LAN $1$ is a cellular configuration. The Gateway router can also be configured to support the NAT. The central office server supports DHCP for the internal LAN. All gateway routers connect via a serial link and use IPv$4$ public IP addresses which can be set as a static address. The IPv$4$ public addresses should be $172\mathrm{.}0\mathrm{.}10\mathrm{.}1$; $172\mathrm{.}0\mathrm{.}20\mathrm{.}1$; and, $172\mathrm{.}0\mathrm{.}30\mathrm{.}1,$ for LAN$1,$ LAN$2,$ and LAN$3,$ respectively.