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Re: [Xen-users] "routed" networking under Xen 3.2.1 / HVM?

  • To: deshantm@xxxxxxxxx
  • From: "Ray Barnes" <tical.net@xxxxxxxxx>
  • Date: Tue, 13 May 2008 07:00:46 -0400
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 13 May 2008 04:01:22 -0700
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On 5/12/08, Todd Deshane <deshantm@xxxxxxxxx> wrote:
Hi Ray,

I don't have a good intuition for what you are trying to do yet.
I've reread my original remarks and I'm not sure how I could further clarify them.  But to be (hopefully) blatantly clear, I'm looking for a means to do routed networking to an HVM guest.

But when you say host networking, do you mean host-only networking?
If so then you can use dummy devices for that purpose and just bridge
off of them.
Correct - host-only networking.  If HVM supports this consistently then it should meet my requirement, as I've been doing the same with VMWare GSX without issue.  To that end, I've tried 'ifconfig dummy0', adding a bridge called "testbridge" and adding dummy0 to the bridge.  Then under my xen HVM config file, specifying 'bridge=testbridge'.  According to what I've read, this should be sufficient to network betwen the HVM guest and my dom0 but I have no pings.  Right off the bat I noticed that 'ifconfig dummy0' says NOARP - not sure if that's some kind of limitation to the dummy interface.  But lack of ARP would certainly keep me from pinging it.  I didn't try setting a static ARP at both ends (it wouldn't work for my environment anyway, working ARP is a requirement).  However I did see a post to xen-users where someone suggested 'brctl addbr xenbr1 ; ifconfig xenbr1'.  This works just fine for "host networking" and allows me to route exactly as expected - thanks for the insight!
To that end, a few more questions.  I'm accustomed to running custom scripts using the script= tag within the [vif] block - will I run into any pittfalls if I create/destroy the bridge here?  Or should I create the bridge at boot-time?  If the latter, is there a recommended means of doing this under RHEL/CentOS, perhaps with something in /etc/sysconfig/network-scripts?  Also, any idea as to the limit of bridges per system?  I recall reading somewhere that Xen has bridges labeled xenbr0-xenbr7 or something, although I'm able to create custom named bridges like "dom12345" - any insight on theoretical maximums there? 
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