Know Your Network: Switches, Bridges, and Routers

Thursday Oct 16th 2008 by Rafael Hernandez
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It isn't magic. Your data ends up where it needs to be thanks to some key components of your network infrastructure. Understanding their capabilities and the differences between each is a solid first step in planning your network.

That panel of blinking lights staring you right in the face is key to your network infrastructure. Whether it's piled up on racks, or stacked together in a closet somewhere, bridges, routers and switches all play different roles in keeping your devices communicating with one another - not to mention keeping the Internet at large going.

In this article, we'll be taking a look at how each handles your information and what it does with it along the way.

In The Beginning

The old, trusty network hub was a handy device that saw many businesses expand upon their computer networks allowing for relatively simple deployment (at the time) of the expensive Ethernet technology. As beloved as they were, their design exhibited some performance issues when traffic passed over it.

This was due to the fact that it blindly broadcasts data over all physical ports, aside from the one that the data originated from. This invariably caused "collisions" when any other device attempted to transmit at the same time.

These collisions severely degraded the speed at which any connected computer could communicate since the hub needed time to resolve them as part of the CSMA/CD scheme that governed their operation. The time it took to retransmit frames meant slower speeds for the increasingly relied upon network segments and their ever-increasing workloads. The public broadcast of each packet also meant that any device connected to the hub could easily snoop on information being transmitted, a security nightmare to be sure.

Having no processing capabilities to speak of, the hub simply acts as a repeater, which is somewhat of a waste when you consider the wealth of information stored in a packet's header. The header has all manner of useful information that allows more robust networking gear to prioritize delivery and check data integrity, which a hub blindly ignores and passes along to any connected device.

Of course the onward march of technology meant the rather expensive switches of the day became more and more affordable as competition increased and embedded processors became cheaper and more abundant.

The Switch

The network switch is designed to efficiently handle any traffic it receives given its network-optimized, or often times, general purpose processors and its segmented connections between each physical port eliminating the device-wide collision issues found in hubs. The separate connections for each port isn't completely responsible for the improved performance as the on board processor is designed to read a data packet's header information and immediately route it to the correct physical port.

Netgear 24-port switchThat's not all a switch is limited to. Many high grade products have a fair measure of configurability and management features allowing one to set up Virtual LANs within their network, control link speeds for each individual port, and monitor data moving over the switch, something that normally wouldn't be easily possible given the separate links these devices maintain.

While Ethernet is a common connection, enterprise-grade routers and switches typically have modular interfaces that can accept new boards that sport support for established or newer high-speed interfaces such as Fibre Channel and ATM.

The Bridge

Given the switch's capabilities, you would think that a bridge would be a redundant piece of hardware given that it performs many of the same functions... and you'd be correct.

The network bridge is designed to seamlessly connect two or more smaller network segments into one harmonious whole. They generally contain fewer physical ports, but with switches able to play the same role, you'll likely find the latter keeping things together on your networks.

Plugging your LAN segments into the same bridge/switch does make getting your networks talking to each other a simple process and the link speed controls can come in handy when you have to share those Internet links with several dozen, or hundreds, of machines.

Another thing you'll want to keep your eye on when dealing with multiple networks being bridged is just how much traffic is passing through them and how many connections it's going to be tracking. The requirements are exponential so you'll be looking at some robust gear such as Cisco's Catalyst 2960 series of switches for small to medium sized needs while enterprise endeavors are no doubt mulling over Cisco Nexus 7000 switches.

The Router

Seeing as the trend is to build upon the smaller segments of a network in order to get to the next big thing, you'll invariably hit the router - the granddaddy of network devices.

A home router, for instance, will typically connect a few computers to the Internet at large, passing on the data you generated to your ISP for forwarding to its destination. Along the way it's bound to hit sophisticated pieces of equipment designed to handle quite a bit more data than your connection can muster.

Cisco XR 12000 RouterRouters operate on Layer 3 of the OSI Model, which handles figuring out the optimal path for your data to reach its endpoint. Switches/bridges function on layer two, which determines the quickest way to deliver the information that it is keeping track of by matching up a connected device's MAC Address with the IP Address it was communicating with.

Routers are far more interested in the IP Address that data packets are destined to be delivered to and the priority of the information being sent, usually set by the router's maintainer.

Those IP Addresses are, of course, doled out in large blocks to Internet Service Providers, institutions and corporations at large so there are a ton of them. So many in fact that the old IPv4 standard is quickly running out of usable numbers, given the number of Internet capable devices and people receiving Internet service the old 32 bit addresses is making way for IPv6 which boasts many more workable addresses.

The focus on simply delivering the data simplifies things a tiny bit for this workhorse, giving it more free time to learn routing information from any other routers connected to it or in close enough proximity, thereby allowing your data to be sent over the best possible path. Should that path not be available due to, say, construction equipment somehow severing important connections, the router will select the next best link.

These machines tend to be located where large clusters of smaller networks reside or even high powered blocks of servers that require a generous amount of bandwidth in order to operate optimally. If you are beyond the point of wiring a small business, you're likely scoping out hardware like the Cisco 2800 series of routers. At the very high-end, are Cisco routers like the XR 12000 series pictured above.

Although synonymous with networking, Cisco isn't the only game in town. Outfits like Juniper Networks, 3Com and Foundry Networks, to name a few, compete hard for your computer networking budget.

Whether a switch, bridge or router, each device type plays an important role in keeping your IT operations going while the end user is none the wiser. At times, they may seem to overlap in functionality, but the few key distinctions make it so that each layer is only processing the data it needs to, keeping things running smoothly on WANs and LANs alike.

This article was first published on EnterpriseITPlanet.com.

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