DNS Scavenging and DHCP

[brahma]

Well thanks to all your tips on this forum, DNS scavenging ran on my network this morning and scavenged 704 records!! So I no longer have duplicate IP addresses in my DNS!!! Thanks guys.

 

How long should I wait before reducing the lease time on my DHCP servers now - current lease is set to 14 days. Recommendations on here are to set to 7 days. I thought about setting laptops to 2 days.

 

Thanks,

[powdarrmonkey]

Set the lease time whenever. Current leases are not affected.

[Geoff]

Make sure you update your scavanging times to reflect your lease length though.

[brahma]

DNS Scavenging currently set to 7 and 7. I'm gonna set DHCP lease to 8 days.

[Geoff]

Scavanging will remove valid DNS records if you set things like that.

[kingswood]

Scavanging will remove valid DNS records if you set things like that.

 

Sure will

[brahma]

Why's that guys? Have I got the numbers round the wrong way? Should I set the DHCP lease to a number below DNS Scavenging then?

[SYNACK]

Why's that guys? Have I got the numbers round the wrong way? Should I set the DHCP lease to a number below DNS Scavenging then?

 

Yes otherwise the computer will delete leases that are still valid and possibly in use becasue they have not expired yet.

[powdarrmonkey]

Yes otherwise the computer will delete leases that are still valid and possibly in use becasue they have not expired yet.

 

Not quite. It will delete the DNS A and PTR records that are associated with leases, not the leases themselves. This means that for a supposedly valid lease, you won't be able to use nslookup on either type of record if it has been scavenged.

 

Scavenging purpose: when DHCP is configured to create the DNS records for you, it doesn't remove them. Scavenging removes records that haven't been updated in the time you give it, so that you don't end up with a million out of date DNS records for machines that have long since moved on.

 

Therefore, your scavenging time should be equal to or greater than your lease time, but for maximum efficiency not more than a day or so.

Edited July 29, 2008 by powdarrmonkey