This has been somewhat of an adventure with regard to IP addresses, multi-booting, NetworkManager or network, etc. For basically all of my Linux computers, one of them booting 4-5 different distros, some using NetworkManager and some using network / static IP, I've had boot issues. They were all 192.x.x.x addresses. The new modem is using a 10.x.x.x scheme. I didn't bother changing the modem so first boot with the different distros is getting me long timeouts with sendmail, sm-client and mount.nfs. This is because the boxes cannot get a valid IP address now and
the fact that /etc/hosts has the 192.x.x.x addresses hard coded. Fortuanely, in most cases I'm able to mount the partition for the non-booting distro, make changes and reboot. For the 2 headless standalones I've had to attach keyboard and monitor and wait for the timeouts before making changes locally. I've also had to change /etc/exports on the server and in some cases /etc/resolv.conf.
Imagine if I were a Linux admin and had to deal with this on hundreds on networked boxes. Woah!