802.1p query

Hopefully someone can help me with this as I can't find the answer on Cisco's website.

I have a Juniper Netscreen Firewall which is routing traffic between VLAN's on a Cat 2960 via an 802.1q trunk between the two devices. On one VLAN sits an IP PBX. Incoming voice traffic is received on the Untrusted Interface of the Firewall and forwarded to the PBX via the trunk.

From what I can tell the Netscreen does not support 802.1p. From a

Sniffer trace I can see that incoming RTP which is marked EF has a COS value of 0 by the time it arrives at the 2960. Outgoing RTP that is marked EF is also marked COS 5 which is to be expected as 2960's support 802.1p.

So my question is how does the Catalyst treat the incoming voice?

From what I understand, when traffic is received on a trunk, the

switch looks at the Layer 2 COS vlaue only. Although I can configure "mls qos trust dscp" on the trunk port connected to the Netscreen, will the switch look at the DSCP value or does it still look at the COS value? Does anyone know of any show or debug command's that can prove this?



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