Computer Technology Support

As a CCNA candidate, you most likely have some background in PC hardware and workstation support. If so, you’re already familiar with loopback interfaces, particularly 127.0.0.1, the loopback address assigned to a PC.

When you’re learning all about the different physical interfaces for your CCNA exam - serial, ethernet, and BRI, among others - there’s one logical interface you need to know about, and that is - you guessed it! - the loopback interface.

What isn’t as immediately apparent is why we use loopback interfaces on routers and switches to begin with. Many of the Cisco router features that can use loopbacks are intermediate and advanced features that you’ll learn about in your CCNP and CCIE studies, but these features all come back to one basic concept: If the loopback interface on a router is down, that means the router is unavailable as a whole.

In contrast, a physical interface being down does not mean the router itself is out of commission. A router’s ethernet port can go down, but the other physical interfaces on that router are still operational. Since a loopback interface is logical, there’s nothing physical that can go wrong with it.

As I mentioned, you’ll learn different Cisco router and switch features that utilize loopback interfaces as you climb the Cisco certification ladder. There’s one misconception about Cisco loopback interfaces that you want to get clear on now, though. You’re probably familiar with loopback interfaces on a PC, and may even know that the address range 127.0.0.0 is reserved for loopback addressing.

Note that this reserved address range does not apply to loopbacks on Cisco devices, however. If you attempt to assign an address from this range to a Cisco loopback interface, you get this result:

R1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R1(config)#interface loopback0

R1(config-if)#ip address 127.0.0.2 255.255.255.0

Not a valid host address - 127.0.0.2

R1(config-if)#ip address 127.1.1.1 255.255.255.0

Not a valid host address - 127.1.1.1

The range 127.0.0.0 is reserved for host loopbacks (such as PCs), not routers or switches. The most commonly used address from this range is 127.0.0.1 – if you can’t ping that on a workstation, that means you can’t ping yourself, which means there’s a problem with the TCP/IP install itself.
Keep these details in mind on the exam and in the workplace, and you’re on your way to CCNA exam success!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 100 free certification exam tutorials, including

Just a few short years ago a PDA anti virus was not necessary. The viruses, worms, Trojan horses and the like were the concern of PC owners only. But as we all know things in the online world change very fast, and these days all PDA’s surf the web frequently. The popularity of PDA’s and the ease of access to wireless surfing at wi-fi hotspots is a blessed phenomena. But while this is a good development, new throats enter the arena. Today’s worlds of pocket pc’s is as dangerous as the regular PC’s. Numerous viruses, Trojan horses and key loggers are speeded each day, thus forcing PDA owners to arm themselves with the proper protection.

Let’s take a look a few of the treats that have immerged in today’s PDA environment:

1. If you are surfing the web, there are types of viruses and Trojan horses who “know” how to penetrate your PDA and do their worst. You therefore need proper protection from infected files, just like any PC user who surfs the web, downloads files, reads emails etc. The rule of thumb is : if a PC needs this protection, than a PDA user needs it too.

2. IF you are surfing and downloading emails wirelessly, than you need even better protection. If the information you beam and receive in not encrypted, a hacker can read your e-mails and attachments, see what websites you visit, and even worse, steal your personal and financial information. A hacker can even illegally download copyrighted material or launch attacks using your identity. This calls for a Wireless Home Network Security protection system which makes sure all the information you send from your PDA in encrypted, so no hacker can reach it and grab it form thin air. The McAfee or the Caspersky products are recommended for this matter.

3. If you are using your PDA to access sensitive material like your bank account, you need to be extra careful and make sure both your communication and your PDA itself are secured. Don’t rely only on the security measures that the bank’s website have because they are rarely enough to stop a really good hacker.

Just like in the PC world, You need to stay updated and on top of things. You’ll want to update your anti-virus every day through the live update option that most anti-virus software products have. This will ensure your PDA has maximum protection. Always remember that it’s better to take care of this in advance as it’s always more painful and expensive to revive a computer that was taken by a virus.

Ron Heller is the owner and operator of pdaonlinecenter.com pdaonlinecenter.com
- a website devoted to PDA, pdaonlinecenter.com/palm-pilot-software.html Palm
Pilot software, PDA accessories, PDA computers and more.

Cat5 cable is the original Ethernet cable, and includes four twisted pairs in a single jacket. The twisted pair design helps reduce interference from external sources and other pairs (also known as crosstalk). Its performance specifications were designed for use with up to 100Mbit/s networks in fact, the most common usage for Cat5 cable is 100BASE-TX Ethernet.

In 2001, Cat5e (or enhanced Cat5) was designed, with stricter specifications for performance and speed. The biggest difference between Cat5 and Cat5e is that Cat5e can be used with Gigabit networks, networks like 1000BASE-T that boast transfer speeds of up to 1000Mbit/s. Cat5e also has slightly modified wiring for even greater protection from far end crosstalk.

In general, Cat5 has been almost completely replaced by Cat5e. While you can still find Cat5 cable out there, you can often find Cat5e at almost the exact same price. You may not notice a difference in performance for a home network, but virtually all business settings will benefit from exclusively using Cat5e.

UTP or STP?

The “TP” in both STP and UTP stands for “Twisted Pair.” As mentioned previously, Cat5 cables include 8 total wires, each twisted with another to create four twisted pairs. This balanced pairing is crucial in avoiding crosstalk and establishing a high signal-to-noise ratio even in interference-rich environments.

STP is Shielded Twisted Pair. Each pair in the cable is covered in a metal sheath, which provides protection against EMI (Electromagnetic Interference). The drawbacks to shielding are a heavier cable without the same level of flexibility as UTP (Unshielded Twisted Pair). STP is also a slightly more expensive cable and all of its jacks and terminators are shielded to be effective, which can add up over long distances.

UTP has no additional shielding around its individual twisted pairs, and thus does not require that its terminators and jacks also be shielded. Additionally, it is a light, thin, and flexible cable. This means that it is easy to wire between walls and won’t take up the space that you may need for additional wiring.

Conclusion

Unless you have specific needs, UTP Cat5e cable is the best solution for most of your networking needs. Not only is it reliable, fast, and easy to work with, it’s also the cheapest LAN cable on the market.

For additional shielding, go ahead and pay the extra for STP but remember that the cable will have less flexibility and needs shielded counterparts when planning your networking.

Jimmy is a technogeek with sewelldirect.com SewellDirect.com and a connoisseur of fine cabling. Feel free to check out Sewell Direct’s complete line of sewelldirect.com/UTP-Cat-5e-LAN-Cable-Roll-with-Pull-Box-1000-ft.asp bulk Cat5e cable and sewelldirect.com/Networking networking solutions.