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Here’s a quick and basic how-to in preparing Xen with multiple bridges with multiple NICs for DomUs on Xen in SLES10.

Objective:
Deploy networking on Xen DomU’s using multiple bridges on multiple NICs. Host OS will utilize two NICs for WAN and LAN connections. Guest OS will utilize two NICs also for WAN and LAN connections. Host OS and Guest OS are using different WAN connections and LAN connections.

Step 1: Verify Xen Presence
Make sure that you have Xen installed. If not, you can do:

1. Open up YAST.

2. Click on ‘Software’, then click on the ‘Filter’ parameters box, and choose ‘Patterns’.

3. Verify that ‘Xen Virtual Machine Host Server’ is checked/selected. If not, then check it. The required packages for Xen are shown on the right panel.

4. To make sure, you can check for software dependencies by click on the ‘Check’ button at the bottom of the YAST window.

5. Click ‘Accept’ and let YAST install the packages.

After installation, Xen’s tools will be located in /etc/xen.

Step 2: Prepare NICs for DomUs
By this time, we’ll need to identify which physical NICs we are going to allocate for the DomUs. For our example, our machine has 4 physical NICs labelled ETH0, ETH1, ETH2, and ETH3 respectively. ETH 0 and ETH1 will be used by the host SLES10 (Dom0), while ETH2 and ETH3 will be used by the guest OS (DomU).

To specifically restrict our host from using ETH2 and ETH3, we will need to only initialize the NICs and not declare an IP address nor do we configure them using DHCP. To do just that, we need to:

1. Open up YAST.

2. Click on Network Devices, then click on Network Card.

3. In the Network Cards list, select ETH2 and then set it to ‘None Address Setup’. This will initialize the NIC without an IP address and our host OS will have no use of the NIC which serves our purpose quite perfectly.

4. Click ‘Next’ then Finish.

Do the same for ETH3. Do not forget to setup ETH0 and ETH1 to connect to your desired network.

Step 3: Prepare Xen with multiple bridges
Before we can configure Xen for multiple bridging, we will need to let Xen restart. The optimal way will be to reboot the entire system, or we can just stop the Xen daemon and restart it back up. We can do a Xen daemon restart only if we have already logged into the Xen-enabled kernel of SLES10. If not, we definitely will need to reboot and log into the Xen-enabled kernel.

After booting via the Xen-enabled kernel, we will need to do some preparations before we install our guest OS (vm/DomU). We will need to prepare our network bridges first before our guest OS can use the physical NICs we allocated for our guest OS. We will need two bridges for our guest OS to connect to WAN and LAN. To prepare the bridges, we will need to stop the Xen daemon, and create a wrapper script that utilizes the network-bridge script that comes with the Xen package of SLES10. To stop the Xen daemon, do:

# rcxend stop

We will need to put the wrapper script at /etc/xen/scripts/ along with other Xen tools. The following is a sample wrapper script.

#!/bin/bash
dir=/etc/xen/scripts
“$dir/network-bridge” “$@” vifnum=0 bridge=xenbr0 netdev=eth2
“$dir/network-bridge” “$@” vifnum=1 bridge=xenbr1 netdev=eth3

Save the file as br-wrapper_script or whatever filename you specify. Chmod the file to executable using:

# chmod o+x br-wrapper_script.

After creating the wrapper script, we will need to modify Xen’s configuration to use our wrapper script instead of network-bridge directly. The file of interest here is /etc/xen/xend-config.sxp.

# vi xend-config.sxp

Look for the entry that contains (network-script network-bridge) and change it so that it will become (network-script br-wrapper_script). The config file call our own wrapper script instead of the default network-bridge script.

After the necessary modifications, restart the Xen daemon by entering rcxend start at the terminal. Check if our bridges were created by using ifconfig:

Once, you see xenbr0 and xenbr1 then you are good to go.

Step 4: Utilizing multiple bridges for the Xen DomU
Xen DomUs can be created through YAST using the virtualization tools.

If “Create Virtual Machines” and “Virtual Machine Manager” is not present, click on Install Hypervisor and Tools. However, if you’ve installed Xen beforehand, you’d have these tools already.

To utilize the multiple bridges, you’ll need to make some side steps in the workflow when you create your virtual machine. Make sure that when you reach the virtual machine summary, click on “Network Adapters”.

Create the necessary number of paravirtualized NICs. In our case we need two.

Make sure that each virtual NIC will be linked to the correct bridge (previously created). Your virtual NIC 0 must be linked to xenbr0, and virtual NIC 1 will be linked to xenbr1.

Exit the Network Parameters workflow and continue with your virtual machine installation.

More info at:
SuSE Linux Enterprise Server 10 VM Network Configuration Examples by Glen Davis (Novell)
NIC Bonding with Xen Virtualization by Joe Harmon, Jim Short
Xen Source Official Site

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