Omniswitch 7700 floodrate problem.

[sailsoft]

Very strange and unexplainable issue we run into. Maybe someone has an idea ?

On our site we have a plant that uses a Omniswitch 7700 as core with 802.1Q links running at 100 MB/s to 6850's.
A server is connected to the 7700, the PLC's are connected to the 6850. All are in the same VLAN.
The server broadcasts at a peak of 27 pps towards the PLC's. Since the server has been replaced by a new one, running on 100 MB/s the PLC's report missed packages constantly.
The old server had a 10 MB/s link.

I made a 10 minute capture of the traffic sent by the server.

I then took a spare 7700 and connected 2 PC's. 1 replaying the captured packages, the other one running a sniffer.
After replaying the 18039 packages in the capture, indeed the sniffing PC misses arround 700 packages.
Also the interface counters do not match between the 2 used interfaces.

The only way to get all replayed packages over to the capturing PC, is to increase the flood limit on the interface connected to the sniffing PC to 94 MB/s !!!!
When configured to a lower value, packages get lost.

According to the documentation incomming flood rate on a port is fixed a 5 MB/s, so my conclusion is that the default rate on the outgoing port of 47 MB/s should be sufficient.

When I replace the 7700 with another 6850, no packages get lost with default settings.

I tried several 5.4.1.xxx software version including the latest.
I even tried the latest 5.1.6, but that made no difference.

Does anyone have an idea what is going on ?