[lug] Dial up domain and routing question

Nate Duehr nate at natetech.com
Thu Mar 15 11:47:08 MST 2001

"Atkinson, Chip" wrote:

> Greetings,


> I'm trying to work out a weird scheme where I can dial in to another machine
> and use only one of the 5 available IP addresses.
> Here's the desired setup --
> Remote machine(s): DSL with 8 static IPs (5 available for use)
> local machine: Dial into remote machine and use one of the 5 available
> static IPs.
> Without subnetting and dividing up the 8 IPs, is this possible?  I was
> thinking I could alias two IPs on the machine with the modem and then
> redirect all traffic to one of the aliased IPs to the dialed in machine.

So you want to set up a ppp link that uses one of the available IP's on
your subnet?  Sounds simple enough ('cause I've had that set up here for
a couple of years now at home.  Heh heh...) unless I misinterpreted what
you're trying to do?

In my case, there's a modem hanging off of one of the machines here for
me to be able to dial in to home with... and I wanted to be assigned a
static IP that was NOT the IP of the machine I was dialing into for the
PPP link.

First, you'll need IP Forwarding compiled in and turned on in your kernel...

echo 1 > /proc/sys/net/ipv4/ip_forward

Also in /etc/ppp/options (on my Debian machine) I added:


(So the local machine would proxy arp requests for the IP of the modem
dial in)

Then I also had to add an /etc/ppp/options.ttyS1 file with :


Where telluride is the machine that has the modem attached, and ppp is
the name of the DNS/hosts entry for the IP I want handed out on the
modem line.  I think you can also do this like:

Is what I described what you're trying to do?

I also tweaked a number of other ppp settings for my environment, but
these were the key ones to getting the dialup working with its own IP
address.  Other stuff like the ms-dns setting in the options file (hands
out the DNS server properly if I dial in with a Windows machine) and
others were just for convenience.  (Setting the MTU to 512, et cetera.)


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