4 位元優先欄位說明用來表示 RFC 1883,但是 RFC 1883 已不被 RFC 2460 採用 (Solaris 8 應用 RFC 2460)。 因此,優先欄位已由 8 位元的「通訊類別」欄位所取代。優先區段也應該用以下的「通訊類別」區段取代。
Originating nodes and forwarding routers can use the 8-bit Traffic Class field in the IPv6 header to identify and distinguish between different classes or priorities of IPv6 packets.
The following general requirements apply to the Traffic Class field.
The service interface to the IPv6 service within a node must provide a means for an upper-layer protocol to supply the value of the Traffic Class bits in packets originated by that upper-layer protocol. The default value must be zero for all 8 bits.
Nodes that support a specific use of some or all of the Traffic Class bits can change the value of those bits in packets that they originate, forward, or receive, as required for that specific use. Nodes should ignore and leave unchanged any bits of the Traffic Class field for which they do not support a specific use.