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Re: AW: [Xen-users] xen and vlans

To: "Lockenvitz, Jan \(EXT\)" <Jan.Lockenvitz.extern@xxxxxxxxxxxxxx>
Subject: Re: AW: [Xen-users] xen and vlans
From: Alvin Starr <alvin@xxxxxxxxxx>
Date: Thu, 15 Dec 2005 09:59:47 -0500
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Lockenvitz, Jan (EXT) wrote:

I think it should be sufficient to do as following:
- create and test the vlans as normal (i think you already did this) - try to create the bridge as follows (for the first try without starting xend):
# network-bridge start netdev=vlan100 bridge=xenbr0

at least this was working on my debian testing installation but i have a problem now with incorrect tcp checksums in dom0 or domU. See my post: http://lists.xensource.com/archives/html/xen-users/2005-12/msg00412.html

Please have a look whether you have the same problem.


This is just conjecture and I have not yet had time to verify this but I believe the following is happening. 802.1q vlans add 4 bytes to the packet for the vlan managment. this makes the max packet size 1504 bytes but the standard MTU is 1500.
The bridge software may not deal well with oversized packets.
I also found an old email that relates to this but I am not sure if it still holds true. http://mail-index.netbsd.org/tech-net/2002/12/10/0001.html

I believe the answer is to create the vlans on the Dom-0 and then bridge the device over to the Dom-U and not have the Dom-U run the vlan software at all.

Alvin Starr                   ||   voice: (416)585-9971
Interlink Connectivity        ||   fax:   (416)585-9974
alvin@xxxxxxxxxx              ||

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