DNS Scavaging and DHCP reservations

[phir3]

Will scavaging affect DHCP reservations? We have a few hundred servers that have DHCP reservations (i know i know .. i didnt set this up and it isnt going to change). Aging has been enabled on AD integrated DNS zones for awhile but I just recently enabled the server to scavange
records. When I look at an A record, in advance view, for 1 of the servers it shows the time stamp as being several months old (when the reservation was first created i'm guessing) so I am afraid these records will be removed. Is this correct? If so, am I going to have to manually protect these records?

 

[ShackDaddy]

Scavenging will not affect DHCP reservations. What you do in DNS has no affect on whether DHCP will hand out a reservation.

Chances are, next time the DHCP server renews that particular reservation, it will create a new A-record for that host with an updated timestamp. Assuming that you've enabled the features that allow dynamic DNS updates.

Dave Shackelford
Shackelford Consulting

 

[phir3]

These servers basically have a 99.9% uptime and have DHCP reservations. How often do these host communicate back to DHCP for updates? Do they follow the normal lease times? If those server records get scavenged then its going to be a huge mess. If it just takes time for DHCP to update these timestamps then I need to push out the Scavenging interval to reflect that.

 

[ShackDaddy]

What's your current DHCP lease time? Each server should renew its lease when the lease time gets to the 50% mark.

Dave Shackelford
Shackelford Consulting

 

[phir3]

refresh - 2 day
no-refresh - 2 day
dhcp lease - 3 day
sacavenging interval - 1 day

I was pretty sure that reservations still "renewed" but ive never used dhcp on servers before so i wanted to make sure. The thing the worried me was that some of the server A records had a time stamp from last month. With the above settings, the servers (which are 99.9% uptime) shouldnt have a time stamp any older then 3 days right? Why do I see time stamps that are a month old or older?

 

[ShackDaddy]

I think the servers are updating their own DNS record. If you look in your DHCP Admin options, you'll see that there are some different ways to configure things, including having the DHCP server do all the dynamic DNS updates. Switching over to that method may keep the timestamp more current. That's the "Always dynamically update DNS A and PTR records" option.

Dave Shackelford
Shackelford Consulting

 

[phir3]

We have that option enabled. I think it may just be a timing issue with a busy DNS server and replication, DHCP lease times, ect. Hopefully the scavenging interval I have isnt to short. I am new to this infrastructure and noticed some other house cleaning issues that need to be dealt with. For instance, some DHCP scopes do not have the "Remove A and PTR records when lease expires" option selected.

Our main Primary FLZ is eligible for scavenging at noon today so I guess I will find out how it handles reservations soon enough. Thanks again for your post. Hopefully this thread will show up on Google and help someone else in the future.

Someone else also suggested enabling DHCP option 202 on scopes so that servers are forced to fully release their ip on shutdown. This would force a new time stamp on server DHCP reservation records after patch management, if the patch requires a reboot.