Conflicting Microsoft recommendations for DNS scavenging - looking for third opinions

Hi Rob,

Generally speaking it makes most sense for the Aging Intervals to be approximately equal to your DHCP Lease length for all Dynamically Updated zones. After all, most of the record changes and duplicates are caused by changes in DHCP clients.

With the 7 Days No-Refresh and 7 Days Refresh mentioned above that would work well with a 14 Day DHCP Lease. The two Intervals run in order, No-Refresh then Refresh, which means a record will always exist for the duration of the DHCP Lease as a minimum.

For large networks such as yours you may find it makes sense to increase the No-Refresh Interval as the expense of Refresh (lets say 10 Days No-Refesh and 4 Days Refresh if the Lease is as long as 14 Days).

I'm not sure how familiar you are with the Scavenging Process, but No-Refresh is there simply to minimize unnecessary Replication Traffic. It stops a Refreshed Timestamp being replicated around your network everytime a client checks in but doesn't exclude the Update Command. As soon as a client performs a successful Refresh on entering the Refresh Interval the timer is reset and the record is back in a No-Refresh state.

The minimum you can realistically set for this is 1 Day for each Interval. Any lower and Service Records registered by the Domain Controllers will be removed, those are only Refreshed once in every 24 hour period.

The environment I work on is similar in size to yours. We made several changes to reduce the overhead of managing DNS including the Scavenging changes. As well as that we consolidated the majority of the Reverse Lookup Zones into a single Zone as each is under the Class A Private Range, 10.0.0.0 which we replicate to our Forest rather than having hundreds of smaller zones.

Chris

Christ-Dent:

I totally agree with everything you said, and I am familiar with the scavenging process. What I am really curious about is, if we set it to the recommended one day (actually it's got to be two, with the refresh), and our DHCP leases are one day, then even with the no refresh period, a lot of records will be refreshing every day, versus the 7/7 period we have now. Maybe it's negligable traffic, but I am not a networking expert with a sniffer.

I like what you did with the reverses. Someone did that with the 10.x.x.x net before I started, but others had also created 10.x.x.x subnets and delegations, and we also have a ton of 172.x.x.x and 192.168.x.x subnets. Thousands and thousands of IPs in use. I am not sure how I can consolidate at least most of the subnets into a single zone, but we are looking at doing that. I need more DNS expertise.

Thansk for the comments.

-- Rob --