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

[Alexandre Kouznetsov <alk@xxxxxxxxxx>]

Hello.

El 13/08/12 11:49, Raj Mathur (ààà ààààà) escribiÃ:
> 1. Presumably the bridge forward delay is there for a purpose.  Can
> reducing that value result in other problems?
Check the thread I have referenced (2012-04-03 08:42 -0500), this 
question has been raised there.
Generally speaking: _should_ be no problem.
At least I have not encountered any (yet), and nobody has raised his 
hand to tell he had some. It has mainly to do with STP, which becomes 
relevant only when there is a ethernet loop risk. In any case, I disable 
STP on my VM bridges and pay specific attention not to put more than one 
physical interface in the same bridge, hope that eliminates possibility 
of looping.
In a attempt to prevent surprises, I do not reduce the delay to 0, it is 
set to something closer to the defaults instead. 5 seems to be just 
small enough to allow gPXE to do it's job.
> 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.
Not sure if it's a good idea. 15 (the usual default) seems to be as good 
as 5. Personally, I prefer to leave this kind of things alone: set once, 
make it persistent, leave it static unless there is a good reason to 
change it dynamically.
brctl seems not to offer a _nice_ interface to get the forward_delay 
value. If you wish to parse a multi-colon output, try "brctl showstp 
<bridge>". Also, you could check under /sys/devices/virtual/net/*.
Greetings.

--
Alexandre Kouznetsov


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