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ThinkCore W311/321/341 Linux User’s Manual Managing Communications
4-12
Enabling NAT at Bootup
In most real world situations, you will want to use a simple shell script to enable NAT when the
W341 boots up. The following script is an example.
#!/bin/bash
# If you put this shell script in the /home/nat.sh
# Remember to chmod 744 /home/nat.sh
# Edit the rc.local file to make this shell startup automatically.
# vi /etc/rc.d/rc.local
# Add a line in the end of rc.local /home/nat.sh
EXIF=‘eth0’ #This is an external interface for setting up a valid IP address.
EXNET=‘192.168.4.0/24’ #This is an internal network address.
# Step 1. Insert modules.
# Here 2> /dev/null means the standard error messages will be dump to null device.
insmod ip_tables 2> /dev/null
insmod ip_conntrack 2> /dev/null
insmod ip_conntrack_ftp 2> /dev/null
insmod ip_conntrack_irc 2> /dev/null
insmod iptable_nat 2> /dev/null
insmod ip_nat_ftp 2> /dev/null
insmod ip_nat_irc 2> /dev/null
# Step 2. Define variables, enable routing and erase default rules.
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
export PATH
echo “1” > /proc/sys/net/ipv4/ip_forward
/bin/iptables -F
/bin/iptables -X
/bin/iptables -Z
/bin/iptables -F -t nat
/bin/iptables -X -t nat
/bin/iptables -Z -t nat
/bin/iptables -P INPUT ACCEPT
/bin/iptables -P OUTPUT ACCEPT
/bin/iptables -P FORWARD ACCEPT
/bin/iptables -t nat -P PREROUTING ACCEPT
/bin/iptables -t nat -P POSTROUTING ACCEPT
/bin/iptables -t nat -P OUTPUT ACCEPT
# Step 3. Enable IP masquerade.
Dial-up Service—PPP
PPP (Point to Point Protocol) is used to run IP (Internet Protocol) and other network protocols over
a serial link. PPP can be used for direct serial connections (using a null-modem cable) over a
Telnet link, and links established using a modem over a telephone line.
Modem / PPP access is almost identical to connecting directly to a network through the
W311/321/341’s Ethernet port. Since PPP is a peer-to-peer system, the W311/321/341 can also
use PPP to link two networks (or a local network to the Internet) to create a Wide Area Network
(WAN).
NOTE Click on the following links for more information about ppp:
http://tldp.org/HOWTO/PPP-HOWTO/index.html
http://axion.physics.ubc.ca/ppp-linux.html
The pppd daemon is used to connect to a PPP server from a Linux system. For detailed
information about pppd see the man page.
Example 1: Connecting to a PPP server over a simple dial-up connection
The following command is used to connect to a PPP server by modem. Use this command for old
ppp servers that prompt for a login name (replace username with the correct name) and password
(replace password with the correct password). Note that debug and defaultroute 192.1.1.17 are