MCR LANCP SHOW DEVICE /ALL /COUNT -> Data overruns

[Richard Stockdale · Accepted solution]

I did some experiments. I was a bit concerned that perhaps these packets were full-size VLAN tagged packets and the driver gives the device 1518 byte packets which wouldn't have enough room for the 4 byte VLAN tag (never mind that the driver does not support VLANs on the device and so nothing would have worked anyway).

Then Tony Abdella sent me a packet trace and the problem was immediately obvious. As Bill Hall said in one of the replies - the DE600 is not as good as the DE500 in some regards. The DE600 is actually much better than the DE500 for large segmented or chained transmit packets but much worse than the DE500 for small packets.

The packet trace showed an ARP request followed by a flood of minimum size packets. The DE600 just can't cope with line rate minimum size packets, and so you see data overruns and lost packets.

The only choice is to get a more capable NIC, such as a DEGXA which can run at line rate on any packet size at 100 mbits.

Note that the DEGXA, like most gigabit NICs can't run at line rate at 1000 mbits/sec for packet sizes below a few hundred bytes (at least with a conventional interrupt-based system implementation), but it does quite well and has enough buffering to withstand large bursts of line rate minimum size packets at 1000 mbits/sec.

-Dick

[Bill Hall]

Art,

If you are interested in taking Dick's advice and would like to "upgrade" to the DEGXA but need the dual port density of the DE602, I highly recommend Nemonix Engineering's DEGX2-TA. We have both ES40s and ES47s with four DEGX2-TA in each.

If I recall correctly, at VMS 7.3-2 the version of the SYS$EW5700 driver that supports both the HP DEGXA-TA and the Nemonix DEGX2-TA to is included in one of the VMS LAN ECOs. I don't recall which one.

The price on the Nemonix DEGX2 is very good also.

Bill

[Art Wiens]

Based on the findings by HP support / engineering, and testing the DEGXA 1Gb card HP loaned us, we have 12 - DEGXA's on order.

I still find it hard to believe the DE60x (we also tested a single port DE600) can be overrun, it was only ~400 multicast packets, but in the end, going "faster" is always desirable! ;-)

Cheers, and thanks HP!
Art

[Art Wiens]

DE60x 100Mb nics were being overrun by "bursts" of multicast packets when connected to Cisco 3750 switches.

The DEGXA 1Gb nic does not exhibit this issue.

Art