RE: [ActiveDir] DNS Scavenging and DHCP Lease Expiration Times

[Marcus Oh]

Title: Message

Thanks Todd… very helpful!  So it sounds like we have the reverse going on… J   -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Todd Povilaitis Sent: Tuesday, September 02, 2003 8:00 PM To: [EMAIL PROTECTED] Subject: RE: [ActiveDir] DNS Scavenging and DHCP Lease Expiration Times   If DHCP returns an IP address to the pool for re-use before the A records are scavenged, then multiple A records will resolve to the same address until scavenging comes along.  DHCP only manages the PTR records.   This is not a problem if your clients initiate all of the connections (or "pull" everything to them).  However, the reverse is not true.  If you wish to poll your desktops and servers (or "push" a connection onto them), then you may not be attaching to the machine that you think you are when you attempt to resolve names.  This is because multiple host names are resolving to the same IP address.   I've run into to this situation while working on a data warehousing app which connects to each machine in the environment to retrieve WMI class attribute values and store them in a central SQL repository.  The solution would appear to be: set the zone "no-refresh" period to 24 hours (1 day), set the zone "refresh" period to 48 hours (2 days), and set the server scavenging interval to 72 hours (3 days).   no-refresh - reduces replication traffic for multiple reboots which typically occur when a machine is new. refresh - accounts for the possiblity that one client may refresh its A record at 00:01 while another may refresh its A record at 23:59.  A 48 hour offset is needed to capture this behavior and eliminate the possibility of scavenging valid A records.   Finally, the using the default DHCP lease of 8 days,  the lease would come up for renewal at 96 hours (4 days), and lease expiration would occur at 192 hours (8 days).  In any case, no A record could have the same IP address.   Hope this angle is helpful.   __________________ Todd Povilaitis LAN Administrator Huntington Hospital [EMAIL PROTECTED] Phone: (626) 397-3392 Fax: (626) 397-2901 -----Original Message----- From: Joe [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 02, 2003 16:01 To: [EMAIL PROTECTED] Subject: RE: [ActiveDir] DNS Scavenging and DHCP Lease Expiration Times <eg> It is fine until the time DHCP doesn't respond. :op   I would expect though unless you have way more nodes than IP addresses you will find people getting the same IP's over and over. My laptop seems to get the same three IP addresses in the three locations I go to (home building wired, dev building wireless, dev building wired).   -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Roger Seielstad Sent: Tuesday, September 02, 2003 11:22 AM To: '[EMAIL PROTECTED]' Subject: RE: [ActiveDir] DNS Scavenging and DHCP Lease Expiration Times <Quietly hides the 4 hour lease time on his DHCP scopes> Actually, I advocate the shorter the better, but my environment is predominantly laptops. Between people moving across our subnets, and more often people taking their laptops onto home networks (or other corporate networks, as the case may be). The net effect is that every time the clients change networks, they basically lose the ability to recover their prior lease (at least 50% of the time, if the DHCP server isn't entirely brain dead). At that point, you've got a lot of leases that are left hangling. Then again, there is precious little traffic generated in DHCP transactions, so a short lease time isn't buying a significant jump in network traffic, either. -------------------------------------------------------------- Roger D. Seielstad - MTS MCSE MS-MVP Sr. Systems Administrator Inovis Inc. >  -----Original Message----- > From:         Joe [mailto:[EMAIL PROTECTED]] > Sent: Sunday, August 31, 2003 9:31 AM > To:   [EMAIL PROTECTED] > Subject:      RE: [ActiveDir] DNS Scavenging and DHCP Lease > Expiration Times > > None to me either. > > However that DHCP lease time seems short. How many DHCP > servers do you have per site? With that lease time you should > probably have a couple or a guarantee to be able to not have > an outage of the server greater than 3 days or more > preferably (to me) more than 1.5 days - lease half-life. > > About the only time I would recommend to anyone to go below > 7-14 days on lease times is if they are trying to switch > values for some of the networking components through DHCP. > > What is the idea behind the 3 day lease time? > >    joe > > >  -----Original Message----- > From:         [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]  On Behalf Of > Rick Kingslan > Sent: Saturday, August 30, 2003 12:32 PM > To:   [EMAIL PROTECTED] > Subject:      RE: [ActiveDir] DNS Scavenging and DHCP Lease > Expiration Times > > None that occur to me off the top of my head. > > Rick Kingslan  MCSE, MCSA, MCT > Microsoft MVP - Active Directory > Associate Expert > Expert Zone - www.microsoft.com/windowsxp/expertzone >  > > > _____________________________________________ > From:         [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]  On Behalf Of Marcus Oh > Sent: Friday, August 29, 2003 4:56 PM > To:   [EMAIL PROTECTED] > Subject:      [ActiveDir] DNS Scavenging and DHCP Lease > Expiration Times > > Hey folks, > > Our DNS scavenging cycle is 7 days.  Our DHCP leases expire > every 3 days.  Are there any notable drawbacks or problems in > changing the DNS scavenging time period to match the DHCP > lease expiration time period? > > Thanks! > > Marcus