Table of contents
Basic header of IPV6
IPV6 still supports connectionless transmission, but the protocol data unit PDU is called a packet, and some textbooks also use the name datagram
The main changes introduced by IPv6:
1. Larger address space increased from 32 bits to 128 bits
2. Extended address hierarchy
3. Flexible header format
4. Improved options: IPv6 allows datagrams to contain control information with options, and the options are placed in the payload
5. Allow the protocol to continue to expand
6. Support plug and play
7. Support resource pre-allocation: support real-time video and other requirements, and ensure a certain bandwidth and delay application
8. Change the header to 8-byte alignment: the length of the header must be an integer multiple of 8 bytes, the original IPv4 header is 4-byte alignment
Traffic class: distinguish the class or priority of different IPv6 datagrams (traffic in Lenovo operating system~)
Flow label: 20-bit flow is a series of datagrams from a specific source to a specific destination on the Internet. The routers on the path passed by the flow guarantee the specified quality of service. All datagrams belonging to the same flow have the same flow label
Payload length: 16 bits specify the number of bytes of the IPv6 datagram except the basic header (all extended headers are counted in the payload), the maximum value is 64KB
Next header: 8 bits equivalent to the protocol field or optional field of IPv4
Hop limit: The 8-bit source station sets the hop limit when the datagram is sent out. When the router forwards the datagram, the value in the hop limit field is -1. When the value of the hop limit is 0, the data report discarded
Source address and destination address: both are 128 bits
Extension header for IPv6 datagrams
IPv6 puts the function of options in the original IPv4 header in the extension header, and leaves the extension header to the hosts at the source station and the destination station at both ends of the path for processing, and the routers that the datagram passes through do not process these extension headers, which greatly improves Router Processing Efficiency
Six extension headers
Six extension headers are defined in RFC 2460 Extension
header "Next Header" field value
1. Hop-by-hop option 0
2 Routing selection 43
3. Fragmentation 44
4. Authentication 50
5. Encapsulation security payload 51
6 .Destination option 60
IPv6 address
There are three basic types of destination addresses: unicast, multicast, and anycast
IPv6 adopts the colon hexadecimal notation, which allows to omit the 0 in front of the number, which is beneficial to write 0000 as 0
Zero compression is allowed, such as 0:0:0:0 is written as:: and any address can only use zero compression once
Transition from IPv4 to IPv6
Adopt a step-by-step evolution approach, and at the same time must make the installed IPv6 system backward compatible
