Network routing: A complete guide to network routing techniques and protocols

Network routing is an important part of network communications. Routing helps your network components select the best network path from the available choices. This makes network communication efficient and reliable. The hardware components that enable this are called routers. Monitoring and managing routers are an indispensable part of network administrators' everyday tasks. Since routers can make or break your network connectivity and availability, it is important to understand how routers and routing techniques work. On this page, we dive into the details of:

Routing 101: Routers, routes, and network communication

Networks rely on both wired and wireless routers that perform two important network functions. They manage network traffic and allow multiple devices to use the same internet connection. Routers also connect different packet-switched networks to their subnets.

How does network routing work?

Routers maintain a log of all the available network paths in a built-in database called the "routing table". This table needs to be constantly updated to ensure the paths logged are complete per the real-time path in the network.

Every time a router receives a network data packet, it inspects the packet header to obtain details about where the packet is headed. Based on this information, the router checks its routing table and forwards the packet in the most effective network route. This way, the packet traverses from one router to another until it reaches its destination network and ultimately the destination device.

For instance, in the network below, route 2,4 might seem shortest and more efficient when compared to route 1,3,5. However, this route might be suffering from low bandwidth and network connectivity issues. This is where network routing protocols step in and calculate the best route, i.e., route 135, and forward the network packet to network 1. Which is then forwarded to network 3, and so on.

Routers vs. other network communication enablers

Before we dive into the details of routing protocols, let's quickly learn about the distinct data packet management functionalities of routers when compared to similar network components–switches and modems.

Routers vs. switches: Both routers and switches handle data packets in the network. While switches enable communication by handling and forwarding IP packets between devices within the same sub network, routers manage the packets between multiple LAN and WAN networks.

Also, core routers act as the core of your network communication. They handle high-volume data packets and enable forwarding between the connected networks. They do not communicate with the external world, such as the internet.

Routers vs. modems: Many networks use network hardware with routers and modems designed into one component. While they often coexist and enable internet connectivity to different network devices, the routers and modems perform different functions. Routers are responsible for distributing signals to multiple network devices. Modems, convert signals from the internet to digital signals processable by your network devices.

For instance, using a router, multiple devices in the LAN can access the internet at the same time. With a modem, only one device can connect to the internet at a time.

This is where edge routers play an important role as they enable communication between the external internet and your core routers.

Techniques and protocols that enable network communication

Based on the routing information exchange technique followed by the routing protocols, they are classified into three main categories as follows:

  • Distant vector routing (DVR) and link state routing (LSR): Both dynamic routing algorithms work based on the exchange of routing information between the router and its neighbor. While DVR uses the Bellman-Ford algorithm to update its routing table using information from its neighbors, LSR relies on Dijikstra's algorithm and floods information to all the other routers in the network. Routing tables created and shared in these algorithms include, neighbor, topology, and route calculation tables.
  • Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP): In IGP, the routers within an autonomous network environment exchange routing information within routers in the constituent sub networks. EGP helps routers from different autonomous networks, i.e., networks with different control centers, exchange routing information within themselves. However, EGP is less common in networks since it is only used in cases where a device needs to communicate out of its default network.
  • Classful and classless routing: In classful routing, network routers do not define the subnet mask as a part of its routing update. While it is the easier routing technique when it comes to routing fault detection, it takes up significant bandwidth due to the need for frequent routing updates. This has made classful routing an outdated approach that most network admins have replaced in their network. On the other hand, the classless routing technique adds the variable length subnet mask to its routing updates. This requires less frequent routing updates and consumes significantly less bandwidth when compared to classful routing.
  • Routing protocols

    Here's a look into the five common routing protocols organizations deploy based on their networking requirements,

    Routing Information Protocol (RIP)

    RIP is one of the earliest routing protocols popularly used in intra-domain networks that rely on DVR. Network admins deploy two versions of RIP–RIPv1 and RIPv2 based on their networking requirements.

    • RIPv1: It is a classful routing protocol that routes network communication based on the hop count. It measures the hop count for an IP data packet from its current router to the destination network. Comparing the hop counts of all the available paths, RIPv1 selects the optimal route for the packet to be forwarded. Here, the routers update their routing table by broadcasting their data to all the routers in the network.
    • RIPv2: It is a classless routing protocol that offers advanced capabilities, such as enhanced security, when compared to RIPv1. In this protocol, the routers update their routing table by multi-casting their data.

    While RIPv1 and RIPv2 can be used across WANs and LANs, their limited capabilities posses scalability challenges to network admins. For instance, RIPv2 can support router journeys for 15 hops or less. To overcome this difficulty and enhance routing scalability and communication, CISCO routers came up with two other protocols mentioned below.

    • Interior Gateway Routing Protocol (IGRP): This is a classful routing protocol that works on the foundations of RIP. IGRP by default works up to 100 hop counts. It can also be configured to work up to 255 hop counts. While it can automatically update routing information, it exhibits slow data convergence and higher bandwidth consumption.
    • Enhanced Interior Gateway Routing Protocol (EIGRP): This is a classes routing protocol that works on the foundations of RIP. It enhances efficiency when compared to RIP and IGRP by offering faster data convergence.

    Open Shortest Path First (OSPF)

    OSPF is a classless link state routing protocol commonly used within autonomous networks. It operates by selecting and forwarding the IP packet through the shortest network path to reach the packet's destination. OSPF does this by first building multiple databases on the network's topology with information from the link state advertisements by other routers in the network. These advertisements offer a detailed description of the network paths, distance, and resource consumption. This information help OSPF identify the shortest path for the IP packet and forward the IP packet to its destination. OSPF also offers various authentication capabilities for enhanced data security.

    This has made OSPF a widely used routing protocol in large, enterprise networks.

    Exterior Gateway Protocol (EGP)

    EGP simply focuses on reachability and communication between autonomous systems. Its routing table includes information such as the list of recognized routers, routing costs, and the addresses of all the nearby routers. This helps the routers establish a list of neighbors for routing, checking their status, and updating if any change has been detected. While widely used during the early days of networking, many network admins have now replaced it with border gateway protocol. This is due to EGP's limited capability to handle tree-like topologies and its inability to support multipath routing.

    Border Gateway Protocol (BGP)

    BGP is the latest and a popularly used routing protocol in the networking world. It is built on the foundations of EGP and is classified as a distance path vector protocol. BGP has two variations based on how it is used.

    • Internal BGP: IBGP enables network communication between routers within an autonomous system. It does not interact with devices outside the autonomous network.
    • External BGP: EBGP enables network communication between different autonomous systems i.e., inter-domain network routing.

    BGP works by choosing the best path for the packet to reach its destination. By default, the shortest path is selected as the best path. However, network admins can configure BGP to choose the best path based on different metrics, such as the path cost. Network admins can also configure BGP manually to automate network discovery and topology information updates. Also, BGP offers enhanced security with its authentication capability which allows only approved routers to exchange routing information with each other. These routing capabilities offered by BGP have helped network admins to configure network routing as per their networking needs.

    Intermediate System-to-Intermediate System (IS-IS)

    IS-IS is classified as a link state, interior gateway, classless routing protocol. Unlike other commonly used routing protocols, IS-IS is not based on the IP addresses and instead on an OSI layer 3 protocol called Connectionless Network Service (CLNS). However, network administrators can also deploy integrated IS-IS to enable IP-based routing in their networks. IS-IS works by grouping routers into different areas. Network routing within an area using IS-IS is called level 1 routing, and routing between areas is called level 2 routing. To enable packet forwarding, IS-IS relies on two addresses—Network Service Access Point (NSAP) to identify network service access points and Network Entity Title (NET) to identify network routers.

    Routers and routing protocols, and why you should care

    • Route flapping: When left unmonitored, route flapping can have serious cascading network issues. It increases network latency and can slow down and impact the performance of network routers. Network admins need to carefully select and deploy routing protocols and constantly monitor router performance to avoid route flapping.
    • Persistent routing loops: Scenarios such as the improper deployment of distant vector routing protocols can easily cause persistent routing loops in the network. This causes issues such as increased latency and link failure, which ultimately leads to significant packet loss and bandwidth consumption.
    • Resource utilization issues: Routing issues, when left unmonitored, can consume significant router resources causing router performance degradation. For instance, route flapping can easily cause rapid route recalculations that consume a significant amount of the router's CPU resources.
    • Network performance: Network routing issues, such as increased latency, route flapping, link failure, and rapid route recalculations, can cause performance degradation. This reduces the overall quality of the network for end users and impacts network connectivity. Network admins require a proactive router monitoring solution that enables in-depth insights into crucial router metrics.
    • Enhanced network security: With the ability to visualize their network topology, network admins can fine-tune their routing protocols, such as BGP and IS-IS, to enhance network security and avoid packet leakage.

    How ManageEngine OpManager helps you seamlessly manage your network routers

    OpManager's advanced router monitoring capability helps you keep a close watch on your network router's performance, health, and uptime. It helps you to track router availability using different availability monitoring polls such as ICMP, TCP, or SNMP, and enables you to,

    • Track critical performance metrics: With OpManager's enhanced network performance monitor, you can stay ahead of network issues by monitoring crucial performance metrics with ease. Detect issues before they disrupt your network and quickly carry out remediation tasks with in-depth insights into the managed routers.
    • Visualize your network topology: Generate different network maps of your network topology with OpManager's network topology mapper and effectively plan router placement and configuration. This helps you easily classify and configure interdomain and intradomain routers as per network needs.
    • Analyze bandwidth consumptions: Stay in the know about your network router's and WAN link's bandwidth utilization. Easily identify routes consuming significant network bandwidth and carry out necessary actions.
    • Optimize network resource management: OpManager offers proactive resource utilization monitoring and instantaneous alerting with adaptive threshold-based alerts. This helps you maintain your network resource utilization at optimal levels and avoid running into issues such as resource exhaustion.
    • Enhance capacity planning with granular reports: OpManager offers a comprehensive assortment of network performance reports that offer actionable insights for simplified router management. Understand how your router resources have been used over a period of time and plan ahead for future needs. You can also create automated report schedules that send you your required reports to the configured email at the set time intervals.
    Network routing

    That's not all! OpManager has much more to offer for advanced and simplified network performance monitoring. Interested? Schedule a personalized free demo, or download a 30-day trial of OpManager today!

 

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