----- Original Message -----
Sent: Wednesday, September 03, 2003 1:00
AM
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
<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).
<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
