Internet connection sharing

Andrew andrew.hodgson at
Thu Jun 12 02:46:41 BST 2003

> > > Daniel Finnimore wrote:
> > >
> > > I have my FreeBSD box now connected to using PPP over a
> > > 56K modem. This box has a static ip of and the gateway is
> > > set to same. I want to route my windows pc thru this Freebsd
> > > connection but can't. When the internet connection is up I can ping
> > > the but not the isp (from windows). I have flushed the
> > > firewall but still no joy. For now all I want is a connection, I will
> > > wall it all up when I can see the outside world.
> >
> > It seems odd that you can only ping the gateway when PPP is working,
> > they should see each other all the time. Are you connecting them
> > directly via ethernet? It also seems slightly odd that your ISP would
> > approve of as a static IP...are you not getting an address
> > via DHCP?
> He'll get a `proper' address assigned by his ISP also but he's also
> assigned the class C address to the gateway which his Windows machine
> can see...I think. It's not clear exactly what the address of his
> Windows machine is but I'm assuming it's on the same class C subnet.

Quite. I confess to not having a lot of experience with ppp, I'm a little
bit spoiled on my nice cable connection ;-) Also, I use ipfilter, so have
never even looked at ipfw/natd! Talk about experienced...

> > Also, are you using ipfw/natd or ipfilter/ipnat?
> ppp(8) has got a -nat switch:

Aha! That I did not know.

>    The -nat flag (or -alias flag for backwards compatibility)
>    does the equivalent of a ``nat enable yes'', enabling ppp's
>    network address translation features.  This allows ppp to
>    act as a NAT or masquerading engine for all machines on an
>    internal LAN.
> From natd(8):
>    This program provides a Network Address Translation
>    facility for use with divert(4) sockets under FreeBSD.
>    It is intended for use with NICs - if you want to do NAT
>    on a PPP link, use the -nat switch to ppp(8).
> I don't use either but it seems the -nat switch to ppp seems worth a try
> - assuming it hasn't been tried already.

Seems like it shouldn't be that problematic. But then, I had loads of
trouble just maintaining a connection with ppp, kind of put me off it a bit.
Although that may have been down to the modem,  or the line itself. To
Daniel - good luck!


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