Internet Logical Addressing

Introduction to Logical Address

Whenever a program is running, an address is generated by the Central Processing Unit called Logical Address which do not exist physically, it only exists virtually and hence it is also called as a virtual address. The central processing unit’s physical memory location can be accessed by using this virtual address as a reference and the set of all the logical addresses generated by the central processing unit is called logical address space and the mapping of these logical addresses to the physical addresses is done using a hardware device called memory management unit.

Functions of Logical Address

In any business, there may be multiple networks. There may be a single website with multiple VLAN’s associated with it and each of those VLAN will be connected to a different network. Or there may be multiple websites and each of these sites may be connected to a different network or multiple networks depending on the requirements. There will be hosts connected to the networks and each of these hosts is associated with NIC and the physical addresses are referred to as the MAC addresses burned into the NIC’s. The data frames from one host to another host on the same network are delivered using the physical addresses which is used by the second layer. The third layer consists of logical addresses and they are assigned to the third layer through DHCP. The third layer addresses will be used by the host of one network to communicate with the hosts of other networks. If a host of one network is trying to communicate with the host of other network, it will check for the third layer address of the destination host and compare it with the third layer address of its own. If the addresses are found to be on the same network, then the host will try to spot the second layer address of the destination network and send the data frame directly to the second layer of the destination host. And if the destination host is found on a different network, then o configures a gateway to send the data frame to the second layer of the destination host in a different network. The gateway finds a path destination host on a different network by using third layer address and the packet is forwarded to the destination network through this gateway. The physical addresses do not that survive when the data frames are moved across different networks. The frame headers hold the physical addresses and the logical address is used to remove the physical address from the header and discards it thereby making way for logical addresses to forward the data frames to the destination network.

Declaration of Logical Addresses Using Different Methods

The communication of computers happens through the internet. The data that is transmitted from one computer will have to pass through several local area networks (LAN) and wide area networks (WAN) before reaching the destination computer. For such communications to take place between the computers, we need a scheme of addressing called global addressing scheme which is also called logical addressing or logical address. The logical addresses in any network of the TCP or IP layer is referred using internet protocol (IP) address. The length of the addresses in the internet are 32 bits long. Therefore, there are maximum of 2 raise to the power of 32 addresses and these addresses are referred to as internet protocol version 4 (IP version 4/ IPv4) addresses and popularly known as internet protocol (IP) addresses.

Public and Private Addresses
For homes and small businesses, the entire local network (LAN) is exposed to the Internet via one public IP address. Large companies may have several public IPs.

In contrast, the devices within the local network use private addresses not reachable from the outside world, and the router enforces this standard. The same private address ranges are used in every network, which means every computer within the company has the identical private IP address of a computer in thousands of other companies.

Logical vs. Physical
An IP address is a logical address that is assigned by software residing in the router or server, and that logical address can change from time to time. For example, a laptop is likely to be assigned a new IP when it starts up in a different hot spot. However, there is a physical address built into every unit of hardware, which cannot change. In order to locate a device in an IP network, the logical IP address is converted to a physical address by a resolution protocol .

Static and Dynamic IP
Network infrastructure devices such as servers, routers and firewalls are assigned permanent “static” IP addresses. A user’s machine can also be assigned a non-changing static IP by the network administrator; however, it is generally configured to accept an address automatically . Internet service providers may periodically change the IPs in the modems of their home users, but business users must have consistent “static” IPs for servers that face the public. See dynamic IP address and static IP address

An IPv4 address is used to define the connection of the device to the internet in a unique and a universal manner. Because they are unique, one IPv4 address defines just one connection of the computer the internet. There can never be more than one IPv4 address for two devices connected to the internet at the same time.An IPv4 address is used to define the connection of the device to the internet in a unique and a universal manner. Because they are unique, one IPv4 address defines just one connection of the computer the internet. There can never be more than one IPv4 address for two devices connected to the internet at the same time.

The total number of addresses used by the protocol constitutes the address space for IPv4 and it has a specific address space. If N bits are used to define the address in a protocol, then 2 raised to the power of N is the address space. 32-bit address format is used by IPv4 which means 2 raised to the power of 32 or 4,294,967,296 is the address space.

There are two methods to declare an IPv4 address. They are:

Binary Notation

· IPv4 address is displayed in the form of 32 bits in binary notation. Each octet is refereed to as byte in binary notation.

· An example of IPv4 address in binary notation is 10001000 01101010 11111110 11111100.

Dotted Decimal Notation

· A decimal point or a dot is used to separate the bytes when the IPv4 addresses are represented in the form of decimals because IPv4 addresses are more compatible when written in the form of decimals.

· An example of IPv4 address in dotted decimal notation is 120.150.1.4. Every number in a decimal dotted notation is a value in the range 0 to 255.

Features

· The logical addresses are generated by the central processing unit.

· The logical addresses can be accessed by the users directly. The physical addresses can be accessed through logical addresses.

· Corresponding to the programs running on the operating system, a set of logical addresses are generated by the central processing unit which is called logical address space.

· The logical addresses can be viewed by the users directly.

· There can be several variations of logical addresses.

· Changes can be made to logical addresses.

IPV4 addresses

An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a device (for example, a computer or a router) to the Internet. They are unique so that each address defines only one connection to the Internet. Two devices on the Internet can never have the same IPV4 address at the same time.

On the other hand, if a device operating at the network layer has m connections to the Internet, it needs to have m addresses, for example, a router.

The IPv4 addresses are universal in the sense that the addressing system must be accepted by any host that wants to be connected to the Internet. That means global addressing.

Address Space

IPv4 has a certain address space. An address space is the total number of addresses used by the protocol. If a protocol uses N bits to define an address, the address space is 2N

IPv4 uses 32-bit address format, which means that the address space is 232 or 4,294,967,296

Version 4 and 6 (IPv4 and IPv6)
The original IP Version 4 addressing scheme defined 32 bits to hold the IP address, and it is still widely used today. However, a larger Version 6 address was subsequently created, and both are in use. It will take a long time before the newer IPv6 is the only system in use.

Authors:

Vishwajeet Mote

Mohit Marathe

Shreyas Mandaokar

Siddhesh Memane

Sudhanshu Mandhania