High Level Overview: Transmitting

• A NAT router is configured with at least one private interface and at least one public interface

• • The private interfaces have private IP addresses
  • The public interfaces have public IP addresses

• The NAT:

• • Examines the IP addresses, IP protocol and ports of a packet going from the private address space to the public address space
  • Maps the source IP address to the NAT’s public interface IP address
  • Maps the source port number to a unique (per the NAT’s chosen public IP address) source port number
  • Re-writes the source IP address with the NAT’s public interface IP address
  • Re-writes the source port with new port number
  • Re-calculates the appropriate checksums / sequence numbers
  • Transmits the modified packet