Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

When a new system is added to our network (i.e. we plug a machine into the network) DHCP seems to be doing some funky things.

  • The new computer cannot obtain an IP address
  • Something gets reset: All the machines say the network cable is unplugged

So I'm guessing something along the line modem, router, switch is faulting. If someone could point me in the right direction it would be greatly appreciated.

share|improve this question

closed as not a real question by ChrisF, Mokubai, KronoS, Daniel Beck, iglvzx Jul 16 '12 at 3:55

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

We can't help you without more information. What DHCP server, what clients? Does it happen to any client or only a few specific ones? What are the components in your network? Is this a corporate network or at your home? Please edit your question and tell us a bit more. – slhck Aug 19 '11 at 14:45
What is providing your DHCP service - your router or a server? Has the DHCP scope run out of addresses? Is it only one specific new system that causes this behaviour? many unknowns! – Linker3000 Aug 19 '11 at 14:50

I've experienced this peculiar set of problems from time-to-time at a few sites over the years, particularly the intermittent "network cable unplugged" pop-up messages. I discovered that the solution was to perform a deep power cycle of the effected computer(s).

Additionally, using a good power bar helped to prevent further repeats of the same set of problems for most of the computers (I show a picture of a really good power bar in my answer to the question " Is it bad to leave your computer on during a thunderstorm? ").

To perform a deep power cycle:

  1. Shut down the computer as usual
  2. Physically un-plug the power cord
  3. Use the power switch to attempt to power the computer on (this will fail, but you might see the LEDs blink on the front for a moment as any remaining power is extinguished)
  4. Physically plug the power cord back in
  5. Power on the system

If this resolves the problem for you, then you may have some power fluctuation issues at this site. A power bar like the one I suggested in my answer to that other question seems to help at the sites I've noticed these problems at (I used an AC volt meter to measure the power and discovered different power levels at different times of the day; apparently the local hydro company says this isn't a problem because the variations are within acceptable limits), but if they vary too much then a battery backed UPS unit may be a good solution (even if it only provide a few minutes of standby power, what you're after is the consistency of the power levels).

Of course, making sure your system and its network drivers are up-to-date is always recommended.

share|improve this answer
Not all UPS equipment will be useful in this scenario - only those UPS units which operate in the 'Line Interactive' mode will ensure a consistent output over a varying input range. Otherwise, sound advice, +1. – Mike Insch Aug 19 '11 at 16:44
@Mike Insch: Thanks for clarifying that, it's important (+1) as it clarifies my point that "what you're after is the consistency of the power levels." – Randolf Richardson Aug 19 '11 at 17:12

Not the answer you're looking for? Browse other questions tagged .