After refering to documentation: *mls qos trust dscp* Classify an ingress packet by using the packet DSCP value (most significant 6 bits of 8-bit service-type field). For a non-IP packet, the packet CoS is used if the packet is tagged. For an untagged packet, the default port CoS value is used.
So: mls qos trust device cisco-phone mls qos trust dscp should trust DSCP sent by IP phone, but remark everything from the PC (native vlan) to 0 by default or whatever is configured with "mls qos cos X" Comments apprieciated ;) kobel On Thu, Jan 27, 2011 at 19:46, Miron Kobelski <findko...@gmail.com> wrote: > 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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