Re: [Xen-users] Xen networking troubles

[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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