[Xen-users] multiple bridges on non-addressed interfaces

[Steve Wray <steve.wray@xxxxxxxxx>]

Hi there,

I'm researching our upgrade path from Debian Etch to Debian Lenny and the 
newer version of Xen which that brings to the table.
There have been some networking issues which I've been unable to resolve.

Example:

I have two servers each server has four NICs.

One NIC should be for the exclusive use of dom0 and is not used in any domU.

The rest of the NICs should be bridged to the domUs and should not have IP 
addresses assigned in dom0.
At least one (bridged) interface per server is on our internet front end. 
We don't want to waste address space on the dom0s plus we don't want the 
security exposure of dom0 having an interface directly on the internet. 
Therefore in the past I have not allocated these interfaces IP addresses.
In earlier versions of Xen I had this working fine, under Debian Etch, by 
using configurations in /etc/network/interfaces such as:
auto eth3
iface eth3 inet manual
up /etc/xen/scripts/network-bridge start vifnum=3 bridge=xenbr3 netdev=eth3

in the newer version of Xen this is simpler and we have:

up /etc/xen/scripts/network-bridge start netdev=eth3

Lovely. And with the updated format of the network-bridge script brctl show 
reveals the correct assignment of bridges.
However, this only actually *works* (for the domUs) if the interface is 
assigned an address in dom0.
Ie:

auto eth2
iface eth2 inet static
  address 172.16.2.253
  netmask 255.255.255.0
  up /etc/xen/scripts/network-bridge start netdev=eth2

works while this:

auto eth2
iface eth2 inet manual
  up /etc/xen/scripts/network-bridge start netdev=eth2

does not.

I'm not sure if what is going wrong here is a problem with my understanding 
of Xen or Debian Lenny networking...


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