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Importance of IP
The IP protocol is considered a key protocol in the OSI stack. This particular shape is given by the fact that at lower levels the protocols differ depending on the physical structure of the network and higher levels there are different protocols depending on the type of information that must be developed / carry. IP is, instead, the most widespread transmission protocol layer 3.
Currently there are two versions of IP v4 and v6.

Limitations of IPv4
- Running out of address space (32bit). This fact is caused by:
- Large number of combinations are reserved for multicast addresses to private addresses, addresses indeterminate, broadcast addresses.
- Fragmentation of the addresses, given by a large number of addresses assigned, but not actually used.
- Routing scalability, because all IP networks to be achieved must be announced, BGP packets that are exchanged various Aunonomous System (AS), as it increases the fragmentation and the number of addresses assigned become increasingly large, generating routing tables increasingly difficult to see.

Methods of allocating IPv4 addresses
-NAT, even if they go against the idea that the router can not unpack the packages at a level higher than 4, with which it is possible to assign different logical addresses to groups of hosts with the same IP address, through the use of ports TCP / UDP.
-Criteria for assigning addresses more careful. The IANA has begun to assign the nets "/ 8" to regional agencies.Each agency may request a new / 8 when no more than "/ 9" addresses available for allocation, or when you do not have enough addresses to cover all the addresses that will be used within 18 months (rate of consumption of addresses).
-Reassigning the addresses that were used

Features of IPv6
According to IPv6, the headers are to be fixed length (40B):
Version-(4bit), in reality it is not used, because the layer 3 protocol is already known in a field of the layer 2 protocol.
Traffic-class (8bit) manages the quality of service (QoS).
Flow label (20bit).
-Payload length (16 bits) indicates the length of the load data of the packet (max 64Kb).
Next-header (8 bits) indicates whether the successive bits refer to another IPv6 header or an upper layer protocol (eg TCP). In this way you can specify the following options in the header.
Hop limit (8 bits) indicates the maximum number of routers that the packet is the first traversable discarded.This field is useful to avoid that IP packets will continue to run in the case of loops in the topology of the network.
Source IP address (128bit).
Desitination IP-address (128bit).

Features of IPv6
IPv6 does not allow the fragmentation at the router level, as it was in IPv4, in fact, the fragmentation must be made directly from the sender of the package. In addition, IPv6 is no longer present in the checksum, as it is understood that the error checks at lower levels are quite accurate.
Introduces some problems:
-Difficulty in locating the headers of level 4, since the number of header is not fixed, and the type of higher-level protocol is indicated only in the last header.
-Addresses very large.
Fragmentation-assigned to the sender of the package.
-Tables of DNS is not unique, since it is possible to have multiple addresses for an interface.
The buffer solutions are hindering the migration to IPv6, although it will soon be necessary.

There are 3 types of addressing:
-Unicast: sent the package to reach a single destination.Will recognize two types of addressing unicast:
- Local link, which is the address needed to communicate within a subnet.
- Global, which is the public IP address. There may be more of a global address for interface.
- Site-local home address within a subnet.
-Multicast packet must reach all the interfaces of a multicast group. To identify the multicast listeners on a network is a protocol, which replaces the IPv4 IGMP.
With IPv6, has been taken off the broadcast address because it consumes too much computing resources and banda. It has been replaced by standard multicast groups, which are attributed to the machines when they connect to the network. For example, to know the network address is no longer sent a broadcast message, but a message directed to all multicast routers in the network.

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