notes to help me remember

Tag Archives: DHCP

MAC Address Filtering on Server 2003

I was just looking at one of my posts from last March about mobile lab connectivity. One thing I can add is that we set our lab laptops so that Windows cannot turn off the wireless. This way students are less likely to lose their network connection once they get one. We have also greatly increased the number of access points in the buildings (which has led to new issues with wireless interference and channel selection).

I wanted to add the link for MAC address filtering on Server 2003. Despite doubling the number of addresses available, we have again started to run out occasionally at one location. Blocking DHCP access to non district computers using MS Callout Filter is discussed here.  Found the download and instructions here on Mark M Manning’s blog. Thanks Mark!

Locating a Device by IP Address

IP address conflicts pop up here and there, sporadically.  Sloppiness borne of haste on our part, outside devices on our network, or the occasional access point that resets to its defaults.  These can all lead to IP address conflicts.  These are generally just an annoyance, and don’t result in any difficulties.  Tracking them down can be frustrating and not worth the effort.  But I recently got a little frustrated with a persistent conflict and decided to find a tool to help track it down.  I found a handy little utility called Zenmap (ver 5.51) that provides a handy GUI for Nmap.   Available from, this utility spits out useful information gleaned from the item connected to the network at the IP address you enter into the program.  It can show info about the type and name of the device that help identify what is causing an IP conflict on the network.  Helped me find the wireless access point that I had set up with a static IP and no reservation in DHCP (sloppiness, as I said).  Zenmap was kinda fun to use, and other than the single eye logo for the program, I am pleased with it.  (Not so much the logo, just not a favorite of mine.)

I’m Trying to Join the Domain!

Routine setup of a couple of late entries to the new computer line-up for this year.  Doing the final stuff before turning them over to the expectant users.  You know, join the domain, add printers, put a few desireable links on the desktop, etc.  Whoops, donk!, Windows 7 informs me in a mildly verbose message:

Computer Name/Domain Changes

The following error occurred attempting to join the domain “nnnn”:

An attempt to resolve the DNS name of a domain controller in the domain being joined has failed.  Please verify this client is configured to reach a DNS server that can resolve DNS names in the target domain.  For information about network troubleshooting, see Windows Help.

OK, Google time.  Several sites advise to manually set the DNS IP address in the IPv4 settings, join the domain, then reset the settings to what they should be.  Not wanting to trek over to the server to figure out what the proper DNS IP address is, I try one or two most likely suspects, have no luck, run out of time, and go home for the weekend.

Back to it the following week, I again Google the error, find the same advice, and also one helpful comment that seems so obvious.  Someone, somewhere (may have been a Tom’s Hardware forum), mentions that you may put the correct information in the DHCP settings.  Well, of course!  Why is it that the obvious solution (as well as the best one) so often eludes me.  Taking a look to find the IP address for the DNS, I realize why the poor computer was having a problem.  I decided to leave the straightening out of that situation to someone more informed than me, but I did locate an appropriate IP address for a DNS.  I plugged it into the TCP/IP properties and joined up with the Domain.