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In Linux when I connect to PPPoE via the pon command, the plog command shows two IP addresses:

  • local IP address (which is my internet public IP)
  • remote IP address (which I don't know what is it?)

All my question is about what is this "remote IP address"?

When I run the ifconfig ppp0 command it shows "local IP address" and "remote IP address" as "inet addr" and "P-t-P" respectively.

When I traceroute to some IP, the first hop is this "remote IPaddress", and when I traceroute from some other IP to my inet IP, there is no sign of this "remote IP address".

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1 Answer 1

PPPoE refers to Point-to-Point Protocol over Ethernet. The "P-t-P" you are seeing is specifically "Point-to-Point".

What this effectively means is a method of tunnelling an internet connection over an ethernet network, most likely through your local exchange. This works by you being given a local IP address for your modem and then the address for the remote machine that you need to use as a gateway for your internet connection.

As per that Wikipedia article:

By using PPPoE, users can virtually "dial" from one machine to another over an Ethernet network, establish a point to point connection between them and then securely transport data packets over the connection.

The machine you are "dialling" (the remote IP) is going to be the gateway for your internet service provider.

The reason it always shows up in an outbound connection is because it has to in order for you to have a valid internet connection. I suspect that the reason it does not show up on an incoming tracert may be because it is not actually your machine that is getting the connection. You may well have a disposable "local" IP address that is not seen outside of your local telephone exchange.

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and what is the difference between my p-t-p server and the inet ip server? i think both are doing the same. –  sia Aug 26 '12 at 20:33
    
The only difference is in how the connection is set up and handled by your local telephone exchange or internet service provider, the actual job happening is the same. –  Mokubai Aug 26 '12 at 22:01

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