Three minutes to understand NAT (address translation technology) Past and Present
As we all know, only the 32-bit IP address, only a maximum of 4,290,000,000 addresses, but also to remove reserved addresses, multicast addresses, can address only about 3.6 billion, but at the moment there are several hosts trillion, not so much IP address how do behind with IPv6, but the current IPv4 is still the mainstream. In fact, IPv4 address shortage problem is not new, as early as 20 years ago, IPv4 addresses will run out of the question had been placed in front. It makes us want to know, it is what makes this crisis delayed the technology to do for 20 years. It is NAT technology, is the primary means to address current IP address is not enough. NAT can be converted to a global IP when private IP external communications. That is, technology is a way to the private IP and global IP into each other.
Definitions:
NAT is Network Address Translation Network Address Translation acronym.
NAT is a private IP address into a routing through the boundary external IP address, this conversion map at the boundary recording NAT routing address conversion table, when the external data is returned, the routing query technique using NAT NAT translation table, then the destination address replace the IP address of the user network.
For Internet access needs of the internal network and the use of private addresses, it is necessary to deploy NAT gateways in the export position of the tissue, when the message leaves the private network into the Internet, will replace the source IP address for the public network, usually the export of equipment interfaces address. An external access request after reaching the target, the performance by the Organization initiated the export of equipment, and therefore requested a response from the server can be exported back to Internet gateway. Gateway then export destination IP address of the source host address private network, back inside. This point of view, the network hosts no longer need a public IP address.
NAT technology in three ways: static NAT, dynamic NAT, PAT Port address multiplexing.
Static NAT:
an internal host to occupy a separate IP public network, this is called one model, how many private addresses internal and external communication needs, many external IP address and the corresponding configuration would not save the external network IP so mainly in order to achieve some special networking requirements. For example the user wishes to hide the true internal IP host, or two overlapping IP addresses for communication networks.
Dynamic NAT:
configured on a router external IP address pool, when the internal computer and the external communication needs, they were removed from an external network ip address pool, and bind their relations to the NAT table, after communication this external network ip will be released, it can be supplied to other internal computer, the IP and DHCP lease similar.
PAT (port address Translation, port address multiplexing)
most commonly used NAT technology, the use of the core in the fact that the port number to achieve the conversion of public and private networks. For the plurality of IP addresses, a border router assigned to their external IP network, by using the different port and the external IP network to communicate, the NAT most typical mode of an application.
Public network ip: 191.4.4.1, network ip: 192.168.1.2/192.168.1.3.
Advantages:
Ø save public IP address.
When address overlap, provide solutions.
flexibility to connect to the public network.
in the network change is to avoid renumbering.
really hide the internal server IP address.
Disadvantages:
Ø address translation will increase the swap delay.
resulting in end to end IP can not be tracked.
cause some applications will not run properly.
Photos from the network.
TA: Madina
Reprinted: http://www.ie-lab.cn/