ipv6 header...

turn on ipv6 between two routers, use ospf on the interfaces and look at a header cap just like Iljitsch said... how do you pronounce that? ill-jitch?

as jitchy says, the header length is no longer required because the ipv6 header is always 40 bytes long... there is comfort in that...

according to rfc2460:

   Version              4-bit Internet Protocol version number = 6.

   Traffic Class        8-bit traffic class field.  See section 7.

   Flow Label           20-bit flow label.  See section 6.

   Payload Length       16-bit unsigned integer.  Length of the IPv6
                        payload, i.e., the rest of the packet following
                        this IPv6 header, in octets.  (Note that any
                        extension headers [section 4] present are
                        considered part of the payload, i.e., included
                        in the length count.)

   Next Header          8-bit selector.  Identifies the type of header
                        immediately following the IPv6 header.  Uses the
                        same values as the IPv4 Protocol field [RFC-1700
                        et seq.].

   Hop Limit            8-bit unsigned integer.  Decremented by 1 by
                        each node that forwards the packet. The packet
                        is discarded if Hop Limit is decremented to
                        zero.

the header checksum is gone and source and destination are painfully obvious, excepting being 4X as long... (32 v 128)

read this http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_9-3/ipv6_internals.html

or the last post for jitchy's v4/v6 comparison...

by virtue of less fields, no checksum, always 40 bytes, it is streamlined...

IPv6 no longer has a header checksum to protect the IP header, meaning that when a packet header is corrupted by transmission errors, the packet is very likely to be delivered incorrectly. However, higher-layer protocols should be able to detect these problems, so they are not fatal. Also, lower layers almost always employ a Cyclic Redundancy Check (CRC) to detect errors.