[c-nsp] 6500 - Is it possible to sniff DSCP values over RSPAN?

[Andy Ellsworth]

Cat6509, Sup720-3BXL, 12.2(18)SXF7 (modular), 6748 line cards.

I've got slots in a VoIP PBX plugged into a couple dozen ports on two
6748 linecards. The ports attached to the PBX are configured with "mls
qos trust dscp". Globally, I've configured "mls qos". A "sh queue int"
on one of the ports connected to the PBX reveals:

Interface GigabitEthernet1/27 queueing strategy:  Weighted Round-Robin
  Port QoS is enabled
  Trust state: trust DSCP
  Extend trust state: not trusted [COS = 0]

I'm trying to verify via a sniffer that the PBX is properly tagging its
outbound traffic with a DSCP value of 46 (which it is supposedly
configured to do). I don't have a sniffer in the same data center as
this 6500, so I'm sending the traffic via RSPAN to a dedicated sniffing
box (CentOS 4/Ethereal). The layer 2 path for the RSPAN session passes
from this 6500 to a 7200, into an L2TPv3 tunnel over the 'net to another
7200, through another 6500, and finally through two 3560s to the sniffer.

The RSPAN session works fine, and I see all the traffic I want to see,
but all my DSCP values are zero. Before I go digging into the PBX to
figure out why it's not marking DSCP properly, I'd like to see if anyone
has successfully passed non-zero DSCP values over an RSPAN session.

Thanks...

-Andy