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What are different concepts of Network Address Translation (NAT)?

NAT or Network address Translation provides one–to–one translation of the IP addresses. This is usually called as the basic NAT or one–to–one NAT.
In this type, only the following things that include the IP address can be changed:

  • IP header checksum
  • Any other checksum of higher level

– The rest of the packet is not changed for the functionality of TCP and UDP.
– For the other higher level protocols some additional translation is required.
– Basic NATs are used for establishing an interconnection between the two IP networks whose addressing is compatible.
– It’s a usual thing to keep the whole IP address space hidden that consists of private IP addresses in some other address space and behind a single IP address or group of IP addresses.
– The address space here is usually public.
– The higher level info of the ports must be altered by one–to–many NAT in order to keep the handling of the packets unambiguous in the outgoing communications.
– Also, a translation table should be maintained for the correct translation of the return packets.
– This is usually termed as the NAPT or network address and port translation. Some other names are:

  • Port address translation or PAT
  • IP masquerading
  • NAT overload
  • Many – to – one NAT and so on.

– Being the most common type, this is usually called NAT.
– The communication is enabled via the router on the origination of a conversation in the masqueraded network.
– This happens because by this the translation tables are established.
– Web browser operating in a masqueraded network can access an external website but a web site in the masqueraded network cannot be accessed by an external or outside browser.
– Network administrator is empowered by most of the NAT devices to configure the entries in the translation table to be used permanently.
– This is what that is called the ‘static NAT’ or sometimes also as the port forwarding.
– Earlier, NAT was a popular tool for the alleviation of the consequences that occur because of the IPv4 address exhaustion.
– It is now a common as well as an indispensable part of the routers that are used in office and home internet connections.
– A number of systems using NAT do so for enabling several hosts on one private network for accessing internet via one IP address.

There are some serious drawbacks of using NAT concerning the quality of the internet connection.
– It requires a lot of careful attention for its proper implementation.
– The IP model of end–to–end connectivity is broken by almost all types of NAT across the network.
– It becomes difficult in accepting the incoming signals for the systems behind NAT because of the NAPT.
– As a consequence of this, some NAT traversal methods have to be devised for alleviating these problems.

NAT Hair-pinning or NAT Reflection or NAT Loop back

– With this feature the user from inside the LAN is able to make a connection with its own address.
– This NAT concept is particularly useful in case of a website with domain hosted at that address.
– It resolves the domain name if a custom DNS server is not being used.

Visibility of Operation

– In NAT operations, transparency is maintained with all the hosts, be they internal or external.
– The internal host has the awareness about the TCP/ UDP port and true IP address of the host.
– The internal host may use the NAT device as a default gateway.
– On the other hand, the external host has knowledge of only the NAT device’s public IP address and the port that communicates on behalf of the internal host.

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