Problem with cxgb, mac-vlans, and UDP checksum offloading.

Hello!

This is with kernel 2.6.23, plus our hacks, but the mac-vlan logic is part of the official kernel now. OS is Fedora 8. I have applied patch 1 and 3 of those sent a few weeks ago for the cxgb as well.

While testing NFS on mac-vlans on cxgb, we noticed that
UDP packets have incorrect checksums when sent from
the mac-vlan device on a cxgb interface to another system. When sending from a regular ethernet device (cxgb), it works fine.
When we disable rx and tx UDP checksums on the mac-vlan device, it works fine. When we use e1000 interfaces (which also do rx/tx UDP checksumming), mac-vlans & NFS works fine with mac-vlan rx/tx checksumming on (the default value).

So, there seems something weird about the cxgb NIC when used with mac-vlans. Perhaps it is somehow paying attention to MAC addresses when it determines if it should csum a packet or not?

If you want to test it yourself, grab the latest iputils package and create MAC-VLANs like this:

ip link add link eth0 name eth0#0 address 00:11:22:33:44:55 type macvlan

If you would like a packet trace or any other debugging, please let me know.

Thanks,
Ben

Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com