Subject: Re: firewall problems with 2 DSL (PPPoE) feeds that alternate between ppp0 & ppp1
To: Alicia da Conceicao <>
From: Olaf Seibert <>
List: tech-net
Date: 11/30/2002 01:43:52
On Fri 29 Nov 2002 at 08:22:17 -0500, Alicia da Conceicao wrote:
> Also, does anyone know of any hardware DSL modem or DSL router that
> will do PPPoE internally, and then forward the external (static)
> PPPoE IP address to the ethernet link, so that the NetBSD can
> ifconfig the ethernet interface directly with the real IP address.

I am doing something like that with an Alcatel SpeedTouch Home (or Pro)
ADSL modem (which normally does PPTP). But it is actually a gross hack
and partly depends on bugs in the modem's PPP implementation and weird
routing stuff on the NetBSD side.

See and
(in Dutch, maybe there are translated versions somewhere).

> All existing DSL routers can do PPPoE, but a NetBSD server would
> connect to its LAN port, and would only be able to ifconfig a
> non-routable address, and would not be able to ifconfig the real
> (static) IP address provided by the DSL provider.

The trick depends on the modem passing on packets to the global IP
address from the WAN side through on its LAN interface, and the NetBSD
interface having the same address - and routing stuff so that this
actually works in both directions.

    # Hack default route to go over the modem
    route add -net -netmask -ifp tlp0 -cloning -interface
    # ^^ (error checking in the route adding code (sys/net/rtsock.c,
    # route_output, case RTM_ADD) insists on having a gateway (so we add a
    # "random" one) (1.5.x wants an address on one of the subnets of the
    # interface).  Adding -interface cancels its presence again...  The use of
    # a host address for the -net option does not matter since the netmask is
    # applied to it.
    route add default
    route change default -ifp tlp0

tlp0 is the interface that connects to the modem. is a non-routable address of the LAN interface of the
modem. is my global static IP address.

> Thanks in advance.
> Alicia.
___ Olaf 'Rhialto' Seibert - rhialto@       -- Woe betide the one who feels
\X/  -- remorse without sin - Tom Poes, "Het boze oog", 4444.