Question bout mapped drives.

[lck092580]

We have a AD set up and the users that login get mapped drives, "o: p: q: r:" which are actually folders on our DCs.. the problem I'm having is that I'm unable to see those drives that everyone's seeing. I checked my login on a DC and it's the same as everyone elses. So my question is:

1. what's wrong with my login?
2. if i wanted to, how do i add another drive (like s? Like what do i fire up? (i tried looking but couldn't find it).

Thanks

T

 

[brontosaurus]

You must be using local profiles? Go to one of these users when they're logged in and write down the paths to these drive mappings (e.g. \\servername\sharename). Then, log in on your own, right click My Computer, choose Map Network Drive, choose your drive letter, and enter the appropriate path....be sure to check off "reconnect at logon".

 

[lck092580]

Hey brontosaurus.. thanks for the reply. Ur suggestion actually raises a question..

Isn't AD supposed to make it easy for admins to administer new logins to users?.. what I mean is that if the admin has to do what u said to every login he sets up then wouldn't that be a waste of time?.. Ideas?

T

 

[brontosaurus]

that's why they invented login scripts....

 

[BradSQLGuy]

Bronto is right. You are probably not set up to run a login script. If you are supposed to run a script and have before then you need to disconnect your network cable completely and let it sit for 15 seconds. Reseat the cable and reboot. That will clear any charge in the cable that can cause interference with login scripts. If you aren't set up to run scripts then like bronto said you will have to map them maually. -Brad
A+, MCSE NT4, MCDBA SQL7

-Best cartoon of all time :-D 'Spongebob Squarepants'

 

[lck092580]

Thanks for the help guys.. I guess i'm going to have to do em manually. Thanks.

T

 

[farooge]

"That will clear any charge in the cable that can cause interference with login scripts."

what?

 

[BradSQLGuy]

Sometimes I have users who can't connect to mapped drives. I have scripts in place to automatically map for the users. It is very very common for a patch cable build up resistance or have a charge inside it. When that happens it interferes with the logon scripts and even network connectivity. Unless you support multiple users in a Corporate environment then you possibly have not heard of this. It can happen on a LAN at home as well but not very common. That type of problem 90% of the time will mainly interfere with the logon scripts (hence you don't commonly use those at home). -Brad
A+, MCSE NT4, MCDBA SQL7

-Best cartoon of all time :-D 'Spongebob Squarepants'

 

[chicocouk]

About this charge in the network cable ... where are you getting this information from? What makes you think that it's a charge in the cable that's the problem, or that disconnecting the cable will get rid of the charge?

I've never heard of this before, and am very curious to know where you learned this

 

[GlenJohnson]

Would love to hear more about this myself. Thanks.


Glen A. Johnson
Microsoft Certified Professional
glen@nellsgiftbox.com

"Nothing ever becomes real till it is experienced -- even a proverb is no proverb to you till your life has illustrated it."
John Keats (1795-1821); English poet.

 

[BradSQLGuy]

At the high frequencies you can't look at the cable as a usual cable. On higher frequency it works as a waveguide. Characteristic impedance is specific resistance for electro-magnetic waves. So: It's the load the cable poses at high frequencies. The high frequency goes (dependent of cable of course) usually from 100kHz and up.

If you feed a sinusoidal electrical AC signal of reasonable frequency into one end of the cable, then the signal travels as an electrical wave down the cable. If the cable length is an extremely large number of wave-lengths at the frequency of that AC signal, and you measure the ratio of AC Voltage to AC current in that traveling wave, then that ratio is called the characteristic impedance of the cable.

In practical cables the characteristic impedance is determined by cable geometry and dielectric. The cable length has no effect of it's characteristic impedance.

With the exception of wireless systems, networks rely on cable to conduct data from one point to another. In the case of copper-wire-based, unshielded twisted-pair (UTP) cabling, data is conveyed in the form of electric, digital signals. Because these signals are essentially bursts of electricity, the electrical characteristics of the cable itself greatly affect the integrity of the signal being transmitted. A bad length of cable or a poor cable installation can result in signal loss or distortion, and consequently, network failure.

To minimize such occurrences, cable vendors test their cables to guarantee performance. However, this doesn't make their products fault-proof; bad cabling does exist. In some cases, the error lies in improper cable installation. Network managers can use cable testers to ensure that a cable can conduct signals correctly. They can also use cable testers to verify if a cable is properly installed and to troubleshoot faulty cable.

A solid grounding in the electrical properties of UTP is a good way to learn how cable can affect the performance of a network.

THE ELECTRICAL CIRCUIT
A network can be broken down in simplistic fashion into an electrical circuit metaphor. In this case, a network essentially comprises energy sources, conductors, and loads. An energy source is a network device that transmits an electrical signal (data). The conductors are the wires that the signal travels over to reach its destination, which is usually another network device. The receiving device is known as the load. In its entirety, the connected network is a completed circuit (See Figure ).

When an energy source transmits a signal, it is outputting an electric charge onto the conductor by applying voltage to the completed circuit. Voltage is measured in volts. The voltage propels the charge across the cable, and the flow of the charge is known as a current, which is expressed in amperes, or amps.

In the computer world, the electric signal transmitted by an energy source is a digital signal known as a pulse. Pulses - in the form of a series of voltages and no voltages - can be used to represent a series of ones and zeros. Digital pulses form bits, and a series of eight bits creates the almighty byte.

The key to a successful signal transmission is that when a load receives an electrical signal, the signal must have a voltage level and configuration consistent with what had been originally transmitted by the energy source. If the signal has undergone too much corruption, the load won't be able to interpret it accurately.

In short, a good cable will transfer a signal without too much fudging of the signal, while a bad cable will render a signal meaningless.

PROPERTY LIMITS
Due to the electrical properties of copper wiring, the signal will undergo some corruption during its transit. Obviously, signal corruption within certain limits is acceptable. Once the electrical properties exceed the limits prescribed to a certain cable type, the cable is no longer reliable and must be replaced or repaired.

As a signal propagates down a length of cable, it loses some of its energy. So, a signal that starts out with a certain input voltage will arrive at the load with a reduced voltage level. The amount of signal loss is known as attenuation, which is measured in decibels, or dB. If the voltage drops too much, the signal may no longer be useful.

The table lists the attenuation values allowable at the end of 100 meters of Category 3 through 5 UTP.

(Please note that the attenuation and near-end crosstalk [NEXT] values in the table are performance specifications detailed in Telecommunications Systems Bulletin [TSB] -67, written by the Electronics Industry Association/Telecommunications Industry Association [EIA/TIA]. All other values are suggested limits, not standards. In addition, the table shows limits for certain frequencies, although different frequencies can operate on each category of cabling. The limits for some properties vary according to frequency.)

Attenuation has a direct relationship with frequency and cable length. The higher the frequency used by the network, the greater the attenuation. Also, the longer the cable, the more energy a signal loses by the time it reaches the load.

A signal loses energy during its travel because of electrical properties at work in the cable. For example, every conductor offers some resistance to a current. Resistance, which is measured in ohms, acts as a drag on the signal, restricting the flow of electrons through the circuit and causing some of the signal to be absorbed by the cable. The longer the cable, the more resistance it offers.

Due to its electrical properties, a cable not only resists the initial flow of the current, it opposes any change in the current. The property that forces this reaction is called reactance, of which there are two relevant kinds: inductive reactance and capacitive reactance.

In an inductive reaction, a current's movement through a cable creates a magnetic field. This field will induce a voltage that will work against any change in the original current.

Capacitance is a property that is exhibited by two wires when they are placed close together. The electrons on the wires act upon each other, creating an electrostatic charge that exists between the two wires. This charge will oppose change in a circuit's voltage. Capacitance is measured in farads or picofarads.

Reactance can distort the changes in voltage that signify the ones and zeros in a digital signal. For example, if the signal calls for a one followed by a zero, reactance will resist the switch from voltage to no voltage, possibly causing the load to misidentify what the voltage represents.

IMPEDING PROGRESS
When you combine the effects of resistance, inductance, and capacitance, the result is the total opposition to the flow of the current, which is known as impedance and is measured in ohms. It's important for components of a circuit to have matching impedance. If not, a load with one impedance value will reflect or echo part of a signal being carried by a cable with a different impedance level, causing signal failures. For this reason, cable vendors test their cables to verify that impedance values, as well as resistance and capacitance levels, comply to standard cable specifications.

It's also important for the impedance of a cable to be uniform throughout the cable's length. Cable faults change the impedance of the cable at the point where the fault lies, resulting in reflected signals.

Cable testers use this trait to find cable faults. For example, a break in a wire creates an "open circuit," or infinitely high impedance at that point. When a high frequency signal emitted from a cable tester encounters this high impedance, it will reflect back towards the tester like an ocean wave bouncing off a seawall. Similarly, a short circuit represents zero impedance, which will also reflect a high frequency signal, but with an inverted polarity.

If you'd like to read more about this feel free.

http://www.networkmagazine.com/article/NMG20000724S0012

-Brad
A+, MCSE NT4, MCDBA SQL7

-Best cartoon of all time :-D 'Spongebob Squarepants'

 

[beamrider]

I appreciate the lesson in Ohm's law, but I would be more interested in knowing how this applies to what we do in a practical sense. After 29 years in computers and setting up hundreds of networks, I have never seen a problem correction that could be attributed to unplugging the cable to let the "bad stuff out". I have replaced bad cable, of course, but if my cable characteristics are such that I would need to apply leeches periodically, I think I would have replaced it a long time ago. Just wondering if this is a real issue?

 

[BradSQLGuy]

Okay Beamrider let me SPELL it out for you. I'm not making cable impedence up. It happens. And if you've spent '29 years in computers' then you have without a doubt seen where a cable reset fixes the problem. The issue was he was unable to see drives that others could. That tells me that there is possibly connectivity problem and checking the cable is a very basic step to take. It's amazing you say you've worked 'in' computers for 29 years. Tell me how you do that? Computer networking wasn't even introduced publicly 29 years ago. You must have been working with the government on their defense systems back in '75 when ARPANET was implementing the first packet switching. If you read my post more carefully and maybe understood basic physics you would see how cables CAN build impedance. If you don't understand I apologize. Good luck to you. -Brad
A+, MCSE NT4, MCDBA SQL7

-Best cartoon of all time :-D 'Spongebob Squarepants'

 

[chicocouk]

Not wanting to annoy anyone, but I'm still unclear as to why cable impedance should primarily affect logon scripts, or why unplugging a cable and plugging it back in again should get rid of cable impedance. I'm fairly sure no'one has actually addressed that issue here. Impedance will not just "go away" if you unplug and reseat a cable, and i agree with beamrider that faulty cable should be tested, and replaced.

I believe it's also very possible to "work in computers for 29 years" without having worked on arpanet, or indeed, without working in networking for all of that time.

Please don't take any of this personally, i'm simply interested in whether this is actually relevant, or just received wisdom. Ie, this solves the problem, so it must be due to this reason, 'cos Bob once told me it, so it must be true.

 

[GlenJohnson]

My 2 cents worth, and it has nothing to do with ohms law, but it does have to do with authenticating. I was setting up a new compaq server with two nics. After about a two week period, I started hearing from my users that they couldn't log onto the domain. They could access the novell server, but couldn't get on the domain. After scratching my head for about a week, I decided to re-boot all the servers. (Don't ask why, I was at the end of my rope.) While re-booting the new server, people could log onto the domain. Set up a couple of perf mons, found out one nic was sending out bad broadcasts. Kept getting worse. I disabled that nic, all authentication was good. Moral of the story, hardware can affect authentication. I've not seen the cable problem, but it doesn't surprise me. Glen A. Johnson
Microsoft Certified Professional
glen@nellsgiftbox.com

"Life is a succession of lessons which must be lived to be understood."
Ralph Waldo Emerson (1803 - 1882); US philosopher, poet, essayist.

 

[lck092580]

I dunno about this but both brad and glen's opinions make sense. I'm happy that i checked back @ this old msg that has taught me a lot in a few minutes. Thanks for ur experiences.

T