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Is it possible to connect my private network to the ISP router without a Network Address Translator (NAT) feature enabled on my router? As I understand, in a single-homed scenario connection to ISP, ISP router defines a static route on its router and I need to define a default gateway on our router and advertise this gateway to all members of our network.

I think without the NAT feature on my router, this scenario doesn't work, no?

A.A
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3 Answers3

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Without NAT, you can't use private IPv4 addresses in your network (with Internet connectivity). You'll need to get a sufficient IP address range from your ISP, at least one address for each device with Internet access.

You'll still need a router but it could route public-to-public without any need of NAT. Note that this is the standard way to connect IPv6.

Any private-to-public or public-to-private routing requires NAT for IPv4. (Alternatively, a proxy could be used for many protocols but from the addressing perspective, there isn't much difference.)

Zac67
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There is absolutely no need to use NAT or private addresses to connect a network to the Internet. NAT was only designed as a short term solution to work around the lack of IPv4 addresses (and yes: NAT is old. People noticed that we are running out of vintage IP (IPv4) ages ago).

There are two different scenarios, it doesn't matter if they are vintage IP or IP (IPv6)

a) Your ISP provides you with a large enough range of public IP addresses. BGP might be used here but it's not necessary.

b) You have your own public IPs. Here the use of BGP is more common but also not absolutely necessary.

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There are two main differences between a "with NAT" and a "Without NAT" scenario.

  1. With NAT you can use anything from the huge range of private IP addresses, without it you are limited to the public addresses you are allocated.
  2. To operate without NAT, your ISP must allocate a block of IPs and route it to your router.

How hard this will be depends on how big a block you want and what type of internet connection you are buying. If you are buying a broadband package from a cheap ISP then don't expect to get an IP block. Some more expensive broadband providers will provide blocks, and if you are buying a leased-line or similar service then a block would be expected.

(the above all applies for IPv4, for IPv6 even the smallest customers tend to get blocks, unfortunately they are sometimes dynamic blocks which makes them rather more annoying to use)

Peter Green
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