# PppoE possible over bridge ?

## javeree

What follows is probably a dump question, but one never knows if it is possible.

Until recently, I had a PC acting as a router using a USB modem towards internet, and an ethernet interface connected to a bridge switch where the rest of the network connects. The PC supports NAT between the net.ppp0 and net.eth0. So it looks like

internet - USB Modem - ppp0 interface - NAT PC - net.eth0 - switch - other PCs

My ISP now converts me to VDSL and sends me a modem/router (NAT) with ethernet interface. A short look at the available router functionality shows is it lacking a lot of functionality that I need. In the short term, I am setting up a different PC for the following configuration:

 *Quote:*   

> internet - Modem/NAT router - net.eth1  - NAT PC - net.eth0 - switch - other PCs

 

This has two disadvantages:

1. this does NAT twice, and I have to manage things like firewall settings/port forwarding etc.. twice

2. The PC with two ethernet interfaces is very noisy. I wanted to use a silent PC, but that has only one interface.

I have learned it is possible to switch off the router functionality of the modem and set it in bridged mode. I still have to do that, but I guess it would look like

 *Quote:*   

> internet - Modem (bridged mode) - net.ppp over net.eth1  - NAT PC - net.eth0 - switch - other PCs

 

Now comes the question:If I want to use a silent PC, I have only one ethernet interface. I am wondering if it is possible to do the following:

 *Quote:*   

> 
> 
> NAT PC - net.eth0 AND net.ppp0 over net.eth0 - switch - other PCs
> 
>                                |
> ...

 

So I want to continue to use net.eth0 to connect to the switch and the rest of the network (providing dhcp, dns, NAT, ...)

AND, I want to use net.ppp over the same net.eth0 to connect to the modem that is not connected directly to the ethernet interface, but through the switch.

Of course, in order to do NAT, the router PC should act as a dhcp client on the net.ppp interface to get an IP address from the modem.

Is such a setup possible ? or do you MUST have two ethernet interfaces in order to be able to act as a NAT router towards the internet ?

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## JC99

Here is my setup: Internet - Modem - eth0 (Gentoo) eth1 - switch - 3 computers on my network.

As I understand it you need 1 ethernet card (ppp0 over eth0) to connect to the internet and 1 ethernet card (eth1) to connect to your network. I've never read anything about doing it all on eth0.

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## javeree

neither have I ever read such a thing, so that is why I am asking  :Smile: 

My current setup is indeed as you mention, but my problem is that I want to replace the current box wit a fanless PC, which only has one physiscal interface.

I was actually thinking something along the lines of being able to distinguish between vlan tagged and untagged ethernet frames, or some similar trick.

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## Jaglover

You can do it, your interfaces will be eth0 and eth0:1 (virtual NIC, not eth1). Although I'd get a USB ethernet adapter instead.

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