DHCP and DNS - transcender question

[Maxxxie]

Hi all,

I am just getting into the swing of the win2k MCSE and am studying for 216. I'm using Transcenders to practice, as I have in the past. I have an issue with the answer given on one of the questions. I'll post it here (hope this is not verboten) and would like some feedback:

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You administer a Windows 2000 network that consists of 4 subnets. All servers run Windows 2000 Server, all clients run Windows 2000 Professional. DNS and AD are deployed on the network. You want to implement DHCP on the network.

The Windows 2000 Servers will not be DHCP clients, so you manually assign their IP addresses and other necessary TCP/IP information. All Windows 2000 Professional computers will be DHCP clients. All win2k Pro clients are configured with the default settings regarding the registration of resource records in DNS. On each of the 4 subnets, you install DHCP on one of the win2k servers.

You want to achieve the following goals:



* The DHCP servers should be prevented from assigning IP addresses that are already on the network
* The DHCP servers should automatically create DHCP clients' A records in DNS
* The DHCP servers should automatically create DHCP clients' PTR records in DNS
* The DHCP servers should configure each DHCP client with a unique and appropriate IP address and subnet mask
* The DHCP servers should configure each DHCP client with the IP address of an appropriate gateway.


You plan to take the following actions:

* On each DHCP server, configure one scope for the respective subnet
* In each scope, exclude the addresses of the win2k servers
* On each DHCP server, configure the 003 Router option at the scope level
* Configure each win2k Pro client to automatically receive their IP address, subnet mask and default gateway configurations from DHCP
* Configure DNS to accept dynamic updates
* Configure the DHCP servers to automatically update DNS according to client requests
* Authorise each DHCP server in AD
* On each DHCP server, activate the scope

Which goals will you accomplish (select all that apply)?

A. The DHCP servers will not lease addresses that are already in use on the network
B. The DHCP servers will automatically create A records for DHCP clients
C. The DHCP servers will automatically create PTR records for DHCP clients
D. The DHCP servers will configure each DHCP client with a unique and appropriate IP address and subnet mask.
E. The DHCP servers will configure each DHCP client with a unique and appropriate default gateway.


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I gave answers A, D and E. Transcender claims the answer is A, C, D and E.

No DNS settings have been defined in any of the server or scope options. How does the DHCP server know which DNS server to send the PTR updates to?

Is it assumed that the clients are already DNS-aware as they were previously statically-assigned and there is no mention of changing the clients for automatic DNS assignment?

If that's true, do the clients communicate their DNS settings back to the DHCP server? If so, during what part of the process does this happen?



Thanks in advance!
Max.

[Orion IV]

Hi.

I think you are making the problem harder than it is supposed to be. Regular use of DHCP will be giving the clients an IP, subnet, gateway and DNS when using AD. If the clients has no DNS they cant find the DC and log on to the domain.

The point about answer C is whether or not the clients register their own IP in DNS (host and PRT records) or if the DHCP server does this for them, and it is stated that the DHCP servers are configured to automatically update DNS according to client requests. This will if my memory serves me correctly result in that the W2k clients will register their own host record by themselves in the forward lookup zone, but the DHCP server will add (and remove) the PRT record in the reverse lookup zone. (Well, just look this fact up in the dokumentation or study material you use and see if I'm totally wrong, but I think this is the way things are).

Hope this helps,
OIV
_________________
MCSA 2000:Security, MCSE 2000:Security, PCSE, GSEC, DRUNK+
I can handle pain until it hurts!

[Maxxxie]

Hi Orion IV,

Thanks for that, I think I've managed to suss out the answer to my question.

I agree that is the behaviour that would be exhibited by the DHCP server (let client register A records and have the DHCP server register PTR records). According to the win2k server resource kit (TCP/IP Core Networking Guide), there is an option called FQDN which is transmitted in the DHCPREQUEST packet. Left at the default, this is 0 which is the behaviour described above (server updates PTR, client updates A). That's fine, I understand that part.

By default, unless configured to do so, the DHCP server will not assign anything more than IP address and subnet mask. Everything else is a server or scope option.

I think what tripped me up is that because there was no mention of assigning DNS settings via DHCP, I didn't make the assumption (as I should've) that the clients were already DNS-aware from having been previously statically-configured. I just assumed that since there was no DNS option defined, the clients were not DNS-aware at all. Stupid assumption on my part!

It made me wonder how the DHCP server knows which DNS server to update. I realise now that I didn't think too hard about what the DHCP server does with the contents of the FQDN option. It looks for the DNS server authorative for the client's FQDN and that is how it determines which DNS server to update - whether or not DNS is specified in an option.


Cheers,
Max.