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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)
                     9  IPv6 Datagram Encapsulation and Formatting

Previous Topic/Section
IPv6 Datagram Overview and General Structure
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
IPv6 Datagram Extension Headers
Next Topic/Section

IPv6 Datagram Main Header Format
(Page 2 of 3)

IPv6 Next Header Field

The Next Header field is one of the most important additions to the IPv6 datagram format. When an IPv6 datagram uses extension headers, this field contains an identifier for the first extension header, which in turn uses its own Next Header to point to the next header, and so on. The last extension header then references the encapsulated higher-layer protocol—since the higher-layer protocol’s header appears at the start of the IPv6 Data field, it is like the “next header” to the device receiving the datagram. For some folks this is a bit tough to see conceptually; much more detail on how the field works (including a useful illustration) can be found in the next topic, describing extension headers. Some of the most common values for Next Header in IPv6 are shown in Table 69.


Table 69: Common IPv6 Next Header Values

Value (Hexadecimal)

Value (Decimal)

Protocol / Extension Header

00

0

Hop-By-Hop Options Extension Header
(note that this value was “Reserved” in IPv4)

01

1

ICMPv4

02

2

IGMPv4

04

4

IP in IP Encapsulation

06

6

TCP

08

8

EGP

11

17

UDP

29

41

IPv6

2B

43

Routing Extension Header

2C

44

Fragmentation Extension Header

2E

46

Resource Reservation Protocol (RSVP)

32

50

Encrypted Security Payload (ESP) Extension Header

33

51

Authentication Header (AH) Extension Header

3A

58

ICMPv6

3B

59

No Next Header

3C

60

Destination Options Extension Header


The total length of the main IPv6 header format is 40 bytes. This is double the size of the IPv4 header without options, largely because of the extra 24 bytes needed for the monstrous IPv6 addresses. There are only 8 bytes of non-address header fields in the IPv6 main header, compared to 12 in the IPv4 header.


Previous Topic/Section
IPv6 Datagram Overview and General Structure
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
IPv6 Datagram Extension Headers
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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