Lock to a DHCP Server

Let's say
VLAN1 has DHCP_A Server
VLAN2 has DHCP_B Server

Laptop1 on VLAN1 will get an IP Address from DHCP_A Server, but when Laptop1 goes to VLAN2, I want Laptop1 to try to get it's address from DHCP_A instead of DHCP_B, I know LAptop1 can't go anywhere or get any IP Adress.

The long and short of it is that this is not going to be possible. DHCP was simply not designed to operate in this way. I?ll start by explaining a little bit about how DHCP works.

When you connect your client to the network and request a DHCP assigned address you broadcast your desire to all computers on the network. This is a network broadcast not simply talking to one specific server (hence no setting for specific server). When a DHCP server receives your request it responds according to it?s configuration with the information that the client needs to connect to the network.

If there were more than one DHCP server on the network it would cause erratic behavior on the client side. You would never know which DHCP information you would end up with because the client would receive the information from the server that responded first.

To avoid broadcasting to all computers on the network you would have to filter the broadcasts at the router, or simply subnet your VLANs so that none of them could talk to each other.

I am pretty sure that you want is to configure your clients statically. That way when connecting to a foreign network, the configuration wouldn?t change and the clients would not request DHCP addresses in the first place (and probably not be able to communicate on the foreign network).

Hope this helps.

Lets clarify one thing here. The others are correct that 2 DHCP
servers on the same subnet COULD cause issues, but only if they
share or overlap the same scope address'.

DHCP is a network service and as such requires redundancy in
any LAN. Without that redundacy, if the only DHCP server died,
the clients needing an address might auto assign a 169.254.y.z
address. Older clients might get nothing. network access would
stop.

While Microsoft has been contridictory on their examples, the
standard is to have two DHCP servers, each with unique scopes
that come from the same subnet. An example would be that:

DHCP A: 192.168.1.100 --> 192.168.1.150
DHCP B: 192.168.1.151 --> 192.168.1.200

With that said, the answer is still that DHCP requests are
answered by any available DHCP server that receives the
broadcasted request. If a client gets more than 1 offer it chooses
the one it feels is best. if more than 1 seem best, it chooses the
first response it got from those.

You could use some form of sub-domains. A client will always
try the Authorized DHCP in it's logon domain first as I recall.

Good Luck,

razz

As per Microsoft (Sorry again but the PC is off and the Mac does
not wrap URLS correctly on this site so you will need to copy the
2 line URL):

http://msdn.microsoft.com/library/default.asp?url=/library/en-
us/wcetcpip/html/cmconnon-configurableparameters.asp

"The following values are created and used internally by the
TCP/IP components. They should never be modified using the
Registry Editor. They are listed here for reference only. These
entries are located under the
HKEY_LOCAL_MACHINE\Comm\\Parms\Tcpip
subkey."

Again, DHCP is a broadcast Request. It can not be locked.

razz

Razz2 is right. Just because you found a key in the registry that displays the current DHCP server does not mean that you will be able to "lock" it through the registry.

Even though you rejected my answer doesn't make it any less true.