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| | + | [[Category:Linux]] |
| | The firewall (FW) is a key component of your server's security. | | The firewall (FW) is a key component of your server's security. |
| | | | |
| − | =Principle=
| + | You can search Internet to get all the related theory. My aim is not to explain that over here but just to give you HOW to setup a Firewall with IpTables. |
| − | | |
| − | This is how a firewall works:
| |
| − | | |
| − | [[File:FW_principle.png|none|FW principle]]
| |
| − | | |
| − | | |
| − | You can search Internet to get all the related theory. My aim is not to explain that over here but just to give you HOW to do that. | |
| − | | |
| | | | |
| | The following codes and examples are based '''iptables''' and '''ip6tables'''. | | The following codes and examples are based '''iptables''' and '''ip6tables'''. |
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| | | | |
| | + | =Principle= |
| | | | |
| | + | This is how a firewall works: |
| | | | |
| − | =Enable modules=
| + | [[File:FW_principle.png|none|FW principle]] |
| − | | |
| − | First things first! Before writing any rule you have to enable the required modules in your current O.S.
| |
| − | | |
| − | | |
| − | - Note -
| |
| − | | |
| − | If your server is hosted over Internet then you're probably using a custom Kernel (such as OVH, Tripnet, ...). In that case most modules are already enabled.
| |
| − | | |
| − | | |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | MODPROBE=`which modprobe`
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| − | | |
| − | | |
| − | echo -e " "
| |
| − | echo -e "-----------------------------"
| |
| − | echo -e " Enable networking modules"
| |
| − | echo -e "-----------------------------"
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| − | | |
| − | # IPv4
| |
| − | echo " ... IPv4"
| |
| − | $MODPROBE ip_tables
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| − | $MODPROBE iptable_filter
| |
| − | $MODPROBE iptable_mangle
| |
| − | # Allow to use state match
| |
| − | $MODPROBE ip_conntrack
| |
| − | | |
| − | # IPv6
| |
| − | echo " ... IPv6"
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| − | $MODPROBE ip6_tables
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| − | $MODPROBE ip6table_filter
| |
| − | $MODPROBE ip6table_mangle
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| − | | |
| − | # Allow NAT
| |
| − | echo " ... NAT"
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| − | $MODPROBE iptable_nat
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| − | | |
| − | # Allow active / passive FTP
| |
| − | echo " ... FTP"
| |
| − | $MODPROBE ip_conntrack_ftp
| |
| − | $MODPROBE ip_nat_ftp
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| − | | |
| − | # Allow log limits
| |
| − | echo " ... burst limit"
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| − | $MODPROBE ipt_limit
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| − | | |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | =Default policy=
| |
| − | | |
| − | This is how you defined a default policy.
| |
| − | | |
| − | | |
| − | Note:
| |
| − | * You have to adjust the policy to your own settings
| |
| − | * You should NOT set the INPUT in ACCEPT mode. That's risky!
| |
| − | | |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | IPTABLES=`which iptables`
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| − | IP6TABLES=`which ip6tables`
| |
| − | | |
| − | echo -e " "
| |
| − | echo -e "------------------------"
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| − | echo -e " Flush existing rules "
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| − | echo -e "------------------------"
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| − | | |
| − | $IP6TABLES -F
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| − | | |
| − | $IPTABLES -t filter -F
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| − | $IPTABLES -t filter -X
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| − | | |
| − | # delete NAT rules
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| − | $IPTABLES -t nat -F
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| − | $IPTABLES -t nat -X
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| − | | |
| − | # delete MANGLE rules (packets modifications)
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| − | $IPTABLES -t mangle -F
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| − | $IPTABLES -t mangle -X
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| − | | |
| − | echo -e " "
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| − | echo -e "------------------------"
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| − | echo -e " Default policy"
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| − | echo -e "------------------------"
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| − | echo -e " || --> OUTGOING reject all "
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| − | echo -e " --> || INCOMING reject all "
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| − | echo -e " --> || --> FORWARDING reject all (each redirection manual needs configuration)"
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| − | | |
| − | | |
| − | # INCOMING = avoid intrusions
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| − | # OUTGOING = avoid disclosure of sensitive / private data
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| − | $IPTABLES -P INPUT DROP
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| − | $IPTABLES -P FORWARD DROP
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| − | $IPTABLES -P OUTPUT ACCEPT
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| − | | |
| − | $IP6TABLES -P INPUT DROP
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| − | $IP6TABLES -P FORWARD DROP
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| − | $IP6TABLES -P OUTPUT DROP
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| − | | |
| − | echo -e " ... Reject invalid packets"
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| − | $IPTABLES -A INPUT -p tcp -m state --state INVALID -j DROP
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| − | $IPTABLES -A INPUT -p udp -m state --state INVALID -j DROP
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| − | $IPTABLES -A INPUT -p icmp -m state --state INVALID -j DROP
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| − | $IPTABLES -A OUTPUT -p tcp -m state --state INVALID -j DROP
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| − | $IPTABLES -A OUTPUT -p udp -m state --state INVALID -j DROP
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| − | $IPTABLES -A OUTPUT -p icmp -m state --state INVALID -j DROP
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| − | $IPTABLES -A FORWARD -p tcp -m state --state INVALID -j DROP
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| − | $IPTABLES -A FORWARD -p udp -m state --state INVALID -j DROP
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| − | | |
| − | $IP6TABLES -A INPUT -p tcp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A INPUT -p udp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A INPUT -p icmp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A OUTPUT -p tcp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A OUTPUT -p udp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A OUTPUT -p icmp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A FORWARD -p tcp -m state --state INVALID -j DROP
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| − | $IP6TABLES -A FORWARD -p udp -m state --state INVALID -j DROP
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| − | | |
| − | | |
| − | echo " ... Avoid spoofing and local subnets"
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| − | # Reserved addresses. We shouldn't received any packets from them!
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| − | $IPTABLES -A INPUT -s 10.0.0.0/8 -j DROP
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| − | $IPTABLES -A INPUT -s 172.16.0.0/12 -j DROP
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| − | $IPTABLES -A INPUT -s 192.168.0.0/16 -j DROP
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| − | $IPTABLES -A INPUT -s 169.254.0.0/16 -j DROP
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| − |
| |
| − | # Only localhost on Loopback interface + no forward
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| − | $IPTABLES -A INPUT ! -i lo -s 127.0.0.0/24 -j DROP
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| − | $IPTABLES -A FORWARD -s 127.0.0.0/24 -J DROP
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| − | $IP6TABLES -A INPUT ! -i lo -s ::1/128 -J DROP
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| − | $IP6TABLES -A FORWARD -s ::1/128 -J DROP
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| − | | |
| − | | |
| − | # No IPv4 -> IPv6 tunneling
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| − | echo " ... Do not allow IPv4 @ tunnel in IPv6 !! Use native IPv6 instead !!"
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| − | $IP6TABLES -A INPUT -s 2002::/16 -j DROP # 6to4 tunnels
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| − | $IP6TABLES -A FORWARD -s 2002::/16 -j DROP
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| − | $IP6TABLES -A INPUT -s 2001:0:/32 -j DROP # Teredo tunnels
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| − | $IP6TABLES -A FORWARD -s 2001:0:/32 -j DROP
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| − |
| |
| − | # Block IPv6 protocol in IPv4 frames
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| − | echo " ... Block IPv6 protocol in IPv4 frames"
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| − | $IPTABLES -A INPUT -p 41 -j DROP
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| − | $IPTABLES -A OUTPUT -p 41 -j DROP
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| − | $IPTABLES -A FORWARD -p 41 -j DROP
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| − | | |
| − | | |
| − | echo -e " ... Keep ESTABLISHED connections "
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| − | $IPTABLES -A INPUT -m state --state ESTABLISHED -j ACCEPT
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| − | $IPTABLES -A FORWARD -m state --state ESTABLISHED -j ACCEPT
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| − | $IPTABLES -A OUTPUT -m state --state ESTABLISHED -j ACCEPT
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| − |
| |
| − | $IP6TABLES -A INPUT -m state --state ESTABLISHED -j ACCEPT
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| − | $IP6TABLES -A FORWARD -m state --state ESTABLISHED -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -m state --state ESTABLISHED -j ACCEPT
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| − | | |
| − | | |
| − | echo -e " ... Keep RELATED connections (required for FTP)"
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| − | $IPTABLES -A INPUT -m state --state RELATED -j ACCEPT
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| − | $IPTABLES -A FORWARD -m state --state RELATED -j ACCEPT
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| − | $IPTABLES -A OUTPUT -m state --state RELATED -j ACCEPT
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| − | | |
| − | $IP6TABLES -A INPUT -m state --state RELATED -j ACCEPT
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| − | $IP6TABLES -A FORWARD -m state --state RELATED -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -m state --state RELATED -j ACCEPT
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| − | | |
| − | # Allow localhost communication
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| − | echo -e " ... Allow localhost"
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| − | $IPTABLES -A INPUT -i lo -s 127.0.0.0/24 -d 127.0.0.0/24 -j ACCEPT
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| − | $IPTABLES -A OUTPUT -o lo -s 127.0.0.0/24 -d 127.0.0.0/24 -j ACCEPT
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| − | | |
| − | $IP6TABLES -A INPUT -i lo -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -o lo -j ACCEPT
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| − | | |
| − | </syntaxhighlight>
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| − | | |
| − | | |
| − | | |
| − | | |
| − | | |
| − | =Protocol(s) enforcement=
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| − | | |
| − | | |
| − | <syntaxhighlight lang="bash">
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| − | IPTABLES=`which iptables`
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| − | IP6TABLES=`which ip6tables`
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| − | | |
| − | | |
| − | echo -e " "
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| − | echo -e "------------------------"
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| − | echo -e " Protocols enforcement"
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| − | echo -e "------------------------"
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| − | echo " ... Enable common Linux protections"
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| − | # Avoid broadcast echo
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| − | echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
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| − | # avoid TCP SYN Cookie
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| − | echo 1 > /proc/sys/net/ipv4/tcp_syncookies
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| − | # protection against bogus responses
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| − | echo 1 > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
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| − | # Avoid IP Spoofing (discard non routable IP@)
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| − | for f in /proc/sys/net/ipv4/conf/*/rp_filter; do echo 1 > $f; done
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| − | # Avoid ICMP redirect
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| − | echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
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| − | echo 0 > /proc/sys/net/ipv4/conf/all/send_redirects
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| − | echo 0 > /proc/sys/net/ipv6/conf/all/accept_redirects
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| − | # Avoid Source Routed
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| − | echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
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| − | echo 0 > /proc/sys/net/ipv6/conf/all/accept_source_route
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| − | | |
| − | ## Check TCP window
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| − | echo 1 > /proc/sys/net/ipv4/tcp_window_scaling
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| − | ## Avoid DoS
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| − | echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
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| − | echo 1800 > /proc/sys/net/ipv4/tcp_keepalive_time
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| − | ## Adjust TTL value
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| − | echo 64 > /proc/sys/net/ipv4/ip_default_ttl
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| − | | |
| − | # Port forwarding in general
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| − | echo " ... Enable forwarding"
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| − | echo 1 > /proc/sys/net/ipv4/ip_forward
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| − | echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
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| − | | |
| − | | |
| − | | |
| − | echo -e " ... Layer 2: ICMP v4"
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| − | # ICMP packets should not be fragmented
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| − | $IPTABLES -A INPUT --fragment -p icmp -j DROP
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| − | | |
| − | # Limit ICMP Flood
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| − | $IPTABLES -A INPUT -p icmp -m limit --limit 1/s --limit-burst 1 -j ACCEPT
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| − | $IPTABLES -A OUTPUT -p icmp --icmp-type 0 -j ACCEPT
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| − |
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| − | # Avoid common attacks ... but blocks ping :(
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| − | # [Network, Host, Protocol, Port] unreacheable + [Destination Host, Destination network] prohibited
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| − | #$IPTABLES -A OUTPUT -p icmp --icmp-type 3 -j DROP
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| − | | |
| − | | |
| − | echo -e " ... Layer 2: ICMP v6 "
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| − | # Feedback for problems
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 1 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 2 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 3 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 4 -j ACCEPT
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| − |
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| − | # Router and neighbor discovery
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 133 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 134 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 135 -j ACCEPT
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 136 -j ACCEPT
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| − | | |
| − | $IP6TABLES -A OUTPUT -p icmpv6 --icmpv6-type 133 -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -p icmpv6 --icmpv6-type 134 -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -p icmpv6 --icmpv6-type 135 -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -p icmpv6 --icmpv6-type 136 -j ACCEPT
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| − |
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| − | # Ping requests
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| − | $IP6TABLES -A INPUT -p icmpv6 --icmpv6-type 128 -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -p icmpv6 --icmpv6-type 128 -j ACCEPT
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| − | | |
| − |
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| − | echo " ... Layer 4: TCP # check packets conformity"
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| − | # INCOMING packets check
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| − | # All new incoming TCP should be SYN first
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| − | $IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j DROP
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| − | # Avoid SYN Flood (max 3 SYN packets / second. Then Drop all requests !!)
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| − | $IPTABLES -A INPUT -p tcp --syn -m limit --limit 1/s --limit-burst 3 -j ACCEPT
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| − | # Avoid fragment packets
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| − | $IPTABLES -A INPUT -f -j DROP
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| − | # Check TCP flags -- flag 64, 128 = bogues
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| − | $IPTABLES -A INPUT -p tcp --tcp-option 64 -j DROP
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| − | $IPTABLES -A INPUT -p tcp --tcp-option 128 -j DROP
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| − | echo " ... Layer 4: TCP # Avoid NMAP Scans"
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| − | # XMAS-NULL
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
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| − | # XMAS-TREE
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ALL ALL -j DROP
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| − | # SYN/RST Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
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| − | # SYN/FIN Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
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| − | # SYN/ACK Scan
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| − | #$IPTABLES -A INPUT -p tcp --tcp-flags ALL ACK -j DROP
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags SYN,ACK SYN,ACK -j DROP
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| − | # FIN/RST Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
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| − | # FIN/ACK Scan
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| − | $IPTABLES -A INPUT -p tcp -m tcp --tcp-flags FIN,ACK FIN -j DROP
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| − | # ACK/URG Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ACK,URG URG -j DROP
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| − | # FIN/URG/PSH Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags FIN,URG,PSH FIN,URG,PSH -j DROP
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| − | # Stealth XMAS Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
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| − | # XMAS-PSH Scan
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP
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| − | # End TCP connection
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags ALL FIN -j DROP
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| − | # Ports scans
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags FIN,SYN,RST,ACK SYN -j DROP
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| − | $IPTABLES -A INPUT -p tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
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| − | | |
| − | </syntaxhighlight>
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| − | | |
| − | | |
| − | | |
| − | | |
| − | | |
| − | | |
| − | | |
| − | =Allow services and network protocols=
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| − | | |
| − | ==DHCP==
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| − | | |
| − | DHCP client:
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| − | | |
| − | <syntaxhighlight lang="bash">
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| − | IPTABLES=`which iptables`
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| − | | |
| − | # DHCP client >> Broadcast IP request
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| − | $IPTABLES -A OUTPUT -p udp -d 255.255.255.255 --sport 68 --dport 67 -j ACCEPT
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| − | $IPTABLES -A INPUT -p udp -s 255.255.255.255 --sport 67 --dport 68 -j ACCEPT
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| − | $IPTABLES -A OUTPUT -p udp --dport 67 -j ACCEPT
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| − | $IPTABLES -A OUTPUT -p udp --dport 68 -j ACCEPT
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | ==DNS==
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| − | | |
| − | This will allow your computer to perform DNS requests:
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| − | | |
| − | <syntaxhighlight lang="bash">
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| − | IPTABLES=`which iptables`
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| − | IP6TABLES=`which ip6tables`
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| − | | |
| − | $IPTABLES -A OUTPUT -p udp --dport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IPTABLES -A OUTPUT -p udp --sport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IPTABLES -A INPUT -p udp --sport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IPTABLES -A INPUT -p udp --dport 53 -m limit --limit 100/s -j ACCEPT
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| − | | |
| − | | |
| − | $IP6TABLES -A OUTPUT -p udp --dport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IP6TABLES -A OUTPUT -p udp --sport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IP6TABLES -A INPUT -p udp --dport 53 -m limit --limit 100/s -j ACCEPT
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| − | $IP6TABLES -A INPUT -p udp --sport 53 -m limit --limit 100/s -j ACCEPT
| |
| − | </syntaxhighlight>
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| − | | |
| − | | |
| − | ==LAN communication==
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| − | | |
| − | To allow communication in the local network, without any restrictions:
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| − | | |
| − | <syntaxhighlight lang="bash">
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| − | IPTABLES=`which iptables`
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| − | LAN_ADDRESS="172.16.50.0/24"
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| − | | |
| − | $IPTABLES -A INPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -j ACCEPT
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| − | $IPTABLES -A OUTPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -j ACCEPT
| |
| − | </syntaxhighlight>
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| − | | |
| − | | |
| − | ==FTP client==
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| − | | |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | IPTABLES=`which iptables`
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| − | | |
| − | # FTP client - base rules
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| − | $IPTABLES -A INPUT -p tcp --sport 21 -m state --state ESTABLISHED -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j ACCEPT
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| − | | |
| − | # Active FTP
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| − | $IPTABLES -A INPUT -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT
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| − | $IPTABLES -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j ACCEPT
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| − | | |
| − | # Passive FTP
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| − | $IPTABLES -A INPUT -p tcp --sport 1024: --dport 1024: -m state --state ESTABLISHED -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p tcp --sport 1024: --dport 1024: -m state --state ESTABLISHED,RELATED -j ACCEPT
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | ==VPN==
| |
| − | | |
| − | Adjust the following to your own port, network ID and protocol:
| |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | IPTABLES=`which iptables`
| |
| − | | |
| − | INT_ETH=eth0
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| − | IP_LAN_ETH=`/sbin/ifconfig $INT_ETH | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'`
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| − | | |
| − | INT_VPN=tun0
| |
| − | VPN_PORT="8080"
| |
| − | VPN_PROTOCOL="udp"
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| − | LAN_ADDRESS_VPN="172.16.60.0/24"
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| − | | |
| − | echo -e " "
| |
| − | echo -e "------------------------"
| |
| − | echo -e " VPN configuration"
| |
| − | echo -e "------------------------"
| |
| − | | |
| − | echo " "
| |
| − | echo -e "# VPN interface : $INT_VPN"
| |
| − | echo -e "# VPN IP @ : $LAN_ADDRESS_VPN"
| |
| − | echo -e "# VPN port : $VPN_PORT"
| |
| − | echo -e "# VPN protocol : $VPN_PROTOCOL"
| |
| − | echo -e "-------------------------------------- "
| |
| − | | |
| − | # Allow devices communication $ETH0 <--> tun0
| |
| − | $IPTABLES -t nat -A POSTROUTING -s $LAN_ADDRESS_VPN -o $INT_ETH -j MASQUERADE
| |
| − | $IPTABLES -A FORWARD -s $LAN_ADDRESS_VPN -j ACCEPT
| |
| − | | |
| − | echo -e " ... Allow VPN connections"
| |
| − | $IPTABLES -A INPUT -p $VPN_PROTOCOL --dport $VPN_PORT -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p tcp --dport $VPN_PORT -j ACCEPT
| |
| − | | |
| − | echo -e " ... Allow everything to go through VPN - all INPUT,OUTPUT,FORWARD"
| |
| − | $IPTABLES -A INPUT -i $INT_VPN -m state ! --state INVALID -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -o $INT_VPN -m state ! --state INVALID -j ACCEPT
| |
| − | $IPTABLES -A FORWARD -o $INT_VPN -m state ! --state INVALID -j ACCEPT
| |
| − | | |
| − | echo -e " ... Allow VPN network communication (required for client <> client comm.)"
| |
| − | $IPTABLES -A INPUT -s $LAN_ADDRESS_VPN -d $LAN_ADDRESS_VPN -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -s $LAN_ADDRESS_VPN -d $LAN_ADDRESS_VPN -j ACCEPT
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | | |
| − | | |
| − | =Servers=
| |
| − | | |
| − | | |
| − | ==SSH==
| |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | # SSH - max 3 connection request per minute
| |
| − | $IPTABLES -A INPUT -p tcp -m limit 3/min --limit-burst 3 --dport 22 -j ACCEPT
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | ==DHCP==
| |
| − | | |
| − | | |
| − | This is how you enable a DHCP server with TFTP (netBoot) :
| |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | IPTABLES=`which iptables`
| |
| − | | |
| − | # Allow LAN communication
| |
| − | # ... Required for NFS and the NetBoot ...
| |
| − | $IPTABLES -A INPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -m state ! --state INVALID -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -m state ! --state INVALID -j ACCEPT
| |
| − |
| |
| − | ########################
| |
| − | # INPUT filters
| |
| − | ########################
| |
| − |
| |
| − | ##### DHCP client ######
| |
| − | # Broadcast IP request
| |
| − | $IPTABLES -A OUTPUT -p udp -d 255.255.255.255 --sport 68 --dport 67 -j ACCEPT
| |
| − | # Send / reply to IPs requests
| |
| − | $IPTABLES -A INPUT -p udp -s 255.255.255.255 --sport 67 --dport 68 -j ACCEPT
| |
| − |
| |
| − | ###### DHCP server ######
| |
| − | # Received client's requests [udp + tcp]
| |
| − | $IPTABLES -A INPUT -p udp --sport 68 --dport 67 -j ACCEPT
| |
| − | $IPTABLES -A INPUT -p tcp --sport 68 --dport 67 -j ACCEPT
| |
| − | | |
| − | # NetBoot - TFTP server
| |
| − | $IPTABLES -A INPUT -p udp -s $LAN_ADDRESS --dport 69 -j ACCEPT
| |
| − |
| |
| − |
| |
| − | ########################
| |
| − | # OUTPUT filters
| |
| − | ########################
| |
| − | # DHCP [udp + tcp]
| |
| − | $IPTABLES -A OUTPUT -p udp --dport 67 -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p tcp --dport 67 -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p udp --dport 68 -j ACCEPT
| |
| − | $IPTABLES -A OUTPUT -p tcp --dport 68 -j ACCEPT
| |
| − |
| |
| − | # TFTP NetBoot
| |
| − | $IPTABLES -A OUTPUT -p udp --dport 69 -j ACCEPT
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | Note the difference between the broadcast request that every computer should allow and the plain OUTPUT allow on ports 67,68 for the DHCP server !!
| |
| − | | |
| − | | |
| − | | |
| − | | |
| − | | |
| − | =Advanced feature=
| |
| − | | |
| − | | |
| − | ==Port forwarding==
| |
| − | | |
| − | | |
| − | ===Principle===
| |
| − | | |
| − | The aim is to reach a server located behind the actual server we are working on.
| |
| − | | |
| − | | |
| − | [[File:FW_port_forwarding.png|none|FW port forwarding - without NAT]] | |
| − | | |
| − | | |
| − | [[File:FW_port_forwarding_with_NAT.png|none|FW port forwarding - with NAT]]
| |
| − | | |
| − | | |
| − | To do a port forwarding you have to:
| |
| − | * Allow forwarding for the target
| |
| − | * Open the incoming port [input + output]
| |
| − | * Register the target server and allow POST-ROUTING operations on it
| |
| − | * Route the incoming port to the target server + port number
| |
| − | | |
| − | | |
| − | Requirements:
| |
| − | * Enable port forwading
| |
| − | * The current server must be able to reach the target {server,port}
| |
| − | | |
| − | | |
| − | | |
| − | ===IpTables script===
| |
| − | | |
| − | | |
| − | You have to declare the following only ONCE in all your FW script:
| |
| − | | |
| − | | |
| − | | |
| − | '''Enable module'''
| |
| − | | |
| − | <syntaxhighlight lang="bash">
| |
| − | #### Requirement: enable port forwarding in general
| |
| − | echo 1 > /proc/sys/net/ipv4/conf/eth0/forwarding
| |
| − | echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | | |
| − | '''Allow forwarding for [all,some] requests'''
| |
| | | | |
| − | <syntaxhighlight lang="bash">
| |
| − | #### Requirement: allow forwarding
| |
| − | # Allow all forwarding
| |
| − | $IPTABLES -A FORWARD -J ACCEPT
| |
| − | # Allow forward for some particular network or IP @
| |
| − | $IPTABLES -A FORWARD -s 172.16.50.0/24 -J ACCEPT
| |
| − | $IPTABLES -A FORWARD -s 5.39.81.23 -J ACCEPT
| |
| − | </syntaxhighlight>
| |
| | | | |
| | | | |
| | + | This is how you can use a firewall at home | work: |
| | | | |
| − | '''Perform port forwarding'''
| + | [[File:FW_usage.png|none|FW usage]] |
| | | | |
| | | | |
| − | You have to do the following for each computer / server you plan to serve:
| |
| | | | |
| − | <syntaxhighlight lang="bash">
| + | The firewall performs: |
| − | ####
| + | * Basic security check |
| − | # 1. Open target port
| + | * Security policy's enforcement |
| − | $IPTABLES -A INPUT -p tcp --dport 3389 -j ACCEPT
| + | * IP, port filtering |
| − | $IPTABLES -A OUTPUT -p tcp --dport 3389 -j ACCEPT
| + | * Port forwarding and NAT |
| | | | |
| − | # 2. Enable Port forwarding to Windows server 192.168.100.10
| |
| − | $IPTABLES -A POSTROUTING -d 192.168.100.10 -t nat -j MASQUERADE
| |
| | | | |
| − | # 3. Redirect services to target server
| |
| − | $IPTABLES -A PREROUTING -t nat -p tcp --dport 3389 -j DNAT --to 192.168.100.10:3389
| |
| − | $IPTABLES -A PREROUTING -t nat -p tcp --dport 81 -j DNAT --to 192.168.100.10:80
| |
| − | </syntaxhighlight>
| |
| | | | |
| | + | =Next steps= |
| | | | |
| | + | See [[Template:Menu_content_security#Firewall]] |
| | | | |
| − | ==Source address filtering== | + | =Note= |
| | | | |
| − | You can restricted the access of a particular service to a limited set of source networks, IP @.
| + | All this knowledge is the result of years of experiments and trials. Don't hesitate to search over Internet for more advanced || simpler rules. |
| | | | |
| | | | |
| − | Example:
| |
| | | | |
| − | <syntaxhighlight lang="bash">
| |
| | | | |
| − | # Only allow company's offices to access our Tomcat
| + | =References= |
| − | $IPTABLES -A INPUT -p tcp --dport 8088 -s 192.168.1.0/24 -j ACCEPT # Sweden LAN
| |
| − | $IPTABLES -A INPUT -p tcp --dport 8088 -s 90.83.80.64/27 -j ACCEPT # FR remote
| |
| − | $IPTABLES -A INPUT -p tcp --dport 8088 -s 90.83.80.123/27 -j ACCEPT # FR remote
| |
| − | $IPTABLES -A INPUT -p tcp --dport 8088 -s 77.68.140.115/24 -j ACCEPT # DK remote
| |
| − | $IPTABLES -A INPUT -p tcp --dport 8088 -s 0.0.0.0/0 -j DROP # DROP all the rest !
| |
| | | | |
| − | </syntaxhighlight>
| + | * My education at Telecom Bretagne [http://www.telecom-bretagne.eu/] && Chalmers [http://www.chalmers.se/en/] |
| | | | |
| | + | * How to set IPv4 as default: http://bruteforce.gr/make-apt-get-use-ipv4-instead-ipv6.html |
| | | | |
| − | Don't forget to drop all the rest at the end !!
| + | * Working years and some co-workers help: |
| | + | ** Julien Rialland |
