486 | IPv6 Addressing
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Traffic Class (8 bits)
The Traffic Class field deals with any data that needs special handling. These bits define the packet priority
and are defined by the packet Source. Sending and forwarding routers use this field to identify different
IPv6 classes and priorities. Routers understand the priority settings and handle them appropriately during
conditions of congestion.
Flow Label (20 bits)
The Flow Label field identifies packets requiring special treatment in order to manage real-time data
traffic. The sending router can label sequences of IPv6 packets so that forwarding routers can process
packets within the same flow without needing to reprocess each packet’s head separately.
Payload Length (16 bits)
The Payload Length field specifies the packet payload. This is the length of the data following the IPv6
header. IPv6 Payload Length only includes the data following the header, not the header itself.
The Payload Length limit of 2 bytes requires that the maximum packet payload be 64 KB. However, the
Jumbogram option type Extension header supports larger packet sizes when required.
Next Header (8 bits)
The Next Header field identifies the next header’s type. If an Extension header is used, this field contains
the type of Extension header (Table 22-1). If the next header is a TCP or UDP header, the value in this field
is the same as for IPv4. The Extension header is located between the IP header and the TCP or UDP
header.
Note: All packets in the flow must have the same source and destination addresses.
Table 22-1. Next Header field values
Value Description
0 Hop-by Hop option header following
4 IPv4
6 TCP
8 Exterior Gateway Protocol (EGP)
41 IPv6
43 Routing header
44 Fragmentation header
50 Encrypted Security
51 Authentication header
