Let me start by describing the icons and images that you can see at the top. I will begin with the one on left. This is the logical representation for a router, which we use everywhere in topology, maps, and network diagrams. It is a widely used icon. It is a small, circular or cylindrical shape that has four arrows. This is what describes a router. That’s quite logical. What is a physical router? The image below shows what a physical router looks like. This router is a Cisco 2900 series router, which we would use in enterprise-grade and business-grade networks. Keep in mind that not all physical routers are the same. Although they come in many different types, one thing unites them all is their purpose.
What a router does
What is the purpose and function of a router? A router’s purpose is to route traffic between networks. If I’m on my own LAN and want to communicate with the internet and send traffic to it, I will need to use a router or other routing service. That’s the purpose of a router or routing service: to take traffic from one network, and allow it to be routed to another network.
Most common router
An IP router is the most popular type of router. There are many other protocols that can be used to route between networks. The most popular layer three network is the Internet Protocol network. The most popular type of router is an IP router. IP is the most widely used type of router, and it can be found on any router, even the one at your home.
IP routers route IP packets between networks. If I’m on my network and need to communicate with the internet using IP, I will send IP packets to, let’s just say, a Google server. My router at home will know how to route my packet onto the internet. That’s it.
Let’s look at our diagram to help us understand this better. As you can see, there are two LANs. These are two physically separate LANs. There are two switches that connect LAN one and another that connects LAN 2. Hosts on line one can communicate with those on line two. The hosts on LAN 2 can communicate with each other, but not to one another. They are physically separated by their respective networks. Some type of router service is required to transfer traffic from LAN 1 to LAN 2. These switches would need to be connected to our router via different router interfaces. If the router interfaces are configured with an IP address, it will automatically be able route traffic between LANs and allow LAN 1 to communicate with LAN 2 and vice versa.
This diagram shows a more detailed representation of the actual topic. Routers can route traffic from one network into another, so they are called the gateway device or network gateway. If I’m on LAN 1, and I need traffic to go to another network, I will need to send it to my gateway device which is going to a router. This is often called the default gateway in network technology. If you’ve heard this term before, it usually refers to a router or other device capable of routing traffic. It could also be a firewall, as firewalls are capable of routing most of the time. It is important to understand the default gateway. It is a term we hear all the time. It refers to the router that connects with your LAN.
We mentioned earlier that our router connects us to one LAN to the other LAN. Are there other types of networks available than LANs or local area networks? Yes, there are. We have LAN 1 and LAN 2. But are there other types of networks? Or is there another type that I might want to access? It’s the internet. Our routers will also connect to the internet.
Connecting to the internet requires a different type connection. It is not a LAN connection, or a local network. It’s a Wide Area Network Connection. Your router connects to your internet service provider via a WAN connection. It is possible to connect routers to WANs. They can connect to LANs and to WANs over a wide area network. These are some other terms used in networking. This is what routers enable us to do – send traffic between LANs and WANs, and communicate between LANs and WANs and all our different types.
Routers are versatile and a must-have tool in any network. Without routers, the internet wouldn’t work. The internet is actually a collection of many networks and routers that connect all these networks together. This is an extremely important fact. This is the most important device you must know as a network engineer. You need to be able to set up, connect and troubleshoot. Our routers connect to external services. However, we also use them for other purposes.
On the backside of a router we can see that there are a few different Ethernet interfaces. Three are available on this particular model router. Three Gigabit Ethernet interfaces are available. These interchangeable slots are for line cards and can be found on the left or across the back. These slots can be removed and a new type of card can be inserted to provide a different type network connection. We might connect to a T1 connection, or ATM to connect to our WAN. Maybe we have a circuit from our voice service that we need for connection to the public switch.