IP Header

This section reviews the IPv4 header. It describes the fields and compares them to the fields in the IPv6 header.

IPv4 Header Format

IP packets are carried over link-layer technologies such as Ethernet (10 Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1000 Mbps), Frame Relay, and many others. Each link-layer technology family has its own link-layer frame that carries IP packets. As shown in Figure 2-1, an IP packet is carried between the frame header and frame trailer of a link-layer frame. An IP packet has two fundamental components:

  • IP header— The IP header contains many fields that are used by routers to forward the packet from network to network to a final destination. Fields within the IP header identify the sender, receiver, ...

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