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More CCNA and CCNP candidates than ever before are putting together their own home labs, and there’s no better way to learn about Cisco technologies than working with the real thing. Getting the routers and switches is just part of putting together a great CCNA / CCNP home lab, though. You’ve got to get the right cables to connect the devices, and this is an important part of your education as well. After all, without the right cables, client networks are going to have a hard time working!

For your Cisco home lab, one important cable is the DTE/DCE cable. These cables have two major uses in a home lab. To practice directly connecting Cisco routers via Serial interfaces (an important CCNA skill), you’ll need to connect them with a DTE/DCE cable. Second, if you plan on having a Cisco router act as a frame relay switch in your lab, you’ll need multiple DTE/DCE cables to do so. (Visit my website’s Home Lab Help section for a sample Frame Relay switch configuration.)

If you have multiple switches in your lab, that’s great, because you’ll be able to get a lot of spanning tree protocol (STP) work in as well as creating Etherchannels. To connect your switches, you’ll need crossover cables.

You’ll need some straight-through cables as well to connect your routers to the switches.

Finally, if you’re lucky enough to have an access server as part of your lab, you’ll need an octal cable to connect your AS to the other routers and switches in your lab. The octal cable has one large connector on one end and eight numbered RJ-45 connectors on the other end. The large connector should be attached to the async port on your AS, and the numbered RJ-45 connectors will be connected to the console ports on your other routers and switches.

Choosing and connecting the right cables for your Cisco CCNA / CCNP home lab is a great learning experience, and it’s also an important part of your Cisco education. After all, all great networks and home labs all begin at Layer One of the OSI model!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions! Details are on the website.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! And coming in 2007 — Microsoft Vista certification from The Bryant Advantage!

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USB has become the Colossus of computer connectivity, standing astride the world of computing accessories and peripherals with the self-confident ease of a standard that has triumphed over its opponents. Parallel and serial protocols are virtual dinosaurs, being phased out almost universally by computer manufacturers. Firewire (IEEE 1394) still maintains a presence in certain nice markets, in large part due to the dogged determination on Apple Computers and Sony to keep pushing the standard. But what has caused USB to become the standard of choice for computer connectivity?

The first answer is speed. For years, computers used serial (RS-232) and parallel (IEEE 1284) for data connection and transmission between computers as well as devices. However, the transmission speed of these protocols are slow, averaging 4mbps with the most recent parallel revision and an average 58,000bps with serial connections. In contrast, USB 1.1 has a 12mbps transfer speed and USB 2.0 high speed can go as high as 480 mbps. The speed difference coupled with the durability, universality, and simplicity of the USB connection easily tolled the death knell for serial and parallel ports.

This still fails to explain the ascension of USB over Firewire. Though Firewire has a max transfer speed of 400 mbps (80 mbps slower than the USB 2.0 standard), when it comes to transferring large quantities of data Firewire actually has the advantage of USB. Apparently, USB’s transfer rate tops out at 480mbps but its average speed is quite a bit slower. Firewire, on the other hand, has a consistent 400mbps transfer rate, making it ideal to transfer large files or data streams such as audio and video. It is this constant high-speed connection that has made Firewire the connection of choice for multimedia applications.

Firewire’s downfall comes not in design quality but in price. Where USB is actually quite inexpensive for manufacturers to implement, Firewire costs $1-$2 per connection. Thus, fewer manufacturers have made devices that support Firewire, relegating the standard to the multimedia computing niche. In addition, a minor factor is the slightly less durable nature of the Firewire connector.

That said, there is a strong possibility that several years from now, USB will no longer be the standard of choice as its successor, Wireless USB, comes into the computer connectivity market. Boasting USB 2.0 speeds, similar ease of connectivity, and the complete absence of tangling wires, Wireless USB could easily become the de facto standard of the future.

Nathan Kartchner works in Product Development for Sewell Direct, an online distributor of USB adapters and other connectivity products. Look for Wireless USB products as they become available.

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CCNA exam success depends largely on noticing the details, and this is especially true of configurations involving directly connected serial interfaces. And of course, it’s not enough to notice these details - you’ve got to know what to do about them!

A Cisco router is a DTE by default, but directly connecting two DTEs with a DCE/DTE cable is not enough. In the following example, R1 and R3 are directly connected at their Serial1 interfaces. The line goes up briefly after being opened, but the line protocol goes down after about 30 seconds.

R3(config-if)#int s1

R3(config-if)#ip address 172.12.13.3 255.255.255.0

R3(config-if)#no shutdown

2d18h: %LINK-3-UPDOWN: Interface Serial1, changed state to up

2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up

R3(config-if)#

2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down

The problem is that one of the routers needs to act as the DCE in order for the line protocol to come up and stay up. If this were your CCNA / CCNP home lab, you could just go over and look at the DTE/DCE cable to see which router had the DCE end of the cable attached. In this example, though, we don’t have physical access to the routers. How can we tell which router has the DCE end of the cable attached?

R3#show controller serial 1

HD unit 1, idb = 0×1C44E8, driver structure at 0×1CBAC8

buffer size 1524 HD unit 1, V.35 DCE cable

The show controller command gives us this information. (There’s a lot more output that this with this command, but it’s unimportant for our purposes.) The router with the DCE end of the cable needs to supply a clock rate to the DTE, and we’ll do just that with the interface-level clockrate command.

R3#conf t

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

R3(config)#int serial1

R3(config-if)#clockrate 56000

2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up

In just a few seconds, the line protocol goes up and stays up.

When troubleshooting a connection, always run show interface first. If you see the combination shown below, the connection is physically fine but logically down. That’s generally the result of a needed keepalive not being present. With Frame Relay, it’s probably an LMI issue, but with directly connected serial interfaces the issue is most likely the DCE end of the connection not supplying clockrate.

R3#show interface serial 1

Serial1 is up, line protocol is down

Troubleshooting is a big part of the job, and it’s a big part of the Cisco CCNA and CCNP programs as well. Know your show and debug commands and you’re on your way to passing the CCNA!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Get your CCNA study guide with The Bryant Advantage!

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To pass the CCNA exam, you’ve got to master quite a few services and routing protocols that may be new to you. Between RIP, IGRP, EIGRP, OSPF, and switching, there are hundreds of details you’ve got to absorb! It’s easy to spend all your time on those topics and not pay proper attention to “easier” technologies, and then all of a sudden on exam day you can’t quite remember the details of those particular services.

One setup you’ve got to be more than familiar with is directly connecting serial interfaces on Cisco routers. This is also a valuable skill to have in your home lab, since it allows you to add segments to your network setup.

A Cisco serial interface is operating as a DTE by default. The problem is that when you take a cable and connect two routers directly by their serial interfaces (with a DTE/DCE cable, that is!), they’re both waiting for the other to send them a clock rate. One of the interfaces must act as the DCE and that interface must send the clock rate.

If you can see the DTE/DCE cable, you can tell by looking which router has the DCE interface connected to it - the letters “DTE” or “DCE” will either be molded into the connector itself, or if it’s an older cable there should be a little piece of tape on the cable that tells you what the interface type is. But what if you have no access to the cable, or there are other cables all around it and you can’t see what type it is?

Run the command “show controller serial x”, with x representing the interface number the cable’s connected to. There will be quite a bit of output from this command, but the information you need is right at the top:

R1#show controller serial 1

HD unit 1, idb = 0×1DBFEC, driver structure at 0×1E35D0

buffer size 1524 HD unit 1, V.35 DTE cable

I left off the 16 or so rows of information that comes after this, but this is the information we need right now. If R1’s got the DTE cable end, the other router should have the DCE end:

R3#show controller serial 1

HD unit 1, idb = 0×1C44E8, driver structure at 0×1CBAC8

buffer size 1524 HD unit 1, V.35 DCE cable

We know now that R3 needs to supply a clock rate to R1. There’s a hint of a problem in just that little bit of command output - do you see what it is? Let’s run show interface serial1 to get more information.

R3#show int s1

Serial1 is up, line protocol is down

The line protocol is down because there is no clockrate being supplied by R3. If there has been, we would have seen that in the output of show controllers serial 1.

This is simple enough to fix, though! We’ll use the command clockrate 56000 on R3’s serial1 interface, and the line protocol will soon come up.

R3(config)#int s1

R3(config-if)#clockrate 56000

1w2d: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up

This is a simple concept, but there are a few details you must keep in mind! For a home lab configuration, you’ll need a DTE/DCE cable to make this work. If you cannot see the cable connectors, run show controllers serial x to see if the router has the DTE or DCE end of the cable attached. On the interface with the DCE attached, use the clockrate command to bring the line protocol up. It’s just that simple!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Get your CCNA study guide with The Bryant Advantage!

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How to test serial port RS232 Connection step-by-step?

This is call a loop back test method.

This method will send and receive data in same port call ‘LOOP BACK TEST’.We use HyperTerminal Software to Send and receive data (Standard software in Window XP home Version and professional Version).

Why we should to do this method?

When the interface hardware device have some problem occors or hardware function not properly.This method is Easy way to Troubleshooting by yourself.

Hardware Requirement (Nothing)

Software Requirement (HyperTerminal)

Skill Requirement (Nothing)

Accessoires (Bunch , Paper clip or anything can connect DB9 pin)

- Step one - Prepare

Find something connect (Short) your target com port (DB9 Pin) somebody call Serial Port Pin 2-3.
Shutdown your Computer Use it short Pin 2-3 (Pin 2-3 only - Be careful short other Pin).
Use a bunch, or Paper clip)

- Step Two - Prepare

Start up the computer and Run Hyper Terminal Software
Note : Start Menu > Program > Accessoires > Communication > Hyper Terminal

- Step Three - Configuration

Configuration Hyper Terminal Connection Setting

Enter Connection name (may be use “test my com port)

Select target com port to test (com1,com2,com…n)

Properties Connection then Click “Restore to Defaults“

- Step Four - Test

Perform a loopback test Press any Key… On Keyboard

If you see any character on the screen Hyper Terminal - comport was normally.

For more information and resources see =>http://interface.centraltreasure.com Computer Hardware PC Interface Knowledge Base Site

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