Packet Marking

Packet Marking

Packet marking involves the manipulation of a 1-byte (8-bit) field within the IP packet header called the type of service, or ToS, byte. Network devices use this byte of data to determine the relative priority and handling requirements of incoming packets. The ToS byte contains data for one of two widely adopted mechanisms:

In either case, a series of bits is flagged within the ToS byte to identify the relative priority and handling requirements of the packet. Accurate handling of marked packets can be ensured only when adjacent devices are in agreement about how packets are handled based on their marking. Figure 3-10 shows the IP packet header containing the ToS byte.

Figure 3-10. IP Packet Header Containing ToS Byte

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