In this article I describe the ARP Address Resolution Protocol in computer network for CCNA exam. ARP Address Resolution Protocol is related to Link layer of TCP/IP Suite model. ARP Address Resolution Protocol used to convert an IP address into a physical address such as an Ethernet address of a computer. Data packet transmission on layer 2 depends on the physical address of devices. The physical address of all devices mapped with an IP address. ARP Address Resolution Protocol forward the data packets by checking the physical address of related IP address on the packet.
This process is done for data packet switching on a layer 2 switch. A computer identified by the physical address and IP address in the network. On layer 2 data link layer of OSI reference model the ARP Address Resolution Protocol works to forward the packet on the basis of MAC address of the computer. Similarly RARP protocol works in reverse to ARP protocol. The RARP protocol identify the IP address of a device against the MAC address. ARP and RARP both protocol works on link layer of TCP/IP suite model.
Routing and Routed Protocols provides the connectivity between different networks for data packets flow from one network to another network. A standard routing table is maintained by the routers for data packet flow between different networks.
Before going to learn about ARP Address Resolution Protocol in detail, it became helpful to remember the OSI suite and TCP/IP suite model. There are many manufacturer of computer machine in the market. Initially when computers became single user public computer. The computers communicate with only same brand machines. It happens because there was no any fix standard for data transfer between different devices. It is very difficult to make communication with each other when the hardware are of different brands or company. In this article I describe the some basic part of OSI reference layer and TCP/IP Suite model basic concepts in networking with the ARP Address Resolution Protocol.
OSI reference model basic concepts
OSI reference model in computer network followed by various vendors to overcome the compatibility problem. After implementation of OSI reference model in computer network, equality maintains by all manufacturer. In 1970 the Open Systems Interconnection (OSI) reference model was created by the International Organization for Standardization (ISO). The OSI model was meant to create inter-operable network with different manufactured devices. In this article I describe some layered approach of TCP/IP Suite model basic concepts in computer network. Before understanding the TCP/IP Suite model basic concepts it is necessary to know about the 7 layers of OSI reference model because the basic work of each layer is described in the OSI reference model. You can read the full article related to OSI reference model in computer networking here.
Importance of OSI reference model forARP Address Resolution Protocol
Before going to know about the ARP Address Resolution Protocol at link layer. It is necessary to know the function of layers in OSI model and TCP/IP model. Initially not only hardware but software also not supported for work the different computer brand. It became very difficult for all computer users to working without implementation of OSI reference model in computer network. It is necessary then to make some common protocols for all vendors of computer. Before implementation of OSI reference model in computer network, all vendors implements their own protocols on computer hardware and software.
In networking OSI reference model became helpful. OSI reference model describes the flow of data between nodes in any network. Data from one computer application to another computer application transfer by following some common protocols. The OSI reference layer also become beneficial for troubleshooting the network problems. TCP/IP and Cisco three layered hierarchical model of Cisco became more helpful alongside the OSI reference model.
The Layered Approach in computer network
The Layered approach was the best way to make equality for all computer devices. Layers are not physical but following some protocols. Protocols are for connectivity, connections, data transfer and more. All manufacturer begin to follow the layered approach for OSI reference model in computer network. The OSI reference model change in TCP/IP reference model and later on Cisco three layered hierarchical model. OSI layer architecture have 7 layers. TCP/IP reference model convert these 7 layers into only four layers. After that Cisco three layered hierarchical model converts these 7 layers into three layers. Some layers combined to work in a single layer.
OSI is acronym for open system interconnection. The OSI is a logical reference OSI reference model in computer network. OSI model helps for data flow between different devices and operating systems. All manufacturer used their own architecture before invention of OSI reference model. It was very difficult to establish data communication between different devices. To overcome this problem international organization for standardization (ISO) created the open systems interconnection (OSI) reference model. OSI reference model make data flow possible between different operating system, devices and hardware. Later the OSI model adopted by Cisco as Cisco three layered hierarchical model.
Structure of OSI reference model related to ARP Address Resolution Protocol
OSI reference model in computer network consist of 7 layers. These 7 layers further divided into two groups. First 3 layers works for application communication and remaining 4 layers works for data flow. Application, presentation and session layers define the application communication. Transport, network, data link and physical layers define the data flow. Networking protocols works only on last four layers.
TCP/IP Suite model basic concepts for ARP Address Resolution Protocol
TCP/IP is acronym for Transmission Control Protocol/Internet Protocol (TCP/IP suite model). In this section of the article I describe about TCP/IP suite model basic concepts in detail. TCP/IP suite model is a reference model like OSI layers. Instead of 7 layers of OSI reference model. TCP/IP suite model consist only four layer. All seven layers are merged into four layers only. TCP/IP suite model was designed and implemented by Department of Defence (DoD). TCP/IP developed to preserve data integrity.
The main purpose to develop the TCP/IP is to provide security in the network. A lots of protocols works on each layer to provide a secure network.
It is necessary to understood the protocols used in TCP/IP Suite model basic concepts. IP addressing play an important role in TCP/IP Suite model basic concepts. By using the IP address and subnet masking broadcast domain breaks. It will improve the performance of the network. Breaking broadcast domain increase the data flow speed. Here IP stands for IPV4 only. We ignore the IPV6 for some time in this article. It will make it easy to understand the TCP/IP Suite model basic concepts.
A snap of TCP/IP Suite model basic concepts
In the decade of 1970’s TCP/IP suite model developed by DoD. In the initial stage TCP/IP suite model divided into two segments TCP and IP. Later its name registered with combined name of TCP and IP like TCP/IP model. ARPA, the Advanced Research Projects Agency of DoD officially authorised to use TCP/IP suite model. TCP/IP model was working well so it was adopted by many organisations. In today scenario it is mostly using reference model for networking. Internet is the best example of using TCP/IP.
Process or Application layer of DoD model in TCP/IP Suite model
This is the first layer of TCP/IP of DoD model. It is combination of top three layers of OSI reference model. The functions of Application layer, presentation layer and session layer in OSI model works in single layer process layer. This layer supports the point to point communication and controls the user interface. The data encryption and decryption also done at this layer. Example of some protocols functions at this layer are TLS Transport Layer Security, FTP, LPD, TFTP, SMTP.
Transport layer of DoD model in TCP/IP Suite model
Transport layer of TCP/IP is same as the Transport layer of OSI reference model. It supports the TCP and UDP protocol. This protocol converts the main data segment into packets and transport to the internet layer. The responsibility of Transport layer is to combine the segments and built the data. The data should be reconstruct in its real form. Transport layer is also responsible for creating end-to-end communication between sender and receiver. This layer ensure the delivery of segment in sequence at the receiving device. This property maintains the data integrity.
Internet layer of DoD model in TCP/IP Suite model
Internet layer of TCP/IP is similar to the network layer of OSI reference model. Routing protocols functions on Internet layer of TCP/IP model. Addressing and filtering of packets is main responsibility of Internet layer of TCP/IP model. This layer provides the transmission of packet in the whole network. Some example of protocols functions on internet layer are ICMP, ARP and IP.
Link layer of DoD model in TCP/IP Suite model
Link layer is the least layer of TCP/IP. Basically link layer is combination of data link and physical layer of OSI reference model. Link layer is also known as Network Access layer. It works on MAC address based data transmission. Link layer handles the frame and bits. It receive the bits and constructs frame from merging bits in a sequence. In case of any bit is missing this layer request to re transmit the bits. Ethernet, FDDI, WAP etc functions on this layer. There is no any preset specification for link layer. Link layer functions on any type of existing media.
ARP Address Resolution Protocol Explained in brief
ARP Address Resolution Protocol is a process to map the IP address of a device with the physical address. IP address is a layer 3 protocol while the physical address of any device belongs to layer 2. so the ARP Address Resolution Protocol translate the 32 bit IP address to the 48 bit MAC address of the device. ARP Address Resolution Protocol works only in IPv4 address system. In IPv6 the ARP Address Resolution Protocol replaced with the neighbour discovery protocol. In next article you can read in detail about the NDP.
ARP Address Resolution Protocol is a link layer protocol in TCP/IP model. The ARP protocol provides the mapping of IP address to MAC address. ARP Protocol works in a LAN. In any network two terms required to identify any host. IP address and MAC address of any host are necessary to connect any network. MAC address is link layer related term and IP address is internet layer protocol in TCP/IP model.
All computer and devices keep the unique 48 bits physical address. This 48 bits address known as MAC address. MAC stands for Media Access Control. MAC address never changed of any device whether it connected or not in any network. IP address allotted by network administrator to each device connected in network. The IP address may be changes according to requirement by network. IP address is logical address. When a device called via IP address, Device replied with it’s MAC address. MAC address and IP address tables maintained via Switch.
Working of ARP Address Resolution Protocol in a LAN
All devices allotted a unique 32 bit IP address in a network. This IP address used to identify the devices. This IP address is dynamic and not permanent address. So we need any other term which will never changed. 48 bit MAC address used as an unchanged address. The switch which connects all devices maintain a ARP cache record table. This table contains the MAC address of all devices with associated IP address.
When a packet transmitted from a device, it contains the IP address of destination device. But IP is not fix for any device so packet sent to associated MAC address device. The device identified by the switch-port of switch. It is responsibility of switch to deliver the packet to correct destination.
In case of HUB the packet sent to all devices in the network. The destination device identify the packet. If packet is not for a device, that device will drop the packet. ARP protocol not works in case of HUB used in a network.
ARP Address Resolution Protocol request broadcasts from switch to all devices in the LAN. Suppose a new device connected in the LAN. When this new device recognize that the ARP request IP address allotted to it. This new machine reply the ARP request with its MAC address. By following this process the ARP table updated in all network devices. This process is also beneficial to know whether IP address changed in any device.
RARP Reverse Address Resolution Protocol
ARP protocol used to get the MAC address of device. When a host want to know its IP address from switch another protocol RARP used by device. RARP request packets e sent by devices with MAC address. Other devices reply the IP address associated with broadcast MAC address, which maintains the ARP cache table. The device which send the RARP request then get the IP address assigned.
In this article I describe the ARP Address Resolution Protocol in computer network for CCNA Exam. I hope you found this article helpful for any query or suggestions you may drop a comment below or contact us. Your suggestions are always welcome by us.
