Specifically, setting up bridged networking under Linux to enable a KVM virtual machine. I had this working just fine up until the point where I upgraded this server to hardy, whereupon everything fell apart. Thanks to the folks on freenode.net/#kvm, I discovered that my interface configuration was broken.

To summarise, I have:

1 Physical network interface
3 IP addresses (2 of which are assigned to the host OS, one to the guest VM).

It turns out that if you have a bridge set up on the interface, assigning a second IP address should be an alias to the bridge, not the first IP’s interface.

Initially, I had something like this:

auto eth0
iface eth0 inet manual

auto br0
iface br0 inet static
        address xxx.xx.xxx.xxx
        netmask xxx.xxx.xxx.xxx
        broadcast xxx.xx.xxx.xxx
        gateway xxx.xx.xxx.xxx
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

auto eth1
iface eth0:1 inet static
        address xxx.xx.xxx.xxx
        netmask xxx.xxx.xxx.xxx
        broadcast xxx.xx.xxx.xxx
        gateway xxx.xx.xxx.xxx

There are several things wrong with this. The first is that the gateway should not be specified on the second interface. It wasn’t a problem in gutsy, but hardy did things somewhat differently, with the result that networking was completely disabled on reboot. IPMI to the rescue, fortunately.

Having fixed that, things seemed to work ok, but I was informed that the secondary IP should more accurately be assigned to the bridge, like this:

auto eth0
iface eth0 inet manual

auto br0
iface br0 inet static
        address xxx.xx.xxx.xxx
        netmask xxx.xx.xxx.xxx
        broadcast xxx.xxx.xxx.xxx
        gateway xxx.xx.xxx.xxx
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

iface br0:0 inet static
	address xxx.xx.xxx.xxx
        netmask xxx.xxx.xxx.xxx

One swift edit, and things are working swimmingly well. One of the folks on freenode #kvm hinted that he might spend some time soon writing some, you know, documentation on this process, so in future it won’t require reading dozens of blog posts (like this one) to understand what the hell you’re doing. Sounds like a great plan to me. The most defining characteristic of the current documentation is that it’s almost as shallow as Paris Hilton, and decidedly less thick too.

Last night, Monday 23rd December, I went to bed and started experiencing my usual coughing fit that I’ve been getting when going to bed. Only this time, it wouldn’t stop. Sarah got all concerned and insisted we go to the ER to get it checked out. I wasn’t a huge fan of this idea, it being 1am and all, and me not wanting to have yet more needles stuck in me, but I eventually grudgingly agreed to go.

We got there, explained the symptoms to the doctor, and he sent me off for a lung scan again (same as the one I had before). Oddly enough, there was no sign of the clot in my right lung, but there were 2 new clots in my left lung. Once again, they admitted me to the hospital.

At this point, I think my exact words were.. “Oh well, at least the year can’t get any worse than this”. Someone needs to hit me next time I say that.

After admitting me, a hematologist came by and talked to me and said that he was concerned that I was generating new clots. It seems having Factor V Leiden shouldn’t be enough to just cause this to happen randomly, so he wanted to do a cat scan. They made me drink these 2 jars of stuff with the consistency of wallpaper paste. I had a hard time keeping it down, but it was ok in the end.. The cat scan revealed.. swollen lymph nodes! Which means.. I probably have cancer (lymphoma). I’m out of the hospital now, but I’m going back on Friday when they’ll take a biopsy of one of my lymph nodes and find out for certain if this is the case. It seems likely, since this would also explain the sudden onslaught of clots.

On the plus side, this does mean that I have something which can be cured, and hopefully won’t have to spend the rest of my life on the blood thinning drugs. I guess we’ll see..