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DHCP TTL value

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Sunday, February 24, 2013 3:56 AM

Hi all,

can anyone explain me where does Host records TTL (20mins) come from when it gets registered by DHCP? I know when i do manually it gets SOA's TTL (1hr default) but how about DHCP?   it is server 2008R2 and only way i was able to change it was via group policy.

i tried all registry tweaks including: 

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\DefaultRegistrationTTL

and one more in DHCPserver folder but none of them work. none of the keys mentioned in microsoft articles exist.

Thanks in advance

All replies (4)

Sunday, February 24, 2013 4:35 AM

Hi, if you mean Dynamic DNS, this thread in the NIS forum may help: http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/d97cf295-1345-4be7-bfcd-6d59436d93b2/

Don
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Monday, February 25, 2013 9:46 AM

Hi Luksharp,

By default, when the DNS Client service registers A and PTR RRs for a computer, it uses a default caching Time To Live (TTL) of 15 minutes for host records. This determines how long other DNS servers and clients cache a computer's records when the records are included in a query response.

However, If the DNS Server service dynamically registers records for its own zones, the default TTL is 20 minutes. You can change the TTL in the properties of each resource record.

You can also change the default setting by modifying the DefaultRegistrationTTL entry in the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services \Tcpip\Parameters

The entry has a DWORD value and lists the TTL in seconds (If this key does not exist, please manually create it). A small value causes cached entries to expire sooner, which increases DNS traffic but decreases the risk of entries becoming stale. Expiring entries quickly is useful for computers that frequently renew their DHCP leases. A large value causes cached entries to be retained longer, decreasing DNS traffic but increasing the risk of entries becoming stale. Long retention times are useful for computers that renew their DHCP leases infrequently. Quote from: Dynamic Update

More references:

DNS Processes and Interactions

Resource records reference

DNS Architecture

HOW TO: Modify Time to Live on Domain Name System Records

Hope this helps.

Jeremy Wu
TechNet Community Support

Monday, February 25, 2013 5:20 PM

Hi Jeremy,

thanks for the response,

DefaultRegistrationTTL key did not exist on my server and i created it with the value of 900 (15mins) i deleted the old A record and used ipconfig /registerdns to recreate the record in the dns but, it still had 20mins of TTL. is there anything i am doing wrong, maybe i need to wait some time registry changes to populate? 

again, i am able to change it via group policy but, i am trying to find where it's coming from.

thanks again

Saturday, August 3, 2013 2:05 PM

This will probably help http://support.microsoft.com/kb/322989

To Configure the TTL Value

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

A new feature has been introduced with this fix. You can use this feature to configure the TTL value in the registry.

  1. Click Start, click Run, type regedit.exe, and then click OK.

  2. Locate and then click the following key: **HKLM\SYSTEM\CurrentControlSet\Services\DhcpServer\Parameters
    **

  3. Double-click the DynamicDNSTimeToLive value. 

    NOTE: If this value does not exist, create it as a DWORD value.

  4. Set the DynamicDNSTimeToLive value to the TTL value that you want to use. Set the value in seconds (for example, for a value of 20 minutes, set the value to 1200).

  5. Click OK.

  6. Quit Registry Editor. The new value takes effect the next time that the DHCP service is started.