Cisco CCNA Certification: The Hidden Details Of Telnet

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What’s the difference between Video Conferencing and Telepresence?

Telepresence picks up where video conferencing left off. Telepresence IS real time, full-high-definition, immersible sound and vision. Telepresence IS most importantly: the feeling of being “there” when you’re “here”. Telepresence is lifelike, video conferencing is not. Telepresence is that hi-line Mercedes AMG, video conferencing is a Ford Escort - Period.

Why Telepresence now?

Video conferencing has been around a while now but has always lacked the feeling we spoke about above. Jumpy computer screens, broken audio and poor lighting add to the impersonal touches of video conferencing (ie slow motion camcorder on top of your computer monitor). Finally, technology, bandwidth, vision and sound have all converged on video conferencing to create the telepresence experience. It’s about time! Crystal clear surround sound and real-time full-high-definition visual effects enhance the feeling of being there – thus telepresence. That nervous twitch, roll of the eyes, sniffle, tap of the foot – things you see when you’re present and sitting across a conference room table – things you don’t see or feel from video conferencing, but do with telepresence.

Today, what “real” uses are there for Telepresence?

There is no short answer even possible here. We’ll name a few, more like we’ll put your imagination to work. Imagine a single specialist doctor in Canada treating patients in Haiti via telepresence. Robots in space doing the actual work while the telepresence operator dons his telepresence helmet and gloves at his workstation in Texas. Meeting your Russian company vice president while you’re in the executive telepresence room at the office in Denver. Just a few…

What are “real” savings of Telepresence?

Your imagination still working on the last answer? Don’t let up yet! What carbon footprint? Don’t need that airplane ticket to go check on your staff in Russia now do you? What lost life in the Iraqi war? Unmanned drones and soldiers via telepresence. Military and combat cost savings? Immeasurable. Less travel costs, airline frustration, fuel, lost time, carbon emissions, etc. Those are tangible, real savings to name just a very limited few.

You starting to see what telepresence can do that video conferencing can’t? We hope you see what we’re seeing! Telepresence – its time has arrived!

Check out the video thread in Section 8 of the Telepresence Forum where you can watch some Telepresence YouTube videos! If a picture is worth a thousand words, a video must be worth a million!

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!