FW: PPP Interface doubt

[JOBY THAMPAN]

Hi friends,

  For the last few days I am checking whether dhcp relay can be run over ppp
interface

  For that I created a setup like this

  Linux Mach 1
  Eth0 interface   -     DHCP Server with IP 192.168.10.1

  Linux Mach 2
  Eth1 interface   -     Got IP from DHCP Server as 192.168.10.130
  Eth0 interface   -     Run a PPPoE Server
  ppp0 interface formed with IP as 192.168.30.1
  
  Linux Mach 3
  Eth0 interface   -     Run PPPoE Client
  ppp0 interface formed with IP as 192.168.30.10
  Eth1 interface   -     Gave Static IP as 192.168.40.1
  DHCP Relay is running in this machine 
  DHCP Relay is listening on ppp0 interface and eth1 interface (pppoe is
running on eth0 so i think there is no need to listen on eth0 interface).

  Windows Machine
   Eth0 interface   -    Connected to Eth1 interface of Linux Mach 3
   
   When we release and renew as if the normal case I am expecting an IP as
192.168.40.X

   But this is not happening????
   
   DHCP Discover (as broadcast) is sent from Client machine to Server
Machine
   and Server is responding with DHCPOFFER

   But this DHCPOFFER is not getting out of ppp interface to reach Client
machine.


   Without ppp interface if we connect normally through eth interface I got
the IP in the range 192.168.40.X


   so i checked the dhcp source code.

   I have certain doubts in code
   
   1) In discover.c file in discover_interfaces function.
   	I saw a checking whether

           /* Skip non broadcast interfaces (plus loopback and
                   point-to-point in case an OS incorrectly marks them
                   as broadcast). Also skip down interfaces unless we're
                   trying to get a list of configurable interfaces. */
                if (((!(ifr.ifr_flags & IFF_BROADCAST) ||
                      ifr.ifr_flags & IFF_LOOPBACK ||
                      ifr.ifr_flags & IFF_POINTOPOINT) && !tmp) ||
                    (!(ifr.ifr_flags & IFF_UP) &&
                     state != DISCOVER_UNCONFIGURED))
                        continue;

		Please explain why it is so?

    2) PPP Interfaces have no hardware address, will it be the reason??

		
Rgds
Joby
    


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