Quality of Service and performance characterization of IPv6 relative to IPv4

II.5.4 Comparison of IPv4 and IPv6 Headers

Fields of the IPv4 Header	Fields of the IPv6 Header	Comparison of IPv4 and IPv6 Headers
Version (4-bit)	Version (4-bit)	Same function but the IPv6 header contains a new value.
Header length (4-bit)	--	Removed in IPv6. The basic IPv6 header always has 40 octets.
Type of service (8-bit)	Traffic class (8-bit)	Same function for both headers.
--	Flow label (20-bit)	New field added to tag a flow for IPv6 packets.
Total length (16-bit)	Payload length (16-bit)	Same function for both headers.
Identification (16-bit)	--	Removed in IPv6 because fragmentation is handled differently in IPv6.
Flags (3-bit)	--	Removed in IPv6 because fragmentation is handled differently in IPv6.
Fragment offset (13-bit)	--	Removed in IPv6 because fragmentation is handled differently in IPv6.
Time to live (8-bit)	Hop limit (8-bit)	Same function for both headers.
Protocol number (8-bit)	Next header (8-bit)	Same function for both headers.
Header checksum (16-bit)	--	Removed in IPv6. Link-layer technologies and upper-layer protocols handle checksum and error control.
Source address (32-bit)	Source address (128-bit)	Source address is expanded in IPv6.
Destination address (32-bit)	Destination address (128-bit)	Destination address is expanded in IPv6.
Options (variable)	--	Removed in IPv6. The way to handle this option is different in IPv4.
--	Extension headers	New way in IPv6 to handle Options fields, fragmentation, security, mobility, Loose Source Routing, Record Route.^24(*)

Table 2: Comparison of IPv4 header and IPv6 Header

Source: http://www.ciscopress.com/articles/article.asp?p=31948&seqNum=1&rl=1, (August 23, 2006)

II.5.5 New Extension Headers

The IPv6 specification currently defines 6 Extension Headers:

· Routing Header - Similar to the source routing options in IPv4. Used to mandate a specific routing.

· Authentication Header (AH) - A security header which provides authentication and integrity.

· Encapsulating Security Payload (ESP) Header - A security header which provides authentication and encryption.

· Fragmentation Header - The Fragmentation Header is similar to the fragmentation options in IPv4.

· Destination Options Header - This header contains a set of options to be processed only by the final destination node. Mobile IPv6 is an example of a destination Options Header.

· Hop-by-Hop Options Header - A set of options needed by routers to perform certain management or debugging functions.

* ²⁴ http://www.ciscopress.com/articles/article.asp?p=31948&seqNum=1&rl=1, (August 22, 2006)