Re: set up gateway for PPP to Ethernet?

On 22 May 2006, in the Usenet newsgroup comp.os.linux.networking, in article
<447218a6_1@xxxxxxxxxxxx>, Kaitlyn Luna wrote:

My DSL router box is at 192.168.1.1, and it is my gateway to the
Internet. My ISP gives me a Class B IP address, and since I don't run
bind, I use my ISP's DNS servers which also have Class B addresses. My
Linux system is at 192.168.1.3 on eth0.

OK - so you are using either NAT or masquerading on the DSL router. Key
questions - are you allowed to run more that one box on the 192.168.1.x
range? Are these static or DHCP configured addresses? Darn, you didn't
think it worth mentioning your Linux distribution or release - that might
have helped.

I'm not presently using routed or gated, but I'm willing to use them if
it would help.

Definitely NOT wanted. You use those when you have two or more ways to
reach a common destination AND the routers that lead to that destination
support a routing protocol such as RIP, OSPF, or similar.

I'm running pppd from /etc/inittab, listening to /dev/ttyS0. I want my
PDA to be able to reach the Internet. ppp0 is at 10.10.10.1 and the PDA
is at 10.10.10.200. I can change these to 192.168.1.* if it would help.

If your DSL only supports one host on the LAN, leave the ppp link on the
existing network, and use IP-Masquerading on the Linux box, so the router
only sees one host.

If your DSL box allows multiple hosts with STATIC addresses, set the ppp
link to use 192.168.1.x, and set the Linux box to 'proxyarp' (pppd options
might be '192.168.1.151:192.168.1.4' and 'proxyarp' - see the man page).

If your DSL box allows multiple hosts, but requires DHCP, I'd go with the
masquerading option above.

The PDA does support PPP and lets me specify DNS IPs (again, my ISP's
Class B servers), but doesn't let me provide a gateway IP.

The gateway for the PDA box is the local ppp address of the Linux box.
With ANU style ppp, you need only specify 'defaultroute' on the PDA box.

What should I do to set up a routing table so that the PDA will be able
to reach the Internet?

Depends on which of the options you choose. On the PDA, you need only
specify the 'defaultroute' option, and the pppd on that box will handle it.
On the Linux box, you'll either proxyarp (need only supply that option to
pppd) or masquerade (see the IP-Masquerade-HOWTO or Masquerading-Simple-HOWTO
as appropriate).

708351 Nov 14 2005 IP-Masquerade-HOWTO
17605 Jul 21 2004 Masquerading-Simple-HOWTO
183087 Jul 19 2000 PPP-HOWTO

The last one is near useless, but it's all we have now.
http://axion.physics.ubc.ca/ppp-linux.html or
http://www.theory.physics.ubc.ca/ppp-linux.html (same page) may provide some
additional clues.

Old guy
.

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