VMware guest networking just stopped working [solved]

I just spent some time figuring out why the hell VMware guest networking (all virtual machines, Windows and Linux) just stopped working! I couldn’t remember to have anything changed except a kernel update on the host system, but the VMware kernel module compiled fine against it, and also the VMware services are running as they should.

I’m usually configuring my VMs to have access to the outside world via VMware’s NAT feature, which always worked fine for me.
While analysing the problem, I found out that the default NAT network address is 10.0.0.0 (on interface vmnet8). Now guess what happened! Some tomfool over at my ISP configured a host to have the IP address 10.0.0.1, which is handed out by the VMware DHCP service as the default gateway to all VMs. I found that out by running a traceroute on 10.0.0.1, which gave me several hops to a host, probably belonging to my ISP. The workaround is simple: just add the network address of the NAT interface (vmnet8) on the host. This can be done with vmware-config.pl on Linux hosts, and I’m sure there is also a way to do that on Windows hosts. I set it to a 192.168.x.y address, which works well now.
I really wonder how this could have happend – I always believed that the 10.x.y.z addresses aren’t being routed! Then why is this D-Link router AND the DSL router/modem combo in this flat routing requests to 10.0.0.1 to the Internet? Anyone?