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DNS Scavneging  refresh / no refrish intervals

Posted on 2014-10-05
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Last Modified: 2014-10-08
Hi all, i have read this document in the past and would like some clarification if possible. In the enable phase section of the document it gives an example of no refresh / refresh being set to 3 days and record scavening to 3 days. This suggests the record will be scavenged every 9 days. Therefore if i wanted to start at a safer level would it be best to increase these parameters, as scavening has never been enabled. What would be a recommended starting point

thanks

http://blogs.technet.com/b/networking/archive/2008/03/19/don-t-be-afraid-of-dns-scavenging-just-be-patient.aspx
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Question by:cwstad2
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by:Cliff Galiher
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That really depends on the environment. The number of clients, the pressure on your address space, the amount of client churn....a "safe" window for a small 25-seat private network will be very different than 500-seat network with a lot of BYOD devices. There is just no "safe" way to even answer your question.
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by:cwstad2
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It's about 2000 clients.  There are a lot of duplicate records hence the need to  enable it
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by:Cliff Galiher
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Any reason you aren't comfortable with the defaults?
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by:cwstad2
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Hi Cliff just as a precaution really.  Just want to start higher and lower it gradually.  If I wanted it to scavenge records over a certain period would it be best to increase the no refresh only?
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by:Cliff Galiher
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My personal opinion is that if there is a problem, delaying the times just delays you knowing about it. It either won't scavenge at all, so you wait longer to see it not do anything Or it is too aggressive and deletes "live" records. It wouldn't matter if it does that on day 9 or day 20. It'd be an annoyance either way. I don't see where starting high and cranking down gains you safety or diagnostic benefit.
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by:cwstad2
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Thanks for the information.  One last thing would you recommend the DHCP lease be more than the refresh / no refresh period
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Cliff Galiher earned 500 total points
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No. Otherwise you could find a record gets scavenged when a device still has the IP address because it hasn't renewed because its lease hasn't expired. I believe that is covered in the scavenging document.
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by:cwstad2
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So if I have a lease period of 8 days would I need to set the refresh / no refresh to 9 days
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by:Cliff Galiher
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Need? No. But those would not be unreasonable.
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by:cwstad2
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so if i leave my lease period to 8 days, scavenging period to 7, and refresh / no refresh to 7. Would that be ok
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Why are we going in circles?
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by:cwstad2
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Thanks Cliff
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