A network device that forwards packets from one network to another. Based on internal routing tables, routers read each incoming packet and decide how to forward it. The destination address in the packets determines which line (interface) outgoing packets are directed to. In large-scale enterprise routers, the current traffic load, congestion, line costs and other factors determine which line to forward to.
At the Edge and In Between
Most routers in the world sit in homes and small offices and do nothing more than direct Web, e-mail and other Internet transactions from the local network to the cable or DSL modem, which is connected to the ISP and Internet. Sitting at the edge of the network, they often contain a built-in firewall for security, and the firewall serves all users in the network without requiring that the personal firewall in each computer be turned on and configured. See firewall and personal firewall.
However, in the larger company, routers are also used to separate local area networks (LANs) into subnetworks (subnets) in order to balance traffic within workgroups and to filter traffic for security purposes and policy management.
Routers in the Core
Within a large enterprise, routers serve as an internet (lower case "i") backbone that connects all internal networks, in which case they are typically connected via Ethernet. Within the global Internet (upper case "I"), routers do all the packet switching between the backbones and are typically connected via T3, ATM or SONET links. See collapsed backbone.
Routable Protocols
Routers route messages transmitted only by a routable protocol such as IP or IPX. Multiprotocol routers support more than one protocol; for example, IP "and" IPX. Messages in non-routable protocols, such as NetBIOS and LAT, cannot be routed, but they can be transferred from LAN to LAN via a bridge.
Because routers have to inspect the network address in the packet, they do more processing and add more overhead than a bridge or switch. Routers work at the network layer (layer 3) of the protocol, whereas bridges and switches work at the data link layer (layer 2), also known as the "MAC layer." See OSI model.
Specialized Machines or Regular PCs
Most routers are specialized computer-based devices optimized for communications; however, router functions can also be implemented by adding software to a server. For example, NAT32 is software from Microsoft that enables a PC to function as a router to the Internet for machines on the network. The major router vendors are Cisco Systems and Nortel Networks.
Router Terminology
Routers used to be called "gateways," which is why the term "default gateway" means the router in your network (see default gateway). In older Novell terminology, routers were also called "network-layer bridges." For more details on the routable protocol layer (network layer 3), see OSI model and TCP/IP abc's. See layer 3 switch, route server, router cluster and routing protocol.
Route Forwarding
Routing tables hold the data for making forwarding decisions. Although this is a simple example, routing tables become very complex. Static routing uses fixed tables, but dynamic routing uses routing protocols that let routers exchange data with each other.
Cisco Routers
For years, Cisco has been the leading router vendor, and these high-end, carrier-grade 7600 models process up to 30 million packets per second (pps). Cisco also makes smaller routers for less intensive applications. (Image courtesy of Cisco Systems, Inc.)
At the Edge and In Between
Most routers in the world sit in homes and small offices and do nothing more than direct Web, e-mail and other Internet transactions from the local network to the cable or DSL modem, which is connected to the ISP and Internet. Sitting at the edge of the network, they often contain a built-in firewall for security, and the firewall serves all users in the network without requiring that the personal firewall in each computer be turned on and configured. See firewall and personal firewall.
However, in the larger company, routers are also used to separate local area networks (LANs) into subnetworks (subnets) in order to balance traffic within workgroups and to filter traffic for security purposes and policy management.
Routers in the Core
Within a large enterprise, routers serve as an internet (lower case "i") backbone that connects all internal networks, in which case they are typically connected via Ethernet. Within the global Internet (upper case "I"), routers do all the packet switching between the backbones and are typically connected via T3, ATM or SONET links. See collapsed backbone.
Routable Protocols
Routers route messages transmitted only by a routable protocol such as IP or IPX. Multiprotocol routers support more than one protocol; for example, IP "and" IPX. Messages in non-routable protocols, such as NetBIOS and LAT, cannot be routed, but they can be transferred from LAN to LAN via a bridge.
Because routers have to inspect the network address in the packet, they do more processing and add more overhead than a bridge or switch. Routers work at the network layer (layer 3) of the protocol, whereas bridges and switches work at the data link layer (layer 2), also known as the "MAC layer." See OSI model.
Specialized Machines or Regular PCs
Most routers are specialized computer-based devices optimized for communications; however, router functions can also be implemented by adding software to a server. For example, NAT32 is software from Microsoft that enables a PC to function as a router to the Internet for machines on the network. The major router vendors are Cisco Systems and Nortel Networks.
Router Terminology
Routers used to be called "gateways," which is why the term "default gateway" means the router in your network (see default gateway). In older Novell terminology, routers were also called "network-layer bridges." For more details on the routable protocol layer (network layer 3), see OSI model and TCP/IP abc's. See layer 3 switch, route server, router cluster and routing protocol.
Route Forwarding
Routing tables hold the data for making forwarding decisions. Although this is a simple example, routing tables become very complex. Static routing uses fixed tables, but dynamic routing uses routing protocols that let routers exchange data with each other.
Cisco Routers
For years, Cisco has been the leading router vendor, and these high-end, carrier-grade 7600 models process up to 30 million packets per second (pps). Cisco also makes smaller routers for less intensive applications. (Image courtesy of Cisco Systems, Inc.)
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Bountiful WiFi BWRG1000 Wireless Router
- Amazing signal strengthVery impressive range, coverage far superior to anything i have ever tried! I tried their other product for a hotel scenerio, the Bountiful Managed Access Point 1000G and its range was just like this super blue router. I was pleasantly surprised by the controller solution which gave me...
- Discussion threads 2009-11-20
- Inside the Google Chrome OS security model
- The proof will be in implementationAll of these lofty goals are one thing. Making it happen in code is quite another. It sounds like they are just giving a laundry list of what people want them to say. I'm in the "believe it when I see it" camp. Good intentions...
- Discussion threads 2009-11-19
- Live from Googleplex: Chrome OS details revealed
- Ubuntu 9.10 has more immediate potentialMight I suggest trying Ubuntu 9.10? A phenominal OS with much more to offer then even Windows 7.Open source, free and ready to try today...http://blogs.techrepublic.com.com/10things/?p=1122http://www.tuxradar.com/content/vista-windows-7-ubuntu-904-and-910-boot-speed-comparisonhttp://www.youtube.com/watch?v=lYgWE6Svpaghttp://www.youtube.com/watch?v=16-nad9N3pgNot that I have readI'd stick with 904immediate potential to sink in obscurityGoogle was Linux's last fleeting chance to turn...
- Discussion threads 2009-11-19
- FAA hit with network glitch; Flight plans go manual
- Another glitch with a linux network? Its hard to believe people still use it for anything critical like the FAA and flight tracking. Its a toy OS and should not be used when the lives of people are dependent upon it.Cisco supplies the network backboneIt will be interesting to see...
- Discussion threads 2009-11-19
- Samsung upgrading its UbiCell CDMA base station to 3G next year
- Samsung has announced that their UbiCell Personal CDMA Base Station will go 3G in 2010. But other than that, it's pretty hush hush. Basically, the station eliminates the need for any pesky land line services. The plug-and-play station provides in-home cellular service securely over...
- Blog posts 2009-11-17
- Synology Disk Station DS409slim - NAS server
- Synology Disk Station DS409slim is a true miniature powerhouse in the network-attached storage device market. It's the first 2.5-inch hard drive-based NAS server we've reviewed that offers hot-swappable capability. However, that is its least impressive feature. The server did well in our performance tests and, like other Synology products we've...
- Product reviews 2009-11-16
- More evidence of the coming collision between home broadband and the smart grid
- Collision?Not the word I would have used.In any event, I think this is a positive and necessary direction to go. In order to manage more diversified, less dependable/consistent sources of energy, the demand side HAS TO be managed. Without it, we are just setting ourselves up for a lot of...
- Discussion threads 2009-11-16
- Aluratek WMQ137AM 3G Wireless USB/PCMCIA Cellular Router - Retail
- Aluratek 3G USB/PCMCIA routerIt's probably my error, but I can't get any of three computers to see the Aluratek router and Aluratek does not respond to support questions. I can't say if it works with my ZTE USB modem since it will not install. I bought it in Texas and...
- Discussion threads 2009-11-15
- Microsoft probing Windows 7 zero-day hole
- I hope Jeremy got some sleep last nightbecause he probably won't be getting much in the near future.first of many zillionsis there anything worse than being MS security programmer?poor bastards.YesYeah, being a mindless repetitive troll.yeah, being a poor Mac user. yeah, being a poor Mac user....
- Discussion threads 2009-11-12
- Cloud Engines Pogoplug
- Photo gallery:Cloud Engines PogoplugWouldn't it be nice to quickly access your data from anywhere without a complicated network setup? That's exactly what the Cloud Engines Pogoplug offers. Priced at $100, this tiny gadget turns any USB external storage devices--anything from a Seagate FreeAgent Go to a Western...
- Product reviews 2009-11-10
- No more servers? Rackspace says IT workers are tired of them
- And, as servers move to the cloud, fewer and fewer will be Windows servers.When you deploy thousands, you can pay millions in licensing for Windows, and, then Windows is less stable and less secure.RE: No more servers? Rackspace says IT workers are tired of themI wonder how well those outsourced...
- Discussion threads 2009-11-10
- Nofeel FTP Server (32-bit) 3.6.3812 (Windows)
- Powerful, secure, and easy-to-use FTP server specially written for Windows 2000/XP/2003/Vista/2008. Enable users to have real-time interaction with server, including current and past connections full details, server current and permanent stat, ability to stop file transferring or disconnect any connection. Rich server settings are provided, including but not limited to...
- Software downloads 2009-11-10
- IP Address Menu 6.0 (Mac)
- You want to display your current IP address in the menu bar? You want to display your user name, your computer name, the IP address, the subnet mask and the MAC address of each of your network interface at the same time? You want your Mac to automatically send an...
- Software downloads 2009-11-09
- Linksys WRT160N
- Basic functions OK but no USB storage!Router is advertised to allow the add-on of a USB external hard drive. I've spent 12+ hours on Linksys phone calls with tech people, supervisors, and customer service and still cannot get this feature to work. They replaced the router under warranty, but still...
- Discussion threads 2009-11-08
- WD TV Live HD Media Player
- The first few rounds of network media streamers we tested weren't necessarily recommendable. Sure, this was partially because most of these devices depend on Windows Media Center for connectivity and content, but we also had issues with their interfaces and performance.Fast forward a year and it's safe to say that...
- Product reviews 2009-11-07
- NetGear WNHDEB111 HD Gaming Wireless N Networking Kit
- Editors' note: As the NetGear WNHDEB111 HD Gaming Wireless N Networking Kit is a gaming networking accessory, we didn't put it through the same testing process we use for wireless routers.While home wireless products continue to invade the marketplace, the demand for high-speed wireless performance increases. At this point,...
- Product reviews 2009-11-05
- Open source needs successful champions
- Open Source powers the Internet period!Open_Source powers the ENTIRE Internet withrouters/switches/servers you name it like Microsoft sitting behind caching Linux distroname servers.Now you tell me what does it need now???It is the FUTURE of smart devices, appliancedriven infrastructure, just like VMware using a Linux derived kernel and it is #1...
- Discussion threads 2009-11-05
- Microsoft fixes IE patch again
- A Patch To Fix A PatchMicrosoft is up to its old tricks again.Yes, Microsoft IS up to its old tricks...... fixing things that don't work, repairing broken code, and generally looking after its customers. Too bad they can't do the same for you. (Fixing things that don't work)@Confused...
- Discussion threads 2009-11-04
- Internet performance management makes data center consolidation possible
- There are many more advantages to consolidation... Virtual switch technology... Virtual switch technology, is far faster than anything Ciscoor other hardware router vendors can push through your INTRAnet.... In the era of mashups... and multi database applications, you want internet connections that are at memory transfer speeds, not...
- Discussion threads 2009-11-02
- Apple TV update looks good but doesn't offer much more
- I second your thoughts, Sam.The updates were nice, but hardly worth it from the functional standpoint. Yes, Netflix would be nice, although iTunes provides most, if not all, of what Netflix would, doesn't it?One thing Tim Cook mentioned during the most recent earnings call was that Apple was going to...
- Discussion threads 2009-10-30
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
- The best support in the Linux business
-
If Linux is going to power your mission-critical applications, you'd better have the best support known to business. Novell was rated the top provider of Linux technical support.
- Learn more >>
- The best support in the Linux business
-
If Linux is going to power your mission-critical applications, you'd better have the best support known to business. Novell was rated the top provider of Linux technical support.
- Learn more >>
- The more you simplify, the more you save
-
When you transition from your existing Red Hat environment to SUSE Linux Enterprise from Novell, you can recognize dramatic cost savings, perhaps as much 50%
- Learn more >>
- Learn more about tools to grow your business
-
The Business Essentials Guide provides you useful tools and templates to help grow your business and save you time with automated shipping solutions.
- Save time with the UPS Business Essentials Guide
Meet Doc
-
-
Here to help you with your Document Management Needs
- Check out Doc’s Blog on ZDNet
- Help your company, help the earth I want to share with you the Environmental Defense Fund Paper Calculator, which allows you to gauge your organization's environmental impact.
- Which is Greener: Paper or Digital? The Answer May Surprise You Anything we can do to reduce paper consumption is good. But what about the impact of digital waste?
-
Produced by
ZDNet and -
