Discovered on transplanting mirrored SATA disks to a new case, that by default udev now has persistent network device naming. I was expecting eth0 and eth1 and got eth2 and eth3.

Spotted as kern.log has:
udev: renamed network interface eth0 to eth2
udev: renamed network interface eth1 to eth3

In particular the file /etc/udev/rules.d/70-persistent-net.rules showed what was happening.

Thanks to:
http://cs.thefoleyhouse.co.uk/blogs/karl/archive/2006/09/28/SuSE-10.1-_2200_eth0-renamed-to-eth1_2200_.aspx

Sometimes I yearn for a simpler times when device files were simply files...