[c-nsp] Multicast issues on 7600s with WS-6748-sfp blades

[John Neiberger]

We have a weird problem on some 7606s with WS-6748-SFP blades. We have
a whole bunch of multicast streams running through these routers and
there are multicast receivers directly attached. We had a problem
where one particular multicast stream would occasionally have dropped
packets resulting in MPEG CC errors on the receiver. We were able to
prove that the source was clean, as were the paths between the source
and the receiver. The receiver was not seeing MPEG CC errors on any
other stream, which is really odd.

Here's where it gets even stranger. When we moved the receiver to
another port, like from 23 to 24, the receiver still saw the errors.
We moved it to port 25 and the errors apparently went away. Our only
guess is that this could potentially be an issue with the ASICs on the
blade. Ports 13-24 are controlled by one ASIC (I believe a Rohini
ASIC), and the four Rohini ASICs connect to two Janus ASICs. That is
as I understand it. I may be wrong. When we moved the receiver from
port 24 to 25, we moved to a different Rohini ASIC and possibly to
another Janus ASIC. Regardless, according to our video guys the
problem cleared up after the move.

Have any of you ever experienced anything like this? Could this really
be a problem on the Rohini or Janus ASICs? What sort of problem would
only affect certain multicast groups and not others?

Thanks