DHCP Reservation Behavior

[Cameron Frasnelly]

Tough one...

We have many remote sites that our currently static with TWO ip addresses
bound to the ethernet port of the remote router which is set up to relay
DHCP requests to a Win2K DHCP server. Here's where it get's interesting.

We have a scope setup on the DHCP server for the SECONDARY ip range of the
remote branch in which we make reservations based on MAC. How does Win2k
DHCP server know to return the ip from the IMPROPER scope (basically not the
primary gateway of the remote router) .

This works at some sites and not at others. Hope that makes sense...

 

[Herb Martin]

Tough one...

We have many remote sites that our currently static with TWO ip addresses
bound to the ethernet port of the remote router which is set up to relay
DHCP requests to a Win2K DHCP server. Here's where it get's interesting.

We have a scope setup on the DHCP server for the SECONDARY ip range of the
remote branch in which we make reservations based on MAC. How does Win2k
DHCP server know to return the ip from the IMPROPER scope (basically not the
primary gateway of the remote router) .

This works at some sites and not at others. Hope that makes sense...

That isn't very clear so I am going to guess that I understand....

When a "BootP forwarding router" or "DHCP relay agent" (or equivalents
whatever
you call them) 'hears' a client DHCP Discover broadcast it looks at the
"gateway"
field and if that field is STILL all 0's it places it's OWN IP in that
field.

Subsequent forwarders of course skip this step because the field is no
longer empty.
When the Discover reaches the DHCP server it searches for a scope suitable
to be
on the same subnet with that embedded IP address.

My guess would be that the gateway always puts it's "primary" or "first" IP
from
the listening NIC in that field.

 

[Marc Reynolds [MSFT]]

It isn't very clear to me either, but I agree with Herb's take on this
issue. The DHCP Server will assign an address based on the GIADDR field
which is the IP address of the router or relay agent. You may need to look
at how that is configured.
If this is not the case please post more details clarifying the issue.

Thanks,
Marc Reynolds
Microsoft Technical Support

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

 

[Simon Taylor]

jhvjv

That isn't very clear so I am going to guess that I understand....

When a "BootP forwarding router" or "DHCP relay agent" (or equivalents
whatever
you call them) 'hears' a client DHCP Discover broadcast it looks at the
"gateway"
field and if that field is STILL all 0's it places it's OWN IP in that
field.

Subsequent forwarders of course skip this step because the field is no
longer empty.
When the Discover reaches the DHCP server it searches for a scope suitable
to be
on the same subnet with that embedded IP address.

My guess would be that the gateway always puts it's "primary" or "first" IP
from
the listening NIC in that field.