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 (as shown in the following table). If the next header is a transmission control
protocol (TCP) or user datagram protocol (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.
The following lists the Next Header field values.
Value Description
0Hop-by-Hop option header
4IPv4
6TCP
8Exterior 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 table is not a comprehensive list of Next Header field values. For a complete and current
listing, refer to the Internet Assigned Numbers Authority (IANA) web page.
Hop Limit (8 bits)The Hop Limit field shows the number of hops remaining for packet processing. In IPv4, this is known as
the Time to Live (TTL) field and uses seconds rather than hops.
Each time the packet moves through a forwarding router, this field decrements by 1. If a router receives a
packet with a Hop Limit of 1, it decrements it to 0 (zero). The router discards the packet and sends an
ICMPv6 message back to the sending router indicating that the Hop Limit was exceeded in transit.
458 IPv6 Addressing