########
*filter
########

:INPUT   ACCEPT [0:0]
:FORWARD DROP   [0:0]
:OUTPUT  ACCEPT [0:0]

# Remove all rules from all chains,
# delete all user-defined chains.
-F
-X

# Allow all loopback (lo) traffic and reject anything
# to localhost that does not originate from lo.
-A INPUT   -i lo                -j ACCEPT
-A INPUT ! -i lo -s 127.0.0.0/8 -j REJECT
-A OUTPUT  -o lo                -j ACCEPT

# Allow all outgoing traffic.
-A OUTPUT -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
-A INPUT  -m conntrack --ctstate ESTABLISHED     -j ACCEPT

# Allow incoming ICMP ping.
-A INPUT  -p icmp --icmp-type echo-request -j ACCEPT
-A OUTPUT -p icmp --icmp-type echo-reply   -j ACCEPT

# Allow outgoing ICMP ping.
-A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
-A INPUT  -p icmp --icmp-type echo-reply   -j ACCEPT

# Deny other ICMP.
-A INPUT  -p icmp -j DROP
-A OUTPUT -p icmp -j DROP

# Allow incoming SSH.
-A INPUT  -p tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED     -j ACCEPT

COMMIT