What is a router?

Routers allow devices to connect and share data over the Internet or an intranet. A router is a gateway that passes data between one or more local area networks (LANs). Routers use the Internet Protocol (IP) to send IP packets containing data and IP addresses of sending and destination devices located on separate local area networks. Routers reside between these LANs where the sending and receiving devices are connected. Devices may be connected over multiple router “hops” or may reside on separate LANs directly connected to the same router.

Once an IP packet from a sending device reaches a router, the router identifies the packet’s destination and calculates the best way to forward it there. The router maintains a set of route-forwarding tables, which are rules that identify how to forward data to reach the destination device’s LAN. A router will determine the best router interface (or next hop) to send the packet closer to the destination device’s LAN. Once a device sends an IP packet, routers determine that packet’s best route over the Internet or intranet to reach its destination most efficiently and in accordance with quality-of-service agreements.

What Problems Do Routers Solve?

Routers operate at the network layer to solve a fundamental problem facing bridged Layer 2 networks. In a bridged network, as the number of connected devices rises, the frequency of frame collisions increases as devices compete for bandwidth. This results in the reduction of the network bandwidth available. Routers were introduced to reduce collision domains to manageable subnetworks and to permit compute devices to route data efficiently between subnetworks regardless of whether the destination device is directly connected or several network hops away.

Both physically integrated and virtual disaggregated routers are used. Physically integrated routers are developed on merchant or custom ASICs with an integrated network operating system, and virtual routers are deployed to support cloud implementations.

Three basic router types are deployed today:

Access routers: An access router connects subscribers to their provider’s network so they can reach the Internet or private networks. Wireless and wired access routers support these networks to enable compute devices to connect to Wi-Fi and Ethernet LANs.

Edge routers: Edge routers logically define subscriber services, apply policy, meter services, and otherwise manage subscriber sessions. Edge routers typically support multiple edge services, including business, residential, video, mobile, and data center edge functionality for potentially hundreds of thousands of subscribers.

Core routers: Core routers forward packets across the Internet or private network backbones to interconnect communication networks. These routers must efficiently forward packets at high speed while preventing bottlenecks and packet loss.

Routers provide the essential building blocks network operators need to build robust networks. Operators can use routers to configure performance metrics with sophisticated routing algorithms and create traffic engineering policies to alleviate network congestion and maintain quality of service for subscribers.

How Do Routers Work?

The router’s primary function is determining the most efficient routing path for a packet to traverse the network. As the Internet has evolved, routing protocols have grown in sophistication. Some routing protocols leverage static metrics to determine the best route, while dynamic routing protocols calculate routes by leveraging software-defined networking and metrics calculated on the fly.

Routing protocols are classified into three main categories:

Distance-vector and link-state protocols: One way of classifying routing protocols is based on whether it leverages distance-vector metrics or link-state information to determine the best route. Distance-vector protocols use the number of intermediary routers between two given hosts as a metric to determine the best path to route a packet. Link-state protocols, in contrast, calculate the speed and cost of resources for each potential hop. Link-state protocols maintain three types of tables — a neighbor table, topology table, and routing table — and share updated information with adjacent routers to select the routing path.
Interior gateway and exterior gateway protocols: Interior Gateway Protocols (IGPs) are routing protocols that periodically exchange routing data within an autonomous system (AS), which is a collection of one or more networks managed by one carrier or enterprise. Exterior Gateway Protocols (EGPs), on the other hand, are designed to communicate routing and reachability information with routers in different autonomous systems.
Classful and classless protocols: Classful protocols don’t include subnet mask information during routing updates. These older protocols focus on identifying entire networks rather than individual IP addresses. Over time, however, classful protocols have largely been replaced by classless routing protocols, which share subnet mask information during routing updates. You find this characteristic in RIPv2, EIGRP, OSPF, and IS-IS protocols.

Types of Routing Protocols

With this understanding of routing protocols categories, let’s look at seven common routing protocols:

Routing Information Protocol (RIP): RIP was one of the first routing protocols created in the early days of routed networking. The protocol comes in two versions: RIPv1 and RIPv2. The first version, RIPv1, is a classful protocol which broadcasts its IP table to all routers in the network. RIPv2, a classless protocol, updates its routing table through a multicast address and uses authentication to secure the routing information. With a maximum hop count of 15, RIPv2 is suitable for smaller networks.
Interior Gateway Routing Protocol (IGRP): Unlike RIP, IGRP supports 255 hop counts and is widely used in large networks. This routing protocol has the characteristics of distance-vector and classful protocols. IGRP evaluates multiple metrics such as bandwidth, delay, load, and reliability to compare routes, and it is resistant to routing loops.
Enhanced Interior Gateway Routing Protocol (EIGRP): This protocol is an enhanced version of IGRP and is a distance-vector, interior gateway, and classless protocol. It uses the reliable transport protocol (RTP) and the Diffusing Update Algorithm (DUAL) to improve routing efficiency and accelerate the convergence process.
Open Shortest Path First (OSPF): OSPF is a link-state, interior gateway, and classless protocol. It maintains databases describing the entire network topology and uses the shortest-path-first (SPF) algorithm to calculate the route’s efficiency based on distance and required resources. When the topology changes, OSPF uses the Dijkstra algorithm to recalculate network paths and quickly converges on a new routing topology.
Exterior Gateway Protocol (EGP): EGP is used on routers that reside on the edge of an autonomous system. It exchanges routing data with other gateway hosts across different autonomous systems. EGP shares and updates network databases between the connected routers to ensure all routing tables — recognized routers, route costs, and network addresses tables — are updated. EGP was widely used by large organizations, but due to its lack of support for multipath networking environments, it has since been replaced by Border Gateway Protocol.
Border Gateway Protocol (BGP): BGP is a type of exterior gateway and distance-vector protocol. BGP determines the best path based on a long list of metrics — path length, origin type, router identification, neighbor IP addresses, and more. BGP allows administrators to customize routes to match their network needs and securely exchanges routing information with authenticated routers.
Intermediate System-to-Intermediate System (IS-IS): IS-IS is a link-state, interior gateway, and classless protocol, designed for routers within autonomous systems. The protocol broadcasts link-state information throughout its network. Each IS-IS router collects the flooded network information and constructs its database of the network's topology. IS-IS uses a modified version of the Dijkstra algorithm.

For additional information on other advanced network routing protocols, please see:

Juniper Router Implementation

Juniper Networks offers a robust portfolio of software-defined networking routers to help service providers, cloud operators, and enterprises transform their networks to meet today’s demands and future growth. We optimize each router family — ACX, MX, PTX, and SSR — to meet the needs of access, edge, and core, as well as cloud and data center networks. Juniper’s innovative router portfolio is packed with scale and efficiencies that allow network providers to adapt to unforeseen changes in the market as they build their networks up and out.

ACX Series Routers: High-performance ACX Series Routers serve metro access, aggregation, and data center use cases. They are energy-efficient, MEF 3.0 compliant, and support 5G high-precision timing and synchronization. The latest ACX routers, the ACX7000 family, are multiservice routers ideal for cloud metro deployments.

MX Series Routers: The MX Series provides multiservice edge routing functionality with industry-leading flexible logical scale. MX Series routers have unparalleled versatility and support business, residential, video, mobile, and data center service edge use cases.

PTX Series Routers: Juniper’s core routing portfolio, PTX series routers, are powered by Juniper’s custom Express ASICs and offer best-in-class throughput. These routers are 400G-capable and 800G-ready, with flexible filtering to keep ahead of hyperscaler demands and support native 400G inline MACsec.

Session Smart Routers: Juniper’s Session Smart™ Routers take software-defined routing and SD-WAN to a new level. Deploy it as software on customer premises equipment (CPE), on data center network servers, and in the cloud, or as an appliance for branch sites that offers multiple WAN link options.

See Juniper Routers for more details on these and additional portfolio routers in Juniper’s portfolio.

Router FAQs

What is the use of a router in networking?

A router links two or more local area devices to the Internet. Once devices are interconnected, this forms a network. Through packet switching, the router transfers Internet data packets from a central wide area network (WAN) connected to the Internet. The router then pushes the secured Internet traffic through to devices within the network. This can include computers, tablets, phones, and smart TVs within range of the router.

Is a router the same as Wi-Fi?

While a router can broadcast a wireless signal (Wi-Fi) to connected and enabled devices, it isn’t only for Wi-Fi. Routers also offer hard-wired connections to the Internet. Once the router connects to Internet data through hard wire or Ethernet, it can then translate that connection into a transmittable Wi-Fi signal that capable devices can pick up. You can also hard-wire your computer into the router and use it for a wired Internet link. You may prefer this if you have security, speed, or reliability concerns.

Do you need a router for Wi-Fi?

Although routers are usually used to transmit Wi-Fi to capable devices, other hardware can also provide wireless functionality. Gateways are modem/router combinations that can provide a wireless signal. Additionally, if you have access to a wireless hotspot from someone’s cellular device, you can use that signal to connect to the Internet. There’s also a scenario called ad hoc, which is a communication setting that allows multiple computers to link directly to each other and the Internet without help from a router. You can connect the computers by using an Ethernet crossover cable or enabling the computers’ wireless cards to talk to each other. You can also share files with multiple computers, known as a multi-hop ad hoc network without a router.

What is the difference between a router and a modem?

A modem connects directly to the Internet to secure and translate Internet data packets. These days, most manufacturers combine the two in devices known as “edge routers” or “gateways.” Modems were once primarily for residential situations, whereas edge, core, or gateway routers offer more density, ports, and bandwidth and are primarily meant for enterprise.

If your business continues to grow, you can connect switches to the edge router or gateway to transmit connections to additional devices. When they aren’t combined, the major difference between a router and a modem is that modems connect directly to the Internet and can only provide one or two devices with Internet connection through a direct or wired link. A router, on the other hand, connects to the modem or a WAN, acquires the translated and secured data packets, and then broadcasts packets through wireless, Ethernet, or fiber to many users in your local network.

Do I need a router if I already have a modem?

Usually. If you want to connect more than one device to a hard-wired or wireless signal, you should get a router and/or switch. If you already have a router and need even more connections to upscale your business or service, a switch can link to the router to add even more bandwidth. Modems usually aren’t capable of wireless connections or don’t have enough bandwidth to support several users. Theses days most modems are actually modem/router combinations that are only ideal for residential use.

What routing solutions does Juniper offer?

Juniper Networks has a range of adaptable and scalable core and edge routers, gateways, and switches to fit most enterprise needs.

Our routers’ industry-leading features include:

SDN and SD-WAN enabled
AI and machine learning capabilities
Automation
Cloud-optimized form factor
400/800 GbE ready
Rich, multiservice edge and timing features

Juniper Networks also has a series of Session Smart Routers, which use SD-WAN to your business’s advantage. These core routers have access to software and reinforced WAN connectivity that adapts to fix inefficient processes that may drive up operational costs. It uses data from cloud access to monitor and predict more efficient solutions for your business. While all our routers have high-level performance, security, and availability requirements, Session Smart Routers have far more stringent performance protocols. Session Smart Routers also offer maximum flexibility, as they can be deployed and managed on white-box CPE, on data center servers, or in the cloud.

Session Smart Router features include: