qos/auto qos config question


Just started studying QoS.

When configuring auto qos for a voip phone, configs for qos need to be on the switch facing the phone, trunk from that swith to another uplink switch, then onto another upstream switch until it reaches a layer 3 device? On all ingress/egress interfaces?

Then on the routers, configs for auto qos need to be set to the neighboring router, the to the switch/es it connect to then to the final dest switch interfaces to the end voip phone?

Also what if that voip traffic traverses - eg mpls routers, qos for mpls like exp bit need to be config'd?

Thanks guys, Ive been looking for a good link but still cant find one that talks about the whole path.



  • In general, you want to mark traffic as close to the source as possible.  You can then simply match that traffic on subsequent interfaces in the traffic path.  You want/need qos available end-to-end if at all possible.  Aside from policing, QoS is more or less an egress function since you can't queue or prioritize traffic that's already on the wire.

    Some switches will destroy your QoS markings if you don't tell them not to, and in general mls-qos can be a PITA.

    In the case of MPLS, you may need to create class maps/policy maps that translate from DSCP to EXP and back at your edges.  You'll also probably have to pay the SP to honor (or preserve) your markings.

    JMO, YMMV, etc.

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