Default QinQ behaviour for MTU and REORDER flag

["Jean-Grégoire Foulon" <jg.foulon.dev@xxxxxxxxxxxxxx>]

Hello,

I am currently working with multiple Vlan stacking and
the behaviour of QinQ in the kernel is not always consistent. On some
hardware I have to use set the reorder flag to 0 for the QinQ to be
working, while on other, it just work whether this flag is 1 or 0.
I tested with the Fedora core 7 (kernel 2.6.21) on the following machines
Dell PC with Intel Corporation 82540EM Gigabit Ethernet Controller (rev 02)
Compaq laptop with Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)

On the Dell, I don't need to set the reorder flag to 0 but on the Compaq I need to do it.
Another even stranger thing is that on kernel 2.6.9 I need to set the
reorder flag to 0 if I want to stack 3 VLAN but I don't need to do it when I
stack only 2 VLAN...
What is the default behaviour ? Is there a bug for the support of one of those network adapter ?
is QinQ officially supported by the Linux kernel ? Someone posted a patch for 2.6.11, is it needed for 
2.6.21 ?

The
other problem I have is the fragmentation and MTU behaviour: the MTU of
a vlan device is the same as the MTU of its ethernet device (1500 in my
case), I think it should be less to reflect the size use by the vlan
header, no ?


When I use the command  "ping -t 2000 <ip address>":
-on a network interface : it works
-on a level 1 vlan: it works
-on a level 2 or higher vlan: it fails

When I use the command  "ping -t 1468 <ip address>":
-on a network interface : it works
-on a level 1 vlan: it works
-on a level 2 vlan: it works
-on a level 3 vlan: it fails

When I use the command  "ping -t 1464 <ip address>":

-on a network interface : it works

-on a level 1 vlan: it works

-on a level 2 vlan: it works

-on a level 3 vlan: it works

A level 3 vlan has a maximum packet size 4 bytes smaller than a level 2 vlan.
When
I change the MTU manually the "ping -t 2000 <ip address>" command
works on level 3 vlan, so it should make sense to reduce it when a VLAN
device is created, no ?
I am trying to modify a 2.4 kernel to do so, and it seems to work, may I by breaking something else ? 

Regards,

Jean-Gregoire
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