need help forwarding packets to lan

need help forwarding packets to lan

Post by cl2 » Thu, 01 Jan 1998 04:00:00

Hey.. I have two machines, both with ip addresses assigned by my isp, one
using linux and one using (ugh) win98. The problem is, only one machine
(specifically one ethernet card) can receive packets from the inet
connection. I need to get linux to forward packets for the other machine
from the internet onto the lan, and from the lan to the internet.

Before anyone says to use ip masquerading, I am using ip masquerading right
now, but that makes it so I can only use one of my 3 ip addresses, and I
cannot for instance run ftp servers on both machines on the default port.
Also telnetting to both machines on default telnet port is out, etc....

I can get the linux box to listen for traffic for both ip addresses, what i
need to do now is get it to take packets for one address and send them out
over its lan interface, and vice versa. If anyone knows how I can do that,
or even just what to look at to find out how to do it, I would be most

Thanks in advance,


need help forwarding packets to lan

Post by Randall Loomi » Sat, 03 Jan 1998 04:00:00

If the connection to your ISP is a point-to-point link, you might
have a problem, the ISP might not route traffic for more than one
IP address to your connected host (hence the name point-to-point) and
probably screwd.
Thus, the only way to get multiple machines on your LAN to talk over the
internet, is to IP Masquerade them to that one IP address the P2P link
is willing
to talk to.
If that's not your situation, and your ISP link will route multiple IP
traffic through your connection, you probably want to do something like
enabling IP Fwd/Gateway on your linux box and setting up your routing
table using the route cmd so that traffic for IP addr2 is routed through
the NIC connecting your linux box to your Win98 box.
The Linux Network Administrator's Guide and man route, in addition to
the various howto's should offer some help.

|/\|     Zanshin Systems                Randall Loomis


1. IP-Forwarding PPP-LAN but not LAN-LAN


We have a Linux-Server (SuSE6.2) with 2 network-cards (different
TCP/IP-networks on each card).
We cannot allow any IP-Forwarding between these two cards.

Now - the problem is that we also want to use a modem for a PPP-connection
to one of these TCP/IP-networks.
At the moment this is only working when we set IP_FORWARDING to "yes"; but
now the Linux-Server may also
forward IP-traffic between both network cards.

I'm looking for a simple solution to solve this problem.
I haven't yet worked with firewalls, but in my opinion I will need to use

Does anyone have any experiences / hints to help me in this problem?

Thanks in advance

Martin Pauly

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