How do routers determine the best path? Routers are a critical part of networking, but what actually happens when you enter a destination into your web browser?
You might expect the router to simply send the request out to the internet and wait for a response, but that’s not always how it works. In fact, routers can use a variety of methods to determine the best path for your data.
Edon Lazaj has created this guide to help you understand how routers work and how they select the best path for your data. After reading this guide, you’ll have a better understanding of what goes on behind the scenes when you browse the web.
What is Layer 3?
To make the design and troubleshooting easier and group all the vendors into a common platform, the Open System Interconnection (OSI) model was created. This model is a seven-layer network architecture that standardizes the way in which data is sent and received by different devices on a network.
Layer 3 is the third layer of the OSI model, and it is where routing takes place. Routers operate at Layer 3 and they use logical addressing (IP addresses) to send data from one network to another.
Layer 3 networking enables communication between two or more networks, and it is the foundation for most Wide Area Networks (WANs). WANs connect different LANs together, and they typically use Layer 3 protocols such as IPv4 and IPv6 to route traffic between them.
Layer 3 networking is also the foundation for many Virtual Private Networks (VPNs). VPNs use Layer 3 technologies to create a secure,encrypted tunnel between two or more devices. This tunnel can cross over public networks, such as the Internet, and it can be used to connect different LANs together.
Layer 3 networking is an important part of almost all modern networks, and it is a key technology for anyone who wants to learn about routers and routing.
Why do we need Logical Addresses
We need logical addresses because physical addresses are not always unique. For example, two devices in different parts of the world may have the same physical address. Logical addresses are unique and can be used to identify a specific device or network. There are two types of logical address:
IP address
A numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address consists of four numbers separated by dots, such as 192.168.0.1. An IPv4 address is 32 bits long, which means it can theoretically be used to address 2^32 (4,294,967,296) devices. IP addresses are assigned to devices by network administrators. IP addresses are usually assigned dynamically, which means that a device’s IP address can change over time.
MAC address
A unique identifier assigned to each network interface controller (NIC) that allows it to be identified on a network. A MAC address consists of six numbers separated by colons, such as 01:23:45:67:89:ab. A MAC address is 48 bits long, which means it can theoretically be used to address 2^48 (281,474,976,710,656) devices. MAC addresses are assigned to devices by the manufacturers of the devices. MAC addresses are usually assigned statically, which means that a device’s MAC address does not change.
Reasons that we need routing
Simply, because each device is only aware of the connecting networks, it needs some kind of information to be able to send data beyond the local network.
This is the job of a router, which is a device that connects two or more networks and forwards data between them. Routers use routing protocols to exchange information about the reachability of destinations on the connected networks. Based on this information, routers build routing tables that are used to determine the best path for forwarding data.
Routing is necessary because it allows devices to communicate with each other regardless of their physical location. Without routing, devices would only be able to communicate with other devices on the same network.
How can we accomplish routing?
The achievement of the routing process is guaranteed by the existence of all the possible networks in the routing database. The most important step towards the success of routing is, therefore, the insertion of all the possible networks in the database. This can be accomplished by two methods which are:
Static Routing
It’s the simplest form of routing. In static routing, network administrators manually configure the router with the routes to each destination network. Static routes are typically used for small networks or for networks that don’t change often.
Dynamic Routing
Dynamic routing is a more sophisticated form of routing. In dynamic routing, routers communicate with each other to exchange information about reachable destinations. Based on this information, they automatically build and update their routing tables. Dynamic routing is typically used for large networks or for networks that change often.
Next, we will have a look at router switching function.
What is Router Switching Function?
Router Switching Function is a process where the router forwards packets from one interface to another based on the destination address of the packet. The router uses a routing table to determine the best path to forward the packet.
The routing table is a database that contains information about all the possible routes that a packet can take, and it is constantly being updated as new information about routes becomes available. When a packet arrives at a router, the router looks up the destination address in its routing table and then forwards the packet to the next hop on the best path to the destination.
Routing Decision
One of the main functions of routers is to determine the best route to send packets. To make this determination, routers use a routing protocol. A routing protocol is a set of rules that govern how routers communicate with each other to exchange information about the best routes to reach a destination.
The most common routing protocols are the Interior Gateway Protocols (IGP), which are used within an autonomous system, and the Exterior Gateway Protocols (EGP), which are used between autonomous systems. The two main IGPs are the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF). The two main EGPs are the Border Gateway Protocol (BGP) and the Intermediate System to Intermediate System (IS-IS).
There are also a number of hybrid protocols, which combine aspects of both IGPs and EGPs. The best known of these is the Enhanced Interior Gateway Routing Protocol (EIGRP).
The Best Route
The determination of the best route implies the evaluation of several routes to the same destination, in order to choose the most efficient one. In order to do this, routers use a metric, which is a number that represents how good a particular route is.
The most common routing metric is the hop count, which is simply the number of routers that a packet must pass through to reach its destination. The lower the hop count, the better the route.
However, other factors can also affect the choice of route, such as the amount of traffic on a particular link or the delay caused by passing through certain routers. As a result, more sophisticated metrics have been developed that take these factors into account.
Load Balance
What happens if a routing table has two or more routes with identical metrics? In this case, the router will load balance between the routes, meaning that it will send packets over both routes.
Load balancing can be static or dynamic. Static load balancing is where the router is configured to use a certain percentage of each route. Dynamic load balancing is where the router automatically adjusts the amount of traffic sent over each route based on conditions such as link utilization.
Both static and dynamic load balancing can be used with any metric, but they are most commonly used with hop count because it is easy to configure and does not require constant monitoring.
The Best Route Through a Router That Has Multiple Routing Protocols Configured
It is possible to configure a router with several routing protocols and several static routes. In this case, the router will use the best route from each protocol.
The best route is determined by comparing the metrics of the routes. The route with the lowest metric is chosen as the best route.
If two or more routes have the same metric, then the router will load balance between the routes.
The best route from each protocol is only used if the router has a route to the destination in that protocol. If the router does not have a route to the destination in a particular protocol, then the best route from that protocol is not used.
It is also possible to configure the router to prefer one routing protocol over another. In this case, the router will only use the best route from the preferred protocol, even if there is a better route in another protocol.
The preferred protocol is only used if the router has a route to the destination in that protocol. If the router does not have a route to the destination in the preferred protocol, then the best route from another protocol is used.
Preferring one routing protocol over another can be useful when using static routes and dynamic routing protocols. For example, if static routes are used for local networks and a dynamic routing protocol is used for external networks, then it might be desirable to prefer the static routes over the dynamic routes. This ensures that traffic stays within the local network unless there is no route available in the local network.
How to determine the best path?
The best path is the path that meets the criteria set by the network administrator. The criteria can include things like shortest path, lowest cost, or highest bandwidth. Once the criteria have been set, the router uses a routing algorithm to determine the best path. The most commonly used routing algorithms are:
- Dijkstra’s algorithm: Dijkstra’s algorithm is a graph-based algorithm that finds the shortest path from a given node to all other nodes in the graph.
- Bellman-Ford algorithm: The Bellman-Ford algorithm is a vector-based algorithm that finds the shortest path from a given node to all other nodes in the graph.
- A* algorithm: The A* algorithm is a heuristic-based algorithm that finds the shortest path from a given node to all other nodes in the graph.
These are just a few of the many routing algorithms that are available. Each has its own strengths and weaknesses, so it’s important to choose the right one for your particular network.
Administrative Distance
Administrative distance is a measure of the trustworthiness of a routing protocol. A routing protocol with a lower administrative distance is more trustworthy than a routing protocol with a higher administrative distance. The administrative distance of a routing protocol is set by the manufacturer of the router. The manufacturer sets the administrative distance based on their own experience and testing.
The most common routing protocols have the following administrative distances:
- Directly connected networks: 0
- Static routes: 1
- EIGRP: 5
- OSPF: 110
- RIP: 120
- BGP: 200
F.A.Q How do routers determine the best path?
How do routers find the shortest path?
Routers use a routing algorithm to find the shortest path. The most commonly used routing algorithms are Dijkstra’s algorithm, Bellman-Ford algorithm, and A* algorithm.
How does a router learn routes?
A router can learn routes in two ways:
- Static Routing: In static routing, network administrators manually configure the router with the routes to each destination network. Static routes are typically used for small networks or for networks that don’t change often.
- Dynamic Routing: Dynamic routing is a more sophisticated form of routing. In dynamic routing, routers communicate with each other to exchange information about reachable destinations. Based on this information, they automatically build and update their routing tables. Dynamic routing is typically used for large networks or for networks that change often.
How does a router determine where to forward data?
A router uses a routing table to determine where to forward data. The routing table is a database of all the known routes in the network. The router uses the routing table to find the best path to the destination.
What device determines the best path across a network?
A router is a device that determines the best path across a network. Routers use routing algorithms to find the shortest path from a given node to all other nodes in the graph. The most commonly used routing algorithms are Dijkstra’s algorithm, Bellman-Ford algorithm, and A* algorithm.
Conclusion
Routers are an essential part of the internet, but what actually happens when you enter a web address into your browser? How do routers determine the best path and how can this affect your browsing experience? We’ve answered these questions and more in our latest blog post. Be sure to check it out to learn everything you need to know about routers!