Packet Format
Figure 9.8 shows the format of an ARP packet. The names of the fields are self-
explanatory. The hardware type field defines the type of the link-layer protocol; Ethernet
is given the type 1. The protocol type field defines the network-layer protocol: IPv4 pro-
tocol is (0800)16. The source hardware and source protocol addresses are variable-length
fields defining the link-layer and network-layer addresses of the sender. The destination
hardware address and destination protocol address fields define the receiver link-layer
and network-layer addresses. An ARP packet is encapsulated directly into a data-link
frame. The frame needs to have a field to show that the payload belongs to the ARP and
not to the network-layer datagram.