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UmweltIT
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DHCP and DNS address lists are out of sync

Hi Experts,

My company has managed printer accounting software operating on all our client systems.  Intermittently, and seemingly without any pattern, users are being sent other user's print confirmation dialogs.  When I log onto the DHCP server to investigate their DNS addresses and DHCP leases I discover that in many cases the DNS address don't match the DHCP lease address.

My server topology (as relates to this issue) is as follows:
DHCP server (also secondary DNS server) with Server 2K3
Primary DNS server with Server 2K3
Print Server (also support DNS server) with Server 2K3

On a subnet within my domain (second site):
DHCP and DNS server with Server 2K3

I have had outside contractors involved in this issue, and they have made a number of changes to DNS address scavenging settings, lease request settings/timeouts, etc.  Just yesterday we changed the primary DNS server to be our DHCP server under the assuption it may be possible that client computers are booting up and receiving their DNS addresses from the support DNS servers before checking their leases with the DHCP server.

What else am I missing?  I read some on this topic (very helpful stuff found at http://www.windowsnetworking.com/articles_tutorials/Troubleshooting-Basic-TCPIP.html ) and am wondering (though it has been dismissed somewhat by the contractors) whether my router may be acting as a "rogue" DHCP server.  If so, how can I ensure that it doesn't interfere with my network?
TCP/IPDHCPDNS

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UmweltIT

8/22/2022 - Mon
Chris Dent


Can you tell me what Scavenging settings and lease settings they've given you?

Given that you have two DHCP servers, did they configure matching credentials for each DHCP server? Or did they add the servers into the DnsUpdateProxy group (I suggest the former, and if they've done the latter, undo it).

"ipconfig /all" on a client will show you the DHCP server used to obtain an address. It should be possible to build a script to check as well, I'll let you know if I succeed ;)

>  DNS addresses from the support DNS servers before checking their leases with the DHCP server

You can't interact with DNS until you have an IP; addressing comes first.

Chris
UmweltIT

ASKER
Hi Chris,

I've attached a screencap of the scavenging properties.  As far as I know, both DHCP servers and all DNS servers have the same settings (I was of the understanding that DNS would replicate all settings across automatically, much as it updates arress lists).  All my clients (except the ones on the second site) are receiving DHCP from my DHCP/DNS server; the second site is receiving from their DHCP/DNS server.

Some other settings that have sprung to mind:
All DNS servers are set to look at 127.0.0.1 for their DNS address lists first and if not found will then search the domain.
dns.jpg
Chris Dent


Such an odd choice for the Refresh Interval, not bad though. What's the DHCP Lease Time at the moment?

If these settings have only just been put in place it'll take a while for the clean up to finish. Can you select View, then Advanced in the DNS Console and open that Aging properties box again? This time it should tell you when the zone can next be scavenged.

Chris
Your help has saved me hundreds of hours of internet surfing.
fblack61
UmweltIT

ASKER
DHCP Lease Time is 7 days at the moment.  The DNS scavenging has been in place for about a week or 2 so far.

Although I've just noticed that only one of my DNS servers is set to scavenge entires, and it's not the one with DHCP running on it.  I'm not at all alone in thinking that the scavenging settings should be identical across all the DNS servers am I?
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UmweltIT

ASKER
Hi Chris, sorry about the late reply.

None of the DNS servers had automatic scavenging enabled!!  I've enabled it for 7 days, and will let you know how it goes.
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UmweltIT

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Well, after setting the automatic scavenging and waiting a week or two, it seems we may be all good.  I haven't heard of/had any problems with DNS (other than a minor hiccup just after I enabled scavenging where I lost a SQL server address.......), so I think it's points time.

Thanks for your help Chris :-)
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