5. 第 3 步：防火墙和设置访问策略

#!/bin/sh
#
# ipchains.sh
#
# An example of a simple ipchains configuration. 
#
# This script allows ALL outbound traffic, and denies 
# ALL inbound connection attempts from the outside.
#
###################################################################
# Begin variable declarations and user configuration options ######
#
IPCHAINS=/sbin/ipchains
# This is the WAN interface, that is our link to the outside world.
# For pppd and pppoe users.
# WAN_IFACE="ppp0"
WAN_IFACE="eth0"

## end user configuration options #################################
###################################################################

# The high ports used mostly for connections we initiate and return
# traffic.
LOCAL_PORTS=`cat /proc/sys/net/ipv4/ip_local_port_range |cut -f1`:\
`cat /proc/sys/net/ipv4/ip_local_port_range |cut -f2`

# Any and all addresses from anywhere.
ANYWHERE="0/0"

# Let's start clean and flush all chains to an empty state.
$IPCHAINS -F  

# Set the default policies of the built-in chains. If no match for any 
# of the rules below, these will be the defaults that ipchains uses.
$IPCHAINS -P forward DENY
$IPCHAINS -P output ACCEPT
$IPCHAINS -P input DENY 

# Accept localhost/loopback traffic.
$IPCHAINS -A input -i lo -j ACCEPT

# Get our dynamic IP now from the Inet interface. WAN_IP will be our
# IP address we are protecting from the outside world. Put this
# here, so default policy gets set, even if interface is not up
# yet.
WAN_IP=`ifconfig $WAN_IFACE |grep inet |cut -d : -f 2 |cut -d \  -f 1`

# Bail out with error message if no IP available! Default policy is 
# already set, so all is not lost here.
[ -z "$WAN_IP" ] && echo "$WAN_IFACE not configured, aborting." && exit 1

# Accept non-SYN TCP, and UDP connections to LOCAL_PORTS. These are
# the high, unprivileged ports (1024 to 4999 by default). This will
# allow return connection traffic for connections that we initiate
# to outside sources. TCP connections are opened with 'SYN' packets.
$IPCHAINS -A input -p tcp -s $ANYWHERE -d $WAN_IP $LOCAL_PORTS ! -y -j ACCEPT 

# We can't be so selective with UDP since that protocol does not
# know about SYNs.
$IPCHAINS -A input -p udp -s $ANYWHERE -d $WAN_IP $LOCAL_PORTS -j ACCEPT 

## ICMP (ping)
#
# ICMP rules, allow the bare essential types of ICMP only. Ping
# request is blocked, ie we won't respond to someone else's pings,
# but can still ping out. 
$IPCHAINS -A input  -p icmp  --icmp-type echo-reply \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT
$IPCHAINS -A input  -p icmp  --icmp-type destination-unreachable \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT
$IPCHAINS -A input  -p icmp  --icmp-type time-exceeded \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT

###################################################################
# Set the catchall, default rule to DENY, and log it all. All other
# traffic not allowed by the rules above, winds up here, where it is
# blocked and logged. This is the default policy for this chain
# anyway, so we are just adding the logging ability here with '-l'.
# Outgoing traffic is allowed as the default policy for the 'output'
# chain. There are no restrictions on that.

$IPCHAINS -A input -l -j DENY

echo "Ipchains firewall is up `date`."

##-- eof ipchains.sh

 

#!/bin/sh
#
# iptables.sh
#
# An example of a simple iptables configuration. 
#
# This script allows ALL outbound traffic, and denies 
# ALL inbound connection attempts from the Internet interface only.
#
###################################################################
# Begin variable declarations and user configuration options ######
#
IPTABLES=/sbin/iptables
# Local Interfaces
# This is the WAN interface that is our link to the outside world.
# For pppd and pppoe users.
# WAN_IFACE="ppp0"
WAN_IFACE="eth0"
#

## end user configuration options #################################
###################################################################

# Any and all addresses from anywhere.
ANYWHERE="0/0"

# This module may need to be loaded:
modprobe ip_conntrack_ftp

# Start building chains and rules #################################
#
# Let's start clean and flush all chains to an empty state.
$IPTABLES -F  

# Set the default policies of the built-in chains. If no match for any 
# of the rules below, these will be the defaults that IPTABLES uses.
$IPTABLES -P FORWARD DROP
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -P INPUT DROP

# Accept localhost/loopback traffic.
$IPTABLES -A INPUT -i lo -j ACCEPT

## ICMP (ping)
#
# ICMP rules, allow the bare essential types of ICMP only. Ping
# request is blocked, ie we won't respond to someone else's pings,
# but can still ping out.
$IPTABLES -A INPUT  -p icmp  --icmp-type echo-reply \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT
$IPTABLES -A INPUT  -p icmp  --icmp-type destination-unreachable \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT
$IPTABLES -A INPUT  -p icmp  --icmp-type time-exceeded \
   -s $ANYWHERE -i $WAN_IFACE -j ACCEPT

###################################################################
# Set the catchall, default rule to DENY, and log it all. All other
# traffic not allowed by the rules above, winds up here, where it is
# blocked and logged. This is the default policy for this chain
# anyway, so we are just adding the logging ability here with '-j
# LOG'. Outgoing traffic is allowed as the default policy for the
# 'output' chain. There are no restrictions on that.

$IPTABLES -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -m state --state NEW -i ! $WAN_IFACE -j ACCEPT
$IPTABLES -A INPUT -j LOG -m limit --limit 30/minute --log-prefix "Dropping: "

echo "Iptables firewall is up `date`."

##-- eof iptables.sh

 

# Accept non-SYN TCP, and UDP connections to LOCAL_PORTS. These are the high,
# unprivileged ports (1024 to 4999 by default). This will allow return
# connection traffic for connections that we initiate to outside sources.
# TCP connections are opened with 'SYN' packets. We have already opened 
# those services that need to accept SYNs for, so other SYNs are excluded here
# for everything else.
$IPCHAINS -A input -p tcp -s $ANYWHERE -d $WAN_IP $LOCAL_PORTS ! -y -j ACCEPT 

# We can't be so selective with UDP since that protocol does not know 
# about SYNs.
$IPCHAINS -A input -p udp -s $ANYWHERE -d $WAN_IP $LOCAL_PORTS -j ACCEPT