Windows 2000 DHCP - DHCPDISCOVER behavior

  • Thread starter Thread starter Pete_Mnemonic
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Pete_Mnemonic

I have a question on Windows 2000 DHCP behavior when using a custom
Subnet MASK. I have a Windows 2000 DHCP Server configured with a
Scope covering 8 Subnets. The DHCP server itself is configured to be
on the 7th Subnet.

All clients are Windows 2000 Professional setup to use a DHCP assigned
address.

I have found that whenever a DHCP client is given a DHCP assigned IP
address by this server, it receives an address on the same subnet as
the DHCP server itself. So, no addresses are issued from the first 6
subnets, but rather it seems that preference is given to the same
subnet as that of the DHCP server.

The network uses no switches and is in effect one flat space. The
question I have is as follows: Is this behavior intended, and if so
is it consistent enough that it can be relied on to always assign DHCP
client address's from the Server's subnet if that subnet has free
addresses available?

I have read RFC 2131 and found the following section on DHCPDISCOVER
behavior, when no previous address exists:

"A new address allocated from the server's pool of available
addresses; the address is selected based on the subnet from which the
message was received (if 'giaddr' is 0) or on the address of the relay
agent that forwarded the message ('giaddr' when not 0)"

I'm not sure how much this is relevant since the subnets are 'virtual'
and there is no relay agent involved.

Any help on this would be greatly appreciated.

Thanks in advance,

Peter T.




==========================================
Scenario configuration
==========================================


Network Address: 145.178.96.0
Subnet MASK: 255.255.248.0

This should allow for the following IP ranges 96.1 - 103.254. 8
subnets:

145.178.96.0
145.178.97.0
145.178.98.0
145.178.99.0
145.178.100.0
145.178.101.0
145.178.102.0
145.178.103.0


The Windows 2000 DHCP server is placed on the 102 subnet, with the IP
address of 145.178.102.250

The DHCP Scope is configured to start at 145.178.96.0 and end at
145.178.103.254.

There are a number of exclusions such as 145.178.96.0, 145.178.97.0
etc, and 145.178.102.250 etc.
 
Hi Pete,

DHCP is working as designed. If you want to have the DHCP server hand out
IP addresses to subnets other than the one it is one, you need to use a
switch or router and DHCP relay (or bootp relay).

Thanks,
Marc Reynolds
Microsoft Technical Support

This posting is provided "AS IS" with no warranties, and confers no rights.
 
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