netdev - Re: change the way e1000 is handling short VLAN frames

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Date:	Fri, 21 Sep 2007 09:37:21 -0400
From:	jamal <hadi@...erus.ca>
To:	Emil Micek <emil.micek@...jasek.cz>
Cc:	"auke-jan.h.kok@...el.com" <auke-jan.h.kok@...el.com>,
	netdev mailing list <netdev@...r.kernel.org>,
	Ben Greear <greearb@...delatech.com>
Subject: Re: change the way e1000 is handling short VLAN frames

On Fri, 2007-21-09 at 14:50 +0200, Emil Micek wrote:
> On Fri, 2007-09-21 at 07:59 -0400, jamal wrote:

> > Which would make it a bug. AFAIK, the minimum VLAN tagged packet going
> > out is 68 bytes.
> Are you sure about this? 

This is what i have always seen. Double checked with google and she gave
me many a url, example:
http://www.cisco.com/warp/public/473/741_4.html
I think you can pretty much trust cisco on something as basic as this.
Also:
http://www.techfest.com/networking/lan/ethernet2.htm

> We did some extensive testing capturing VLAN
> frames going out of our Intel PRO/1000 MT Dual Port Server Adapter
> (82571EB chipset) and we definitely captured VLAN frames shorter then 68
> bytes. Here is text dump of such frame:
> http://www.tkrjasek.cz/mie/cmts_tests/between_linux_and_cmts.txt

Do you have access to another NIC? a tg3 based one will be good to test
for hardware level tagging.

> (note that wireshark captures the frames without 4 bytes FCS (frame
> check sequence) so the above packet is in fact 66 bytes long).
> 
> What is the right behaviour according to specification? In iee802.3,
> minFrameSize is 64bytes. I've never seen any document which'd say that
> VLAN frames should be 68 bytes minimum.

Refer to above.

> Now i'm little confused by your reply, becaouse you write, that VLAN
> frames generated by e1000 should be 68 bytes minimum, which contradicts
> witch our observations.

Miscommunication ;-> I said the packets going out should be 68B
otherwise it is a bug. if e1000 is sending 64B out, it is a bug.

I think any other NIC that doesnt do hardware based vlan tags would be
good to try as well because it uses the software stack to do the
tagging.

cheers,
jamal

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