dpkg --list | grep iptables

Returns

ii  iptables                            1.6.0-2ubuntu3                      amd64        administration tools for packet filtering and NAT

lsmod | grep ip_tables

Returns

ip_tables              24576  4 iptable_filter,iptable_mangle,iptable_nat,iptable_raw

iptables -P INPUT DROP
iptables -P OUTPUT DROP
 
# Allowing Loopback Traffic.
iptables -I INPUT -i lo -j ACCEPT
 
# Allow established connections.
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
 
# Allow SSH in.
# iptables -I INPUT -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -s 192.168.1.2 -j ACCEPT
 
# iptables -A INPUT -p tcp --dport 80 -j ACCEPT
# iptables -A INPUT -p tcp --dport 443 -j ACCEPT
 
# Loading the ip_conntrack_ftp module
 
# iptables -A INPUT -p tcp --dport 21 -j ACCEPT
# iptables -A INPUT -p tcp --dport 20 -j ACCEPT

To have FTP work correctly with iptables, ensure that the ip_conntrack_ftp module is loaded.

modprobe ip_conntrack_ftp

Check that the module is loaded

lsmod | grep conntrack

Returns

nf_conntrack_ftp       20480  1 nf_nat_ftp
nf_conntrack_ipv4      16384  84
nf_defrag_ipv4         16384  1 nf_conntrack_ipv4
xt_conntrack           16384  81
nf_conntrack          106496  9 nf_nat_ftp,nf_nat,xt_state,xt_connlimit,nf_nat_ipv4,xt_conntrack,nf_nat_masquerade_ipv4,nf_conntrack_ftp,nf_conntrack_ipv4
x_tables               36864  25 xt_pkttype,ip6table_filter,ip6table_mangle,xt_length,xt_comment,xt_CHECKSUM,xt_recent,ip_tables,xt_tcpudp,xt_string,ipt_MASQUERADE,xt_limit,xt_state,xt_connlimit,xt_conntrack,xt_LOG,xt_nat,xt_multiport,iptable_filter,ebtables,ipt_REJECT,iptable_mangle,ip6_tables,xt_addrtype,iptable_raw