Network Address Translation

Last updated Nov 8, 2022 Edit Source

IPv4 addresses are only 32 bits long which provides a maximum of 4.29 billion unique IP addresses.

Introduce NAT devices at the edge of the network, each of which would be responsible for maintaining a table mapping of local IP and port tuples to one or more globally unique (public) IP and port tuples (Figure 3-3).

1. Client may not know the public IP address: if the client communicates its private IP address as part of its application data with a peer outside of its private network, then the connection will inevitably fail.
2. NAT table may not have the mapping of a public IP of a packet

Helps the application obtain the public IP and port tuple of the current connection:

1. Discover the IP address and port tuple for the connection
2. Establish the NAT routing entry for the host application
3. Keepalive pings to keep NAT entries from timing out

When STUN fails (blocked by firewall etc.), we can use a relay to transmit the data between peers.

Establishes a set of methods to find the most efficient tunnel between participants: direct connection where possible using STUN if needed and TURN if failure.