[clug] Network routing joy (iptables, bridging, nat)
Francis James Whittle
fudje at grapevine.net.au
Tue Sep 1 06:02:15 MDT 2009
Are you sure it's just NAT that fails, or does PPPoE break entirely?
On Tue, 2009-09-01 at 20:36 +1000, David Tulloh wrote:
> |----------------|
> | br0 |
> | | ||-- LAN
> VM --|-- tap1 eth1==|==||
> VM --|-- tap2 ^ | ||-- Modem, PPPOE
> | | |
> |------------|---|
> |
> /-----\
> | NAT |
> \-----/
> |
> ppp0
>
>
>
> I have a server with a fairly complex networking setup. I've tried to
> depict it above, which should be legible in a fixed-width font.
>
> The server has a single network card, eth1. It connects to a local
> network running on a private subnet.
>
> I have a modem which provides bridging internet access, the server
> connects using ppp. The actual traffic passes through eth1.
>
> Eth1 is bridged in br0 providing access for VMs running on the server
> using tap devices.
>
> The server has a static ip address on br0, it runs a dhcp server that
> controls the rest of the network.
>
> All of the above works correctly.
>
>
> What does NOT work correctly is NAT. I want to route all the traffic
> from the LAN and VMs out ppp0 through a NAT system.
>
> NAT will work without the bridging but I can't get both to work at the
> same time.
>
>
> Honestly I don't really understand the networking stack in Linux
> particularly when it gets this complex. The information I've found
> online talks about multiple NAT hook points including in the routing
> layer with iptables and the bridging layer with ebtables. I've tried a
> number of different approaches and nothing has so far worked.
>
> Can anyone help detangle this mess for me and guide me on the correct
> incantations to make it work?
>
>
> David
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