my best so that you understand me, all my apologies.

I have some difficulties with QoS on ME 3400. My problem is : i tried to prioritised a traffic with a dscp value 46. I would have a traffic with dscp 0 that fills my bandwidth and when I send a bandwidth tag with dscp 46 traffic will be prioritised and the no tag traffic will be decrease. I want that all my traffic took all the bandwidth (I wouldn't  like to reserve bandwidth's quantity not used). I tried to match ip dscp with 46 in a class-map and prioritised on a output service policy but no results.

Thanks you to taking time to answer.

Have a good day.

[Joseph W. Doherty]

I've rarely used the ME3K series, so I'm going to address general QoS, rather than specifics for a ME3400.

One important concept to understand, your QoS needs first to be applied to the "bottleneck" interface, and if that's not possible, you often can force an upstream interface, that you control, to be a bottleneck. This so traffic will queue at an interface where you've have the QoS policy you want.

On 3K switches, often you need to globally enable QoS for it activate. Also, on those switches, often there are a limited number (often 4) hardware queues for QoS. Lastly, such switches often support one queue being a priority queue, which when there's congestion, will always be dequeued first (if within it's optional shape limits).

Your task is to insure your DSCP EF traffic is directed to the PQ. (BTW, also on many 3K switches, once you globally enable QoS, you need to "trust" DSCP on ingress interface otherwise the switch will reset the ToS byte to zero.