Knowledge about IPv6 data packets (1)

As the basis of the network, there are currently two types of Protocols: IPv4 and IPv6. To accommodate more information, we have expanded the network address, which is why IPv6 was born. So here we will introduce its structure, that is, the technical knowledge of IPv6 data packets.

Technical Information Overview

An IPv6 packet consists of a 40-byte fixed length IPv6 packet header, an extended packet header, and an upper-layer protocol data unit.

The segment headers in the IPv6 package extension headers are described in detail below.

The unsegmented parts include IPv6 headers, Hop-by-Hop option headers, destination option headers are suitable for transit routers), and route headers. The segmented parts include: authentication headers, ESP protocol headers, destination option headers apply to final destinations), and upper-layer protocol data units. However, in IPv6, only the source node can segment the load, and the IPv6 super large package cannot use this service.

The following describes IPv6 addressing, routing, and automatic configuration.

IPv6 packet: packet header

The length of an IPv6 packet header is fixed to 40 bytes, removing all the options in IPv4, including only eight required fields. Therefore, although the IPv6 address length is four times that of IPv4, the length of an IPv6 packet header is only twice the length of an IPv4 packet header.

Each field is Version 4, and the IP protocol Version number is 6.

TrafficeClass Communication Class): 8-bit, indicating the IPv6 data stream communication class or priority. Function is similar to the IPv4 service type TOS) field.

FlowLabel stream flag): 20-bit, new IPv6 field, marking the data stream that requires special processing by the IPv6 router. This field is used for communication that has special requirements on the quality of service of the connection, such as real-time data transmission such as audio or video. In IPv6, different data streams can exist between the same source and sink, and are differentiated by non-"0" stream tags. If special processing is not required for the vro, the value of this field is set to "0 ".

PayloadLength): 16-Bit Load Length. The Load Length includes the expansion header and upper PDU, and a maximum of 65535 bytes of load length can be expressed by 16 bits. If the number of nodes exceeds this limit, set this field value to "0" and use the JumboPayload option in the Hop-by-Hop option of the expansion header.

Next packet header of NextHeader): an 8-bit header that identifies the packet header type following the IPv6 Header, for example, an extended header) or a transport layer protocol header such as TCP, UDP, or ICMPIPv6 ).

Maximum number of hop segments): 8 bits, similar to TTL of IPv4. Different from IPv4, the packet life cycle is limited by the number of packets forwarded between routers. Each time a packet is forwarded, this field is reduced by 1, and the packet is discarded when it is reduced to 0.

SourceAddress source address): 128 bits, the sender's host address.

DestinationAddress): 128 bits. In most cases, the destination address is the destination address. However, if there is a route extension header, the destination address may be the next router interface in the sender's route table.

IPv6 packet: Extended packet header

An important improvement of the original IPv4 header in the IPv6 Header design is to remove all optional fields from the IPv6 Header and place them in the extension header. In addition to the Hop-by-Hop option extension header, other extension headers are not checked or processed by the Intermediate router, which improves the performance of the router in processing IPv6 groups with options.

Generally, a typical IPv6 package does not have an extension header. The sender adds one or more extension headers only when the router or target node needs to perform some special processing. Different from IPv4, IPv6 extension headers can have any length and are not limited to 40 bytes, so that new options can be expanded in the future. This feature and option processing method allow IPv6 options to be truly utilized. However, to improve the performance of the processing option header and transport layer protocol, the expansion header is always an integer multiple of the 8-byte length.

At present, RFC2460 defines the following six IPv6 extension headers: Hop-by-Hop) optional headers, destination option headers, route headers, segment headers, authentication headers, and ESP protocol headers: