dhcp via ip helper-address

Can the experts explain to me how PC0 gets his dhcp IP address from server 10.10.10.20 (see pic). Thanks

net diagram
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leblancAccountingAsked:
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Jan SpringerCommented:
The layer 3 gateway for the PC picks up the dhcp broadcast traffic and, using the helper-address, forwards the packet on behalf of PC0 to the DHCP server as a DHCPDISCOVER.

If you were to look at DHCP logs, it would appear that the traffic originated from the IP of the interface that had the helper-address configured.

The DHCP server will then send a DHCPOFFER via the layer 3 gateway.

Once the DHCPOFFER is received, PC0 will send a DHCPREQEUST for the IP offered.

When the server sends the DHCPACK to PC0 along with netmask, gateway, DNS servers and possibly other criteria and PC0 accepts it, it will update its adapter with the received information.
Bryant SchaperCommented:
To build on that as well, in a windows DHCP server you also need to have ad sites and services setup so the DHCP server knows what IP address to assign.  They receive the forwarding routers ip address (subnet the pc0 is on, 192.168.200.0) and return an IP for that subnet.  But Jan is right on with how it works, their is a network piece and a AD/DHCP server piece

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Jan SpringerCommented:
or specifically, there is a network piece and a dhcp server piece.

the dhcp server may be Windows or may be Linux (or something else).
leblancAccountingAuthor Commented:
but once the dhcp request gets to dhcp server, how does it know that it has to take 192.168.200.0 dhcp scope?
Jan SpringerCommented:
It will use the "relay IP" to figure to map to the dhcp configuration where that subnet is defined.
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