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Unusual DHCP Leases

Posted on 2003-02-20
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Last Modified: 2010-03-18
I just installed a Windows 2000 Advanced Server to replace a recently retired server.  This new server is a replica of the old one...in that it has the same name, IP Address and Domain.  I installed the new server on an isolated network with 5 PC's connected to it for testing.  When I completed the 'replication' I simply took the old one off the network and put the new one on.  Took 2 seconds and no one knew I have even changed the servers.  

My question is:  I am running DHCP on that server.  Which is functioning as expected.  All of my users are showing in the Address Leases...IP Address - Name - Lease Expiration - Type Unique ID.  The addresses are also reflected in the DNS table...with the corresponding reverse lookup.  

However, I have 5 leases showing up every day that only have the IP Address...no name - it does have the Lease Expiration and Type...BUT the Unique Address (MAC) is 30 alpha-numeric characters long.  These are not showing up in the DNS table either.  

I can not ping those IP's.  I have no idea where they come from.  As a generic trouble shooting gesture, I have been deleting them as soon as they show up...in the theory, I could trace the problems back to the time when I deleted the leases.  This has gone on for 2 weeks now and I have not had any reports of problems after I delete those IP's.  
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Question by:curt_herrman
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5 Comments
 
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Expert Comment

by:lrmoore
ID: 7987983
If you have dial-in or VPN access features enabled on any server, DHCP will "reserve" a block of addresses equal to the number of incomming calls allowed.
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Author Comment

by:curt_herrman
ID: 7988683
As part of my DHCP setup I have started my Scope after the last IP address of my static devices.  My VPN addresses are contained in an exclusion range.  The IP address that keep showing up are the same ones every day and not in my static range of within the exclusion range for VPN
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Author Comment

by:curt_herrman
ID: 7988804
As part of my DHCP setup I have started my Scope after the last IP address of my static devices.  My VPN addresses are contained in an exclusion range.  The IP address that keep showing up are the same ones every day and not in my static range of within the exclusion range for VPN
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Accepted Solution

by:
millerksu earned 320 total points
ID: 8009178
Are you using a Nortel VPN switch?  If so, check the MAC address of the VPN switch. If this is the same as the first 12 digits of the mystery leases, that would be where they are coming from.
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Author Comment

by:curt_herrman
ID: 8009215
That was it.  The 'software' VPN was not the problem...it was the Nortel.  
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