The DHCP server knows what scope to pick the ip address from by looking at
the GIADDR field in the DHCP packet. When the router helpers a DHCP
request to the DHCP server it populates the GIADDR address with the
primary ip address of the router interface that the DHCP broadcast request
was received on. When the DHCP server receives the request it looks at
the GIADDR field then looks to see if it has a scope that matches the ip
subnet of the address in the GIADDR fields. If it does it assigns an ip
from that subnet.
Hope this helps.
Dale
Date: Sun, 16 Jul 2000 20:35:20 -0500
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Subject: RE: DHCP and subnets
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My 2c on this .
When the DHCP broadcasts crosses the router ,it carries that routers mask
and ip info across to the dhcp server ( assuming helpder is there)
the DHCP server on seeing that the reqest came from that particular subnet
issues an ip from a scope ...U could configure multiple scopes and combine
them into one superscope to do this. Hope this helps.
Cheers,Padhu
-----Original Message-----
From: whatshakin
To: [EMAIL PROTECTED]
Sent: 7/16/00 12:11 PM
Subject: DHCP and subnets
Hello folks,
Please clarify this for me.
Hypothetical example: Campus LAN with multiple buildings. Each building
on its own vlan and with its own subnet addressing scheme. All buildings
tied in to a Catalyst 5500 which has RSP doing all the inter-vlan
routing. Data center using a single DHCP server with multiple scopes
(one scope per vlan/subnet etc) to supply all vlans/subnets with their
respective ip addresses. I want to understand how the DHCP server knows
how to hand out the correct ip address from the corresponding subnet to
the workstations that request them. I have come to believe that
initially DHCP servers have no idea whom is requesting an address, they
just hand them out to whoever asks...this is what is confusing. I
understand that each Vlan needs its own gateway address where the
workstations aim their broadcasts and there an ip helper-address
statement in the RSP for each vlan, but I still don't understand how the
DHCP server knows how to hand out the appropriate address when it has
multiple scopes enabled.
TIA for any clarification you can offer.
------------------------------------------------------------------------
Dale E Drummond [EMAIL PROTECTED]
http://www.pobox.com/~dale/
------------------------------------------------------------------------
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