Cisco CCNA Certification: The Hidden Details Of Telnet

Telepresence News and Events October, 2008

WOW! What an amazing month for the Telepresence Industry! First off, did anyone see the Cisco TelePresence Human Network commercials that are airing during this seasons NFL Football games? A great sign that public adoption of Telepresence is near.

In other news from the 24/7 Telepresence Breaking News reel at the Telepresence Forum, BT announced that they’ve launched their inter-company Telepresence solution, Proctor & Gamble implemented new Telepresence rooms, Polycom received a “Rising Star” for their innovations and Verizon Teamed with Cisco to offer new productivity enhancing services using Cisco’s collaboration portfolio. Did I mention this was just a few of the Telepresence highlights from this past week? Hundreds of Telepresence news articles hit the wire this last month, and if the past is any indication of the future, we’ll see those Telepresence news posts double by Spring 2009.

I also noticed that companies like Digital Video Enterprises, Telepresence Options and of course our Telepresence Forum were listed in the Open Directory Project at www.DMOZ.org. Pretty big news considering Telepresence didn’t exist, or even have a category just a month ago or so in the human edited ODP.

Our website traffic amongst our 345+ Telepresence related domains has tripled since early August, another indication that Telepresence is getting ready to explode onto Main Street. People are “hearing” of it, people are “researching” it, and once they’ve performed their due diligence, they’ll “see and feel” what the pioneers of the Telepresence industry have been saying. Telepresence is near; Telepresence is here.

Well that’s it for now Readers. We hope you stop by the Telepresence Forum to learn a little about what the differences between plain old video conferencing and Telepresence are. C'mon by, sign up (free by the way), watch a Telepresence video or two, and drop us a line or comment with your Telepresence thoughts and experiences.

Take care , hope to see you on the Forum!

Your Editor and Administrator - L II
"Ride on the Next Plane of Existence" TM

Telnet is a simple yet powerful program that allows you to connect to a remote Cisco router or switch, and then configure it as though you were right at the console. Telnet is also one of those features that seems so very simple, until you get asked a half dozen questions about it on your CCNA exams. As with all topics, it's the details you know about Telnet that will help you pass the Intro and ICND exams.

Let's take a look at a few of these details. We'll begin by debunking one common belief about Telnet:

Telnet runs at layer 7 of the OSI model, not layer 3!

It's easy to think that Telnet runs at Layer 3 of the OSI model, the Network layer. After all, you're entering an IP address when you telnet in to a router or switch, and you may be on another router when you do it! None of that matters. Layer 3 is strictly the domain of routing. Like other features that require input from the end user, especially authentication, Telnet runs at the Application layer of the OSI model.

Speaking of authentication... .

Cisco routers require a password to be set before anyone can telnet in.

Cisco routers can run quite a few passwords. We can set an enable password, an enable secret, an enable secret and enable password, a password for PPP connections, and even a console password.

All of those are optional, but the telnet password is not. Makes sense – you wouldn't want just anyone telnetting into your router, would you?

If you have no password set on the VTY lines of your router, no one can telnet in. If they try, they'll see this message:

R1#telnet 3.3.3.3

Trying 3.3.3.3 ... Open

Password required, but none set

[Connection to 3.3.3.3 closed by foreign host]

To allow telnet access into a Cisco router, configure the VTY lines with a password and the login command:

R3#conf t

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

R3(config)#line vty 0 4

R3(config-line)#login

% Login disabled on line 2, until 'password' is set

% Login disabled on line 3, until 'password' is set

% Login disabled on line 4, until 'password' is set

% Login disabled on line 5, until 'password' is set

% Login disabled on line 6, until 'password' is set

R3(config-line)#password cisco

Note the messages you get after enabling login. These messages simply indicate that the login won't work until a password is set. The order with which you use the login and password commands don't matter just make sure you use them both.

We're not quite done, though. The remote user can now telnet in, but by default, that user will be placed into user exec mode. If the user is to be allowed to enter privileged exec mode during a telnet session, an enable password or enable secret must be set.

R1#telnet 3.3.3.3

Trying 3.3.3.3 ... Open

User Access Verification

Password:

R3>enable

% No password set

R3>

The user is stuck in user exec until you set a local enable password. Doing so will allow the user to use that password to enter privileged exec mode.

R3#conf t

R3(config)#enable password ccna

R3(config)#^Z

R1#telnet 3.3.3.3

Trying 3.3.3.3 ... Open

User Access Verification

Password: < user entered cisco here>

R3>enable

Password: < user entered ccna here >

R3#

The user is now in privileged exec mode. There's also another method to use so the user is placed directly into privileged exec mode when telnetting in, avoiding the enable password prompt. Use the command privilege level 15 on the VTY lines to do so.

R3#conf t

R3(config)#line vty 0 4

R3(config-line)#privilege level 15

R1#telnet 3.3.3.3

Trying 3.3.3.3 ... Open

User Access Verification

Password: < user entered VTY line password here >

R3#

Note that the user went straight to privileged exec mode.

Managing Telnet Connections

We already know how to use Telnet (a layer 7 application) to access a remote device there are also commands that help us manage telnet connections.

"show sessions" is a common command to see what current telnet sessions are operating.

Telnet sessions do not have to be exited they can be suspended as well. The command to suspend the Telnet session is followed by striking the "X" key.

To resume this telnet session, enter the resume command followed by the session number ("resume 1") and press .

To end a suspended telnet session, enter the disconnect command followed by the session number ("disconnect 1") and press .

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage offers dozens of FREE CCNA and CCNP tutorials and articles. The Bryant Advantage sells the world's most comprehensive CCNA Study Guide in the world, and my exclusive Binary Math and Subnetting Mastery book. My $299 CCNA Online Fast Track is the world's fastest-growing CCNA course. Visit http://www.thebryantadvantage.com today!

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