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Network Address Translation (NAT)
Course: Systems Programming (01:198:214)
23 Documents
Students shared 23 documents in this course
University: Rutgers University
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Network Address Translation (NAT)
While IPv6 was inspired by the worry that rising IP usage would cause the address space to run
out, another method has gained popularity as a means of preserving IP address space. Network
address translation (NAT) is that technology, and it is widely used, which is one of the key
reasons why IPv6 deployment is still in its infancy. Although some people consider NAT to be
"architecturally impure," it is an unavoidable reality of networking life. All hosts that might
communicate with one another over the Internet do not necessarily need to have globally unique
addresses, which is the primary tenet of NAT. Instead, a host might be given a "private address"
that is distinct only inside a more constrained context—for example, the corporate network
where the host is located—but is not necessarily globally unique.
Since the ARPANET was given the class A network number 10, which is no longer in use as a
globally unique address, it is frequently used for this purpose. A locally unique address is
sufficient as long as the host exclusively communicates with other hosts within the corporate
network. It uses a NAT box, a device that can translate from the host's private address to a
globally unique address that is assigned to the NAT box, to communicate with hosts outside the
corporate network. Since only a small portion of the hosts in the corporation are likely to require
the services of the NAT box at any given time, the NAT box may be able to function with a
significantly smaller pool of globally unique addresses than would be needed if each host in the
organization had a unique address.
Therefore, we may envision a NAT box accepting IP packets from a host inside the business and
transforming the IP source address from a private address (let's say, 10.0.1.5) to a globally unique
address (say, 171.69.210.246). When packets sent to 171.69.210.246 from a distant host return,
the NAT box changes the destination address to 10.0.1.5 and sends the packet on to the host. The
main problem with NAT is that it violates the IP service model's fundamental tenet that every
node has a globally unique address. It turns out that this presumption is used by many apps and
protocols. IP addresses are included in the messages of some protocols that operate via IP, such
as application protocols like FTP. If the higher-layer protocol is to function effectively, these
addresses must also be translated by a NAT box, making NAT boxes significantly more
sophisticated than basic IP header translators. They could end up having to comprehend an
increasing number of higher-layer protocols. This thus makes it difficult to deploy new
applications. Even more critical is the fact that NATs make it challenging for an outside device to
initiate a connection to a device on the private side of the NAT since there isn't a public address
to which to submit the connection request in the absence of an established mapping in the NAT
device. The deployment of numerous applications, including Voice over IP, has been made more
difficult by this condition.
Although it is safe to claim that networks would function better without NAT, its abolition
appears unlikely. Although widespread adoption of IPv6 would likely be beneficial, NAT is now
well-liked for a variety of other reasons outside of its original use. If your entire internal network
uses (private) IP addresses that have nothing to do with the provider's address space, for instance,
switching providers becomes simpler. A measure of defense against straightforward attacks is
provided by the fact that NAT boxes' addresses are not globally significant, even though they
