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DHCP scope warning but have lots of free addresses

Posted on 2008-06-19
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Last Modified: 2009-05-21
Hi,

On one of my DHCP scopes I am getting the warning (yellow triangle with exclamation mark) for more than 90% usage of available addresses.

My range is from 10.6.1.50 to 10.6.1.145 (therefore I have 96 availble addresses).  When I click on display statistics it tells me I have 96 addresses, 93 are in use and 3 are availble.  However, and this is the strange part, in the address leases table I only have 45 addresses in use.  Does anyone know why it thinks I have 93???

I can't expand the range as 10.6.1.146 to 10.6.1.239 is on another DC (that one is working fine) and 10.6.1.1-49 and 10.6.1.240-254 are set aside for static devices.

Any ideas? Thanks,

Giles
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Question by:Gilesmp
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2PiFL earned 250 total points
ID: 21821337

What is the duration of the lease?  If it is set too high, addresses will not be "returned" to the pool.
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by:Gilesmp
ID: 21822079
Has previously been set to 3 days, but have now reduced it to 24 hours.

Also, we don't have that many devices in the office to take up all of those addresses (and have very few users coming in with laptops, etc.)
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by:ChiefIT
ChiefIT earned 250 total points
ID: 21842608
This is one case that DNS may effect DHCP. When a client gets an IP address, AD DNS is checked to see if the address is used in DNS. If so, the client will get an NACK, meaning the address is bad. You may have to configure Scavaging to rid yourself of DNS records that are stale. If anything at all, it will help you clear out your DNS.

http://support.microsoft.com/kb/169289

However, the error you are seeing comes from the DHCP scope. It means that 90% of the scope is being used. You may have to broaden your scope to match your address pool.

I think broadening your scope and scavaging DNS records will resolve this issue. To scavange, lookup Dynamic DNS.

DHCP dynamically deletes stale DNS records:
http://support.microsoft.com/kb/932464

An example:
http://www.experts-exchange.com/Networking/Protocols/DHCP/Q_22847336.html
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