Very Computer

by **Andy Bloc** » Fri, 17 Aug 2001 18:25:18

Hi,

I want my LAN to have access to the internet through a LINUX server.
I've been searching for days, literally, and I cannot find a simple
answer to my question. I feel really stupid and vulnerable asking
because I've heard horror stories about how impatient LINUX people
get when they have to deal with someone that doesn't already know
lots and lots about the system, but here goes.

What do I need to forward TCP/IP traffic from one ethernet card on a
LINUX server to another?
eg: cable modem -->ethernet0 on LINUX route to ethernet1 on LINUX
--> LAN

I already have two cards and a simple routing table. The LAN can
ping BOTH ethernet cards on the server but we can't get to the
internet! The LINUX server can reach the internet just fine. What do
I need to do to get ethernet0 and ethernet1 to transmit packets back
and forth?

Thanks a bunch to whoever takes the time to respond.

--
Andy Block
CGS Systems
(734) 668-0222

by **Rick Matthe** » Fri, 17 Aug 2001 19:55:04

Quote:> I want my LAN to have access to the internet through a LINUX server.
> I've been searching for days, literally, and I cannot find a simple
> answer to my question. I feel really stupid and vulnerable asking
> because I've heard horror stories about how impatient LINUX people
> get when they have to deal with someone that doesn't already know
> lots and lots about the system, but here goes.

You'll find plenty of good information here:
http://www.linux-firewall-tools.com/linux/

When you are ready, use the Firewall Design Tool on that site
<http://www.linux-firewall-tools.com/linux/firewall/index.html>
to build your firewall script.

You end up with an excellent firewall designed by Robert Ziegler,
author of "Linux Firewalls", in a minimum of time.

Rick Matthews

--
Thought for the day:
http://mysite.directlink.net/matthews/smiles/started.htm

by **Dean Thompso** » Fri, 17 Aug 2001 22:33:32

Hi!,

Quote:> I want my LAN to have access to the internet through a LINUX server.
> I've been searching for days, literally, and I cannot find a simple
> answer to my question. I feel really stupid and vulnerable asking
> because I've heard horror stories about how impatient LINUX people
> get when they have to deal with someone that doesn't already know
> lots and lots about the system, but here goes.

> What do I need to forward TCP/IP traffic from one ethernet card on a
> LINUX server to another?
> eg: cable modem -->ethernet0 on LINUX route to ethernet1 on LINUX
> --> LAN

> I already have two cards and a simple routing table. The LAN can
> ping BOTH ethernet cards on the server but we can't get to the
> internet! The LINUX server can reach the internet just fine. What do
> I need to do to get ethernet0 and ethernet1 to transmit packets back
> and forth?

To get the basics, you might want to take a look at the IPCHAINS-HOWTO which
is located at http://www.linuxdoc.org. This will help you get what you want
with the ipchains command. If you need to use the iptables command, you might
like to go into http://www.google.com and issue a search string along the
following lines: "iptables nat HOWTO".

See ya

Dean Thompson

by **Andy Bloc** » Sat, 18 Aug 2001 01:11:05

Hi Rick,

Thanks so much for replying to my question. I'll check out the info and
I'm confident I'll be able to make it work, but; do I have to run a
firewall? Is there any way to just forward everything blindly? What I'm
getting at is, what is the mechanism by which ip traffic is forwarded?
Does routing alone take care of this, or is another service needed to hand
things back and forth between one subnet and the other? I thought a
properly configured routing table would move things around all by itself.

Thanks again for helping,

Andy Block
CGS Systems
(734) 668-0222

by **Andy Bloc** » Sat, 18 Aug 2001 01:17:32

Hi Dean,

You are one busy beaver. I mut have seen your name at least a dozen times while I
was searching for answers. As I stated to an earlier respondent - I'll check out
the info and I'm confident I'll be able to make it work, but; do I have to run a
firewall? Is there any way to just forward everything blindly? What I'm getting at
is, what is the mechanism by which ip traffic is forwarded? Doesn't routing alone
take care of this, or is another service needed to move things around? I thought
the routing table alone would do it. (Not the table itself of course, but the
routing in conjunction with the info in the table.) Does it?

Thanks again for for your help,

Andy Block
CGS Systems
Ann Arbor, MI US
(734) 668-0222

by **Andy Bloc** » Sat, 18 Aug 2001 01:20:28

Whoops!!

Correction to the above message.

The line that reads: I'll check out ... do I have to run a firewall?
Should read: I'll check out ... do I have to run ipchains?

Sorry & Thanks,

Andy Block
CGS Systems
(734) 668-0222

by **Per von Zweigberg** » Fri, 17 Aug 2001 23:07:07

> I want my LAN to have access to the internet through a LINUX server.
> I've been searching for days, literally, and I cannot find a simple
> answer to my question. I feel really stupid and vulnerable asking
> because I've heard horror stories about how impatient LINUX people
> get when they have to deal with someone that doesn't already know
> lots and lots about the system, but here goes.

> What do I need to forward TCP/IP traffic from one ethernet card on a
> LINUX server to another?
> eg: cable modem -->ethernet0 on LINUX route to ethernet1 on LINUX
> --> LAN

> I already have two cards and a simple routing table. The LAN can
> ping BOTH ethernet cards on the server but we can't get to the
> internet! The LINUX server can reach the internet just fine. What do
> I need to do to get ethernet0 and ethernet1 to transmit packets back
> and forth?

I assume, that because it's a cable modem, you only have one IP address.

In your current setup, the computers trying to access the Internet are
using private IP's (not routable on the Internet) rather than routable IP's.

Because of this, you'll either have to use a proxy server like dante
(SOCKS), or squid (HTTP). SOCKS proxies are the best solution for the
applications that support it, like some internet instant messaging
programs, internet phones, and streaming media.

For web browsing, a HTTP proxy like squid is a better solution for web
browsing. Running squid will improve your web speed, as the most often used
web pages are "cached" by the proxy server, so that popular web pages don't
need to be got from the internet every time.

Often though, there are applications which work neither with HTTP proxies
nor SOCKS proxies. Then it's good to set up IP masquerading as well. IP
masquerading takes outgoing internet traffic, and changes the IP address to
it's own IP address, thereby enabling communication. This works with many
applications without special setup, but some do get problems, especially
those requiring bidirectional communication, like servers and internet
phones.

You may also want to set up a caching DNS server to lessen the outbound
load for DNS. This will also improve performance significantly.

Here are some helpful addresses:

Google, a great general search engine
http://www.google.com/

The Linux IP Masquerade HOWTO
http://www.linuxdoc.org/HOWTO/IP-Masquerade-HOWTO.html

Information about the dante SOCKS proxy
http://www.inet.no/dante/

Information about squid, a caching HTTP proxy
http://www.squid-cache.org/

The Linux DNS HOWTO
http://www.linuxdoc.org/HOWTO/DNS-HOWTO.html

Good luck and have a nice day :)

--

by **James Knot** » Sat, 18 Aug 2001 01:50:03

Wrong continent. He's a busy wallaby. ;-)

> Hi Dean,

> You are one busy beaver. I mut have seen your name at least a dozen times
> while I
> was searching for answers. As I stated to an earlier respondent - I'll
> check out the info and I'm confident I'll be able to make it work, but; do
> I have to run a firewall? Is there any way to just forward everything
> blindly? What I'm getting at is, what is the mechanism by which ip traffic
> is forwarded? Doesn't routing alone take care of this, or is another
> service needed to move things around? I thought the routing table alone
> would do it. (Not the table itself of course, but the routing in
> conjunction with the info in the table.) Does it?

> Thanks again for for your help,

> Andy Block
> CGS Systems
> Ann Arbor, MI US
> (734) 668-0222

--

james.knott.

by **M. Buchenried** » Fri, 17 Aug 2001 21:33:34

>Hi,
>I want my LAN to have access to the internet through a LINUX server.

OK.

Quote:>I've been searching for days, literally, and I cannot find a simple
>answer to my question.

Go to
http://groups.google.com/advanced_group_search
and search for IP masquerading.

Quote:>I feel really stupid and vulnerable asking
>because I've heard horror stories about how impatient LINUX people
>get when they have to deal with someone that doesn't already know
>lots and lots about the system, but here goes.

We (tinw) only get annoyed by people who don't care about what's been
written before prior to asking the very same set of questions again.

Quote:>What do I need to forward TCP/IP traffic from one ethernet card on a
>LINUX server to another?

[...]

IP forwarding enabled and IP masquerading setup and running.

Michael
--

Lumber Cartel Unit #456 (TINLC) & Official Netscum
Note: If you want me to send you email, don't munge your address.

by **Dean Thompso** » Sat, 18 Aug 2001 21:15:51

Hi!,

Quote:> You are one busy beaver. I mut have seen your name at least a dozen times
> while I was searching for answers. As I stated to an earlier respondent -
> I'll check out the info and I'm confident I'll be able to make it work,
> but; do I have to run a firewall?

You should run a firewall if not to do anything other than block your network
from the outside world where there are nasties including people who have
nothing better to do with their time than check the security defences that you
have put up.

Quote:> Is there any way to just forward everything blindly? What I'm getting at
> is, what is the mechanism by which ip traffic is forwarded? Doesn't routing
> alone take care of this, or is another service needed to move things
> around? I thought the routing table alone would do it. (Not the table
> itself of course, but the routing in conjunction with the info in the
> table.) Does it?

You can enable IP forwarding which passes packets between the various
interfaces on a Linux box, but in some cases you will need to explicitly
provide some IP forwarding rules if you want to redirect certain ports from
your outside gateway point to the inside network. This is especially
necessary in cases where you are dealing with a intra-class network which
doesn't have publically routable IP addresses.

See ya

Dean Thompson

by **k..** » Sun, 19 Aug 2001 04:53:36

Thursday August 16 2001 09:25, Andy Block wrote to All:

AB> What do I need to forward TCP/IP traffic from one ethernet card on
AB> a
AB> LINUX server to another?
AB> eg: cable modem -->ethernet0 on LINUX route to ethernet1 on LINUX

Get FREESCO from http://www.freesco.org, and you'll be up in 15
minutes! :)

KS

KARICO Business Services
Toronto, ON Canada
http://www.karico.ca

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