NAT: Network Address Translation

Internet communication TCP / IP is a protocol widely used for communication via the Internet. The IP address is used to identify the device in the TCP / IP environment. IP addresses are separated as classes, Class A, Class B, and Class C are used for hosts. Class D is used for multicasting and class E is reserved. Each class has a set of predefined IP address numbers. With the development of the Internet, the number of available IP addresses is rapidly decreasing. NAT is designed to address IP exhaustion problems.

NAT - Network Address Translation - is a way for routers to translate IP addresses of packets across the boundaries of the Internet / local network. When computer "A" sends a packet, its IP address "from" is the IP address of computer "A" - in the above example it is 192.168.0.1. When the router passes it to the Internet, it replaces the local IP address with the Internet IP address assigned by the ISP (1.2.3.4 in this example). Also, if there is a response, the router recognizes converting the conversion back, replaces the Internet IP address with the local IP address of the machine "A", and then sends the response packet to the machine "A".

NAT Instance: A Network Address Translation (NAT) instance is used to allow resources in a private subnet to communicate with resources or objects on the Internet. Resources such as EC2 instances residing on private subnets can not attach public IP addresses to their ENIs. Therefore, it can not communicate directly via the Internet via the IGW. Therefore, as with traditional networks, you need to convert private IP over the public interface. Customer Gateway (CGW) and Virtual Private Gateway (VGW): To establish a hardware VPN connection between the enterprise network and the AWS, create and configure a customer gateway (CGW) and a virtual private gateway (VPG) in the VPC need to do it. The customer gateway is a gateway or firewall in the corporate network used to establish this tunnel. The Virtual Private Gateway is the VPN Concentrator at the end of the VPC.

Network Address Translation (NAT) is a standard that allows multiple PCs on a private network to share globally routable IPv4 addresses. With NAT, users can have a large number of addresses internally, and usually can have addresses outside. The main reason for frequent deployment of NAT is to reduce IPv4 addresses. NAT is a direct but temporary solution to the problem of IPv4 address exhaustion and will eventually become unnecessary when deploying IPv6. The Internet technology special investigation committee recognized that the current address space is short in the past ten years.