Marking video conference packets accross a wan

fightclub34fightclub34 MemberMember Posts: 41 ■■□□□□□□□□
I have setup the class and policy maps on a 6500 to catch any af41 and give that priority. My problem is we use all 3550 switches and they are access layer. We do no routing on them. If i have polycom video conference equipment setup on a switchport set to an access port how do mark the packets with af41 since the port is only layer 2. The polycom equipment can be set to mark the packets but will these packets make it through a layer 2 switch port and get to the router as marked. I would like to know how to configure the switchport that is attached to the polycom device


  • pitviperpitviper Member Posts: 1,376 ■■■■■■■□□□
    Which image are you running on the 3550? Can you enter "mls qos trust dscp" under the switchport that the phone is plugged into?

    I've done this on a 3560 running the IP base image which I think is essentially the same as the basic SMI image on the 3550 (could be wrong though).
    CCNP:Collaboration, CCNP:R&S, CCNA:S, CCNA:V, CCNA, CCENT
  • APAAPA Senior Member Member Posts: 959
    Mark with cos 5 on the access port...

    at the 6500 match any packets with cos of 5 and remark them as AF41 on output....

    If you don't remark them as AF41 they will be considered as CS5 = IP Precedence 5 on all future devices as long as they are set to trust the QoS marking on incoming packets.

    If the switch is acting as a Layer 2 device, it has no idea of DSCP as that is considered L3 marking via the ToS byte in the IP header.

    However the 3550 might support a QoS SDM template which allows it to act as a layer 2 switch but still be smart\aware regarding QoS markings above layer 2. I will look into that tonight.....

    CCNA | CCNA:Security | CCNP | CCIP
  • pitviperpitviper Member Posts: 1,376 ■■■■■■■□□□
    I just loaded an IP base (SMI) image onto a cat3550 and verified that it is indeed capable of trusting DSCP markings, even with the non-enhanced image:

    c3550_1(config-if)#mls qos trust ?
    cos Classify by packet COS
    device trusted device class
    dscp Classify by packet DSCP
    ip-precedence Classify by packet IP precedence
    CCNP:Collaboration, CCNP:R&S, CCNA:S, CCNA:V, CCNA, CCENT
  • fightclub34fightclub34 Member Member Posts: 41 ■■□□□□□□□□
    a.p.a would you be willing to show me what a config of an access port would look like on the 3550. Im new to qos im not sure how to mark it as cos 5. Also could you show me the remarking on the 6500
  • dtlokeedtlokee Village Idiot Member Posts: 2,378 ■■■■□□□□□□
    The polycom video conferencing station should mark the traffic, no need to remark it.

    If the 3550 is default then QoS is off and it will not touch the packets. If you have enabled QoS you should set it to trust DSCP as pitviper said. You must ensure all switches in the transit path are configured to trust the markings or they will be remarked (again based on if QoS is enabled)
    The only easy day was yesterday!
  • laidbackfreaklaidbackfreak Senile old fart Member Posts: 991
    ok im following this thread as it something I have to do at work on a mixture of routers and l3 sitches,

    I've been reading through this ;-
    How to Configure Video over IP for Polycom Video Units [Gateway Protocols] - Cisco Systems

    and this :-
    Implementing QoS Solutions for H.323 Video Conferencing over IP - Cisco Systems

    and this for teh switches :
    Cisco Catalyst 3750 QoS Configuration Examples [Cisco Catalyst 3750 Series Switches] - Cisco Systems

    and Im happy to roll out this soloution,

    but what I'd like to know is, would it be possible to use autoqos on the 3750's as at some point I need to roll out a IPT soloution ?
    if I say something that can be taken one of two ways and one of them offends, I usually mean the other one :-)
  • dtlokeedtlokee Village Idiot Member Posts: 2,378 ■■■■□□□□□□
    If you are aware of the changes that auto QoS will make and the implications they will have on the switch then go for it. If you don't understand the changes that it will make then I wouldn't do it.
    The only easy day was yesterday!
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