Name
Protocol Address Length
Synopsis
Specifies the length (in bytes) of the higher-level protocol address found in the Source and Destination Protocol Address fields. For IP, this value is always 4 (32 bits / 8 = 4 bytes).
- Size
Eight bits.
- Notes
ARP can be used with many different higher-level protocols (ARP isn’t restricted to IP), and since each higher-level protocol uses different addressing mechanisms (IP addresses are considerably different from IPX and DECnet addresses), this field is required in order to make sense of the Source and Destination Protocol Address fields further in the ARP packet.
When IPv4 is specified in the Protocol Type field, the value of the Protocol Address Length field is always 4, since IP addresses are 32 bits (four bytes) long.
- Capture Sample
In the capture shown in Figure 3.12, the Protocol Address Length field is set to hexadecimal 04, indicating that the Source and Destination Protocol Address fields are four bytes (or 32 bits) long, the norm for IP.
Figure 3.12. The Protocol Address Length field- See Also
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