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DHCP quickly running out of addresses

Posted on 2005-03-31
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Last Modified: 2010-03-18
I'm getting messages in the DHCP Event Viewer that it is running out of addresses (30 left).  I'm running the "standard" 192.168.0.0/255.255.255.0 scope, with about 10 static entries and the rest go out to clients.  I HAVE noticed that my mail server takes about 10-12 addresses from the server as "RAS" addresses, what's that all about?  Anyway, my question is what's the best solution to allow more addresses to be given out?  Thanks.
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Question by:tenover
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Expert Comment

by:Fatal_Exception
ID: 13675507
How many clients are you supporting?  You can easily increase the amount of host addresses available by changing to a different subnetting scheme.  Your current one allows for 254 hosts minus the static entries for your RRAS and Servers, and should be scoped out in your DHCP server...

For instance, if you want to stay with Classful subnetting, you could even go to the 10.0.0.0 Private Address, which will allow about 16 million hosts...  But, we need to know how many you have first..

FE
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Author Comment

by:tenover
ID: 13675524
Lol....I have about 100-150 DHCP enabled machines and about 20-30 statics (Servers, printers, etc...).  
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by:Fatal_Exception
ID: 13675672
Well, then I would suggest you reconfigure you subnet to allow for more host addresses...  Perhaps going with a Class B: 172.16.0.0 - 172.31.255.255 (subnet mask of 255.255.0.0).  Although this will take a little time, and requires that you work after hours, it will certainly resolve the leasing issue..  

You could also shorten the lease times for your clients using a reg hack..

Key: Tcpip\Parameters\Interfaces\ID for Adapter
Value Type: REG_DWORD - Time in seconds
Valid Range: 1 - 0xFFFFFFFF
Default: None
Description: This parameter is used by the DHCP client service to store the time (in seconds) that the lease on the IP address for this adapter is valid for.

You will have to know the ID for the adapter.  If you decide to try this, I will explain how to find the Adapter ID...

FE
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by:Fatal_Exception
ID: 13675695
BTW:  here is a great list provided by MS on registry hacks that I should have posted above:

http://support.microsoft.com/kb/314053
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Author Comment

by:tenover
ID: 13676680
I'm not worried about working after hours, but if I did your first suggesstion, this would also require that I manually re-map any drives that users have mapped to IP address instead of Name, right?
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Fatal_Exception earned 1000 total points
ID: 13676744
Correct.  Anything mapped to an ip address will have to be re-mapped.  A real pain, especially in your circumstance.  This is why network design is so important, and that it be scalable.  

If I were you, I might try the decreasing your lease times.  But this is only temporary...  if your network grows much, you will be forced to make changes.

Another thing you might think about is subnetting your network into separate broadcast domains.  You can use switches that provide for Vlans, but even so, you will need a router to link the Vlans together.  The only devices I have worked with in this regard are Cisco, and are very expensive solutions, but highly scalable.

FE
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Author Comment

by:tenover
ID: 13676767
Yeah, in my defense, I didn't design this network, it was done by my predecessor.....BUT, I'm in charge now, and don't want to run out of addresses!  We will probably not grow more than 20-25 users (maybe 30 new nodes), so I might be ok with decreasing lease times....Can't I do that on the DHCP server though?  Set it to 24 hours or something?
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Expert Comment

by:Fatal_Exception
ID: 13677319
Absolutely!  I should have thought of that first!  I would even reduce the lease times more than 24 hours..  Try it though, and monitor your event logs until the leasing errors have disappeared...

http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/ServerHelp/794799f4-4610-477e-9bae-7e37afb68334.mspx
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Author Comment

by:tenover
ID: 13677378
Thanks for your help.
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Expert Comment

by:Fatal_Exception
ID: 13677518
Great..  glad I could help!  and thanks!

FE
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