IP address. It is a numerical label that identifies, logically and hierarchically, an interface (communication/connection element) of a device (usually a computer) within a network that uses the IP protocol (Internet Protocol), which corresponds to the level of the network TCP / IP protocol.
This number should not be confused with the MAC address, which is a 48-bit identifier to identify the network card uniquely and does not depend on the connection protocol—used neither from the network.
The IP address can change very often by changes in the system or because the device in charge of assigning the IP addresses within the network decides to assign another IP (for example, with the DHCP protocol), to this form of IP address assignment It is called dynamic IP address (usually abbreviated as dynamic IP).
Internet sites that by their nature need to be permanently connected, generally have a fixed IP address (commonly, fixed IP or static IP), this does not change over time. Mail servers, DNS, public FTP and web page servers must necessarily have a fixed or static IP address since this allows their location on the network. Through the Internet, computers connect through their respective IP addresses.
However, it is more comfortable for human beings to use another notation that is easier to remember, such as domain names; The translation between them is solved using the DNS domain name servers, which in turn facilitates the work in case of change of IP address since it is enough to update the information on the DNS server and the rest of the people They will not find out as they will continue to access the domain name.
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How to decrypt an IP address is a 32-bit address, usually written in the format of 4 whole numbers separated by periods. An IP address has two distinct parts: the numbers on the left indicate the network and are called netID (network identifier). The figures on the right show the computers within this network and are called host-ID (host identifier).
Special IP AddressesUnique addresses When the host identifier is cancelled, that is, when the bits reserved for the computers on the network are replaced by zeros (for example, 194.28.12.0), what is called the network address is obtained. This address cannot be assigned to any of the computers on the network.
When the network identifier is cancelled, that is, when the bits reserved for the network are replaced by zeros, and address of the equipment is obtained. This address represents the equipment specified by the host identifier, and that is in the current network.
When all the bits of the host identifier are 1, the address obtained is called the broadcast address. It is a specific address that allows you to send a message to all the computers on the network specified by the net. Conversely, when all bits of the network identifier is 1, the address obtained is called the multicast address. Finally, the address 127.0.0.1 is called the return loop address because it indicates the localhost.
Network classes IP addresses are divided into categories, according to the number of bytes that represent the network.
A level In a class A IP address, the first byte represents the network. The most significant bit (the first bit on the left) is zero, which means that there are 2 7 (00000000 to 01111111) network possibilities, which are 128 possibilities. However, network 0 (bits with values 00000000) does not exist, and the number 127 is reserved to indicate your equipment.
The available networks of class A are, therefore, networks ranging from 1.0.0.0 to 126.0.0.0 (the last bytes are zeros that suggest that it is undoubtedly a network and not equipment). The three bytes on the left represent the computers on the net. Therefore, the system may contain a quantity of equipment equal to 224-2 = 16,777,214 equipment.
Class B In a class B IP address, the first two bytes represent the network. The first two bits are 1 and 0; This means that there are 214 (10 000 000 00000000 to 10 111111 11111111) network possibilities, that is, 16,384 possible networks. The available systems of class B are, therefore, networks ranging from 128.0.0.0 to 191.255.0.0.
The two bytes on the left represent the computers on the network. The network may then contain a quantity of equipment equivalent to: Therefore, the network may contain a number of equipment equal to 216-21 = 65,534 equipment.
In a class C IP address, the first three bytes represent the network. The first three bits are 1.1 and 0; This means that there are two network possibilities, that is, 2,097,152.
The available networks of class C are, therefore, networks ranging from 192.0.0.0 to 223.255.255.0. The byte on the right represents the network equipment so that the network can contain: 28-21 = 254 equipment.
It is common that in a company or organization a single computer has an Internet connection and the other computers in the network access the Internet through it (usually, we refer to a proxy or gateway).
In that case, only the equipment connected to the network needs to reserve an IP address with ICANN. However, other computers will need an IP address to communicate with each other.
Therefore, ICANN has reserved several addresses of each class to enable the assignment of IP addresses to the computers of a local network connected to the Internet, without the risk of creating IP address conflicts in the network of networks.
These addresses are the following: Class A private IP addresses: 10.0.0.1 through 10.255.255.254; make it possible to create large private networks that include thousands of computers.
Class B private IP addresses: 172.16.0.1 to 172.31.255.254; make possible the creation of medium-sized private networks. Class C private IP addresses: 192.168.0.1 to 192.168.0.254; to establish small private networks.
The subnet mask allows distinguishing the bits that identify the network and those that identify the host from an IP address. Given the address of class A 10.2.1.2, we know that it belongs to the 10.0.0.0 network and the host it refers to is 2.1.2 within it.
The mask is formed by setting to 1 the bits that identify the network and 0 the bits that identify the host. In this way a class A address will have as mask 255.0.0.0, one of class B 255.255.0.0 and one of class C 255.255.255.0.
Network devices perform an AND between the IP address and the mask to obtain the network address to which the host identified by the given IP address belongs.
For example, a router needs to know which network the IP address of the destination datagram belongs to check the routing table and be able to send the datagram through the output interface.
For this, you need to have direct cables. The mask can also be represented as follows 10.2.1.2/8 where the / 8 indicates that the eight most significant bits of the mask are destined to networks, that is / 8 = 255.0.0.0. Similarly (/ 16 = 255.255.0.0) and (/ 24 = 255.255.255.0)
The address space of a network can be subdivided in turn, creating separate autonomous subnets. An example of use is when we need to group all employees belonging to the department of a company.
In this case, we would create a subnet that would include their IP addresses. To achieve this, you must reserve bits from the host field to identify the subnet by setting the network-subnet bits in the mask to one.
For example, address 172.16.1.1 with mask 255.255.255.0 indicates that the first two octets identify the network (because it is a class B address), the third octet identifies the subnet (to 1 bit in the mask).
The fourth Identify the host (at 0 the corresponding bits inside the mask). There are two addresses of each subnet that are reserved.
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