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.
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.
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
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.
What is a subnet?
A subnet, or subnetwork, is a network inside a network. Subnets make networks more efficient. Through subnetting, network traffic can travel a shorter distance without passing through unnecessary routers to reach its destination.
Why is subnetting necessary?
The way IP addresses are constructed makes it relatively simple for Internet routers to find the right network to route data into. However, in a Class A network (for instance), there could be millions of connected devices, and it could take some time for the data to find the right device. This is why subnetting comes in handy: subnetting narrows down the IP address to usage within a range of devices.
Because an IP address is limited to indicating the network and the device address, IP addresses cannot be used to indicate which subnet an IP packet should go to. Routers within a network use something called a subnet mask to sort data into subnetworks.
What is a subnet mask?
A subnet mask is like an IP address, but for only internal usage within a network. Routers use subnet masks to route data packets to the right place. Subnet masks are not indicated within data packets traversing the Internet — those packets only indicate the destination IP address, which a router will match with a subnet.
Supernetting in Network Layer
Supernetting is the opposite of Subnetting. In subnetting, a single big network is divided into multiple smaller subnetworks. In Supernetting, multiple networks are combined into a bigger network termed as a Supernetwork or Supernet.
Supernetting is mainly used in Route Summarization, where routes to multiple networks with similar network prefixes are combined into a single routing entry, with the routing entry pointing to a Super network, encompassing all the networks. This in turn significantly reduces the size of routing tables and also the size of routing updates exchanged by routing protocols.
More specifically,
1. When multiple networks are combined to form a bigger network, it is termed as super-netting
2. Super netting is used in route aggregation to reduce the size of routing tables and routing table updates
There are some points which should be kept in mind while Supernetting :
1. All the Networks should be contiguous.
2. The block size of every networks should be equal and must be in form of 2n.
3. First Network id should be exactly divisible by whole size of supernet.
Advantages of Supernetting –
1. Control and reduce network traffic
2. Helpful to solve the problem of lacking IP addresses
3. Minimizes the routing table
Disadvantages of Supernetting –
1. It cannot cover different area of network when combined
2. All the networks should be in same class and all IP should be contiguous
IPv4 Subnetting
Because of the physical and architectural limitations on the size of networks, you often must break large networks into smaller subnetworks. Within a network, each wire or ring requires its own network number and identifying subnet address.
Figure 1 shows three devices connected to one subnet and three more devices connected to a second subnet. Collectively, the six devices and two subnets make up the larger network. In this example, the network is assigned the network prefix 192.14.0.0, a class C address. Each device has an IP address that falls within this network prefix.
In addition to sharing a network prefix (the first two octets), the devices on each subnet share a third octet. The third octet identifies the subnet. All devices on a subnet must have the same subnet address. In this case, the alpha subnet has the IP address 192.14.126.0 and the beta subnet has the IP address 192.14.17.0.
IPv6 Protocol
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion. IPv6 is intended to replace IPv4. In December 1998, IPv6 became a Draft Standard for the IETF, who subsequently ratified it as an Internet Standard on 14 July 2017.
IPv6 is an Internet Layer protocol for packet-switched internetworking and provides end-to-end datagram transmission across multiple IP networks, closely adhering to the design principles developed in the previous version of the protocol, Internet Protocol Version 4 (IPv4).
In addition to offering more addresses, IPv6 also implements features not present in IPv4. It simplifies aspects of address configuration, network renumbering, and router announcements when changing network connectivity providers. It simplifies processing of packets in routers by placing the responsibility for packet fragmentation into the end points. The IPv6 subnet size is standardized by fixing the size of the host identifier portion of an address to 64 bits.
Transition from IPv4 to IPv6 address
When we want to send a request from an IPv4 address to an IPv6 address, but it isn’t possible because IPv4 and IPv6 transition is not compatible. For a solution to this problem, we use some technologies. These technologies are Dual Stack Routers, Tunneling, and NAT Protocol Translation. These are explained as following below.
Dual-Stack Routers :
In dual-stack router, A router’s interface is attached with IPv4 and IPv6 addresses configured are used in order to transition from IPv4 to IPv6.
In this above diagram, A given server with both IPv4 and IPv6 addresses configured can communicate with all hosts of IPv4 and IPv6 via dual-stack router (DSR). The dual stack router (DSR) gives the path for all the hosts to communicate with the server without changing their IP addresses.
Tunneling:
Tunneling is used as a medium to communicate the transit network with the different IP versions.
In this above diagram, the different IP versions such as IPv4 and IPv6 are present. The IPv4 networks can communicate with the transit or intermediate network on IPv6 with the help of the Tunnel. It’s also possible that the IPv6 network can also communicate with IPv4 networks with the help of a Tunnel.
NAT Protocol Translation:
With the help of the NAT Protocol Translation technique, the IPv4 and IPv6 networks can also communicate with each other which do not understand the address of different IP version.
Generally, an IP version doesn’t understand the address of different IP version, for the solution of this problem we use NAT-PT device which removes the header of first (sender) IP version address and add the second (receiver) IP version address so that the Receiver IP version address understand that the request is sent by the same IP version, and its vice-versa is also possible.
In the above diagram, an IPv4 address communicates with the IPv6 address via a NAT-PT device to communicate easily. In this situation, the IPv6 address understands that the request is sent by the same IP version (IPv6) and it responds.
Conclusion -We saw what internet logical addressing is. The different functions of it and the different methods to declare it. We learned about IP address and the different types of it. Subnet and supernet and why they are necessary. The advantages and disadvantages of supernet and subnet. In the end we saw how to make communication from IPv4 to IPv6 address and the different ways to do it.
References -
Authors -
Vishwajeet Mote
Mohit Marathe
Shreyas Mandaokar
Siddhesh Memane
Sudhanshu Mandhania
