I'm writing this note because of a very frustrating behaviour in OpenSUSE that resets or disconnects a manually set static IP number after a short period of time (after around a minute or so). I couldn't find anything related to this by Googling...

Edit the file /etc/sysconfig/network/ifcfg-<device>

BOOTPROTO='static'
IPADDR='10.0.0.1/24'
STARTMODE='nfsroot'

STARTMODE is the particular parameter to get right - yast2 normally substitutes 'auto' here, which is the cause of the problem.

Some information can be found in the file /etc/sysconfig/network/ifcfg.template.