Asterisk Tutorial 48 — Introducing NAT

Introducing Asterisk and Network Address Translation

Over the past couple of weeks we have received a large number of requests on our YouTube channel, asking us to do a tutorial on Network Address Translation (NAT for short) and NAT tables. Which is why, in this the first in a series of Introducing Asterisk Tutorials on the subject, Mathias gets to grips with explaining NAT and helping us understand what the technology is, what it does, how it works and why we need it.

Moreover, as we referred a lot to NAT and NAT tables during ourIntroducing SIP tutorials, we felt it was only fair to put together a more detailed NAT explanation. What’s more, this tutorial provided Mathias with the perfect opportunity to show off his artistic talents — so sit back, relax and admire.

What is Network Address Translation

As the name Network Address Translation suggests, NAT is the method used to translate a private network IP address into a public IP address. your internal company LAN network in order to access a public network, such as the internet. In an ideal scenario, we would not actually need NAT. However, as many private networks use the same internal IP address structure, the question then becomes how to identify and route access requests and responses correctly within the public domain.

Source vs Destination NAT

Network Address Translation can be performed in both directions. This functionality is known as Source NAT and Destination NAT.

In essence, Source NAT is the translation of an internal private network IP address into a public address and is used when internal users access external networks such as the internet. Using Source NAT is the most common usage and it ensures that the private network address is remains masked, i.e. hidden behind the public IP address.

Destination NAT is effectively the opposite to Source NAT in that this methodology is utilised to translate a public IP (destination) address to a private address. This technique is often used to map a single public IP address to several private IP addresses, i.e. to enable access to a web based service such as a gaming server etc.

Source NAT and Destination NAT are considered to be the two main types of NAT. However, there are other methodologies, but in the main they can be categorised into either Source or Destination NAT.

More Info

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Until next time — Happy VoIPing!

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