Re: MTU problem between 10/100 & Gigabit cards

[Gary Smith <gary@xxxxxxxxx>]

Is their a list of drivers with their corresponding MTU size required.

Some of the old 10/110 as well as gig cards.

Thanks

Gary 

Ard van Breemen wrote:

Hi,
On Fri, Jun 29, 2007 at 05:19:06PM +0100, Gary Smith wrote:
  

I have been running a VLAN configured system for some years using 10/100 
Sundance driver cards without a problem.  I recently tried on a HP 
proliant server using gigabit cards and found a problem related to the 
MTU size for the interface I an using.

The 10/100 cards seem to need a MTU of 1504 bytes, but this size does 
not work with the e1000 gig cards, or the US robotics, Dlink DGE, 
broadcom etc.  I have to move the MTU down to 1500 to make fragmentation 
work and allow it to pass the larger packets.
    

>From what I read, I guesss the vlan on sundance is software only,
and need a special MTU of 1504.
Most gigabit cards (not all!) already strip the vlan tag, so the
driver only sees a payload of 1500 and somewhere else in the
receiver buffer the vlan tag is found.

  

Is this what I should expect from the e1000, broadcom, R8169 drivers for 
gigabit cards?
    

I've been using vlans since 2.4.14 or so, and I have never had to
set the MTU size to 1504 for any of my cards. I do know however
that some of the drivers need the MTU size of 1504 to keep it
from discarding it as a long packet and to cope for the increased
buffer size needed.

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