#### 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
# Setting the 'max_mss' Ansible variable can solve some issues related to packet fragmentation
# This appears to be necessary on (at least) Google Cloud,
# however, some routers also require a change to this parameter
# See also:
# - https://github.com/trailofbits/algo/issues/216
# - https://github.com/trailofbits/algo/issues?utf8=%E2%9C%93&q=is%3Aissue%20mtu
# - https://serverfault.com/questions/601143/ssh-not-working-over-ipsec-tunnel-strongswan
-A FORWARD -s {{ vpn_network }} -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 }} -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]

# 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 -p ah -j ACCEPT
# rate limit ICMP traffic per source
-A INPUT -p icmp --icmp-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 -j ACCEPT
# Allow new traffic to port 22 (SSH)
-A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW -j ACCEPT
# Allow any traffic from the VPN
-A INPUT -p ipencap -m policy --dir in --pol ipsec --proto esp -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 {{ local_service_ip }} -p udp --dport 53 -j ACCEPT

{% if BetweenClients_DROP is defined and BetweenClients_DROP == "Y" %}
# Drop traffic between VPN clients
-A FORWARD -s {{ vpn_network }} -d {{ vpn_network }} -j DROP
{% endif %}

# Forward any packet that's part of an established connection
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
# Drop SMB/CIFS traffic that requests to be forwarded
-A FORWARD -p tcp --dport 445 -j DROP
# Drop NETBIOS trafic that requests to be forwarded
-A FORWARD -p udp -m multiport --ports 137,138 -j DROP
-A FORWARD -p tcp -m multiport --ports 137,139 -j DROP

# Forward any IPSEC traffic from the VPN network
-A FORWARD -m conntrack --ctstate NEW -s {{ vpn_network }} -m policy --pol ipsec --dir in -j ACCEPT

COMMIT