Lecture
The technology of the TCP / IP stack was formed mainly in the late 1970s and since then the basic principles of the basic protocols, such as IP, TCP, UDP and ICMP, have not changed much. However, the computer world itself has changed significantly over the years, so long-overdue improvements in the TCP / IP stack technology have now become a necessity.
The main reasons for which a modification of the basic protocols of the TCP / IP stack is required are as follows.
For several years, the Internet community has been working on the development of a new specification for the basic protocol of the stack - the IP protocol. Many proposals have already been developed, from simple ones, which only provide for expansion of the IP address space, to very complex ones, which lead to a significant increase in the cost of implementing IP in high-performance (and so expensive) routers.
The main proposal for the modernization of the IP protocol is a proposal developed by the IETF group. It is now accepted to call its proposal version 6 - IPv6, and all other proposals are grouped under the name IP Next Generation, IPng.
In the IETF proposal, IPv6 leaves the basic principles of IPv4 unchanged. These include the datagram method of work, packet fragmentation, allowing the sender to set the maximum number of hops for their packets. However, in the details of the implementation of the IPv6 protocol there are significant differences from IPv4. These differences can be briefly described as follows.
IPv6 addressing
The destination and source addresses in IPv6 are 128 bits or 16 bytes long. Version 6 summarizes the special types of version 4 addresses in the following types of addresses:
As in the IPv4 version, addresses in the IPv6 version are divided into classes, depending on the value of several high-order bits of the address.
Most classes are reserved for future use. The most interesting for practical use is the class intended for Internet service providers, called Provider-Assigned Unicast .
The address of this class has the following structure:
010 | Identifier provider | Identifier subscriber | Identifier subnet | Identifier node |
Each Internet service provider is assigned a unique identifier that marks all the networks it supports. Next, the provider assigns unique identifiers to its subscribers, and uses both identifiers when assigning a block of subscriber addresses. The subscriber himself assigns unique identifiers to his subnets and nodes of these networks.
The subscriber can use the subnet technique used in the IPv4 version to further divide the subnet ID field into smaller fields.
The described scheme approximates the IPv6 addressing scheme to the schemes used in territorial networks, such as telephone networks or X.25 networks. The hierarchy of address fields will allow trunk routers to work only with older parts of the address, leaving the processing of less significant fields to subscriber routers.
The host ID field requires at least 6 bytes to be allocated in order to be used directly in the MAC addresses of the local networks in the IP addresses.
For compatibility with the IPv4 version addressing scheme, the IPv6 version has an address class that has 0000 0000 in the upper bits of the address. The lower 4 bytes of this class must contain an IPv4 address. Routers that support both versions of addresses must provide translation when sending a packet from a network that supports IPv4 addressing to a network that supports IPv6 addressing, and vice versa.
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Computer networks
Terms: Computer networks