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[Xen-users] Two bridges on one host, can not communicate on the second,

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Two bridges on one host, can not communicate on the second, what did I miss?
From: "Anders Andersson" <pipatron@xxxxxxxxx>
Date: Sun, 6 Jul 2008 16:23:15 +0200
Delivery-date: Sun, 06 Jul 2008 07:23:51 -0700
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Hello! I'm trying to set up an "internal" bridge on a Xen host (xen
3.2, ubuntu server 8.04 as a host). I am trying to get domU A
communicate with domU B, with no success.

First I followed the instructions in the XenNetworking page on the
wiki to get another bridge with no physical interface connected. I
created a file called /etc/xen/scripts/network-custom:

dir=$(dirname "$0")
"$dir/network-bridge" "$@" vifnum=0
"$dir/network-bridge" "$@" vifnum=1 bridge=dmz netdev=dummy0

After a reboot, this bridge comes up fine, and the output from "brctl
show" looks like the default bridge that the network-bridge script
creates. I have now a pdummy0 interface configured as well, belonging
to the bridge, but that is of course expected.

After this I create two guests: domU_A and domU_B. They are both on
the same network,, with IP number and
respectively. They just have one virtual network interface each, and I
added "bridge=dmz" to them, so they will connect to the dmz bridge.

After I start up both guests, I can see from "brctl show" that their
vif1.0 and vif2.0 have been attached to the dmz bridge, and inside,
the network interface has been configured correctly if I look at them
using ifconfig.

Here is where I fail. They can not access each other through the
network, not with ping, nor with anything else.

Using netcat gives me some slightly helpful message:
domU_B:~# echo hello | nc 9999
(UNKNOWN) [] 9999 (?) : No route to host

The output from "route" shows (sorry if the columns are not aligned correctly):
Destination   Gateway  Genmask        Flags  Metric  Ref   Use Iface      *     U        0         0         0  eth0

I don't have a default gateway, but well, there *is* no gateway, there
are just two clients.

The "ethtool -K eth0 tx off" trick doesn't make any difference.

What's sad here is that networking within the default xen bridge works
great, with exactly the same method of creating  and I have never had
any problems with that. As a matter of fact, keeping the exact same
config, but changing the bridge to the default bridge, makes it
possible to communicate between the guests. But now I would like to
add another bridge, as I would like to learn a little more about

Help! What did I miss? How can I find out where the problem is?

/ Anders

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