Usually I get my official address by DHCP, but apparently the ISP messed up his DHCP servers - suddenly I had an "internal" 192.168.x.y address also on the external Internet interface of my router.
Of course it happened while I was playing City Of Heroes - so I got kicked from the server
But at least I immediately recognized the problem.
For now I changed my router's setting from DHCP to the fixed IP address I had previously - and it seems to work.
I will try to solve this with my ISP tomorrow - until then I cannot say how stable my address will be....
