Gateways implement internet protocol to forward datagrams between networks. Gateways also implement the Gateway to Gateway Protocol (GGP) [7] to coordinate routing and other internet control information.
In a gateway the higher level protocols need not be implemented and the GGP functions are added to the IP module.
+-------------------------------+ | Internet Protocol & ICMP & GGP| +-------------------------------+ | | +---------------+ +---------------+ | Local Net | | Local Net | +---------------+ +---------------+ Gateway Protocols Figure 3.