1. NAT (Network Address Translation)‏

2. NAT
RFC 1631, May 1994
“The IP Network Address Translator (NAT)”
It was evident by the beginnings of the 90s that many more IP addresses would be needed
Many more devices
IPv4 would not be enough
The objective of NAT was to define a mechanism that allowed the sharing of IP addresses by numerous devices
"provide temporarily relief while other, more complex and far-reaching solutions are worked out."
Two decades later NAT is ubiquitous deployment across the Internet
Eventhough IPv6 has been ready for 15 years

3. NAT (Network Address Translation)‏+
ISP

4. NAPT (Network Address Port Translation)‏ 80
1505
Dir IP
Puerto
Dest
Org 80
32655
Dir IP
Puerto
Dest
Org
ISP 80
1505
Dir IP
Puerto
Org
Dest 80
32655
Dir IP
Puerto
Org
Dest

5. NAT header translators 80
1505
Dir IP
Puerto
Dest
Org
Outgoing packet:
IP source address, IP Checksum, and TCP checksum
Incoming packet:
IP destination address, IP checksum, and TCP checksum 80
1505
Dir IP
Puerto
Org
Dest

6. NAT (Network Address Translation)‏
Need for more IP addresses
Without using IPv6
Balance load
Migration from ISPs
NAPT. Ideal for SOHO
Security
“Hide” machines from the exterior

7. NAT (Network Address Translation)‏
Performance
IP and TCP headers modification
IP and TCP checksum recalculation
Access to the table of addresses
Search
writing