Switch/Router Architectures

Appendix BIPv4 PACKET

B.1 Introduction

IP (i.e., IPv4 and IPv6) is a network layer protocol that provides connectionless services to upper-layer protocols (e.g., TCP (Transmission Control Protocol), UDP (User Datagram Protocol), Internet Control Message Protocol (ICMP), Internet Group Management Protocol (IGMP), Open Shortest Path First (OSPF)). The connectionless service is implemented with the basic unit of transport being the datagrams (frequently referred to as packets) that contain the source and destination IP addresses of end-user points and other parameters needed for protocol operation.

The IP layer relies on the underlying network infrastructure for transporting the IP datagrams (packets). This means that IP datagrams are encapsulated (in some cases after segmentation into smaller units) by the frames of the underlying network such as Ethernet, ATM (Asynchronous Transfer Mode), and SONET/SD.H (Synchronous Optical Network/Synchronous Digital Hierarchy). Regardless of the physical layer protocol mix, maximum transmission unit (MTU) sizes of interfaces and speed differences of the links in the underlying networks, the IP layer translates these different layer networks into a common logical IP network that is independent of physical characteristics and differences.

The upper-layer protocols such as TCP, UDP, ICMP, IGMP, and SCTP (Stream Control Transmission Protocol) need not be aware of the hardware, encapsulation methods, and other characteristics of the underlying ...