What’s that?
It translates private IPs and Ports to a public IP and port.
What’s the reason?
There are not enough IPv4 addresses available.
Where’s it used?
It’s part of the ‘(wireless) router‘ and the GGSN.
How does it work?
Client 1 Client 2 Client 3
SRC: 10.0.0.1:443 SRC: 10.0.0.2:443 SRC: 10.0.0.3:80
DST: 20.21.22.23:443 DST: 20.21.22.23:443 DST: 30.31.32.33:80
| | |
|----------| | |----------|
↓ ↓ ↓
|--------------------------------|
| NAPT Session Table | LAN to WAN:
|--------------------------------| Modifies Source-IP
| Private Addr | Public Addr | (Private --> Public)
Public IPv4 from ISP: |--------------------------------|
10.11.12.13 | 10.0.0.1:443 | 10.11.12.13:111 | WAN to LAN:
| 10.0.0.2:443 | 10.11.12.13:222 | Modifies Dest.-IP
| 10.0.0.3:80 | 10.11.12.13:333 | (Public --> Private)
|--------------------------------|
| | | LAN
-----------------------------------------------------------------------------
|----------| | |----------| WAN
↓ ↓ ↓
Server 1 Server 1 Server 2
SRC: 10.11.12.13:111 SRC: 10.11.12.13:222 SRC: 10.11.12.13:333
DST: 20.21.22.23:443 DST: 20.21.22.23:443 DST: 30.31.32.33:80