BBB File /etc/udhcpd.conf
This file determines what addresses are issued when the WiFi is operating in AP mode (client mode doesn't need a DHCP server).
If the BBB is plugged into a wired network (which will only occur at home), then the subnet/router/dns options come into play. If the BBB is acting as a standalone AP, they're inert.
The comment stuff is when the USB Gadget thing is operational. Since that's compiled out of my kernel, it's not applicable.
#start 192.168.7.1 #end 192.168.7.1 #interface usb0 #max_leases 1 #option subnet 255.255.255.252 start 192.168.17.2 end 192.168.17.254 interface wlan0 option subnet 255.255.255.0 option router 172.16.0.128 option dns 172.16.0.1