The IPv6 Packet Header and SRX Series and J-series Devices Overview

This topic identifies the IP version 6 (IPv6) packet header and its extensions and options.

Every IPv6 packet at a minimum has a basic packet header, 40 bytes (320 bits) long. They optionally may have extension headers.

For IPv6 packets, flow processing parses the extension headers and transport layer headers in the following way:

If the software encounters a TCP, a UDP, an ESP, an AH, or an ICMPv6 header, it parses the header and assumes that the packet payload corresponds to the specified protocol type.
If the software encounters a hop-by-hop header, a routing and destination header, or a fragment header, it continues to parse the next extension header.
If it encounters the no-next-header extension header, the software detects that the packet is that of an unknown protocol (protocol equals 0).
For other extension headers, the software parses the header and identifies the packet as belonging to the protocol indicated by the extension header.