Routing and subnetting with Linux and PPP

Routing and subnetting with Linux and PPP

Post by Rune Jacobs » Sat, 16 May 1998 04:00:00

re all,

After a lot of trying and failing, reading HOWTOs, studying the
Network Administrator's guide and so on, without much success, it
seems necessary to pry on the collective intellect of the usenet for
an answer to my sorrows.

A little topology:

At work, I have a class C network. For various reasons, we had to
divide this network into subnets with a netmask of 240, giving us
subnets with 16 addresses (14 ip + net + broadcast) each. We have a
cisco router, delivered by our ISP, on IP address, which
basically forwards anything to, our own
router/firewall/thing. On subnet, ip address I have a Linux box running Slackware 3.0, kernel
2.0.28. This machine acts as a DNS, web, mail, ftp, telnet and PPP
server. Now, at home, I have a similar Linux machine and an Amiga
running Miami 2.1 as it's tcp/ip stack, both of these on my home
ethernet - subnet So, for getting online from home, I
now need to do the PPP thing between my two Linux boxes - fido at work
(, and conan (, and fix the routing
inbetween the two networks.

The good news is that conan and fido can ping each other, telnet to
each other and everything. So when I am sitting at home on conan, I
can telnet to fido and reach the world from there. However, conan can
not ping the gateways ( / or anything else
on the work LAN, with one exception - if I set up a static route on to with a gateway of - then
conan and the gateway can ping each other. But still, nothing else.

My questions are thus:

1) Can I set up a static route to a subnet on the gateway
(, a Morning Star WAN router? What I guess I need to do
on this host is to set a route to the subnet trough (the linux at work), but I'm having a hard time making
it accept this. A route directly to the host, tho,
works, but only for traffic between the gateway and my home Linux box.

2) Do I need to set up any specific routing on either Linux machine,
other than what pppd does upon startup? I am running pppd with the
"defaultroute" option on my home box, and "proxyarp" on the work one.
But I am guessing I need a route to the subnet, or each host, in fido
as well? Can I do this with "route", or do I need something like

3) The Amiga is set up to use conan as it's gateway, and it seems to
be able to ping the same hosts as conan can. But in order to have both
machines online properly, do I need to set static routes directly to
their ip addresses on both the gateway and fido, or can I somehow
making a route entry to the subnet, trough fido?

4) When I do a traceroute to (whereever, outside our network) from
either home machine, it first goes to fido, then for some reason to a
NT host on fido's subnet, and never on from there. I have never made
any kind of routing entry to the NT host. Could this be pppd messing
with fido's routing tables?

I hope this isn't too complex, and that someone can either explain
what I need to set up or where I can get more info about this kind of
setup. Unfortunately, the documentation I've read seems to contain far
too little information about routing within a subnett'ed class C
network trough PPP etc.

If you want to reply by email, please remove the obvious spam block
from my address.

Thanks for your time and effort,

Rune Jacobsen
System Engineer (Trying to bring Linux into a MS-controlled
Euroline AS