Functions Of a Router In Computer Networking

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What is a Router?

A router receives and sends data on computer networks. Routers are sometimes confused with network hubs, modems, or network switches. However, routers can combine the functions of these components, and connect with these devices, to improve Internet access or help create business networks.

How does a router work?

Think of a router as an air traffic controller and data packets as aircraft headed to different airports (or networks). Just as each plane has a unique destination and follows a unique route, each packet needs to be guided to its destination as efficiently as possible. In the same way that an air traffic controller ensures that planes reach their destinations without getting lost or suffering a major disruption along the way, a router helps direct data packets to their destination IP address.

In order to direct packets effectively, a router uses an internal routing table — a list of paths to various network destinations. The router reads a packet’s header to determine where it is going, then consults the routing table to figure out the most efficient path to that destination. It then forwards the packet to the next network in the path

FUNCTIONS OF A ROUTER

Router Functions

The basic routing function can be split into two areas; one is to build a map of the network and for that routers typically use either static routing or dynamic routing protocols. With the help of dynamic routing protocols, routers will let other network devices know about not only the topology of the network but also about network changes. Static routing will be that static and will not adapt to network changes. Both models accomplish the task of building the map of the network in the form of the routing table.

The command and output shown here display the routing table on a Cisco router. With show IP route, an IOS device like this one could show the different destinations, the cost to get there, what is known as the administrative distance to define priorities for different routing protocols, and the next-hop to get to that destination. Notice how the routing protocol that learned that particular entry or destination is shown there in the first column. This is EIGRP, this is RIP, and this is OSPF. With this information, routers will be able to determine where to forward packets. They will do so by sending the packet to the next router in the path according to the info in the routing table. Notice then that routing is based on destination addresses.

Path Determination

During the process of path determination, the routers will consider multiple alternatives to get to the same place; those alternatives result from the redundancy built into most network designs. You want multiple paths, so that if one goes down, other alternatives will become available. In determining the best path, routers will consider several things. One of them is the source of the information, and so you could have multiple dynamic routing protocols or even static routing populating the routing table and telling the router what the options are.

The second piece of information is the cost of taking each path, and knowing that the path is made up of multiple links or hops that are defined by other routers. Then we could add the concepts of the cost in the context of the total path, but that cost is nothing more than the sum of all the costs to reach each hop in the path.

Well, the two decisions are ruled by different pieces of information, for example, in order to define a tie breaker between sources of information, the routers use the administrative distance, so if a routing protocol like OSPF is telling the router information on a destination and also RIP is telling that router information on the same destination, then the administrative distance will define who wins. Once the source is selected, then the cost is what matters; in other words, if OSPF is giving me the information on those two paths, then the cost of the path will define which one I take. This is similar to having two maps to drive from one city to the other. You first select which map you are going to follow and then if the map is giving you more than one option, then you will select the option according to perhaps the amount of time it takes or the amount of miles you have to drive for each option.

Routing Tables

So the routing table contains the network layer intelligence that tells the router how to forward packets to remote destinations. Initially, that routing table is made up of networks that are directly connected to the particular router. They are obviously shown as directly connected networks, after that the way to learn about remote destinations is by either populating the routing table with static routes in which an administrator will tell the router how to get to the destination or by populating the routing table via routing table advertisements coming from other routers.

So routers are gossipy and they will tell each other information that allows them to know about all the gossip in the network. In both cases, static and dynamic routing notice how routers use the reserved subnet addresses or network addresses that contain all 0s in the host portion of the IP address.

In this case, we are talking about a classless subnetted class A address. Network 10 split into subnets similar to a class C. However, in all cases here, the host portion of the address, the fourth byte is all 0s and that represents that subnet or network itself. In other words, these are destination networks or subnets. In the case of remote destinations, the routing table entries show what the next hop is in order to reach that destination. In this case, in order to reach 10.1.3.0, our next-hop is router 2 at 10.1.2.2.

These are categories of routing table entries that could be populated either dynamically or statically. Some of them are born with the router. As soon as the router boots up, it will identify its directly connected active networks and interfaces and define them as reachable destinations, only because of the fact that the router is directly attached or connected to it. Now that is pretty smart, but even smarter is the fact that the routers will communicate with each other, exchange routing information via dynamic routing protocols like OSPF or EIGRP, and then learn not only about those destinations, but also adjust to changes on those destinations.

Routing protocols will be able to identify topology changes and tell each other about them. Soon enough, entries will appear and disappear from the routing table according to availability; again, an administrator could come in and manually insert static entries. This is sometimes not recommended because they will be static and they will not adjust to network changes; in other words, if the entry or the destination goes down, the entry will remain there and the router will still forward packets to a destination that is not available. Perhaps a special case of a static route is the default route. Although they can also be learned dynamically, static defaults are used when no explicit route to a destination is known and so this is the entry that identifies all unknown destinations. The router will say, “If I do not know about a certain destination, I will forward a packet to someone that does, typically another router.”

Routing Metrics

Optimal path selection depends on what is known as the cost to reach a destination across a certain path. Again, the cost of a path is made up of incremental costs for each hop along the path. The cost is also known as metric, and different routing protocols will consider different criteria in order to define the metric. Older technologies and protocols consider the number of routers along the path in order to reach a destination; that is what they call the hop count. Hop count is sometimes not an efficient way to determine cost, because you could have different bandwidths associated with each hop or each link.

In this example the two-hop path is better, because it has more bandwidth available. Other routing protocols start considering bandwidth as a measure of cost, and even more parameters in the criteria, for example, EIGRP considers bandwidth delay, reliability, load, and maximum transmission unit. In that case, a path with enough bandwidth, but one that is fully congested, would not be selected and perhaps another path with less available bandwidth would be selected because it is less congested and more reliable.

Perhaps one of the points and highlights of this lesson is the fact that routing protocol selection, if you are doing dynamic routing, is key in determining the cost or metric and, therefore, how efficient and optimal the path selection will be, but also the convergence time, which is defined by the time it takes for routing protocol to detect a topology change and adjust by selecting an alternative path if the main path is down. There are different categories of routing protocols if you are using dynamic routing that define their cost and metric, but also their behavior under those circumstances.

Distance Vector Routing Protocols

Perhaps one of the points and highlights of this lesson is the fact that routing protocol selection, if you are doing dynamic routing, is key in determining the cost or metric and, therefore, how efficient and optimal the path selection will be, but also the convergence time, which is defined by the time it takes for routing protocol to detect a topology change and adjust by selecting an alternative path if the main path is down. There are different categories of routing protocols if you are using dynamic routing that define their cost and metric, but also their behavior under those circumstances.

Using the distance vector approach, which is one of the categories, routers do not have to really know the whole path toward the destination. They only have to know the direction or vector in which to send a packet. In that sense, it will only keep information in the routing tables related to what the next-hop should be in order to reach a certain destination.

Distance vector protocols suffer from many disadvantages; one of them is that they periodically advertise the routing tables. Some of them use broadcasts to advertise the entire routing table. This creates too much overhead in the network and it may be unnecessary if the network does not really change, so it is really similar to calling everybody to tell them about gossip, by calling them frequently to tell them the same gossip over and over again. Even if the rumor has not changed, it is also similar to telling the whole story over and over again from the start, even though nothing has changed or even though just a piece of the story has changed. RIP, or Routing Information Protocol, is an example of a distance vector protocol. In the case of RIP, it uses a hop count as the measure of cost.

Link-State Routing Protocols

Link-State protocols are more efficient and effective in creating network topologies, sharing them, and selecting the best path as compared to distance vector protocols. There are several differences between the two categories. For example, link state protocols will not broadcast the information per router, it will use multicast where each router advertises via that multicast the link it knows to the neighbors. Secondly, link-state protocols do not advertise periodically. After an initial flood of all the information, yet will only advertise changes to the topology. In other words, if the link goes down then that small change will be advertised via multicast. Third, router not only know about the next hop toward a destination, they know about the whole topological map of the network. Each router after the initial flood will build that map of the network, which includes all the routers and all the links. With that information, each router is capable of browsing those tables via using the shortest path first algorithm, and select the best path toward each destination. This would be installed in a routing table. So, you do not need a chain reaction of events for each router to make a topological changes and change routing decisions. Once there is a change, for example this link going down, that will affect only a little branch of the tree and only that change will be advertised to the network. This is what they call incremental updates. All of these changes and differences make link-state protocols more effective and efficient in dealing with network changes.

What is the difference between a router and a modem?

Although some Internet service providers (ISPs) may combine a router and a modem within a single device, they are not the same. Each plays a different but equally important role in connecting networks to each other and to the Internet.

A router forms networks and manages the flow of data within and between those networks, while a modem connects those networks to the Internet. Modems forge a connection to the Internet by converting signals from an ISP into a digital signal that can be interpreted by any connected device. A single device may plug into a modem in order to connect to the Internet; alternately, a router can help distribute this signal to multiple devices within an established network, allowing all of them to connect to the Internet simultaneously.

Think of it like this: If Bob has a router, but no modem, he will be able to create a LAN and send data between the devices on that network. However, he will not be able to connect that network to the Internet. Alice, on the other hand, has a modem, but no router. She will be able to connect a single device to the Internet (for example, her work laptop), but cannot distribute that Internet connection to multiple devices (say, her laptop and her smartphone). Carol, meanwhile, has a router and a modem. Using both devices, she can form a LAN with her desktop computer, tablet, and smartphone and connect them all to the Internet at the same time.

What are some of the security challenges associated with routers?

Vulnerability exploits: All hardware-based routers come with automatically installed software known as firmware that helps the router perform its functions. Like any other piece of software, router firmware often contains vulnerabilities that cyber attackers can exploit (one example), and router vendors periodically issue updates to patch these vulnerabilities. For this reason, router firmware needs to be updated regularly. Unpatched routers can be compromised by attackers, enabling them to monitor traffic or use the router as part of a botnet.

DDoS attacks: Small and large organizations often are the targets of distributed denial-of-service (DDoS) attacks directed at their network infrastructure. Unmitigated network layer DDos attacks can overwhelm routers or cause them to crash, resulting in network downtime. 

Administrative credentials: All routers come with a set of admin credentials for performing administrative functions. These credentials are set to default values, such as “admin” as the username and “admin” as the password. The username and password should be reset to something more secure as soon as possible: attackers are aware of the common default values for these credentials and can use them to gain control of the router remotely if they are not reset.

Types of routers

Core router

Core routers are generally used by service providers (i.e. AT&T, Verizon, Vodafone) or cloud providers (i.e. Google, Amazon, Microsoft). They provide maximum bandwidth to connect additional routers or switches. Most small businesses will not need core routers. But very large enterprises that have many employees working in various buildings or locations may use core routers as part of their network architecture.

Edge router

An edge router, also called a gateway router or just “gateway” for short, is a network’s outermost point of connection with external networks, including the Internet.

Edge routers are optimized for bandwidth and designed to connect to other routers to distribute data to end users. Edge routers don’t usually offer Wi-Fi or the ability to manage local networks fully. They typically have only Ethernet ports—an input to connect to the Internet and several outputs to connect additional routers.

Edge router and modem are somewhat interchangeable terms, though the latter term is no longer commonly used by manufacturers or IT professionals when referencing edge routers.

Distribution router

A distribution router, or interior router, receives data from the edge router (or gateway) via a wired connection and sends it on to end users, typically via Wi-Fi, though the router usually also includes physical (Ethernet) connections for connecting users or additional routers.

Wireless router

Wireless routers, or residential gateways, combine the functions of edge routers and distribution routers. These are commonplace routers for home networks and Internet access.

Most service providers provide full-featured wireless routers as standard equipment. But even if you have the option to use an ISP’s wireless router in your small business, you may want to use a business-level router to take advantage of better wireless performance, more connectivity controls, and security.

Virtual router

Virtual routers are pieces of software that allow some router functions to be virtualized in the cloud and delivered as a service. These routers are ideal for large businesses with complex network needs. They offer flexibility, easy scalability, and a lower entry cost. Another benefit of virtual routers is reduced management of local network hardware.

How does a router work?

Routers guide and direct network data, using packets that contain various kinds of data—such as files, communications, and simple transmissions like web interactions.

The data packets have several layers, or sections, one of which carries identifying information such as sender, data type, size, and most importantly, the destination IP (Internet protocol) address. The router reads this layer, prioritizes the data, and chooses the best route to use for each transmission.

If you are looking for a new Wi-Fi router for your office, there are some important features you should be aware of.

FEATURES OF A ROUTER

Network type

Look at any router and you will quickly see that there are a number of different networks available. The four most commonly found are 802.1b, 802.1g, 802.1n, and 802.11ac. These designations indicate how fast the router can transfer wireless data, with 802.11ac being the fastest of these four. Those who want to connect multiple devices via Wi-Fi or cable may do better with 802.11ac router.

Throughput

This is closely associated with the router’s network type, and is usually one of the first things listed on router boxes and specifications. To spot the router’s throughput, look for Mbps. This indicates the speed at which the router is supposed to transmit data from your connection to users.

Keep in mind that if you have a 100Mbps internet connection, but a router that is only, say, 80 Mbps, then the total speed will be the lower figure. Therefore, it would be a good idea to get a router with a higher throughput to accommodate faster connections.

Range

This is particularly important for users who will be connecting via Wi-Fi as they will likely not be sitting right beside the router. The farther you are from your router, the slower and weaker your connection will be. Typically, 802.11ac will offer the strongest connections and greatest range.

Bands

On every single router’s box, you will see numbers like 5Ghz and 2.4Ghz. These indicate the wireless radios on the router. A dual-band router will have both 5Ghz and 2.4Ghz radios which allow devices to connect to different bands so as not to overload a connection. Those who connect to a 5Ghz band will generally have better performance, but the broadcast range will be much shorter than the 2.4Ghz radio.

Quality of service (QoS)

QoS is a newer feature that allows the router administrator to limit certain types of traffic. For example, you can use the QoS feature of a router to completely block all torrent traffic, or limit it so that other users can have equal bandwidth. Not every router has this ability, but it is a highly beneficial feature for office routers.

Beamforming

Beamforming is a recent feature that’s becoming a standard in mid- to high-end routers. It is a form of signal technology that allows for better throughput in dead areas of a business. In other words, it can help improve the connection quality with devices behind solid walls or in rooms with high amounts of interference.

By utilizing this technology, routers can see where connection is weak and act to improve it. While this is available on routers with many network types, it is really only useful with routers running 802.11ac. Those who don’t mind paying a higher price point for an increase in network performance should consider this feature.

Multiple input, multiple output (MIMO)

MIMO is the use of multiple antennas to increase performance and overall throughput. MIMO-enabled routers ensure that more devices can connect to one router with less interference.

When it comes to real-world tests, there is often a slight improvement if antennas are configured and aimed properly. However, getting a high-end router with six or more antennae may be an unnecessary cost for small businesses.

There’s a lot to consider when it comes to picking a router, which is why we recommend you contact us. We can evaluate your networking needs and help you find the best set up for your business.

Most routers are multiprotocol routers and are capable of handling multiple network layer protocols. To make this possible, router must be equipped with appropriate software for each protocol to be supported. Unlike bridges, routers can intelligently determine most efficient path from source to any destination. To make this possible, various algorithms such as RIP, OSPF, BGP are used as routing protocols.

Benefits or advantages of Routers

Following are the benefits or advantages of Routers:
➨It provides connection between different network architectures such as ethernet & token ring etc.
➨It can choose best path across the internetwork using dynamic routing algorithms.
➨It can reduce network traffic by creating collision domains and also by creating broadcast domains.
➨It provides sophisticated routing, flow control and traffic isolation.
➨They are configurable which allows network manager to make policy based on routing decisions.

Drawbacks or disadvantages of Routers

Following are the drawbacks or disadvantages of Routers:
➨They operate based on routable network protocols.
➨They are expensive compare to other network devices.
➨Dynamic router communications can cause additional network overhead. This results into less bandwidth for user data.
➨They are slower as they need to analyze data from layer-1 through layer-3.
➨They require considerable amount of initial configurations.
➨They are protocol dependent devices which must understand the protocol they are forwarding

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