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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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I was thrilled when Apple announced its Airport Wi-Fi hardware. Like many others, I
envisioned walking down the street with my iBook constantly connected to the
Internet. We all soon found out how difficult that was, at least without buying a cup
of coffee. A small culture was born from people driving through neighborhoods
looking for Open (Without a password) wireless access points. This scavenger hunt
was not the wireless network we had envisioned. That dream connectivity came
many years after Wi-Fi, and it is called EVDO.

EVDO is short for Evolution-Date Optimized, which like all too many acronyms used
these days tells you nothing about the service. This is unfortunate, because Verizon
Wireless has made EVDO technology extremely accessible to all levels of computer
user. Verizon has made true wireless broadband available. What Verizon offers with
its EVDO service is computer access to the high-speed data network that their
phones use for streaming video content and text messaging. The most astonishing
thing is that it is not dialup speed, but DSL speeds of up to 2 Mbps. Actual speeds
vary considerably as you drive down the Interstate, but you will stay connected. Your
signal is handed off from one cell tower to the next. That’s the genius of this. Your
Internet connection is going through the cell phone network that’s already in most
places you are traveling.

People often think of mobile Internet access as being in the realm of road-weary
business people. The irony is that once upon a time, cell phones also had this image
of being for business only. Now nearly everyone is enjoying the benefits of cell
phones. And again it’s a cell phone company bringing this new service to our lives.
Yes, at first it was mainly for traveling business people, but that’s been changing
fast. It makes sense, for example, for any working parent who has to squeeze work
and a child’s extracurricular activities together. We have many idle moments in our
day, time spent waiting. Verizon’s EVDO service offers us the ability to collect those
idle moments and put them to productive use.

If EVDO sounds good to you, then there are a few more things you need to know as
a Mac user before you sign up. The first is do not go and try to buy this service and
hardware directly from Verizon. Regrettably, the training of Verizon’s staff has not
included Mac information. Many users have reported being sold inappropriate
hardware or turned away altogether for being Mac users. I always appreciate a Mac-
friendly company and because you can buy the same Verizon service from
anywhere, I recommend ordering your EVDO service from EVDOinfo.com. They will
offer the support and expertise of actual Mac users when it comes to EVDO.

To use the mobility of Verizon’s EVDO service you will need to own a 15″ or 17″
PowerBook running OS X 10.3.x or higher. This is because you need to install a PC
card into the PCMCIA slot on your PowerBook. 12″ PowerBooks and iBooks do not
have a PCMCIA slot, so for now you’re out of luck. If you just need to use this
service at home, you can buy an EVDO router that will pickup the Verizon network
and convert it to Wi-Fi, but that’s not a mobile option.

The current Mac compatible card is the Kyocera KPC-650. In Mac OS version 10.3.5,
Apple included built-in support for the PC5220 EVDO card, but later PC5220
firmware changes have broken that support, and the cards are hard to find. The
Kyocera is a well-liked card and now ships with Mac “VZAccess” software and
drivers in the package. After you install the drivers and insert the card, you just
need to activate your card and update PRL. The Preferred Roaming List (PRL) is a
directory of all the cell towers you can connect to. This list will need to be updated
every few months so you can use new cell towers in your area.

Once installed, there will be a new network “location” which will let you switch to the
Verizon EVDO network from your main home network. You will need to launch the
VZAccess application when you want to connect. This may seem like a hassle, but
it’s only one extra step and it will prevent you from connecting unintentionally. This
is important for anyone who is not using an unlimited minute plan. An added
benefit of the KPC-650 is that it will work as your Wi-Fi card as well. Cell Phones
and Wi-Fi both use 2.4 Ghz radios, so the KPC-650 will see both signals and let you
chose which one to use. This is a great feature for PowerBook users who don’t have
Airport Cards installed.

Much like early cell phone phones, EVDO is not thought of as a consumer product.
Advertising and the news media represent this as a business tool. I see it as being
something else. Five years back people would talk about the “last mile” of the
Internet as being a boundary. They were talking about getting high-speed Internet
connections to people’s homes and how DSL and cable were going to solve that
problem. However, it looks to me as though EVDO is the true solution to the “last
mile” problem. The mistake before was thinking that the “last mile” was to a
building, but it really should be to a person and people move. Now, the Internet
can come to you; you don’t have to come to the Internet.

PowerMax’s http://www.powermax.com/ resident Mac expert, Jacob Loeb, has been
using Macintosh computers professionally since 1990. He founded a pioneering Mac
based DVD production company and later worked as an IT administrator for several
Portland, Oregon companies. Over the last four years Jacob has retained a top Apple
Product Professional ranking. As a PowerMax technician he’s repaired, trouble shot,
and tested every model Mac we sell.

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