5. The Internet Protocol (IP)

5.1. Introduction

IP is the workhorse protocol of the TCP/IP protocol suite. All TCP, UDP, ICMP, and IGMP data gets transmitted as IP datagrams. IP provides a best-effort, connectionless datagram delivery service. By “best-effort” we mean there are no guarantees that an IP datagram gets to its destination successfully. Although IP does not simply drop all traffic unnecessarily, it provides no guarantees as to the fate of the packets it attempts to deliver. When something goes wrong, such as a router temporarily running out of buffers, IP has a simple error-handling algorithm: throw away some data (usually the last datagram that arrived). Any required reliability must be provided by the upper layers (e.g., TCP). IPv4 ...

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