diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..85ed0ea
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,144 @@
+Pipfile*
+# Created by https://www.gitignore.io/api/vim,python
+# Edit at https://www.gitignore.io/?templates=vim,python
+
+### Python ###
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+.hypothesis/
+.pytest_cache/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+.python-version
+
+# celery beat schedule file
+celerybeat-schedule
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+### Python Patch ###
+.venv/
+
+### Vim ###
+# Swap
+[._]*.s[a-v][a-z]
+[._]*.sw[a-p]
+[._]s[a-rt-v][a-z]
+[._]ss[a-gi-z]
+[._]sw[a-p]
+
+# Session
+Session.vim
+
+# Temporary
+.netrwhist
+*~
+# Auto-generated tag files
+tags
+# Persistent undo
+[._]*.un~
+
+# End of https://www.gitignore.io/api/vim,python
diff --git a/firewall.nft b/firewall.nft
index 16eb0f3..a3d3c1b 100644
--- a/firewall.nft
+++ b/firewall.nft
@@ -73,10 +73,4 @@ table inet firewall {
 }
 
 table nat {
-# TODO : on met 27 Ips internes par ip publiques
-# Users : 193.48.225.10-119
-# Prerezotage 193.48.225.240-254
-# Aloes : 193.48.225.120-129
-# Federez : 193.48.225.130-199
-# Server : 193.48.225.200-209
 }
diff --git a/firewall.py b/firewall.py
index 621362a..b81ed93 100644
--- a/firewall.py
+++ b/firewall.py
@@ -89,12 +89,35 @@ class Parser:
         return netaddr.EUI(mac, dialect=netaddr.mac_unix_expanded)
     @staticmethod
     def IPv4(ip):
-        """Check an IPv4 validity."""
-        return netaddr.IPAddress(ip, version=4)
+        """Check an IPv4 validity.
+
+        Args:
+            ip: can either be a tuple (in this case returns an IPRange), a
+            single IP address or a IP Network.
+        """
+        if isinstance(ip, tuple):
+            begin, end = ip
+            return netaddr.IPRange(begin, end, version=4)
+        try:
+            return netaddr.IPAddress(ip, version=4)
+        except ValueError:
+            return netaddr.IPNetwork(ip, version=4)
     @staticmethod
     def IPv6(ip):
-        """Check a IPv6 validity."""
-        return netaddr.IPAddress(ip, version=6)
+        """Check a IPv6 validity.
+
+        Args:
+            ip: can either be a tuple (in this case returns an IPRange), a
+            single IP address or a IP Network.
+        """
+        if isinstance(ip, tuple):
+            begin, end = ip
+            return netaddr.IPRange(begin, end, version=6)
+        try:
+            return netaddr.IPAddress(ip, version=6)
+        except ValueError:
+            return netaddr.IPNetwork(ip, version=6)
+
     @staticmethod
     def protocol(protocol):
         """Check a protocol validity."""
@@ -120,13 +143,17 @@ class NetfilterSet:
 
     ADDRESS_FAMILIES = {'ip', 'ip6', 'inet', 'arp', 'bridge', 'netdev'}
 
+    FLAGS = {'constant', 'interval', 'timeout'}
+
     def __init__(self,
                  name,
                  type_, # e.g.: ('MAC', 'IPv4')
                  target_content=None,
                  use_sudo=True,
                  address_family='inet', # Manage both IPv4 and IPv6.
-                 table_name='filter'):
+                 table_name='filter',
+                 flags = []
+                ):
         self.name = name
         self.content = set()
         # self.type
@@ -135,6 +162,7 @@ class NetfilterSet:
         # self.address_family
         self.set_address_family(address_family)
         self.table = table_name
+        self.set_flags(flags)
         sudo = ["/usr/bin/sudo"] * int(bool(use_sudo))
         self.nft = [*sudo, "/usr/sbin/nft"]
         if target_content:
@@ -167,6 +195,13 @@ class NetfilterSet:
                 'Invalid address_family: "{}".'.format(address_family))
         self.address_family = address_family
 
+    def set_flags(self, flags_):
+        """Check set flags validity before saving them."""
+        for f in flags_:
+            if f not in self.FLAGS:
+                raise ValueError('Invalid flag: "{}".'.format(f))
+        self.flags = _flags
+
     def create_in_kernel(self):
         """Create the set, removing existing set if needed."""
         # Delete set if it exists with wrong type
@@ -191,10 +226,11 @@ class NetfilterSet:
         """Create the non-existing set, creating table if needed."""
         create_set = [
             *self.nft,
-            'add set {addr_family} {table} {set_} {{ type {type_} ; }}'.format(
+            'add set {addr_family} {table} {set_} {{ type {type_} ; flags {flags}}}'.format(
                 addr_family=self.address_family, table=self.table,
                 set_=self.name,
-                type_=' . '.join(self.TYPES[i] for i in self.type))
+                type_=' . '.join(self.TYPES[i] for i in self.type)),
+                flags=', '.join(self.flags)
             ]
         return_code = CommandExec.run(create_set, allowed_return_codes=(0, 1))
         if return_code == 0:
diff --git a/nat.py b/nat.py
new file mode 100644
index 0000000..856d2dc
--- /dev/null
+++ b/nat.py
@@ -0,0 +1,188 @@
+#! /usr/bin/python3
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+# Copyright © 2019 Hugo Levy-Falk <me@klafyvel.me>
+
+"""
+Creates the nat set.
+"""
+
+import logging
+from configparser import ConfigParser
+
+import netaddr
+
+from firewall import NetfilterSet
+
+CONFIG = ConfigParser()
+CONFIG.read('config.ini')
+
+
+def create_nat(name, range_in, range_out, first_port, last_port):
+    """Create two nftables tables for the nat:
+        - <name>_address : which link a (or a range of) local address to a
+        public address;
+        - <name>_port : which links a local address to a
+        range of ports.
+
+        Args:
+            name: name of the sets
+            range_in: an IPRange with the private IP address
+            range_out: an IPRange with the public IP address
+            first_port: the first port used for the nat
+            last_port: the last port used for the nat
+        Returns:
+            (<name>_address, <name>_port) which are NetfilterSet
+    """
+    assert last_port >= first_port, (name + ": Your first_port "
+                                     "is lower than your last_port")
+    nb_private_by_public = range_in.size / range_out.size
+    nb_port_by_ip = (last_port - first_port + 1) / nb_private_by_public
+
+    ports = []
+    ips = []
+
+    port = first_port
+    for ip, port in range_in:
+        ports.append((
+            str(netaddr.IPAddress(ip)),
+            "%d-%d" % (port, port+nb_port_by_ip)
+        ))
+        port += nb_port_by_ip + 1
+        if port >= last_port:
+            port = first_port
+    ip = range_in.first
+    for ip_out in range_out:
+        ips.append((
+            '-'.join([
+                str(netaddr.IPAddress(ip)),
+                str(netaddr.IPAddress(ip+nb_private_by_public))
+            ]),
+            str(ip_out)
+        ))
+        ip += nb_private_by_public + 1
+
+    return (
+        NetfilterSet(
+            target_content=ips,
+            type_=('IPv4', 'IPv4'),
+            name=name,
+            table_name='nat',
+        ),
+        NetfilterSet(
+            target_content=ports,
+            type_=('IPv4', 'port'),
+            name=name,
+            table_name='nat',
+        ),
+    )
+
+
+def create_nat_adherent():
+    range_in = netaddr.IPRange(CONFIG['range_in_adherent'])
+    range_out = netaddr.IPRange(CONFIG['range_out_adherent'])
+    first_port = CONFIG['first_port_adherent']
+    last_port = CONFIG['last_port_adherent']
+    return create_nat(
+        'adherent',
+        range_in,
+        range_out,
+        first_port,
+        last_port
+    )
+
+
+def create_nat_federez():
+    range_in = netaddr.IPRange(CONFIG['range_in_federez'])
+    range_out = netaddr.IPRange(CONFIG['range_out_federez'])
+    first_port = CONFIG['first_port_federez']
+    last_port = CONFIG['last_port_federez']
+    return create_nat(
+        'federez',
+        range_in,
+        range_out,
+        first_port,
+        last_port
+    )
+
+
+def create_nat_aloes():
+    range_in = netaddr.IPRange(CONFIG['range_in_aloes'])
+    range_out = netaddr.IPRange(CONFIG['range_out_aloes'])
+    first_port = CONFIG['first_port_aloes']
+    last_port = CONFIG['last_port_aloes']
+    return create_nat(
+        'aloes',
+        range_in,
+        range_out,
+        first_port,
+        last_port
+    )
+
+
+def create_nat_admin():
+    range_in = netaddr.IPRange(CONFIG['range_in_admin'])
+    range_out = netaddr.IPRange(CONFIG['range_out_admin'])
+    first_port = CONFIG['first_port_admin']
+    last_port = CONFIG['last_port_admin']
+    return create_nat(
+        'admin',
+        range_in,
+        range_out,
+        first_port,
+        last_port
+    )
+
+
+def create_nat_prerezotage():
+    range_in = netaddr.IPRange(CONFIG['range_in_prerezotage'])
+    range_out = netaddr.IPRange(CONFIG['range_out_prerezotage'])
+    first_port = CONFIG['first_port_prerezotage']
+    last_port = CONFIG['last_port_prerezotage']
+    return create_nat(
+        'prerezotage',
+        range_in,
+        range_out,
+        first_port,
+        last_port
+    )
+
+
+def main():
+    logging.info("Creating adherent nat...")
+    address, port = create_nat_adherent()
+    address.manage()
+    port.manage()
+    logging.info("Done.")
+    logging.info("Creating federez nat...")
+    address, port = create_nat_federez()
+    address.manage()
+    port.manage()
+    logging.info("Done.")
+    logging.info("Creating aloes nat...")
+    address, port = create_nat_aloes()
+    address.manage()
+    port.manage()
+    logging.info("Done.")
+    logging.info("Creating admin nat...")
+    address, port = create_nat_admin()
+    address.manage()
+    port.manage()
+    logging.info("Done.")
+    logging.info("Creating prerezotage nat...")
+    address, port = create_nat_prerezotage()
+    address.manage()
+    port.manage()
+    logging.info("Done.")