#### The mangle table
# This table allows us to modify packet headers
# Packets enter this table first
#
*mangle

:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]

{% if max_mss is defined %}
# MSS is the TCP Max Segment Size
# See rules.v4 for a more complete explanation
-A FORWARD -s {{ vpn_network_ipv6 }}{% if wireguard_enabled %},{{ wireguard_vpn_network_ipv6 }}{% endif %} -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss {{ max_mss }}
{% endif %}

COMMIT

#### The nat table
# This table enables Network Address Translation
# (This is technically a type of packet mangling)
#
*nat

:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]

# Allow traffic from the VPN network to the outside world, and replies
-A POSTROUTING -s {{ vpn_network_ipv6 }}{% if wireguard_enabled %},{{ wireguard_vpn_network_ipv6 }}{% endif %} -m policy --pol none --dir out -j MASQUERADE

COMMIT

#### The filter table
# The default ipfilter table
#
*filter

# By default, drop packets that are destined for this server
:INPUT DROP [0:0]
# By default, drop packets that request to be forwarded by this server
:FORWARD DROP [0:0]
# By default, accept any packets originating from this server
:OUTPUT ACCEPT [0:0]

# Create the ICMPV6-CHECK chain and its log chain
# These chains are used later to prevent a type of bug that would
# allow malicious traffic to reach over the server into the private network
# An instance of such a bug on Cisco software is described here:
# https://www.insinuator.net/2016/05/cve-2016-1409-ipv6-ndp-dos-vulnerability-in-cisco-software/
# other software implementations might be at least as broken as the one in CISCO gear.
:ICMPV6-CHECK - [0:0]
:ICMPV6-CHECK-LOG - [0:0]

# Accept packets destined for localhost
-A INPUT -i lo -j ACCEPT
# Accept any packet from an open TCP connection
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
# Accept packets using the encapsulation protocol
-A INPUT -p esp -j ACCEPT
-A INPUT -m ah -j ACCEPT
# rate limit ICMP traffic per source
-A INPUT -p icmpv6 --icmpv6-type echo-request -m hashlimit --hashlimit-upto 5/s --hashlimit-mode srcip --hashlimit-srcmask 32 --hashlimit-name icmp-echo-drop -j ACCEPT
# Accept IPSEC traffic to ports 500 (IPSEC) and 4500 (MOBIKE aka IKE + NAT traversal)
-A INPUT -p udp -m multiport --dports 500,4500{% if wireguard_enabled %},{{ wireguard_port}}{% endif %} -j ACCEPT
# Allow new traffic to port 22 (SSH)
-A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW -j ACCEPT

# Accept properly formatted Neighbor Discovery Protocol packets
-A INPUT -p icmpv6 --icmpv6-type router-advertisement -m hl --hl-eq 255 -j ACCEPT
-A INPUT -p icmpv6 --icmpv6-type neighbor-solicitation -m hl --hl-eq 255 -j ACCEPT
-A INPUT -p icmpv6 --icmpv6-type neighbor-advertisement -m hl --hl-eq 255 -j ACCEPT
-A INPUT -p icmpv6 --icmpv6-type redirect -m hl --hl-eq 255 -j ACCEPT

# DHCP in AWS
-A INPUT -m conntrack --ctstate NEW -m udp -p udp --dport 546 -d fe80::/64 -j ACCEPT

# TODO:
# The IP of the resolver should be bound to a DUMMY interface.
# DUMMY interfaces are the proper way to install IPs without assigning them any
# particular virtual (tun,tap,...) or physical (ethernet) interface.

# Accept DNS traffic to the local DNS resolver
-A INPUT -d fcaa::1 -p udp --dport 53 -j ACCEPT

# Drop traffic between VPN clients
{% if BetweenClients_DROP %}
{% set BetweenClientsPolicy = "DROP" %}
{% endif %}
-A FORWARD -s {{ vpn_network_ipv6 }}{% if wireguard_enabled %},{{ wireguard_vpn_network_ipv6 }}{% endif %} -d {{ vpn_network_ipv6 }}{% if wireguard_enabled %},{{ wireguard_vpn_network_ipv6 }}{% endif %} -j {{ BetweenClientsPolicy | default("ACCEPT") }}

-A FORWARD -j ICMPV6-CHECK
-A FORWARD -p tcp --dport 445 -j DROP
-A FORWARD -p udp -m multiport --ports 137,138 -j DROP
-A FORWARD -p tcp -m multiport --ports 137,139 -j DROP
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -m conntrack --ctstate NEW -s {{ vpn_network_ipv6 }} -m policy --pol ipsec --dir in -j ACCEPT
{% if wireguard_enabled %}
-A FORWARD -m conntrack --ctstate NEW -s {{ wireguard_vpn_network_ipv6 }} -m policy --pol none --dir in -j ACCEPT
{% endif %}

# Use the ICMPV6-CHECK chain, described above
-A ICMPV6-CHECK -p icmpv6 -m hl ! --hl-eq 255 --icmpv6-type router-solicitation -j ICMPV6-CHECK-LOG
-A ICMPV6-CHECK -p icmpv6 -m hl ! --hl-eq 255 --icmpv6-type router-advertisement -j ICMPV6-CHECK-LOG
-A ICMPV6-CHECK -p icmpv6 -m hl ! --hl-eq 255 --icmpv6-type neighbor-solicitation -j ICMPV6-CHECK-LOG
-A ICMPV6-CHECK -p icmpv6 -m hl ! --hl-eq 255 --icmpv6-type neighbor-advertisement -j ICMPV6-CHECK-LOG
-A ICMPV6-CHECK-LOG -j LOG --log-prefix "ICMPV6-CHECK-LOG DROP "
-A ICMPV6-CHECK-LOG -j DROP

COMMIT