Home > Articles > Certification > Cisco Certification > CCNA

Routers and Switches and Hubs, Oh My! An Introduction to Network Devices and Their Functions

Sean Wilkins, co-author of CCNA Routing and Switching 200-120 Network Simulator, discusses some of the most common network devices that network engineers need to know and understand.
Like this article? We recommend

Overview

Getting into networking can be a bit overwhelming. Even with your previous experience using computers and other electronic devices, you might discover many devices that you never knew existed. This article starts from the beginning and discusses some of the most common networking device types and their functions within the network.

Hubs

At the simplest side of the equipment scale is the hub. This is a very simple device that connects together multiple local area network (LAN) devices. The only function of the hub is repeating the electrical signals received on one port, relaying those signals to all other connected ports. It does nothing else. Hubs are extinct for the most part in modern networks because, while they are inexpensive, they aren't much cheaper than a simple switch, which provides other functionality. Hubs work at Open Systems Interconnection (OSI) Layer 1.

Bridges/Switches/Multilayer Switches

The next device up the chain is the Ethernet bridge. A bridge is used to connect multiple LAN segments together, forming multiple collision domains. A collision happens on an Ethernet network when multiple devices attempt to "speak" at the same time. By separating two or more LAN segments into multiple collision domains, the bridge reduces the number of collisions that could potentially occur on a LAN segment (fewer LAN speakers on the same segment), which improves network performance.

The next evolution was the network switch. In its simplest form, a switch is a multiport bridge with some additional functionality. The switch almost completely ended the risk of collisions on hub-centered networks.

There are a few categories of switches, distinguished by function:

  • Unmanaged (Layer 2) switch
  • Managed (Layer 2) switch
  • Managed Layer 3 switch (multilayer switch)

Unmanaged Layer 2 Switches

A modern unmanaged switch provides the functionality of a multiport bridge; each of the switch ports is on its own collision domain. Like bridges, the switch has built-in support for the Spanning Tree Protocol (STP), which provides loop prevention when multiple switches (bridges) are connected, introducing the potential for switching loops. A switch also keeps an internal database of the known MAC addresses connected to each port. This information is used to reduce the amount of Ethernet frame flooding that occurs when a device location is unknown (as with hubs).

Managed Layer 2 Switches

A modern managed switch provides all the functionality of an unmanaged switch; in addition, it can control and configure the behavior of the device. This typically introduces the ability to support virtual LANs (VLANs), which is why almost all organizations deploy managed switches versus their cheaper alternatives.

Managed Layer 3 Switches (Multilayer Switches)

The final type of switch is a Layer 3 or multilayer switch (MLS). This type of device provides a mix of functionality between that of a managed Layer 2 switch and a router. (The next section describes routers.) The amount of router function overlap is highly dependent on the switch model. At the highest level, a multilayer switch provides better performance for LAN routing than almost any standard router on the market, because these switches are designed to offload a lot of this functionality to hardware.

Routers

At its most basic, a router performs its functions almost solely at OSI Layer 3. This is because (on modern networks), the router is used to connect Internet Protocol (IP) networks. Since IP is a protocol that runs at OSI Layer 3 and can operate on multiple Layer 1 and 2 technologies (including Ethernet), a router is typically used to connect geographically dispersed parts of a network that use technologies other than Ethernet to connect them; for example, leased line, Frame Relay, or Multiprotocol Label Switching (MPLS) connected devices/offices. Routers also provide the ability to separate IP broadcast domains. This feature is important, as some protocols use broadcast heavily to communicate with hosts.

On most modern networks, multilayer switches are preferred over routers in LAN situations, and routers are used to connect together devices that don't connect using Ethernet.

Modern routers support a number of features that are not limited to OSI Layer 3, including support for network address translation (NAT), firewalling services, access control lists (ACLs), packet inspection, and many others.

Firewalls (VPN Concentrators)

The principal function of a firewall is to protect some portion of a network. A number of different techniques are used; which ones are supported depends greatly on the specific firewall vendor and model. Techniques include access control lists, stateful packet inspection (SPI), and others.

A newer breed of firewall, referred to as next-generation firewalls (NGFWs), are currently being marketed. These firewalls include all the functionality of a traditional firewall (ACL, SPI) and add support for built-in intrusion prevention, deep packet inspection, and virtual private networks (VPNs), as well as a much higher level of application awareness.

Host Intrusion Detection/Prevention Systems (HIDS/HIPS)

As indicated by the name, a Host Intrusion Detection/Prevention System (HIDS/HIPS) is used to protect a single host from an intrusion attempt. An IDS differs from an IPS in that an IDS only detects that someone is attacking; it doesn't mitigate the attack, whereas an IPS can actively mitigate the attack as it happens.

Modern versions of these types of software are focused mostly on intrusion prevention, because most modern-day attacks come with little or no warning and require an accelerated response.

Network Intrusion Detection/Prevention Systems (NIDS/NIPS)

A Network Intrusion Detection/Prevention System (NIDS/NIPS) is different from a HIDS/HIPS system in that it detects or prevents attacks from happening against a group of devices. Similar to their host-based alternatives, NIDS detect attacks as they're happening and report the activity, and NIPS detect and actively take steps to prevent the attack from continuing. This defense can include everything from the dynamic creation of ACLs to shutting down offending ports.

Access Points

An access point (AP) is used in wireless Ethernet networks in place of an Ethernet switch. Typical APs also provide bridging functionality between wired Ethernet and wireless Ethernet hosts.

There are three categories of access points: consumer APs, enterprise autonomous APs, and enterprise lightweight APs.

Most technology people are at least a little familiar with consumer APs, from having such devices in their own homes. These little APs (often called "wireless routers") are used to connect together the wired and wireless clients of a home or small business network. They typically also provide a wide area network (WAN) port for connection to an Internet service provider (ISP). This WAN port is simply another Ethernet port that is separated in the device's configuration to perform routing between a local network and a remote network (typically the Internet). It's also typically used as a zone separator for the built-in firewall.

Enterprise APs consist of two further categories: autonomous and lightweight. An autonomous AP acts as a bridge between the wireless clients on a network and the wired network. Such APs are typically limited to the performance of this main function. These devices may be managed remotely, but the services delivered are all handled within the AP itself.

A lightweight AP also bridges together wireless and wired networks, but it's controlled by a remote controller. This controller performs a number of functions that are built into autonomous APs; the lightweight AP is essentially a brainless device without the wireless controller that controls its actions and configuration. The controller can also perform other functions such as load balancing between APs, interference detection and mitigation, and security functionality.

Content Filters

Content filters are used on some networks to control the type of data that is allowed to pass through the network; one widely known content filter is commonly called "the Great Firewall of China." These devices scan for and remove content that is not wanted. Some common options that are typically seen are limits on types of pornography and violence. This functionality is typically built into modern firewalls and some router platforms.

Load Balancers/Application Delivery Controllers

One term commonly seen in older documentation is the concept of a load balancer, as a separate piece of equipment that solely performed this function. While this was true in the past, modern load balancers use the term application delivery controller (ADC), and they're not limited to performing load-balancing functionality. Their functionality has extended to perform a number of different activities, including the following:

  • Local and global load balancing
  • Network and device health monitoring
  • TCP multiplexing
  • Support for common network routing protocols
  • Application acceleration
  • Denial-of-service protection
  • Web application firewall
  • Support for virtualization and multi-tenancy

Packet Shapers/Policers

A packet shaper or policer controls the flow of information into or out of a specific device. The shaping or policing functionality is typically built into routers (and some switches) to deal with times when network demand outpaces the ability of a device or its port. In situations of no congestion, the shaping and/or policing functionality is not used. When there is congestion, these features will control how the excessive traffic is handled.

Traffic shapers attempt to "shape" the traffic by utilizing congestion functionality built into the used protocols. For example, IP, Frame Relay, and MPLS support marking packets with a varying level of priority bits; this marking affects how the traffic is treated when it's being forwarded through the network. Traffic that is marked as low priority will be dropped first in situations of high congestion.

Traffic policers act a bit more abruptly than shapers; typically policers drop any traffic that exceeds a configured threshold. As long as traffic continues to be transmitted above that threshold, it will be dropped. When the rate decreases, the policer stops dropping traffic.

The exact method used to shape or police traffic depends on the specific feature used and on which vendor's equipment is configured.

Summary

Obviously, a number of different devices are used in a modern network, and the devices covered in this article are just a few of the most commonly discussed network devices. I hope that this article is useful as a reference to help you determine the differences between these devices and how they can be fitted together to provide all of the functionality used on a modern network.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020