Native OS bridge configuration
==============================

The traditional "network-bridge" script attempts to modify existing active
network interfaces to enable bridging. For non-trivial network configurations
though this can be error prone, and the temporary disruption to network
connectivity can upset some applications.  This document outlines how to
configure bridging using an OS' native network configuration files.

Disabling Xen's network scripts
-------------------------------

The first step is to check XenD's network bridge is disabled by
editing /etc/xen/xend-config.sxp and changing the line

 (network-script network-bridge)

To be

 (network-script /bin/true)


Fedora/RHEL Bridging
====================

This outlines how to setup bridging using standard network initscripts
present in Fedora or RHEL distros and their derivatives


Disabling NetworkManager
------------------------

As of time of writing (Fedora 11) NetworkManager does not support bridging,
so it is neccessary to disable it, and revert to "classic" network initscripts

 # chkconfig NetworkManager off
 # chkconfig network on
 # service NetworkManager stop
 # service network start

NB, as an alternative to turning off NetworkManager, you can also add a line
"NM_CONTROLLED=no" to the ifcfg-XXX scripts below

Creating network initscripts
----------------------------

In the /etc/sysconfig/network-scripts directory it is necccessary to create
2 config files. The first (ifcfg-eth0) defines your physical network interface,
and says that it will be part of a bridge:

# cat > ifcfg-eth0 <<EOF
DEVICE=eth0
HWADDR=00:16:76:D6:C9:45
ONBOOT=yes
BRIDGE=br0
EOF

Obviously change the HWADDR to match your actual NIC's address. You may also
wish to configure the device's MTU here using e.g. MTU=9000.

The second config file (ifcfg-br0) defines the bridge device:

# cat > ifcfg-br0 <<EOF
DEVICE=br0
TYPE=Bridge
BOOTPROTO=dhcp
ONBOOT=yes
DELAY=0
EOF

WARNING: The line TYPE=Bridge is case-sensitive - it must have uppercase
'B' and lower case 'ridge'

After changing this restart networking (or better still reboot)

 # service network restart


The final step is to configure iptables to allow all traffic to be
forwarded across the bridge

# echo "-I FORWARD -m physdev --physdev-is-bridged -j ACCEPT" > /etc/sysconfig/iptables-forward-bridged
# lokkit --custom-rules=ipv4:filter:/etc/sysconfig/iptables-forward-bridged
# service libvirtd reload

Alternatively, you can prevent bridged traffic getting pushed through
the host's iptables rules completely. In /etc/sysctl.conf add

 # cat >> /etc/sysctl.conf <<EOF
 net.bridge.bridge-nf-call-ip6tables = 0
 net.bridge.bridge-nf-call-iptables = 0
 net.bridge.bridge-nf-call-arptables = 0
 EOF
 # sysctl -p /etc/sysctl.conf

You should now have a "shared physical device", to which guests can be
attached and have full LAN access

 # brctl show
 bridge name     bridge id               STP enabled     interfaces
 br0             8000.000e0cb30550       no              eth0



Debian/Ubuntu Bridging
=======================

This outlines how to setup bridging using standard network interface config files
on Debian / Ubuntu distributions and their derivatives

Disabling NetworkManager
------------------------

Stop network manager

 sudo /etc/dbus-1/event.d/26NetworkManagerDispatcher stop
 sudo /etc/dbus-1/event.d/25NetworkManager stop

Create two files with only the word 'exit' in them. These files are:

 /etc/default/NetworkManager
 /etc/default/NetworkManagerDispatcher


Altering the interface config
-----------------------------

First take down the interface you wish to bridge

 ifdown eth0

Edit /etc/network/interfaces and find the config for the physical
interface, which looks something like

 allow-hotplug eth0
 iface eth0 inet static
        address 192.168.2.4
        netmask 255.255.255.0
        network 192.168.2.0
        broadcast 192.168.2.255
        gateway 192.168.2.2

Remove the 'allow-hotplug eth0' line, replacing it with 'auto br0',
and change the next line with iface name to 'br0', so it now starts
with

 auto br0
 iface br0 inet static

And then define the interface as being a bridge and specify its ports

       bridge_ports eth0
       bridge_stp off
       bridge_maxwait 5

The complete config should now look like

 auto br0
 iface br0 inet static
         address 192.168.2.4
         netmask 255.255.255.0
         network 192.168.2.0
         broadcast 192.168.2.255
         gateway 192.168.2.2
         bridge_ports eth0
         bridge_stp off
         bridge_maxwait 5

The interface can now be started with

 ifup br0

Finally add the '/etc/sysctl.conf' settings

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

And then load the settings with

 sysctl -p /etc/sysctl.conf


You should now have a "shared physical device", to which guests
can be attached and have full LAN access

 # brctl show
 bridge name     bridge id               STP enabled     interfaces
 br0             8000.000e0cb30550       no              eth0


Other operating systems / distributions
=======================================

[...send patches to this file with instructions....]