Cisco CCNA Certification: The Hidden Details Of Telnet

Telepresence and Holography / Holograms - November 2008

Editor’s viewpoint on their differences, likenesses and future...

We all just recently viewed an historic CNN holographic interview on an historic Election Night. CNN stated this type of imaging has never been done before on National TV and I believe that. I haven’t seen anything like it. The live interview caught me by surprise and sure had the “wow” factor attached to it didn’t it? Here’s a link to the actual interview.

CNN Hologram Video

The question now has to be asked. Is it Telepresence?

I’m no expert on the subject but I’m going to throw my hat into the ring, go out on a limb and say yes, I believe it is. Although I know many video conferencing purists are rolling their eyes and grabbing their guns right about now with my statement.

While I do know that Telepresence still hasn’t been universally defined (Houston, we have a problem), here’s how I see it…. Broken down to its simplest form - “tele” (through electronic means) and “presence” (present). This is how I’m justifying my opinion by lumping holography and Telepresence together. Just as Telepresence is surely an offshoot of video conferencing, holographic imaging (like we viewed on CNN) surely has to be considered an offshoot of Telepresence. The interviewer was “telepresent” from Chicago and beamed into the CNN Election Headquarters. She was most assuredly - “telepresent”. There was negligible latency, the imaging was fantastic and both interviewers were rehearsed on what they would say. I’ve just recently read that CNN actually “downgraded” the experience to make it “movie” quality and not as good as it could have been. Maybe they thought us mere mortals would be shocked if they showed their complete hand. I have a feeling it was so big to them, they didn’t want it to get upstaged by the historic election. I’m willing to bet we’ll see the “true” power of this technology in the upcoming weeks and months when they can put the pedal to the medal and show it off without having it sidetracked.

What an amazing time for this technology (all differences and opinions aside). Telepresence Doctors, nurses, teachers, schools and healthcare (healthpresence) will benefit from the recent gains in this state-of-the-art industry whether holograms, Telepresence or holography. Airlines also have to see the threat to a portion of their business travel. Hell, who wants go through security and fly to Miami for a two-hour conference when you can look them in the eye via Telepresence?

Beam me up Scotty! Simply amazing…!

Visit the free Telepresence Forum for more information and discussion

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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To learn more about Telepresence, the revolutionary new style of immersive video conferencing; visit these websites:

Telepresence - "Ride on the Next Plane of Existence" - Telepresence
Telepresence Web Portal - Telepresence Internet web portal
Telepresence Report - 24/7 breaking Telepresence related news and information
Via Telepresence - Video conferencing via Telepresence
Telepresence Forum - Free user discussion forum for everything Telepresence related
Telepresence Today - Telepresence information and editor qualified headline news
Telepresence Resource Directory - Telepresence web resource directory
Telepresence Tube - Telepresence videos, pictures and more