My linux box which runs CentOs (192.168.1.100) is connected to my ADSL router ( 192.168.1.1). The ADSL is set to pppoe relay aswell.
The ADSL router has port forwarding enable for SSH, OPENVPN , etc to my CentOS box.
I then create a a secound pppoe connection (ppp0) on my linux box which only routes certain traffic through it. Everything works fine except for the incoming traffic from my ADSL.
Any outside connection coming from my ADSL router which is suppose to be forwared to the the CentOS box does not work when I have my ppp0 connection up.
Any ideas on how to get it working
Of course it doesn't. Your network device on the CentOS box "is in the PPPoE mode" and does not expect packets from the other subnet and as such not handle them. Think of it as being a warp hole that opened up right above the device. The PPPoE data is warped in and out of the hole but everything that tries to intercept from outside the hole is being sucked in and destroyed as if was a black hole.
It can be set up to work. You would need either:
* a bridged device with two virtual ones. One of the virtuals is in PPPoE, the other in the LAN
* two physical devices
A third option that might work but I have never tried it:
* set a second IP address on the device that has PPPoE active (i.e. PPPoE IP and 192.168.0.100); this might work as long as the PPPoE IP and the other one are in two distinct subnets such that the routing of packets is well defined in any case.