"Cliff Galiher" <> wrote in message
news:%...
> First, you have to understand that DHCP just hands out addresses. (well,
> technically it can do a lot more, but for the merits of this
> conversation...)
>
> It does NOT control how IP traffic gets from point A to point B at any
> time.
>
> Let's use a valet service as an example. When going to a restaurant (a
> fancy one that invests in silly technology like my example...bear with
> me), the valet types in your license-plate, parks your car, and gives you
> a ticket. Your ticket now has the license-plate and the parking space
> printed on it.
>
> So one night, I go to the restaurant and park my car. I get a ticket that
> says pc-5 is parked in 192.168.0.3. In the DHCP world, this is a lease.
> Two weeks later, you go to the same restaurant and you get a ticket. pc-7
> is parked in 192.168.0.3. Two tickets, same IP. But they aren't in
> conflict because the two cars were not parked there *at the same time.*
> The parking space got reused because it was vacant. Again, in the DHCP
> world, leases expire.
>
> Now to the important stuff. When you ping a machine, the first thing the
> OS does is tries to resolve the machine name to an IP address. There are
> several ways to do this: DNS, WINS, neighbor discovery, etc. But SBS when
> setup properly will use DNS first. So when you manually set the IP
> address if pc-5 to another address...192.168.0.113 in your example, you
> didn't update the DNS entry on the DNS server. So a ping still does the
> DNS lookup, DNS still has a record (you didn't delete that) and pings the
> machine *REGARDLESS OF NAME* at 192.168.0.3. Same goes for pc-7. You are
> manually changing the IP address, but not changing the DNS record.
>
> But the real rub here is that DHCP will update DNS records for you. By
> changing the IP address manually, you were not letting DHCP do what it
> does best. It hands out an address and then updates DNS. If had just
> deleted the DHCP leases from the DHCP server and then rebooted both
> clients (not the server!) they'd have re-requested IP addresses and DHCP
> will *not* issue the same IP to multiple machines at the same time. One
> would've gotten 192.168.0.3 and one would've gotten a new address.
>
> So to answer the two questions you ended with (in order), yes, it sounds
> like pc-5 had 192.168.0.3 at one time. And no, the two machines would not
> have gotten the same IP address.
>
> As an additional note, with any computer that has a shared resource, it is
> best to make sure they always get the same IP address. You can do this
> with DHCP by setting up a DHCP reservation. That way you won't ever have
> the DHCP server handing that address out to another machine, and even
> better, you get the benefit of the DHCP server updating the DNS server.
> Unless you know *exactly* what you are doing, *!!!NEVER!!!* manually
> assign IP addresses. It only causes more headaches and, as you've already
> discovered, causes troubleshooting pains.
>
> -Cliff
>
I just want to add:
By default, a Windows 2000 and newer statically configured machines will
register their A record (hostname) and PTR (reverse entry) into DNS.
If set to DHCP, a Windows 2000 or newer machine will request DHCP to allow
the machine itself to register its own A record, but DHCP will register its
PTR (reverse entry) record.
However one problem with that, if the client shuts down, and later on when
it comes back up past the lease time, it may get a different IP address.
What happens here is a duplicate A record gets created with the new IP
because the client will not update itself due to the current record in DNS
is beyond the lease period. This happens even though DHCP registered the
record. This is because DHCP doesn't own the record, the client does, even
though DHCP registered it.
The way to get around this is you can configure DHCP to update the record
for the client, no matter what the client asks. What we want to do to keep
DNS clean without additional records with the same name but different IP
address in DNS. To do this, DHCP must own the record, not the client, so it
can keep it up to date, no matter if the record is being the lease or not.
Therefore, as long as DHCP owns the record, it will update the record in DNS
when and if DHCP gives the machine a new IP. Otherwise you'll see multiples
A and PTR records of the same in DNS whether scavenging is enabled or not.
I also suggest to configure DHCP to register all DHCP clients, whether the
client supports Dynamic Updates or not. This way all DHCP clients get
registered and DHCP owns the record. I suggest to enable DNS scavenging to
remove stale records, which will keep the zone clean.
For Tim09:
To force DHCP to own records, simply create a user account, (a non-domain
admin account), provide a secure password, go into the DHCP console,
righ-click DHCP server name, properties, Click on the last tab, click on
Credentials button, supply the user account name and password.
To enable scavenging on the zone, please read my blog in the following link:
DHCP, Dynamic DNS Updates , Scavenging, static entries & timestamps, and the
DnsProxyUpdate Group (How to remove duplicate DNS host records)
http://msmvps.com/blogs/acefekay/arc...ate-group.aspx
--
Ace
This posting is provided "AS-IS" with no warranties or guarantees and
confers no rights.
Please reply back to the newsgroup or forum for collaboration benefit among
responding engineers, and to help others benefit from your resolution.
Ace Fekay, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA
2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
For urgent issues, please contact Microsoft PSS directly. Please check
http://support.microsoft.com for regional support phone numbers.
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