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What are features of Dynamic NAT? What exactly does it do?

Dynamic NAT used for mapping an unregistered IP address to a particular registered IP address selected from among a bunch of registered IP addresses.
Overloading is a kind of dynamic NAT for mapping more than one unregistered IP addresses to one registered IP address through different ports.

Features of Dynamic NAT

– The major feature of this type of NAT is that it establishes connections from inside out i.e., from private to public network.
– It requires a pool of IP addresses to be used while making the outbound connections.
– A unique public IP address is assigned to each of the connections.
– This number of public addresses equals the max number of connections made simultaneously.
– Another feature of dynamic NAT is that it shares similarity with the one – to – one correspondence among the addresses.
– Using dynamic NAT a communication to external network can be made via a dynamic NAT address.
– It is more suitable to be used in large networks unlike static NAT that is more common in the smaller networks.
– Dynamic NAT is much better for the networks with high complexity.
– Dynamic NAT does one-to–many mapping.

How is Dynamic NAT used?

– Using Dynamic NAT, an internal IP address can be mapped to a real IP address but not in a static way i.e., when internal host connects with the internet, their addresses may remain same but they are likely to change.
– This happens for every session.
– These addresses are taken from an IP address pool that has already reserved for the public network by our ISP.
– No translations take place until traffic requiring translation is received by the router.
– These translations unlike static translations have a timeout period.
– When the timeout occurs, these translations are removed from the translation table and are made available for the other hosts.
– Consider a router that has been configured for performing dynamic NAT.
– Four public IP addresses have been requested from the ISP.
– These addresses will be mapped dynamically by the router to the internal hosts.
– In each of these sessions, the workstation sends a request to the internet and is assigned some public address.
– This mapping remains until the end of this session.
– A special NAT timeout is used for configuring the router.
– When this timeout occurs, this mapping expires and is reused by another internal host.
– If the users log off, new mappings will be created by the router when they again log in and launch browser.

– Many of the rules that hold good for static NAT also work for dynamic NAT but with few changes.
– The actual process is same and independent of the device that is used.
– The IP addresses in the pool of the router are reserved by the ISP from the network and so no other host on the network which means that no other device or host except the router itself can use it.
– The dynamic mapping thus created will be there only for that session.
– The timeout period is set differently for every NAT device and transport protocol (TCP/ UDP).
– The NAT device being used defines the ability of modifying these timeouts.

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