Xen project Mailing List

2011/12/2 James Dingwall <james.dingwall@xxxxxxxxxx>

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Johan Barelds
Sent: 2 December 2011 10:30
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Xen networking troubles

2011/12/2 James Dingwall <james.dingwall@xxxxxxxxxx>
Thanks for your quick response James!
I tried it and it's not working yet.
On the Windows network card i got the yellow triangle saying: "Unidentified Network".
What should i use for Default Gateway on my HVM btw?
I used now the one IP from my public range that i configured on my eth1
- Do you have a separate device on the 6 IP subnet that is already a router or will your dom0 perform this function? If it will be your dom0 via the eth0 interface then you will need to assign an IP address from the 6 IP subnet to the bridge and enable IP forwarding by adding the line
net.ipv4.ip_forward = 1
to /etc/sysctl.conf and executing sysctl -p
You'll also need to make sure that the rest of your network knows to route the domU subnet via the dom0.
If your eth1 isn't actually connected to the network then you can use the bridge without a physical interface attached to it.

And about setting up the extra bridge breth1: does that stick if i reboot the server?
And if not how can i make ik more permanent?
- To make it permanent you'll need to edit the network scripts. I'm afraid I don't have specific RHEL/CentOS knowledge. But http://acidborg.wordpress.com/2010/01/20/how-to-configure-a-network-bridge-in-red-hat-fedora/ looks like it should give you enough information though.

Hi James,

I do not have a separate device in my IP range that functions as a router.
Can you explain how i assign an IP address from the 6 IP subnet to the bridge?
I assume you mean the xenbr0 bridge?

You would need to assign an IP from the 6 to the new bridge that you created. xenbr0 should have the current IP of your dom0 assigned. From the command line it would be something like:
# ifconfig breth1 192.168.1.1 netmask 255.255.255.248

Let's say the domU subnet is 10.10.10.0/29, usable IPs .1 to .6. The dom0 eth0 interface is wired to a network where 192.168.10.1 is the router.

dom0

eth0 eth1 Physical interfaces
| |
xenbr0 breth1 Bridges (created by Xen or OS script)
192.168.1.10/24 10.10.10.1/29 IP assigned to the bridge
|
domUs
10.10.10.2-6/29, g/w 10.10.10.1 IPs available to domU

The routing table in the dom0 has a default gateway entry that looks like
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 xenbr0

The g/w for the domU indicates traffic should be sent to the dom0, 10.10.10.1. With ip_forward = 1 the dom0 can now use its routing table to forward traffic via the eth0 interface to 192.168.10.1 which will know about the rest of the network. This router must know that return traffic for 10.10.10.0/29 is to be forwarded to the eth0 IP of the dom0, 192.168.1.10 in this example.

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