FIOS Router CLI and DHCP
I recently got Verizon FIOS service. The router Verizon provides is an Actiontec MI424WR. Verizon goes to some trouble to hide the Actiontec branding; but, for example, the Model Name field in the System Monitoring tab on mine says "MI424WR-GEN2".
In the advanced options you can turn on telnet access to the router. That gets you into a command line administration utility, which in turn will let you access a shell (via "system shell"). However I was unable to find a DHCP lease database in the filesystem. There was a /var/state/dhcp directory, but it was empty.
Some searching on the web turned up the fact that the Actiontec MI424WR runs a commercial Linux distro called OpenRG. More searching turned up an OpenRG Configuration Entries Guide. A bit more poking and I found that this command will dump out the DHCP lease database:
conf print dev/br0/dhcps/lease