The RSM work as the BOOTP Relay agent .... this is what happen when the
client request for IP Address :
1 The request packet arrive to the interface (of the catalyst and RSM check
this packet). As a note the DHCP request contain the Router Relay IP Address
field in the packet). The client use UDP packet port 67.
2. The RSM will replace the Router Relay IP addess field in the packet with
the ip address of the interface VLAN configured in the RSM.This will be
usefull because the BOOTP server will use this address to relay its replay
back toward the client via the relay agent, int this case is the RSM.
3. The RSM send the unicast packet from the Client request packet and send
it to the Configured Helper Address.
4. When the BOOTP Server receive the request packet, the server will reply
by using port 67 at the ip address that has been filled into the Relay
router IP Address field by the relay agent.
5. The RSM ( as the relay agent ) then deliver the response to the client -
using either broadcast or hardware Client Address.
Correct me if it is wrong
----- Original Message -----
From: "Stephen Lee" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, July 16, 2000 9:02 PM
Subject: Re: DHCP, and, subnets
> Please correct me if I'm wrong but the way I've seen it work is; If you
have
> the helper address defined on all the vlans in you RSM then, when the
router
> sees a bootp dhcp request from the PC it sends a directed broadcast
towards
> the next hop to the helper address. When it gets to the server the packet
> contains the originating subnet and the server then knows what subnet to
> give an address from. It then sends a unicast packet back to the
originating
> router and the router then forwards it to the pc via its MAC address.
>
> In reply to:
> Hello folks,
> Please clarify this for me. =20
>
> 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.
>
>
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