Create README.md

README.md

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+# xt_NAT
+## Description
+This Full Cone NAT xtables module was developed as a replace for the conntrack NAT to provide Assymetric NAT features on Linux systems that can be used as a Carrier Grade NAT in small ISP networks.
+
+It allows to have 40Gbps NAT on commodity servers like 2*Xeon E5-2698 v3 @ 2.30GHz (2 x 16 Cores) with Intel X710/XL710/X540 10G adapters.
+
+Compatibility tested with Linux Kernel 3.18 and 4.1
+## Features
+* PAT/NAPT work mode - translates many users into a single NAT IP
+* Assymetric (Full Cone) NAT - allows inbound connections from any source IP address and any source port, as long as the NAT rule exists
+* Support of TCP/UDP/ICMP/Generic IP protocols
+* IP Pooling Paired mode - the same NAT IP is used for all sessions of a subscriber
+* Endpoint Independent Mapping - the same NAT_IP:NAT_Port mapping is used for traffic sent from same subscriber IP
+address and port to any external IP address and port
+* Hairpinning - allows communication between two internal subscribers or internal hosts using the NAT IP
+* User quotas support. Default value is 1000 max connections for each user (for each protocol independly)
+* No ALGs for FTP/SIP/PPTP are implemented
+* NAT events export using Netflow v5
+* NAT statistics via /proc interface
+
+## Installation
+```
+$ make
+$ sudo make install
+$ sudo depmod -a
+```
+
+## Usage
+### NAT functionality
+* Define NAT Pool for the xt_NAT module:
+```
+$ sudo modprobe xt_NAT nat_pool=<Start IP>-<End IP>
+```
+* Disable conntrack for the traffic that handled by the xt_NAT module:
+```
+$ sudo iptables -t raw -A PREROUTING -s <Users Net> -j CT --notrack
+$ sudo iptables -t raw -A PREROUTING -d <NAT Pool Net> -j CT --notrack
+```
+* Add iptables rule to use xt_NAT module for User's traffic (from Internet to Users):
+```
+$ sudo iptables -t raw -A PREROUTING -d <NAT Pool Net>  -j NAT --dnat
+$ sudo iptables -A FORWARD -d <Users Net> -i <Uplink iface> -o <Downlink iface> -j ACCEPT
+```
+* Add iptables rule to use xt_NAT module for User's traffic (from Internet to Users):
+```
+$ sudo iptables -A FORWARD -s <Users Net> -i <Downlink iface> -o <Uplink iface> -j NAT –snat
+```
+### NAT Events Export
+Just add ``nf_dest`` option with a list of the Netflow v5 collectors to the xt_NAT module parameters:
+```
+$ sudo modprobe xt_NAT nat_pool=<Start IP>-<End IP> nf_dest=127.0.0.1:2055
+```
+## NAT Statistics
+NAT statistics are available via the ```/proc/net/NAT/*``` directory:
+* /proc/net/NAT/sessions - NAT sessions for all users
+* /proc/net/NAT/users - NAT users with their NAT IPs
+* /proc/net/NAT/statistics - internal counters