What if the IP address is exhausted? NAT and PAT Technical Analysis

This article describes how the IP address is about to run out, how the PAT technology solves such problems, and how to compare the differences between NAT and PAT. I believe this article will help you.

Ip address depletion facilitates the development of CIDR, but the main purpose of CIDR development is to effectively use the existing internet address, and according to RFC1631 (ip network address translator) developed NAT can use the same IP address in multiple INTERNET subnets to reduce the use of registered IP addresses.

NAT can be divided into static NAT, dynamic NAT, and port NAT (PAT ).

Static NAT: each host in the internal network is permanently mapped to a valid address in the external network;

Dynamic NAT: A series of valid addresses are defined in the external network and are mapped to the internal network using dynamic allocation;

PAT: it is a familiar conversion method. PAT is widely used in access devices. It can hide Small and Medium networks behind a valid IP address. Unlike Dynamic Address NAT, PATT maps internal connections to a separate IP address in the external network, and adds a TCP port number selected by the NAT device to the address. That is to say, the port multiplexing technology or the source port technology that changes outbound data maps multiple internal IP addresses to the same external IP address.

Network Address Translation (NAT) is an Internet Engineering Task Force (IETF) standard used to allow multiple PCs on a private network (using private address segments, for example, 10.0.x.x, 192.168.x.x, 172. x. x. x) IPv4 addresses that share a single and global route. The increasing shortage of IPv4 addresses is a major reason for frequent NAT deployment. Internet Connection Sharing in Windows XP and Windows Me and many Internet gateway devices use NAT, especially when connecting to a broadband network through a DSL or cable modem.

NAT is a temporary solution, although it is effective to solve the IPv4 address consumption problem (which is unnecessary in IPv6 deployment. The IPv4 address occupation problem is already serious in Asia and other parts of the world, and is becoming a concern in North America. This is why we have been paying attention to using IPv6 for a long time to overcome this problem.

In addition to reducing the required IPv4 address, because all hosts outside the private network monitor communication through a shared IP address, NAT also provides a hidden layer for the private network. NAT is different from a firewall or proxy server, but it is indeed beneficial to security.

NAT usage:

1. Connect to INTERNE, but there is not enough legal address allocated to the internal host;

2. Change to an ISP whose IP address needs to be reassigned;

3. merge two Intranets with the same IP address;

4. Want to support Server Load balancer (host );

NAT can be used in four ways:

1. translation inside local address ----------- one-to-one internal ADDRESS is translated into an external ADDRESS;

2. overloading inside global address --------- translate multiple-to-one internal ADDRESS into an external ADDRESS, and use the ADDRESS and port number to distinguish different local addresses. This method is called PAT [/color: 43aa144927];

3. tcp load distributing-provides LOAD balancing among multiple high-utilization hosts;

4. handling overlapping network ---- this method is mainly used for interconnection between two Intranets.

NAT address translation means that each Intranet address is converted to an IP address + source port, which requires multiple public IP addresses.

However, due to insufficient IP addresses, PAT may convert the Intranet address into an IP address + port segment. Such a public IP address is usually only one.

For example:

NAT

192.168.0.2: 4444 ----> 202.116.100.5: 4444

192.168.0.3: 5555 ----> 202.116.100.6: 5555

192.168.0.10: 1233 ---> 202.116.100.5: 1233

PAT

192.168.0.2: 4444 ----> 202.116.100.5: 50003

192.168.0.3: 5555 ----> 202.116.100.5: 50004

192.168.0.10: 1233 ---> 202.116.100.5: 50005

In short, PAT-many to 1, nat-many to many.