if your connection require authentication, like pppoe, you can just disable the dhcp on the modem and use statis addresses between the modem and the pi. then th

if your connection require authentication, like pppoe, you can just disable the dhcp on the modem and use statis addresses between the modem and the pi. then the actual connection will be established by the pi via pppoe and the only DHCP would be the pi when it is up. As for the security implications, i agree.. It surely is a crappy design for the network but it can be done..