TCP/IP Tutorial and Technical Overview - IBM Redbooks

vers
Figure 9-3 IPv6 packet containing multiple extension headers
The length of each header varies, depending on type, but is always a multiple of
8 bytes. There are a limited number of IPv6 extension headers, any one of which
can be present only once in the IPv6 packet (with the exception of the
Destination Options Header, 60, which can appear more than once). IPv6 nodes
that originate packets are required to place extension headers in a specific order
(numeric order, with the exception of 60), although IPv6 nodes that receive
packets are not required to verify that this is the case. The order is important for
efficient processing at intermediate routers. Routers will generally only be
interested in the hop-by-hop options and the routing header. After the router has
read this far, it does not need to read further in the packet and can immediately
334 TCP/IP Tutorial and Technical Overview
0 4 12 16 24 31
traffic class
payload length
source address
destination address
nxt hdr: 43 hdr length
hop-by-hop options
nxt hdr: 44 hdr length
routing information
flow label
nxt hdr: 0 hop limit
nxt hdr: 51 reserved fragment offset M
fragment identification
nxt hdr: 6 hdr length
authentication data
TCP header and data