This RFC, part of a pair, defines the requirements for Internet host software, focusing on the communication protocol layers: link layer, IP layer, and transport layer. It is intended to guide vendors, implementors, and users of Internet communication software. The document emphasizes the importance of robustness, error logging, and configuration in host software. It also discusses specific issues such as trailer protocol negotiation, Address Resolution Protocol (ARP), and encapsulation for Ethernet and IEEE 802 networks. The document provides detailed requirements for each layer, including the need for multihoming support and the handling of gateway functions. It aims to ensure that Internet hosts can interoperate robustly and effectively across diverse paths.This RFC, part of a pair, defines the requirements for Internet host software, focusing on the communication protocol layers: link layer, IP layer, and transport layer. It is intended to guide vendors, implementors, and users of Internet communication software. The document emphasizes the importance of robustness, error logging, and configuration in host software. It also discusses specific issues such as trailer protocol negotiation, Address Resolution Protocol (ARP), and encapsulation for Ethernet and IEEE 802 networks. The document provides detailed requirements for each layer, including the need for multihoming support and the handling of gateway functions. It aims to ensure that Internet hosts can interoperate robustly and effectively across diverse paths.