Hi Matthew, I agree about the cos part, adding that you can control the cos value for PC connected to the phone using "switchport priority extend" command with 4 options: * trust * don't trust * overwrite with specific cos value * by default - overwrite with COS 0
But the question is, how DSCP markings from the PC are handled with this configuration? I understand that IP phone marks its RTP and signaling packets with both COS and DSCP and you can choose on the switchport which one you want to trust. But what about the PC markings? PC can only mark using DSCP (no 802.1q header between PC and IP phone). What happens when I decide to trust DSCP in such situation? Both markings from the PC and IP phone are trusted? This would constitute weak solution, since I don't want rogue PC to send all it's traffic as EF... any idea? regards kobel On Thu, Jan 27, 2011 at 00:15, matt...@ciscovoiceguru.com < matt...@ciscovoiceguru.com> wrote: > If you set "mls qos trust cos" then CoS markings will be preserved; > however, any DSCP marking will be written to 0. > > The same holds true for "mls qos trust dscp." Any packet entering the > switch with a CoS marking will be written to 0. > > That is why you have cos-to-dscp and dscp-to-cos mappings. This allows the > packet to essentially become a "blank slate," delete L2/L3 QoS values, and > remap them. > > >
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