Let's tell about IPv4 (RFC-791) - the basic part of stack TCP/IP at present and basic network protocol.
This protocol is engaged in routing in networks, i.e. it directs a package of a way from the sender up to the addressee. The IP protocol sends datagrams. Everyone such datagram except for transferred data comprises also header. Here is format of IPv4 header:
Usually the heading contains 20 octets, i.e. has length of 20 bytes, but this value may be changed. Its all does not simplify process of data transmission.
The most interesting to us on the given theme fields of header are fields of IP addresses (the address of the sender and the destination address), a field "TOS" - Type of Service (initially not used, and now become outdated) and a field "Protocol" (defining structure weeding "data", i.e. according to what protocol they were coded).
So, we shall list common issues of IPv4:
The problem of address space IPv4 is considered the basic, but it not main and not single.
There are also problems connected with transportation of the data, routings consisting complexity and growth of routing tables. Though this problem also tried to solve introduction by classless of interdomain routing (CIDR) but it was not resolved, but IP-administration from it has become complicated. All difficultly to construct and order structure of addresses in 32-bit space...
Then, complexity of IP header processing. Essential fields' number which it contains does not facilitate a life to the processes that work with such headings. In fact some fields of heading have already lost the importance and others could be simplified. Also the variable length of header makes to recalculate constantly the control sum, and at high speeds it will strongly load the processor.
Also there are no some mechanisms necessary to modern measures in IPv4. No mechanisms of information safety and supporting of classes of service. There are no methods of enciphering of data, which now in practice helps very much. And such means should be realized at a network level to not slow applications. To provide support of classes of service is the router's owe to not to rise this problem on the application level that will lead to complication and instability of work.
Realizing these mechanisms on IPv4 in addition is wasting of time. We anyway will have to make changes in all TCP/IP stack, that in any case will lead to some complication of work after transition to the new standard. What for we need all defects of IPv4 if it is possible to realize all at once by means of IPv6?
As a result, it is possible to tell, that IPv4 has served successfully almost 30 years and could serve further, but it is not necessary to stay on the out-of-date protocol that contains incorrigible lacks at a network level when on change to it the excellent alternative: IPv6 for a long time is ready.
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