Reference Guide

548 | IPv6 Routing
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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 header 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 26-1). 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 26-1. Next Header field values
Value Description
0 Hop-by-Hop option header
4 IPv4
6 TCP
8 Exterior Gateway Protocol (EGP)
41 IPv6
43 Routing header
44 Fragmentation header
50 Encrypted Security
51 Authentication header
59 No Next Header
60 Destinations option header
Note: This is not a comprehensive table of Next Header field values. Refer to the Internet
Assigned Numbers Authority (IANA) web page at http://www.iana.org/assignments/
protocol-numbers for a complete and current listing.