After getting Ethernet Bonding working (see my previous post) I tried to get it going with a bridge for Xen.
I used the following in /etc/network/interfaces to configure the bond0 device and to make the Xen bridge device xenbr0 use the bond device:
iface bond0 inet manual
pre-up modprobe bond0
pre-up ifconfig bond0 up
hwaddress ether 00:02:55:E1:36:32
slaves eth0 eth1
iface xenbr0 inet static
pre-up ifup bond0
But things didn’t work well. A plain bond device worked correctly in all my tests, but when I had a bridge running over it I had problems every time I tried pulling cables. My test for a bond is to boot the machine with a cable in eth0, then when it’s running switch the cable to eth1. This means there is a few seconds of no connectivity and then the other port becomes connected. In an ideal situation at least one port would work at all times – but redundancy features such as bonding are not for an ideal situation! When doing the cable switching test I found that the bond device would often get into a state where it every two seconds (the configured ARP ping time for the bond) it would change it’s mind about the link status and have the link down half the time (according to the logs – according to ping results it was down all the time). This made the network unusable.
Now I have deided that Xen is more important than bonding so I’ll deploy the machine without bonding.
One thing I am considering for next time I try this is to use bridging instead of bonding. The bridge layer will handle multiple Ethernet devices, and if they are both connected to the same switch then the Spanning Tree Protocol (STP) is designed to work in this way and should handle it. So instead of having a bond of eth0 and eth1 and running a bridge over that I would just bridge eth0, eth1, and the Xen interfaces.