802.1p priority

802.1p priority lies in the Layer 2 header. It applies to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2.

Figure 26: An Ethernet frame with an 802.1Q tag header

As shown in Figure 26, the 4-byte 802.1Q tag header consists of the 2-byte tag protocol identifier (TPID) and the 2-byte tag control information (TCI). The value of the TPID is 0x8100. Figure 27 shows the format of the 802.1Q tag header. The Priority field in the 802.1Q tag header is called the "802.1p priority", because its use is defined in IEEE 802.1p. Table 12 shows the values for 802.1p priority.

Figure 27: 802.1Q tag header

Table 12: Description on 802.1p priority

802.1p priority (decimal)

802.1p priority (binary)

Description

0

000

best-effort

1

001

background

2

010

spare

3

011

excellent-effort

4

100

controlled-load

5

101

video

6

110

voice

7

111

network-management