The exhaustion of IP addresses has contributed to the development of CIDR, but the main purpose of CIDR development is to effectively use existing Internet addresses, while NAT developed according to RFC1631 (IP NETWORK ADDRESS TRANSLATOR) can be used in multiple Internet subnet The same IP address is used to reduce the use of registered IP addresses.
NAT is divided into: static NAT, dynamic NAT, port NAT (PAT).
Static NAT: Each host in the internal network is permanently mapped to a legal address in the external network;
Dynamic NAT: A series of legal addresses are defined in the external network, which is mapped to the internal network using the method of dynamic allocation;
PAT: It is a conversion method that people are more familiar with. PAT is commonly used in access equipment, it can hide small and medium-sized networks behind a legal IP address. PATT is different from dynamic address NAT. It 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, the technology of port mulTIPlexing, or the technology of changing the source port of outgoing data, maps multiple internal IP addresses to the same external address.
Network Address Translation (NAT) is an Internet Engineering Task Force (IETF) standard used to allow multiple PCs on a private network (using a dedicated address segment, such as 10.0.xx, 192.168.xx, 172.xxx ) IPv4 addresses that share a single, global route. The increasing shortage of IPv4 addresses is a major reason for the frequent deployment of NAT. "Internet Connection Sharing" in Windows XP and Windows Me and many Internet gateway devices use NAT, especially when connecting to a broadband network via DSL or cable modem.
NAT is very effective for solving the problem of IPv4 address consumption (it is not necessary in IPv6 deployment), but it is a temporary solution after all. This problem of IPv4 address occupancy has become more serious in Asia and some other parts of the world, and is increasingly becoming a concern in North America. This is why people have long focused on using IPv6 to overcome this problem.
In addition to reducing the required IPv4 addresses, since 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 firewalls or proxy servers, but it is really good for security.
Several situations of NAT use:
1. Connect to INTERNE, but there is not enough legal address assigned to the internal host;
2. Change to an ISP that needs to reassign addresses;
3. Two INTRANETs with the same IP address are merged;
4. Want to support load balancing (host);
There are 4 usages of NAT:
1.TRANSLATION INSIDE LOCAL ADDRESS ----------- Translate the internal address one-to-one to the external address;
2. OVERLOADING INSIDE GLOBAL ADDRESS --------- Translate many-to-one internal addresses into external addresses, and distinguish different local addresses by address and port number. This method is called PAT [/ color: 43aa144927];
3.TCP LOAD DISTRIBUTING ---- Provide a method of load sharing among multiple hosts with high utilization rate;
4.HANDLING OVERLAPPING NETWORK ---- This method is mainly used for the interconnection of two INTRANET.
NAT address translation refers to the way in which each intranet address is translated into an IP address + source port, which requires multiple public IP addresses.
However, because PAT has insufficient IP addresses, the internal network address will be converted into an IP address + port segment. Such a public network 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 simple terms, PAT-many to 1, NAT-many to many.
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