py-cgnat

Python module for generating CGNAT rules using netmap

Brief

This is a Python library and CLI program for generating firewall rules to deploy Carrier-Grade NAT, besides translating a given IP and port to its private address and vice versa. The methodology consists in building netmap rules at 1:32 public-private ratio, mapping a range of 2.000 ports for each client. Works for any netmask, since that follow the 1:32 ratio:

Private prefix	Public prefix	N. of clients
...	...	...
/20	/25	4096
/21	/26	2048
/22	/27	1024
/23	/28	512
/24	/29	256
/25	/30	128
/26	/31	64
/27	/32	32

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Supported Platforms

• MikroTik RouterOS

Requirements

• Python 3.7+

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How to install it?

Installation can just being done with pip:

pip install pycgnat

How to use it?

1. Command Line Interface

For generating the rules, you can print it in console or save it to a file:

pycgnat 100.64.0.0/20 203.0.113.0/25 gen routeros filename.rsc
pycgnat 100.64.0.0/20 203.0.113.0/25 gen routeros

For translating a private IP to its public one, use the direct option:

pycgnat 100.64.0.0/20 203.0.113.0/25 trans --direct 100.64.2.15
pycgnat 100.64.0.0/20 203.0.113.0/25 trans -d 100.64.2.15

For translatig a public IP and port to its private IP correspondent, use the reverse option:

pycgnat 100.64.0.0/20 203.0.113.0/25 trans --reverse 203.0.113.20:13578
pycgnat 100.64.0.0/20 203.0.113.0/25 trans -r 203.0.113.20:13578

The CLI includes useful help command (supported by argparse framework), so just type:

pycgnat --help
pycgnat -h

2. Python library

You can use the functionalities directly in Python lang. Just import the wanted module to your program:

from pycgnat.translator.reverse import cgnat_reverse

dic = cgnat_reverse(privnet, pubnet, IPv4Address('203.0.113.20'), 13578)
print(dic['private_ip'])

The full pycgnat's documentation is written in the source-code.

Future works

• Add support for other platfoms (I'm using MikroTik for while, so this is the reason for only supporting it at first version).

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

MIT