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[Xen-devel] VLANs with Xen - work with 1 Gbit, doesn't with 100 Mbit cards?

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Tomasz Chmielewski <mangoo@xxxxxxxx>
  • Date: Fri, 02 Feb 2007 19:35:11 +0100
  • Delivery-date: Fri, 02 Feb 2007 10:35:10 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

I have a strange problem with VLANs with Xen 3.0.4. I signalled it on
Xen-users list, but found no definitive solution to it.

I configure VLANs so that they are available in dom0; domUs don't know
that they use VLANs.

I use a stock "network-bridge" comming from Xen for setting up networking:

dir=$(dirname "$0")

"$dir/network-bridge" "$@" vifnum=0 netdev=eth0 bridge=xenbr0

"$dir/network-bridge" "$@" vifnum=1 netdev=eth0.100 bridge=xenbr100

"$dir/network-bridge" "$@" vifnum=2 netdev=eth0.200 bridge=xenbr200

If the server has a 1 Gbit network card (e1000, tg3 module), VLANs work

If, however, I replace the card, and use a 100 Mbit one (Intel/e100 or
Realtek/8139too module), and don't change the scripts, VLANs are not

Why is it so? What is so fundamental in Xen networking that VLANs
behaviour change so much whether one uses a 1 Gbit, or 100 Mbit network

There is one difference between 1 Gbit and 100 Mbit cards - 100 Mbit
cards won't allow to set the MTU bigger than 1500:

# ifconfig eth1 mtu 1501
SIOCSIFMTU: Invalid argument

But I'm not sure if it has anything with the described VLAN problem.

On the other hand, if I configure VLANs in domU, it works fine then (but
it's a bad approach for me, and prefer to have VLANs in dom0 only).

Tomasz Chmielewski

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