[c-nsp] Weird problem w/ packet loss on QinQ ports

[Garry]

Hi,

I'm currently fighting with a weird case of packet loss in a lab
setup... here goes ...

Setup is as follows, two ME3400 with MetraAccess IOS 12.2.46, are
connected to a 4507 through GigE ports. Connections are Trunk links.
VLANs (QinQ, plus other non-QinQ ones) used on the MEs are configured on
the 4507.

Now, when I hook up two PCs to one of the ME each, using a "switchport
access" port, both being in the same vlan, everything is fine. Transfer
rates are fine, no packet loss on floodpings even with large packets (1500).

Now, plugging the PCs into the QinQ ports, which are just configured
with the basic "switchport access" and "switchport mode dot1q-tunnel", I
get about 1% packet loss on flood pings with default packet size, with
increasing loss while increasing packet size. Weird thing is, doing a
tcpdump on the receiving end, I see the packets arriving, though some
aren't answered by the PC. I assume they arrive with incorrect checksum
and therefore are dropped by the stack ...

Anybody have an idea what is going wrong here??? I'm out of ideas ...

Tnx, -garry