IP's are not released after lease expire

2013-02-08

Question

_{Friday, February 8, 2013 8:51 AM}

Hello,

I have Win 2008 server running DHCP, with client lease time as 2hrs.

We have recently updated our clients from win 7 to Win 8 (not sure if this is the cause) (apprx 60-70),

also some mobile connected via wireless.

DHCP don't seems to be releasing IP's as it should.

As I have go in DHCP remove IP manually and then it would start assigning till scope gets full again

in few days.

All replies (6)

_{Tuesday, February 19, 2013 12:35 PM ✅Answered}

Thanks for reply Ace,

I have changed lease time to 8hrs and then 12 hrs - but no help

-DNS ageing and Scavenging are not enabled ( Its a same server)

-IP's are not even cleared on weekends, DHCP should be empty on SAT and SUN,

-I have 2 scopes, when first one get full and even if next one have over 50% IP available, people stop getting IP's

Please suggest further

_{Saturday, February 9, 2013 2:29 AM | 1 vote}

It's recommended to have the lease at least 24 hours. If under 24 hours, unexpected issues occur.

If you have a lot of leases coming and going, I suggest to set it up per the instructions in my DGHCP Config blog below, to keep your leases clean and DNS records clean. You can make it one day, if you like, but the problem is setting up scavenging withsuch a short lease. So you have to make everything match.

The scavenging total time formula is : NoRefresh + Refresh * 2 + scavenge period.
Example:

DHCP lease duration should match the “no-refresh + refresh" values = 6 Days
Zone is set to a 3 day Refresh and a 3 day No-Refresh interval
Server Scavenging period is set to 3 days
The total time is set to 3 day No-Refresh + 3 day Refresh + 3 day No-Refresh + 1 to Scavenging period (1 day to 3 day in this example) = Scavenging

will occur anytime between Day 10 to Day 12
Good discussion on it and an example by Rick Tan:
Thread: "Enable DNS aging and scavenging "
http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/d4ec8490-60cd-4466-951a-203a1ddbfaff/

This link covers the following:
DHCP Service Configuration, Dynamic DNS Updates, Scavenging, Static Entries, Timestamps, DnsUpdateProxy Group, DHCP Credentials, prevent duplicate DNS records, DHCP has a "pen" icon, and more...
Published by Ace Fekay, MCT, MVP DS on Aug 20, 2009 at 10:36 AM 3758 2
http://msmvps.com/blogs/acefekay/archive/2009/08/20/dhcp-dynamic-dns-updates-scavenging-static-entries-amp-timestamps-and-the-dnsproxyupdate-group.aspx

Good summary:
How Dynamic DNS behaves with multiple DHCP servers on the same Domain?
http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/e9d13327-ee75-4622-a3c7-459554319a27

Ace Fekay
MVP, MCT, MCITP/EA, MCTS Windows 2008/R2 & Exchange 2007, Exchange 2010 EA, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP - Directory Services
Technical Blogs & Videos: http://www.delawarecountycomputerconsulting.com/

This post is provided AS-IS with no warranties or guarantees and confers no rights.

_{Tuesday, February 19, 2013 3:15 PM}

Many say that a lease less than 24 hours can cause problems. But I'm sure you already read that in my previous post.

In some cases if looking at the console not refreshing, and you've tried reconciliation and the console still dies not show it , here's a post to check if iit applies to your scenario:

http://social.technet.microsoft.com/Forums/en/winservergen/thread/43c2bcc9-4c4e-420d-96db-11f05843859c

Alsoi in such cases, the client may not be sending a release request, such as wireless clients that just leave the building. But if course the console should reflect it.

This post is provided AS-IS with no warranties or guarantees and confers no rights.

_{Wednesday, February 20, 2013 11:38 AM}

Thanks for reply Ace, I have a very basic question.

If I have set client lease time as 8hrs, if a user who get 1 IP leaves the office in next 2hr, what would happen to that IP

for another 6hrs, will DHCP keep holding it and remove only after 8hrs or should it clean it and assign to another user

when scope is getting full?

_{Wednesday, February 27, 2013 3:17 PM}

Thanks for reply Ace,

I have changed lease time to 8hrs and then 12 hrs - but no help

-DNS ageing and Scavenging are not enabled ( Its a same server)

-IP's are not even cleared on weekends, DHCP should be empty on SAT and SUN,

-I have 2 scopes, when first one get full and even if next one have over 50% IP available, people stop getting IP's

Please suggest further

I'm not sure why this post was marked as an Answer? Maybe I missed something?

This post is provided AS-IS with no warranties or guarantees and confers no rights.

_{Wednesday, February 27, 2013 3:23 PM}

Thanks for reply Ace, I have a very basic question.

If I have set client lease time as 8hrs, if a user who get 1 IP leaves the office in next 2hr, what would happen to that IP

for another 6hrs, will DHCP keep holding it and remove only after 8hrs or should it clean it and assign to another user

when scope is getting full?

Yes, it will wait 8 hours, the lease length, UNLESS the client does a proper shut down, such as clikc Start, then click Shutdown. If the client just unplugs his computer or laptop, or just shuts the lid and walks out, the lease will remain.

Same with iPhones, Windows Mobile, Droids, etc. If they walk out, the lease remains.

More information to understand the whole process, and how Windows 7/2008 R2 and all newer are different than Vista and older:

==================================================================

Restarting a Windows 7 or 2008 R2 DHCP client:

If the client had a current lease prior to the restart, upon restart, it will attempt the RA sequence. If a DHCP server doesn't respond with an ACK, it then attempts to ping the gateway address from it's previous configuration to see if the IP config it previously had is on the same network.

If the gateway responds, it will keep it's current lease for the remainder of the lease and continues on with the 50% and the 87.5% rule of the RA sequence.

If the gateway doesn't respond, the RA sequence kicks in, it releases its current configuration, and starts a fresh DORA sequence.
If DHCP server is not available:
The client will auto-configure its IP address by using the settings on the Alternate Configuration tab (either the APIPA or if configured, an

Alternate IP configuration).
The client will then re-attempt the DORA process.

==================================================================

And understanding the DHCP DORA process (Discover, Offer, Request, Acknowledge):

DORA:

Restarting a DHCP Client -
What happens when a client already has an address after it restarts?
http://technet.microsoft.com/en-us/library/cc958945.aspx

DHCP Client States in the Lease Process
http://technet.microsoft.com/en-us/library/cc958935.aspx

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This post is provided AS-IS with no warranties or guarantees and confers no rights.

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IP's are not released after lease expire

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