[lug] Dial up domain and routing question

Atkinson, Chip CAtkinson at Circadence.com
Thu Mar 15 12:33:04 MST 2001

> -----Original Message-----
> From: Nate Duehr [mailto:nate at natetech.com]
> Sent: Thursday, March 15, 2001 11:47 AM
> To: lug at lug.boulder.co.us
> Subject: Re: [lug] Dial up domain and routing question
> "Atkinson, Chip" wrote:
> > Greetings,
> Hola.
> > 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?

I think you have it right.  Just to clarify, when you say subnet, I am
thinking of the 8 IPs, 6 of which are machine addrs, as assigned by USWest,
and not a split of the 8 IPs into two tiny two machine subsubnetworks.  I
have the subsub network which allows only two machines on each subsubnet and
I want to get away from that.

> 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:
> proxyarp
> (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 :
> telluride:ppp
> 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?

Yes, pretty much.  Are the example addresses you give in the same range and
same netmask as the eth0 port on the ppp server machine?  This would imply
to me that you'd have to have a host route instead of net route on the ppp
server's lan, right?

Would it be possible/reasonable to have the ppp connection IPs as 10.x.x.x
and then have a forwarding rule (or the redirect program) or something so
that you can just use one of the IPs for the ppp connection?  

It seems possible if you specify the host in the routing tables.

> 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.)
> Nate
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