Hi everyone,

As promised, my rc.firewall script. This script does quite a lot to protect
my BBS from script kiddies and those so-called "security companies", who are just running port scanneras because they can.

Note that my fail2ban setup is doing more of the heavy lifting when it comes
to protecting open ports via its "pam-generic" internal filter and the "recidive-subnet" external filter I installed (that filter scans fail2ban's logs and if there are a certain amount of hits coming from a particular netmask, it will ban the entire IP range via CIDR for 26 weeks).

With everything combined, I've never had any issues and enjoy seeing script kiddies try to get in every second of every day. I have no social life... XD

===
#!/bin/sh
#
# NOTE: pfSense and fail2ban handle 90% of the issues below for me
# but it doesn't hurt to have backup...
#
# Outpost BBS rc.firewall script for Slackware 15.
# Modified for MBSE by Sean Dennis on 15 May 2024.
#
# Generated iptables firewall script for the Linux 2.4 kernel and later.
# Script generated by Easy Firewall Generator for IPTables 1.15
# copyright 2002 Timothy Scott Morizot
# Modified for Slackware Linux by Eric Hameleers <alien@slackware.com>
#
# This generator is adapted from the original to work on Slackware Linux.
# Basically, I corrected the path name to the iptables* commands
# and re-wrote this comment.
#
# It can be executed with the typical start and stop arguments.
# If used with stop, it will stop after flushing the firewall.
# The save and restore arguments will save or restore the rules
# from the /etc/sysconfig/iptables file. The save and restore
# arguments are included to preserve compatibility with
# Redhat's or Fedora's init.d script if you prefer to use it.

# You may want to save this script as /etc/rc.d/rc.firewall
# and make it executable, like this:
# chmod +x /etc/rc.d/rc.firewall
# Slackware Linux will then automatically run this script
# with the "start" parameter.

############################################################################### #
# Local Settings
#

# sysctl location. If set, it will use sysctl to adjust the kernel parameters.
# If this is set to the empty string (or is unset), the use of sysctl
# is disabled.

SYSCTL="/sbin/sysctl -w"

# To echo the value directly to the /proc file instead
# SYSCTL=""

# IPTables Location - adjust if needed

IPT="/usr/sbin/iptables"
IPTS="/usr/sbin/iptables-save"
IPTR="/usr/sbin/iptables-restore"

# Internet Interface
INET_IFACE="eth0"
INET_ADDRESS="<redacted>"

# Localhost Interface

LO_IFACE="lo"
LO_IP="127.0.0.1"

# Save and Restore arguments handled here
if [ "$1" = "save" ]
then
.echo -n "Saving firewall to /etc/sysconfig/iptables ... "
.$IPTS > /etc/sysconfig/iptables
.echo "done"
.exit 0
elif [ "$1" = "restore" ]
then
.echo -n "Restoring firewall from /etc/sysconfig/iptables ... "
.$IPTR < /etc/sysconfig/iptables
.echo "done"
.exit 0
fi

############################################################################### #
# Load Modules
#

echo "Loading kernel modules ..."

# You should uncomment the line below and run it the first time just to
# ensure all kernel module dependencies are OK. There is no need to run
# every time, however.

# /sbin/depmod -a

# Unless you have kernel module auto-loading disabled, you should not
# need to manually load each of these modules. Other than ip_tables,
# ip_conntrack, and some of the optional modules, I've left these
# commented by default. Uncomment if you have any problems or if
# you have disabled module autoload. Note that some modules must
# be loaded by another kernel module.

# core netfilter module
/sbin/modprobe ip_tables

# the stateful connection tracking module
/sbin/modprobe ip_conntrack

# filter table module
# /sbin/modprobe iptable_filter

# mangle table module
# /sbin/modprobe iptable_mangle

# nat table module
# /sbin/modprobe iptable_nat

# LOG target module
# /sbin/modprobe ipt_LOG

# This is used to limit the number of packets per sec/min/hr
# /sbin/modprobe ipt_limit

# masquerade target module
# /sbin/modprobe ipt_MASQUERADE

# filter using owner as part of the match
# /sbin/modprobe ipt_owner

# REJECT target drops the packet and returns an ICMP response.
# The response is configurable. By default, connection refused.
# /sbin/modprobe ipt_REJECT

# This target allows packets to be marked in the mangle table
# /sbin/modprobe ipt_mark

# This target affects the TCP MSS
# /sbin/modprobe ipt_tcpmss

# This match allows multiple ports instead of a single port or range
# /sbin/modprobe ipt_multiport

# This match checks against the TCP flags
# /sbin/modprobe ipt_state

# This match catches packets with invalid flags
# /sbin/modprobe ipt_unclean

# The ftp nat module is required for non-PASV ftp support
/sbin/modprobe ip_nat_ftp

# the module for full ftp connection tracking
/sbin/modprobe ip_conntrack_ftp

# the module for full irc connection tracking
/sbin/modprobe ip_conntrack_irc


############################################################################### #
# Kernel Parameter Configuration
#
# See http://ipsysctl-tutorial.frozentux.net/chunkyhtml/index.html
# for a detailed tutorial on sysctl and the various settings
# available.

# This enables SYN flood protection.
# The SYN cookies activation allows your system to accept an unlimited
# number of TCP connections while still trying to give reasonable
# service during a denial of service attack.
if [ "$SYSCTL" = "" ]
then
echo "1" > /proc/sys/net/ipv4/tcp_syncookies
else
$SYSCTL net.ipv4.tcp_syncookies="1"
fi

# This enables source validation by reversed path according to RFC1812.
# In other words, did the response packet originate from the same interface
# through which the source packet was sent? It's recommended for single-homed # systems and routers on stub networks. Since those are the configurations
# this firewall is designed to support, I turn it on by default.
# Turn it off if you use multiple NICs connected to the same network.
if [ "$SYSCTL" = "" ]
then
echo "1" > /proc/sys/net/ipv4/conf/all/rp_filter
else
$SYSCTL net.ipv4.conf.all.rp_filter="1"
fi

# This kernel parameter instructs the kernel to ignore all ICMP
# echo requests sent to the broadcast address. This prevents
# a number of smurfs and similar DoS nasty attacks.
if [ "$SYSCTL" = "" ]
then
echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
else
$SYSCTL net.ipv4.icmp_echo_ignore_broadcasts="1"
fi

# This option can be used to accept or refuse source routed
# packets. It is usually on by default, but is generally
# considered a security risk. This option turns it off.
if [ "$SYSCTL" = "" ]
then
echo "0" > /proc/sys/net/ipv4/conf/all/accept_source_route
else
$SYSCTL net.ipv4.conf.all.accept_source_route="0"
fi

# However, we'll ensure the secure_redirects option is on instead.
# This option accepts only from gateways in the default gateways list.
if [ "$SYSCTL" = "" ]
then
echo "1" > /proc/sys/net/ipv4/conf/all/secure_redirects
else
$SYSCTL net.ipv4.conf.all.secure_redirects="1"
fi

# This option logs packets from impossible addresses.
if [ "$SYSCTL" = "" ]
then
echo "1" > /proc/sys/net/ipv4/conf/all/log_martians
else
$SYSCTL net.ipv4.conf.all.log_martians="1"
fi


############################################################################### #
# Flush Any Existing Rules or Chains
#

echo "Flushing Tables ..."

# Reset Default Policies
$IPT -P INPUT ACCEPT
$IPT -P FORWARD ACCEPT
$IPT -P OUTPUT ACCEPT
$IPT -t nat -P PREROUTING ACCEPT
$IPT -t nat -P POSTROUTING ACCEPT
$IPT -t nat -P OUTPUT ACCEPT
$IPT -t mangle -P PREROUTING ACCEPT
$IPT -t mangle -P OUTPUT ACCEPT

# Flush all rules
$IPT -F
$IPT -t nat -F
$IPT -t mangle -F

# Erase all non-default chains
$IPT -X
$IPT -t nat -X
$IPT -t mangle -X

if [ "$1" = "stop" ]
then
.echo "Firewall completely flushed! Now running with no firewall."
.exit 0
fi

############################################################################### #
# Rules Configuration
#
# Block all Chinanet (China Telecom) connections
$IPT -I INPUT -s 61.177.0.0/16 -j DROP
$IPT -I INPUT -s 180.96.0.0/11 -j DROP
$IPT -I INPUT -s 218.90.0.0/15 -j DROP
$IPT -I INPUT -s 218.92.0.0/15 -j DROP
$IPT -I INPUT -s 218.94.0.0/15 -j DROP

# Block all Digital Ocean connections
$IPT -I INPUT -s 157.230.0.0/16 -j DROP
$IPT -I INPUT -s 170.64.128.0/17 -j DROP
$IPT -I INPUT -s 64.227.128.0/18 -j DROP

# Block all Private Layer connections
$IPT -I INPUT -s 179.43.128.0/18 -j DROP

# Amarutu Technology Ltd., Hong Kong
$IPT -I INPUT -s 183.81.168.0/23 -j DROP

# Lishui Dagangtou Zhixin Internet Bar (LOL)
$IPT -I INPUT -s 61.153.220.160/29 -j DROP

$IPT -I INPUT -s 43.131.224.0/19 -j DROP

# f2b will usuually catch thia but I want to make sure...

# Block Censys "security scans"
# https://support.censys.io/hc/en-us/articles
# /360043177092-Opt-Out-of-Data-Collection
$IPT -I INPUT -s 162.142.125.0/24 -j DROP
$IPT -I INPUT -s 167.94.138.0/24 -j DROP
$IPT -I INPUT -s 167.94.145.0/24 -j DROP
$IPT -I INPUT -s 167.94.146.0/24 -j DROP
$IPT -I INPUT -s 167.248.133.0/24 -j DROP
$IPT -I INPUT -s 199.45.154.0/24 -j DROP
$IPT -I INPUT -s 199.45.155.0/24 -j DROP
$IPT -I INPUT -s 206.168.34.0/24 -j DROP

# Block Palo Alto Networks' "security scans"
$IPT -I INPUT -s 147.185.136.0/24 -j DROP
$IPT -I INPUT -s 165.85.144.0/24 -j DROP
$IPT -I INPUT -s 165.85.145.0/24 -j DROP
$IPT -I INPUT -s 165.85.149.0/24 -j DROP
$IPT -I INPUT -s 165.85.250.0/23 -j DROP
$IPT -I INPUT -s 199.167.52.0/24 -j DROP
$IPT -I INPUT -s 199.167.53.0/24 -j DROP
$IPT -I INPUT -s 202.189.133.0/24 -j DROP
$IPT -I INPUT -s 65.154.226.0/24 -j DROP
$IPT -I INPUT -s 65.155.38.0/24 -j DROP
$IPT -I INPUT -s 66.232.34.0/24 -j DROP
$IPT -I INPUT -s 66.232.36.0/24 -j DROP
$IPT -I INPUT -s 66.232.40.0/24 -j DROP
$IPT -I INPUT -s 72.165.69.0/24 -j DROP

# OVH script kiddies
$IPT -I INPUT -s 87.98.128.0/18 -j DROP

############################################################################### #
# Filter Table
# ###############################################################################

# Set Policies

$IPT -P INPUT DROP
$IPT -P OUTPUT DROP
$IPT -P FORWARD DROP

############################################################################### #
# User-Specified Chains
#
# Create user chains to reduce the number of rules each packet
# must traverse.

echo "Create and populate custom rule chains ..."

# Create a chain to filter INVALID packets

$IPT -N bad_packets

# Create another chain to filter bad tcp packets

$IPT -N bad_tcp_packets

# Create separate chains for icmp, tcp (incoming and outgoing),
# and incoming udp packets.

$IPT -N icmp_packets

# Used for UDP packets inbound from the Internet
$IPT -N udp_inbound

# Used to block outbound UDP services from internal network
# Default to allow all
$IPT -N udp_outbound

# Used to allow inbound services if desired
# Default fail except for established sessions
$IPT -N tcp_inbound

# Used to block outbound services from internal network
# Default to allow all
$IPT -N tcp_outbound

############################################################################### #
# Populate User Chains
#

# bad_packets chain
#

# Drop INVALID packets immediately
$IPT -A bad_packets -p ALL -m conntrack --ctstate INVALID -j LOG \
--log-prefix "Invalid packet: "

$IPT -A bad_packets -p ALL -m conntrack --ctstate INVALID -j DROP

# Then check the tcp packets for additional problems
$IPT -A bad_packets -p tcp -j bad_tcp_packets

# All good, so return
$IPT -A bad_packets -p ALL -j RETURN

# bad_tcp_packets chain
#
# All tcp packets will traverse this chain.
# Every new connection attempt should begin with
# a syn packet. If it doesn't, it is likely a
# port scan. This drops packets in state
# NEW that are not flagged as syn packets.


$IPT -A bad_tcp_packets -p tcp ! --syn -m conntrack --ctstate NEW -j LOG \
--log-prefix "New not syn: "
$IPT -A bad_tcp_packets -p tcp ! --syn -m conntrack --ctstate NEW -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j DROP

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j LOG \
--log-prefix "Stealth scan: "
$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP

# All good, so return
$IPT -A bad_tcp_packets -p tcp -j RETURN

# icmp_packets chain
#
# This chain is for inbound (from the Internet) icmp packets only.
# Type 8 (Echo Request) is not accepted by default
# Enable it if you want remote hosts to be able to reach you.
# 11 (Time Exceeded) is the only one accepted
# that would not already be covered by the established
# connection rule. Applied to INPUT on the external interface.
#
# See: http://www.ee.siue.edu/~rwalden/networking/icmp.html
# for more info on ICMP types.
#
# Note that the stateful settings allow replies to ICMP packets.
# These rules allow new packets of the specified types.

# ICMP packets should fit in a Layer 2 frame, thus they should
# never be fragmented. Fragmented ICMP packets are a typical sign
# of a denial of service attack.
$IPT -A icmp_packets --fragment -p ICMP -j LOG \
--log-prefix "ICMP Fragment: "
$IPT -A icmp_packets --fragment -p ICMP -j DROP

# Echo - uncomment to allow your system to be pinged.
# Uncomment the LOG command if you also want to log PING attempts
#
$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j LOG \
--log-prefix "Ping detected: "
$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT

# By default, however, drop pings without logging. Blaster
# and other worms have infected systems blasting pings.
# Comment the line below if you want pings logged, but it
# will likely fill your logs.
$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j DROP

# Time Exceeded
$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

# Not matched, so return so it will be logged
$IPT -A icmp_packets -p ICMP -j RETURN

# TCP & UDP
# Identify ports at:
# http://www.chebucto.ns.ca/~rakerman/port-table.html
# http://www.iana.org/assignments/port-numbers

# udp_inbound chain
#
# This chain describes the inbound UDP packets it will accept.
# It's applied to INPUT on the external or Internet interface.
# Note that the stateful settings allow replies.
# These rules are for new requests.
# It drops netbios packets (windows) immediately without logging.

# Drop netbios calls
# Please note that these rules do not really change the way the firewall
# treats netbios connections. Connections from the localhost and
# internal interface (if one exists) are accepted by default.
# Responses from the Internet to requests initiated by or through
# the firewall are also accepted by default. To get here, the
# packets would have to be part of a new request received by the
# Internet interface. You would have to manually add rules to
# accept these. I added these rules because some network connections,
# such as those via cable modems, tend to be filled with noise from
# unprotected Windows machines. These rules drop those packets
# quickly and without logging them. This prevents them from traversing
# the whole chain and keeps the log from getting cluttered with
# chatter from Windows systems.
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 137 -j DROP
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 138 -j DROP

# Network File System (NFS) Server
# Please note that additional services must
# be configured in order to support an NFS Server through
# the firewall. Read the help in the generator or this site:
# http://www.lowth.com/LinWiz/nfs_help.html

# NFS Server - portmapper
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 111 -j ACCEPT

# NFS Server - statd
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9400 -j ACCEPT

# NFS Server - NFS daemon
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 2049 -j ACCEPT

# NFS Server - lockd
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9401 -j ACCEPT

# NFS Server - mountd
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9402 -j ACCEPT

# NFS Server - quotad
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9403 -j ACCEPT

# BBS Chat server
$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 60179 -j ACCEPT

# Not matched, so return for logging
$IPT -A udp_inbound -p UDP -j RETURN

# udp_outbound chain
#
# This chain is used with a private network to prevent forwarding for
# UDP requests on specific protocols. Applied to the FORWARD rule from
# the internal network. Ends with an ACCEPT

# No match, so ACCEPT
$IPT -A udp_outbound -p UDP -s 0/0 -j ACCEPT

# tcp_inbound chain
#
# This chain is used to allow inbound connections to the
# system/gateway. Use with care. It defaults to none.
# It's applied on INPUT from the external or Internet interface.

# Web Server

# HTTP
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 80 -j ACCEPT
#IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 8000 -j ACCEPT

# FTP Server (Control)
#$IPT -A INPUT -p tcp --syn --dport 21 -m connlimit --connlimit-above 1 --connlimit-mask 32 -j REJECT --reject-with tcp-reset
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 21 -j ACCEPT

# FTP Client (Data Port for non-PASV transfers)
#$IPT -A INPUT -p tcp --syn --dport 20 -m connlimit --connlimit-above 1 --connlimit-mask 32 -j REJECT --reject-with tcp-reset
$IPT -A tcp_inbound -p TCP -s 0/0 --source-port 20 -j ACCEPT

# Passive FTP
#
# With passive FTP, the server provides a port to the client
# and allows the client to initiate the connection rather
# than initiating the connection with the client from the data port.
# Web browsers and clients operating behind a firewall generally
# use passive ftp transfers. A general purpose FTP server
# will need to support them.
#
# However, by default an FTP server will select a port from the entire
# range of high ports. It is not particularly safe to open all
# high ports. Fortunately, that range can be restricted. This
# firewall presumes that the range has been restricted to a specific
# selected range. That range must also be configured in the ftp server.
#
# Instructions for specifying the port range for the wu-ftpd server
# can be found here:
# http://www.wu-ftpd.org/man/ftpaccess.html
# (See the passive ports option.)
#
# Instructions for the ProFTPD server can be found here:
# http://proftpd.linux.co.uk/localsite/Userguide/linked/x861.html
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 61000:65535 -j ACCEPT

# sshd
#$IPT -A INPUT -p tcp --destination-port 22 -m iprange --src-range 192.168.0.0-192.168.0.255 -d 0/0 -j ACCEPT
#$IPT -A INPUT -p tcp --syn --dport 22 -m connlimit --connlimit-above 1 --connlimit-mask 32 -j REJECT --reject-with tcp-reset
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 22 -j ACCEPT

# telnet
#$IPT -A INPUT -p tcp --destination-port 23 -m iprange --src-range 192.168.0.0-192.168.0.255 -d 0/0 -j ACCEPT
#$IPT -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-above 1 --connlimit-mask 32 -j REJECT --reject-with tcp-reset
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 23 -j ACCEPT

# Network File System (NFS) Server
# Please note that additional services must
# be configured in order to support an NFS Server through
# the firewall. Read the help in the generator or this site:
# http://www.lowth.com/LinWiz/nfs_help.html

# NFS Server - portmapper
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 111 -j ACCEPT

# NFS Server - statd
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9400 -j ACCEPT

# NFS Server - NFS daemon
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 2049 -j ACCEPT

# NFS Server - lockd
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9401 -j ACCEPT

# NFS Server - mountd
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9402 -j ACCEPT

# NFS Server - quotad
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9403 -j ACCEPT

### My ports

# BBS BinkD
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 24554 -j ACCEPT

# BBS mbcico ITN (mailer over telnet)
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 60177 -j ACCEPT

# BBS mbcico IFC (raw)
$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 60179 -j ACCEPT

# Not matched, so return so it will be logged
$IPT -A tcp_inbound -p TCP -j RETURN

# tcp_outbound chain
#
# This chain is used with a private network to prevent forwarding for
# requests on specific protocols. Applied to the FORWARD rule from
# the internal network. Ends with an ACCEPT


# No match, so ACCEPT
$IPT -A tcp_outbound -p TCP -s 0/0 -j ACCEPT

############################################################################### #
# INPUT Chain
#

echo "Process INPUT chain ..."

# Allow all on localhost interface
$IPT -A INPUT -p ALL -i $LO_IFACE -j ACCEPT

# Drop bad packets
$IPT -A INPUT -p ALL -j bad_packets

# DOCSIS compliant cable modems
# Some DOCSIS compliant cable modems send IGMP multicasts to find
# connected PCs. The multicast packets have the destination address
# 224.0.0.1. You can accept them. If you choose to do so,
# Uncomment the rule to ACCEPT them and comment the rule to DROP
# them The firewall will drop them here by default to avoid
# cluttering the log. The firewall will drop all multicasts
# to the entire subnet (224.0.0.1) by default. To only affect
# IGMP multicasts, change '-p ALL' to '-p 2'. Of course,
# if they aren't accepted elsewhere, it will only ensure that
# multicasts on other protocols are logged.
# Drop them without logging.
$IPT -A INPUT -p ALL -d 224.0.0.1 -j DROP
# The rule to accept the packets.
# $IPT -A INPUT -p ALL -d 224.0.0.1 -j ACCEPT


# Inbound Internet Packet Rules

# Accept Established Connections
$IPT -A INPUT -p ALL -i $INET_IFACE -m conntrack --ctstate ESTABLISHED,RELATED
-j ACCEPT

# Route the rest to the appropriate user chain
$IPT -A INPUT -p TCP -i $INET_IFACE -j tcp_inbound
$IPT -A INPUT -p UDP -i $INET_IFACE -j udp_inbound
$IPT -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets

# Drop without logging broadcasts that get this far.
# Cuts down on log clutter.
# Comment this line if testing new rules that impact
# broadcast protocols.
$IPT -A INPUT -m pkttype --pkt-type broadcast -j DROP

# Log packets that still don't match
$IPT -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
--log-prefix "INPUT packet died: "

############################################################################### #
# FORWARD Chain
#

echo "Process FORWARD chain ..."

# Used if forwarding for a private network


############################################################################### #
# OUTPUT Chain
#

echo "Process OUTPUT chain ..."

# Generally trust the firewall on output

# However, invalid icmp packets need to be dropped
# to prevent a possible exploit.
$IPT -A OUTPUT -p icmp -m conntrack --ctstate INVALID -j DROP

# Localhost
$IPT -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPT -A OUTPUT -p ALL -o $LO_IFACE -j ACCEPT

# To internet
$IPT -A OUTPUT -p ALL -o $INET_IFACE -j ACCEPT

# Log packets that still don't match
$IPT -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
--log-prefix "OUTPUT packet died: "

############################################################################### #
# nat table
# ###############################################################################

# The nat table is where network address translation occurs if there
# is a private network. If the gateway is connected to the Internet
# with a static IP, snat is used. If the gateway has a dynamic address,
# masquerade must be used instead. There is more overhead associated
# with masquerade, so snat is better when it can be used.
# The nat table has a builtin chain, PREROUTING, for dnat and redirects.
# Another, POSTROUTING, handles snat and masquerade.

echo "Load rules for nat table ..."

############################################################################### #
# PREROUTING chain
#


############################################################################### #
# POSTROUTING chain
#


############################################################################### #
# mangle table
# ###############################################################################

# The mangle table is used to alter packets. It can alter or mangle them in
# several ways. For the purposes of this generator, we only use its ability
# to alter the TTL in packets. However, it can be used to set netfilter
# mark values on specific packets. Those marks could then be used in another
# table like filter, to limit activities associated with a specific host, for
# instance. The TOS target can be used to set the Type of Service field in
# the IP header. Note that the TTL target might not be included in the
# distribution on your system. If it is not and you require it, you will
# have to add it. That may require that you build from source.

#echo "Load rules for mangle table ..."
===

-- Sean

--- MultiMail/Linux
* Origin: Outpost BBS * Johnson City, TN (618:618/1)