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

["Raj Mathur (ààà ààààà)" <raju@xxxxxxxxxxxxxxx>]

On Monday 13 Aug 2012, Raj Mathur (ààà ààààà) wrote:
> On Monday 13 Aug 2012, Alexandre Kouznetsov wrote:
> > Hello.
> > 
> > El 11/08/12 22:48, Raj Mathur (ààà ààààà) escribiÃ:
> > > 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.
> > 
> > By default, at least in Debian, when you attach a network interface
> > (vif, in this case) to a bridge, there is delay before the packets
> > are forwarded to the newly attached interface. The delay time is
> > configurable via interfaces file or brctl utility.
> 
> Thanks for that information.  That is exactly the problem we were
> facing.
> 
> In our case, the delay was no trouble except when we needed to PXE
> boot to install.  After install, we boot the VM with the normal
> kernel= and root= parameters, and bridge forward delays aren't
> noticeable.
> 
> Two further questions arise:
> 
> 1. Presumably the bridge forward delay is there for a purpose.  Can
> reducing that value result in other problems?
> 
> 2. Is it possible to get the current value of the forward delay from
> a bridge?  If we can do that, we can script a reduced delay when PXE
> booting and installing a VM, then go back to the default delay after
> the VM install is over.

To answer my own questions, a detailed explanation is available at:

http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge#FAQ

Specifically, see:

http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge#Does_DHCP_work_over.2Fthrough_a_bridge.3F

While it doesn't tell you how to get the current value of the Forwarding 
Delay in Linux, it does mention that the default is 30 seconds, and 
gives the pros and cons of changing it.

Regards,

-- 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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