Re: DNS resolution on laptops that move between networks

On Thu, 15 Dec 2005 22:53:41 -0600, "Kevin D. Goodknecht Sr. [MVP]"
<admin@xxxxxxxxxxxxxx> wrote:

>Todd J Heron <todd_heron(delete)@hotmail.com> wrote:
>> "Name" <email@xxxxxxxxxxxxx> wrote in message...
>>> Hello,
>>>
>>> I was wondering how other folks deal with this:
>>>
>>> Our laptop users occasionally work in different buildings throughout
>>> the day. Each building is on a different subnet. They may >use
>>> wireless or plug in. As such, they may get 3 or 4 IP leases during
>>> the day. The problem is, when we try to reach a user's >machine by
>>> name, DNS usually resolves an older (wrong) IP address. How should
>>> we be configured so that DNS always >resolves the most current DHCP
>>> lease for that hostname? This is a Windows 2003 domain with 4
>>> Windows 2003 >DHCP/DNS/WINS servers spread across 2 buildings.
>>> Services are pretty much at defaults.
>>>
>>> The clients generally have XP SP2 with two NICs (wired and wireless,
>>> their choice) Any insight / tips from the field would be
>>> >appreciated, thanks!
>>
>> Duplicate records may exist in DDNS due to DHCP not discarding A & PTR
>> records. On the DHCP server, ensure "Discard A and PTR records when
>> lease is deleted" is enabled under the DHCP server properties > DNS
>> tab.
>
>Todd, the problem with relying with DHCP to delete records is twofold, if
>the record is owned by the machine DHCP won't be able to remove the A or PTR
>record and you would have to make the IP lease such a short time the network
>would be overloaded with DHCP requests. Plus, how many users release their
>IP address before disconnecting from the network?
>Usually the machine will update its A record when it registers, but they
>can't update or overwrite a PTR record they didn't create, so they create a
>new PTR leaving the old one owned by another machine in place which is why
>reverse lookup zones tend to have many PTR records for the same IP.
>
>Now, I believe the real problem is the caching of records because the TTL
>has not expired. The solution for that is to reduce the TTL of Dynamic
>records which is 20 minutes by default. IMO, reducing the TTL of all DDNS
>records for all machines may not be the solution because this may cause too
>much network activity. It would be a good idea to reduce the TTL on the
>laptops. This can be done by moving the laptops to their own Organizational
>Unit then applying a GPO (Works on XP and 2k3 only) to them to register
>their records with a TTL of no more than 5 or 10 minutes.
>The GPO is located here:
>Computer Configuration
> -Administrative Templates
> -Network
> -DNS Client
> -TTL set in the A and PTR records
>
>Of course if you could send a shock to the users if they disconnect the
>cable without first running ipconfig /release, that will do the trick. too.

Thank-you for all of the suggestions!

The "shock users" idea sounds great for a multitude of uses.. is this
in the power of ethernet spec? :)

I checked the DHCP servers and under the "DNS" tab, everything is
checked. (Enable DNS dynamic updates, Always dynamically update,
Discard A & PTR when lease expires, Dynamically update DNS A & PTR for
NT)

There are too many laptops (>100) to realisticaly assign DHCP
addresses to MACs. Plus, with the two NICs per PC, I still wouldn't
know which assignment was current (wired or wireless).

The group policy idea sounds promising although there are a number of
folks still on 2000 pro.

Does this problem come up on your networks? I'm wondering if there is
some step I missed that would have avoided or addressed this problem.

Thanks again

.

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