Subject: Problem with igb and vlans in 2.6.38-rc4

From: Ben Greear <[email-masked]>
Date: Thu, 10 Feb 2011 09:57:01 -0800

We have a user-space app that uses packet-sockets to grab and send
Ethernet frames (basically a user-space bridge).

This has stopped working for VLANs unless we set the physical
port MTU to be vlan-MTU + 4 (ie, 1504 for standard MTU size vlan frames).
I think this started post 2.6.34 kernel..but not exactly sure at this
time.

The test setup is essentially:

client -- vlan 5 -- [ eth4 {software-bridge} eth3 ] -- vlan 5 -- server

The software bridge machine has no VLANs enabled..it is supposed to just
read Ethernet frames from one port and xmit out the other.

The bridge machine sees rx-length errors, and if only one port is
set to 1504, the other shows xmit errors (since it doesn't like sending
a frame 4 bytes larger than MTU probably).

This used to work, and I'm hoping this change wasn't done on purpose.

Thanks,
Ben

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