DHCP Relay + PPP

[JOBY THAMPAN]

Hi all,

	I did a setup like this, All are Linux machines

Machine 2							 Machine 3

_____________________					____________________
|			|192.168.30.1		192.168.30.30	|
|
|PPPoE Server
ppp0----------------------------------------------------------	| ppp0 pppoe
client         |
|		            |					|
|			
|_____________Eth1___|
|_____________Eth1___|
		|192.168.10.130
| 192.168.40.1
		|					Machine 4
|
		|
______________|______ 
		|						|
Eth0	|
Machine 1	|192.168.10.1					|
|
_____________ |________					|
|
|		Eth0     |					|
Client Machine	|
|			|					|
|
|	DHCP Server     |					|
|
|____________________|
|____________________|
	

	DHCP Relay agent is ran on Machine 3 which listens on both ppp0 and
eth1

	DHCP Server is ran on Eth0

	When client machine renews the IP it must get an IP in the range
192.168.40.X

	The working I saw here is when client machine ernwes the IP 
	DHCPDISCOVER is travelling to DHCP Server with GIADDR field
192.168.40.1

	DHCP Server is responding with a DHCP OFFER of 192.168.40.20

	But this offer is reaching only upto ppp0 interface of Linux machine
3

	
Then I did another setup

	
Machine 2							 Machine 3

_____________________					____________________
|			|192.168.30.1		192.168.30.30	|
|
|PPPoE Server
ppp0----------------------------------------------------------	| ppp0 pppoe
client         |
|		            |					|
|			
|_____________Eth1___|
|_____________Eth1___|
		|192.168.10.130
| 192.168.40.1
		|					Machine 4
|
		|
______________|192.168.40.5 
		|						|
Eth0	|
Machine 1	|192.168.10.1					|
|
_____________ |________					|
|
|		Eth0     |					|	DHCP
Relay 	|
|			|					|
Machine	|
|	DHCP Server     |					|
|
|____________________|
|______________Eth1__|
	
|
	
|192.168.40.10
	
|
							Machine 5
|
	
|
	
_____________ |_______
								|
Eth0	|
								|
|
								|
|
								|
Client Machine	|
								|
|
								|
|
	
|____________________|


	In this setup when DHCP Relay is ran on another Machine, client
machine successfully recieved the IP Address 192.168.40.20 from DHCP Server.


	Can somebody please explain me why DHCP Relay when listened on ppp0
interface didn't got the packet???

	Is it because in the first case DHCP Relay listened on pppo which
doesn't have a hardware addresss.


Rgds
Joby





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