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DHCP adress avaliable is 0

Posted on 2012-03-13
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Last Modified: 2012-03-18
DHCP address available= 0%. I can't increase the range. As a result any new pc can't get IP. My DHCP lease reserve the IP address for 2 days. But I am pretty sure I can get some free IP if I can detect which are not connected in Network at the moment. How can I find in DHCP "Address Leases" which are connected & which are not. I don’t have time to ping to test. Is there any quick way to find who are not connected, if I can detect then I will delete them to increase DHCP availability. Thanks in Advance.
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Question by:Silense
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mccarl earned 125 total points
ID: 37718342
Basically, no! As you said, if you can't ping, then there probably isn't any other way of knowing.

Otherwise, can you reduce the DHCP lease expiry time?
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Author Comment

by:Silense
ID: 37718360
It's too diffifult to ping each & every Lease IP Address. Even If I change lease expire day from 2 day to 1 day now then it's not gonna Increase my address lease avaliablity right now. Is there any other way to increase DHCP avaliablity without changing IP address range as I have no room to increase range.
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by:mccarl
ID: 37718379
Not that I know of.
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Assisted Solution

by:Sikhumbuzo Ntsada
Sikhumbuzo Ntsada earned 125 total points
ID: 37718715
You can use http://www.angryip.org/w/Download to check for available IP addresses, if I may ask is there a reason you do not want to increase your DHCP scope?
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Assisted Solution

by:andrew1812
andrew1812 earned 125 total points
ID: 37719355
Try out an ARP based scan with nmap. This would help you identify the devices which are up and running.
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Author Comment

by:Silense
ID: 37719524
In scope range 1-254 all are in use. I can't increase this scope list for ex: 192.168.10.1-192.168.10.254 unless I create new subnet or subnet mask. But we do have latest cisco router but I am not sure how to use vlan to increase or how to create new subnet to increase DHCP scope range.
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Expert Comment

by:Sikhumbuzo Ntsada
ID: 37719551
So your DHCP is handled by a router now a Server?
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Author Comment

by:Silense
ID: 37719777
It's handle by DHCP server but router and network need to support to provide IP range.
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Assisted Solution

by:Otto_N
Otto_N earned 125 total points
ID: 37720528
Your problem is caused by one of two things:

1. Too many devices

You have more than 255 devices that must connect to your subnet.  In this case, you will have to increase the subnet size, perhaps even use a different IP address range to accommodate the larger range.

2. Too much device churn

You have many short-lived connections to your network, and the total active connections at any one time does not exceed the available IP address range.  Then you can reduce your lease time (you can set it as low as 30 minutes, but it is usually limited by the server implimentation). After half this time, clients still active on the network will contact the server to extend its lease, and IP's that are not on the network will be available for assignment when the lease expire.

However, a good idea would be to scope your network properly, so that there should not be such a big contention for IP addresses.  You should rather impliment multiple VLANs (more than one IP subnet, using multiple scopes on the DNS server), and keep the VLANs to well below 200 devices, as Ethernet becomes less efficient with more devices being connected to the same broadcast domain (VLAN).
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Author Comment

by:Silense
ID: 37733016
Would I be able to create 2/3 scope? Currently scope range is from 150-254. There would be any problem if I create another few scope like: 10-100 and 110-140? Thanks.
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Author Closing Comment

by:Silense
ID: 37736375
Thanks to all.
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