Layer 3 is the network layer and its protocol is the Internet Protocol or IP. Devices in an IP network are identified by an IP address that can be dynamically assigned and can change over time. Traditionally, the most connected network device to Layer 3 has been the router that allows you to connect devices over different IP networks. In the seven-layer OSI model of computer networks, the network layer is layer 3. The network layer is responsible for packet routing, including routing through intermediate routers.  The OSI network model defines a set of network “layers”. (Getting started with any change would be beyond the scope of this article, but our blog post “Network Management in a Nutshell” provides a good summary if you want to refresh something.) On the third layer of the OSI model, the network layer, most network engineers focus on their time and expertise. As Darragh commented in my article on the data connection layer, layer 2 is cool, but layer 3 is the one that can put you in places. There are also other protocols that work on layer 3, such as ICMP, IGMP, etc. We`ll talk about that later. The network layer provides the ability to transmit network packets of varying lengths over one or more networks from a source to a destination host.
In the service-layer semantics of the OSI network architecture, the network layer responds to service requests from the transport layer and issues service requests to the data link layer. Layer 3 of the OSI model: The network layer provides the functional and procedural means to transfer variable length data sequences from a source host on one network to a destination host on another network while maintaining the quality of service requested by the transport layer (as opposed to the data link layer that connects hosts within the same network). The network layer performs network routing functions, can also report fragmentation and reassembly, as well as delivery errors. Routers work at this level, send data over the WAN, and enable the Internet. This is a logical, non-hierarchical addressing scheme whose values are selected by the network engineer. A number of layer management protocols belong to the network layer, including routing protocols, multicast group management, network-level information and errors, and network-level address assignment. The network layer can have at least three sub-layers: 1) access to the subnet, which takes into account protocols that deal with the interface with networks, e.B X.25; (2) the convergence of sub-networks used when it is necessary to reduce the level of a transit network to the level of networks on both sides; and 3) independent convergence of the subnet that handles transmission across multiple networks, the best example of this is CLNP or IPv7 ISO 8473. (It handles connectionless transmission of data one hop at a time, from the final system to the incoming router, from the router to the router, and from the outgoing router to the targeting system. It is not responsible for reliable delivery to a next hop, but only for detecting faulty packets so that they can be discarded.
In this diagram, IPv4 and IPv6 with X.25 should be classified as subnet access protocols because they contain interface addresses instead of node addresses.) In route tables, there can be different routes for a specific destination. These routes are provided by various routing protocols. To a destination, all routing protocols can have multiple routes. But with their path calculation, they select the “best path” and add it to the routing protocol. In this way, all routing protocols calculate and add the “Best Route” to the routing table. When a router needs to decide to send a packet to this destination, it looks in the route table and checks the following parameters in the specified order. And determine how it will send. Layer 3 refers to the third layer of the Open Systems Interconnection (OSI) model, the network layer.
What happens when a Layer 3 switch receives a packet from an endpoint? If the packet is destined for another VLAN when checking the packet header, the Layer 3 switch “eliminates” the packet to the routing layer. The Layer 3 routing layer then decides where to send the packet: the switch looks at the MAC address forwarding table to decide on the port to send the outgoing packet to. Hi Jagdish – Good question. The difference between a switch that is a “Layer 2” switch and a “Layer 3” switch is whether it facilitates a routing function (routing is performed on the “Internet Protocol” layer or layer 3 on the OSI model). Most, if not all, managed switches support configuring different Layer 2 VLANs over which you can transfer different Layer 3 IP subnets. The following are examples of protocols that run at the network level. Just because a device is layer 3 compatible doesn`t mean it`s in routing. As a network administrator, you must configure the device to route traffic between VLANs if you wish. You can run a Layer 3-compatible switch in Layer 2 mode only. Much of what we do as network administrators – managing IP addresses and subnets, routing protocols, firewall rules and access control lists (ACLs) and many types of quality of service (QoS) – is made possible by Layer 3 technologies. Layer 2 can make you an expert, but lag 3 is how you get the money. Layer 2 of the OSI model is called the data link layer.
The Layer 2 protocol you probably know best is Ethernet. Devices on an Ethernet network are identified by a Media Access Control (MAC) address, which is usually hard-coded for a particular device and usually does not change. Layer 3 provides routing using a routed protocol and unique addresses. There are layer 3 routed protocols such as IP, IPX, Apple Talk, CLNX, etc. Currently, almost all networks use Internet Protocol (IP) as a Layer 3 routed protocol. And IP offers unique IP addresES. In addition to routed protocol IP and IP addresses, there are other protocols that support routing. These protocols are routing protocols. Layer 3 provides communication between devices that work with various Layer 2 technologies. He is not interested in the Layer 2 protocol used in networks.
It only looks like the L3 address and therefore sends the data to the destination. For two devices to communicate over a typical work or home network, they must have both an IP address associated with Layer 3 (the IP layer) and a MAC address associated with Layer 2 (the Ethernet layer). Layer 3 is responsible for all packet routing between intermediate routers, as opposed to Layer 2 (the data link layer), which is responsible for controlling media access and flow control, as well as checking for errors in Layer 1 processes. Layer 3, the network layer, is more commonly referred to as the layer where routing takes place. The main task of a router is to receive packets from one network to another. Layer 3 protocols and technologies enable network-to-network communication. A Layer 3 switch is simply a Layer 2 device that also performs routing (a Layer 3 function). Another important aspect of routers is that each interface of a router has its own IP address, as each of these interfaces is on a different network. It`s not uncommon for me to visit my family and be asked to fix everyone`s computers. The way I usually respond is that I am asked to fix your computer, like asking the guy who designs highways to fix your car. Yes, cars drive on highways and yes, I go to work every day, but that`s not what I do.
That`s a great analogy, but there`s a major difference between cars on highways and packets on a network and that`s on layer 3. If you think about how cars move from one place to another — even with some of the experimental technologies for self-driving cars — the intelligence that takes the car from one place to another is all in the vehicle. In computer networks, all intelligence is at intersections – Layer 3 devices. The whole package (or the car in this analogy) really knows where it comes from and where it wants to go. The network does the rest. The TCP/IP model describes the protocols used by the Internet.  The TCP/IP model has a layer called the Internet layer, located above the link layer. In many manuals and other secondary references, the TCP/IP Internet layer is equated with the OSI network layer. However, this comparison is misleading because the permissible characteristics of the protocols (e.B.
whether connection-oriented or connectionless), which are placed in these layers, are different in the two models. [Citation needed] In fact, the TCP/IP Internet layer is only a subset of the features of the network layer. It describes only one type of network architecture, the Internet. [Citation needed] Routing protocols work with IPv4. There are also new versions of these routing protocols with improvements. Layer 3 uses routing protocols to calculate routes to destinations. Routing protocols also work on Layer 3. These routing protocols are: Layer 3, uses routing tables. .