Cisco networking 101: Five things you should know

No matter how long you've been working on networks, it never hurts to review the basics every now and then—even seasoned administrators sometimes need a refresher. That's why David Davis has compiled a list of five things every administrator needs to know about Cisco networking.

No matter how long you've been working on networks, it never hurts to review the basics every now and then—even seasoned administrators sometimes need a refresher. Taking a break from your well-honed routine of shortcuts and going over the finer points of networking can even open your eyes to new best practices and troubleshooting methods.

With that in mind, let's look at five things everyone should know about Cisco networking and working with routers.

Know the difference between a home router and an enterprise router

While teaching Cisco networking classes, I often assign students the project of proposing equipment for a company's new network, which would be a frame-relay network. It always surprises me how many students recommended a D-Link, Netgear, or Linksys router to connect to that network.

Such routers are great to connect a home network to the Internet. However, they just aren't adequate for most midsize businesses. These types of routers lack enterprise grade management, troubleshooting features, performance capabilities, reliability options, and the protocols and modules required for most company networks.

For more information, check out "Choose a Cisco router that best fits your organization's needs."

Understand the difference between a router and a switch

This may seem incredibly basic, but it's surprising how many people don't really understand the difference between a router and a switch. Here's a quick review.

A router works at the network layer of the OSI model (Layer 3) and generally connects a LAN to a WAN. So, you need a router to connect to your company's WAN or to the Internet—obviously, the most common use).

On the other hand, a switch connects devices on a LAN. You need a switch to connect two PCs to a server or a router.

For more information, see "Cisco administration 101: Upgrading routers and switches" and "Implement switch security on your network."

Understand how network traffic flows

When you make a request over a network, the system breaks up that request into several smaller pieces. For example, when you click a link on a Web page, a good amount of communication needs to occur in order to serve the requested page. Every graphic is a separate request, and the text is another request.

Every piece of information sent via TCP/IP has an acknowledgement packet. All of these packets can take different paths to travel from sender to receiver.

Understanding this process is invaluable when it comes to troubleshooting. Seeing it in a protocol analyzer and being able to visualize how the communication works is even better.

For more information, see "Clear up network congestion"and "Provide redundancy on your Cisco routers with GLBP."

Understand what a firewall
can—and can't—do

While firewall has become a well-known computer term, many people only vaguely understand its use. And many don't realize that there are many different kinds of firewalls.

There are both software firewalls (such as Windows Firewall or ZoneAlarm) and hardware firewalls (such as Cisco PIX or Checkpoint). Most businesses require a hardware firewall.

A firewall is a great and necessary protection device for most organizations. However, it typically can't protect your company from everything. For example, most firewalls can't protect users from phishing attempts or viruses distributed via e-mail. That's why it's vital to understand what you can expect from your firewall when deploying it.

For more information, check out "Firewall FAQ" and "Get to know Cisco's new security appliance: ASA 5500."

Know the basics of IP addressing

It's a given that the majority of end users don't understand the basics of IP addressing, but it's surprising how many server administrators and developers are also sketchy on the details. Need a refresher course? Here are three vocab terms you need to understand.

  • IP address: Every device has an IP address, which uniquely identifies it on the network.
  • Subnet mask: This tells the device which portion of the IP address defines the network and which portion is for the node (or the host). In other words, the subnet mask tells the computer which IP addresses are on its local network.
  • Default gateway: This is only necessary if the destination IP address that you're sending traffic to isn't on your network. Again, the IP address and subnet mask tell the computer knows which network it's on. When traffic isn't on your network, the device sends that traffic to the default gateway. If you don't need to communicate outside of your organization's LAN, you don't need to define a default gateway.

For more information, check out "Cisco IP subnetting 101: Five more things you should know," "Cisco IP subnetting 101: Learn more about all 1s and all 0s subnet masks," and "Cisco IP subnetting 101: An introduction to supernetting."

Stay tuned: Next time, I'll tell you five more things you need to know about Cisco networking, including Cisco's administrative modes, the various uses of the show command, how private IP addressing and NAT work together and more.

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David Davis has worked in the IT industry for 12 years and holds several certifications, including CCIE, MCSE+I, CISSP, CCNA, CCDA, and CCNP. He currently manages a group of systems/network administrators for a privately owned retail company and performs networking/systems consulting on a part-time basis.

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