nukem from orbit, it's the only way to be sure

nuke it from orbit, it’s the only way to be sure

I think this is the way to really clear out all the stuff in iptables, the arcane packet filtering thing for Linux. At least… I think. My take on it, at least. For somewhat modern Linuxes at the time of this writing, IPv4 only.

Basic method: loop over all the types of tables, flushing… then loop over all the builtin tables for the various types, reset the policies… then erase all chains not in tables.

All this joy in a shell script below.

#!/bin/bash

#
# Usage: $0
#

#
# so many tables, so little time... this simply nukes everything in iptables.
# At least... I think... who really knows?
#
# IPv4 ONLY
#
# Perhaps you can define your own, I'd never see them. Kernels can have
# others in or out... can't find any command to just list the tables,
# probably something simple.
#

# Anyway. Basic method - loop over all the types of tables, flushing...
# then loop over and, based on the builtin tables, reset the policies...
# then erase all chains not in tables.

echo 'killing off routes'

# kill routes
ip route flush cache

# who knew there were so many? "filter" is the default table
types_o_tables=('-t filter' '-t nat' '-t mangle' '-t raw' '-t security')

#
# from the man page:
#
#    filter:
#        This is the default table (if no -t option is passed). It contains
#        the built-in chains INPUT (for packets destined to local sockets),
#        FORWARD (for packets being routed through the box), and OUTPUT
#        (for locally-generated packets).
filter=('INPUT' 'FORWARD' 'OUTPUT')
#    
#    nat:
#        This table is consulted when a packet that creates a new connection
#        is encountered.  It consists of three  built-ins:  PREROUTING (for
#        altering  packets as soon as they come in), OUTPUT (for altering
#        locally-generated packets before routing), and POSTROUTING (for
#        altering packets as they are about to go out).  IPv6 NAT support is
#        available since kernel 3.7.
nat=('PREROUTING' 'OUTPUT' 'POSTROUTING')
#    
#    mangle:
#        This table is used for specialized packet alteration.  Until kernel
#        2.4.17 it had two built-in chains: PREROUTING  (for  altering incoming
#        packets before routing) and OUTPUT (for altering locally-generated
#        packets before routing).  Since kernel 2.4.18, three other built-in
#        chains are also supported: INPUT (for packets coming into the box
#        itself), FORWARD  (for  altering  packets  being routed through the
#        box), and POSTROUTING (for altering packets as they are about to
#        go out).
mangle=('PREROUTING' 'OUTPUT' 'INPUT' 'FORWARD' 'POSTROUTING')
#    
#    raw:
#        This  table is used mainly for configuring exemptions from connection
#        tracking in combination with the NOTRACK target.  It registers at
#        the netfilter hooks with higher priority and is thus called before
#        ip_conntrack, or any other IP tables.  It provides the following
#        built-in  chains:  PREROUTING  (for packets arriving via any network
#        interface) OUTPUT (for packets generated by local processes)
raw=('PREROUTING' 'OUTPUT')
#    
#    security:
#        This table is used for Mandatory Access Control (MAC) networking
#        rules, such as those enabled by the SECMARK and CONNSECMARK targets.
#        Mandatory Access Control is implemented by Linux Security Modules
#        such as SELinux.  The security table is called after the filter
#        table, allowing any Discretionary Access Control (DAC) rules in the
#        filter table to take effect before  MAC  rules.   This table provides
#        the following built-in chains: INPUT (for packets coming into the
#        box itself), OUTPUT (for altering locally-generated packets before
#        routing), and FORWARD (for altering packets being routed through
#        the box).
security=('INPUT' 'OUTPUT' 'FORWARD')

#
# flush the tables
#
echo flushing tables....
for type_o in "${types_o_tables[@]}"; do
    echo -e "\t$type_o"
    iptables $type_o -F
done

#
# reset all the policies
#
echo reset policies
for type_o in "${types_o_tables[@]}"; do
    echo -e "\t$type_o"
    # have to tear out the -t
    pol=$(echo $type_o|awk '{print $2}')
    # echo -e "\t--> $a"

    # it's a bit convoluted... so building this up one step at a time
    e=$(echo \${$pol[\*]})

    # loop over arrays of tables
    for p in $(eval "echo $e"); do
        echo -e "\t\t$p"
    done
done

#
# erase all chains not in table
#
echo erasing chains...
for type_o in "${types_o_tables[@]}"; do
    echo -e "\t$type_o"
    iptables $type_o -X
done

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