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[Xen-users] [SOLVED] domU PXE boot with bridge

  • To: "xen-users" <xen-users@xxxxxxxxxxxxx>
  • From: "Raj Mathur (ààà ààààà)" <raju@xxxxxxxxxxxxxxx>
  • Date: Sun, 12 Aug 2012 09:18:17 +0530
  • Delivery-date: Sun, 12 Aug 2012 03:50:14 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

Trying to PXE boot a domU with xen-qemu-dm on Debian Squeeze.  VIF is 
bridged to a dedicated physical interface.

boot = 'n' in the domU configuration.

The gPXE DHCP client in Qemu would always time out and the VM would halt 
without booting.  On watching the physical interface, I couldn't see any 
DHCP traffic at all.

After hours of tcpdump-ing first the physical then the virtual 
interfaces, realised that the bridge was taking time to come up.  gPXE 
was sending out DHCP requests before the bridge came up, so they never 
reached the wire.  The DHCP requests were visible in the VIF traffic, 
but not in the ETH traffic.


1. Press Ctrl-B to reach the gPXE command line.  Wait for 30-odd seconds 
for the bridge to come up.  Type in: autoboot .  You have to get to a 
domU VNC session fast in order to be able to do this.

2. Insert a 40-second delay into /etc/xen/scripts/vif-common.sh (use a 
sleep after the iptables commands).  Unfortunately, this delays startup 
of all bridged domUs by that long.

Is there a better way, e.g. by somehow forcing gPXE to sleep for some 
time before it tries the DHCP?

In any case, now our automated Debian install is working for bridged 
domU VMs.  Hope this is useful to others with the same problem.


-- Raj
Raj Mathur                          || raju@xxxxxxxxxxxxx   || GPG:
http://otheronepercent.blogspot.com || http://kandalaya.org || CC68
It is the mind that moves           || http://schizoid.in   || D17F

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