Routing NHF--by Skippy
The first thing one needs to do is configure the network interface cards
(NICs) for use.
There are several ways to do this. You
could do it all by hand. But RedHat 5.2
includes a very nice utility called linuxconf.
This is a hierarchical menu system of
configuration options.
First, choose NETWORKING.
Under here are several options. We want BASIC
HOST INFORMATION.
Here, you can select a host name (which
must be a fully qualified domain name).
You can also select which ethernet
adaptors to enable. Since we plan on
using our Linx box as a router, it's safe
to assume we'll need two adaptors.
NOTE: I originally tried to use two 3Com
3C509 cards, but ran into several
problems. So I switched one with a
LinkSys, and everything worked. Your
mileage with two cards of the same type
may differ.
NOTE: You may need to do some
preparations on the cards before
installing them (or before installing
Linux). I would recommend running the
included DOS utilities to manually
configure your NICs IO address and IRQ. I
chose IRQ 10, IO address 300 for my first
card; and IRQ 5, IO address 210 for my
second card.
Now in linuxconf, we select the
first interface, and check the ENABLED
box. Then you specify the configuration
mode: Manual, DHCP, or BOOTP. My first
adapter is connected to my internal
network, and so it is manually configured
with the following information filled
into the following fields:
IP
Address: 90.90.90.1
Netmask: 255.255.255.0
Net Device: eth0
Kernel Module: ne
IO Port: 0x300
IRQ: 10
You can really use _any_ IP scheme you
want; although most folks will tell you
to use 192.168.XXX.XXX. Netmask
is your TCP/IP subnet mask; mine is a
Class C network address (so is
192.168.XXX.XXX, by the way).
The Net Device is the
interface name that Linux will use to
communicate with this device. They are
generally named "eth0" for the
first one, "eth1" for the
second one, etc etc. Kernel
Module is the module that you
will load that provides you kernel with
information about this device. I'm using
the NE2000 module. It's a generic
ethernet module, and ought to work with a
great many NICs. If your NIC is not
listed in the available modules (/lib/module/preferred/net),
try this one.
IO port and IRQ
are the hardware information for your
card.
Now we repeat the same process for the
second card. Check the ENABLED box, and
specify the particulars. My second NIC is
connected to my cable modem, and it gets
its configuration through DHCP. So I
check the DHCP box in linuxconf
for this interface. The only other
information I need to supply to linuxconf
for this interface is the Net
device (eth1), the Kernel
Module (3c509; since it's a 3Com
3c509 card, which has a supported
module), and the IRQ
(5).
If you had other NICs for any reason, you
can configure them by following the same
steps.
Now we need to tell Linux how it will
communicate with the world. Select ACCEPT
from the BASIC HOST CONFIGURATION
screen, and scroll down to the next item:
NAME SERVER SPECIFICATION (DNS).
Check DNS USAGE, telling Linux that it
needs DNS (Domain Name System - the
process by which internet names are
translated into internet IP addresses).
You need to specify at least one
nameserver. So far as I know, _any_ legal
nameserver will work. Your ISP should
have two. Mine are 204.210.252.252 and
204.210.252.250.
Select ACCEPT. Select Quit, and linuxconf
will prompt you to activate the changes.
Say yes.
Well, we're almost set, except that we
need to make sure that Red Hat knows how
to get IP addresses using DHCP. This is
done with the DHCPCD
(DHCP Client Daemon). On my Red Hat CD,
it's an RPM in
/mnt/cdrom/RedHat/RPMS/dhcpcd-0.70-2.i386.rpm.
So cd to that directory and type rpm
--install dhcpcd-0.70-2.i386.rpm and it's in.
Since I come from the Windows frame of
mind, at this point I would reboot my
system. reboot now or shutdown
-Fr now.
When your system comes back online, you
should see the networking information
being displayed during the boot process.
Here's what mine looks like:
sysctl:
ip forwarding off
Swansea University Computer Society IPX
0.34 for NET3.035
IPX Portions Copyright (c) 1995 Caldera,
Inc.
Appletalk 0.17 for Linux NET3.035
ne.c:v1.10 9/23/94 Donald Becker
(becker@cesdis.gsfc.nasa.gov)
NE2000 ethercard probe at 0x300: 00 02 67
00 47 83 eth0:
NE2000 found at 0x300, using IRQ 10.
eth1: 3c509 at 0x210 tag 1, 10baseT port,
address 00 20 af 39 0f ac, IRQ 5.
3c509.c:1.16 2/3/98
becker@cesdis.gsfc.nasa.gov
eth1: Setting Rx mode to 1 addresses.
Everything looks set. Log in as root, and
try to ping something. ping
www.linuxnewbie.org You should get some
responses if everything went right.
Now it's time to configure the routing
function. This is done with an extremely
powerful tool called ipautofw
(IP Auto Forward). If you didn't install
it already, just go to /mnt/cdrom/RedHat/RPMS
and type rpm --install
ipfwadm-2.3.0-6.i386.rpm You now have ipautofw
installed in /usr/bin.
ipautofw uses rules to
tell your system what kind of traffic is
allowed in what direction. It's quite
complex in it's entirety, but we only
need a couple of items:
echo
"1">
/proc/sys/net/ipv4/ip_forward
ipfwadm -F -p deny
ipfwadm -F -a m -S90.90.90.0/24
-D0.0.0.0/0
Edit /etc/rc.d/rc.local and put
these three lines in it. Now every time
you boot, IP forwarding will start, and
your machine is now a router!
Just configure your clients to use the
internal interface on your Linux box as
their default gateway, and supply them
with DNS name servers (probably the same
two you used for your Linux machine!)
Enjoy!!
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