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Comment by aragilar | Hacker News Reader

A NAT is part of a firewall, not a separate thing, so if the firewall is misconfigued, then your NAT may not be working either.

On not running out of (private) IPs, I guess you've never had the fun of having to deal with overlapping ranges (because it isn't the number of IPs that's the issue, it's how the ranges are allocated). While this can still happen on IPv6, there are so many more subnets that this is far less likely.

Also, a key thing that IPv6 makes obvious (which is also true to some extent of IPv4, but that most systems try to avoid showing) is that each link can have multiple IPs (there will be at least one link-local address), and so while your ISP can provide you a public range, you don't need to use it if you do not want to, you can always use an Unique Local Address (ULA - https://en.wikipedia.org/wiki/Unique_local_address), which reduce the chance of overlapping ranges.

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Why do you think NAT is part of a firewall? NAT and firewall are two completely separate things that can exist independently of each other.

Also overlapping ranges are an orthogonal issue that can occur with IPv6 private network range as well.

IPv6 brings not only bigger address range but also a big bag of other things that one cannot ignore, are complicated and which are often a source of problems. That's why people stick with IPv4 even at the cost of NAT, because the number of things they have to care about is much smaller.

> NAT and firewall are two completely separate things that can exist independently of each other.

This is kind of like saying that web browsers don't have to have a graphical interface. Or that a web browser doesn't necessarily support HTTPS. It's correct, but not practically correct.

The reality is that essentially all NAT software you'll actually encounter will be integrated into a stateful firewall because the two systems share so many functions that most projects and products that do one will also do the other. If you have a system with NAT set up and there is no packet filtering, it's most often because you've intentionally gone and disabled all the packet filtering, not because you need separate software for it.

It is important to understand that NAT doesn't have any inherent security to it, but criticizing people for talking like NAT is a feature built into firewalls when NAT is overwhelmingly a feature built into firewalls is a pretty unfair reading when we're talking about general deployments. Even with the technical audience of HN, we're not discussing carrier grade NAT here or other highly specialized or exceptional deployments.

SNAT absolutely has intrinsic features that are utilized for security purposes.

This isn't to disagree with your main point. Many people in this topic have an oddly narrow definition "firewall" that tends to fall along the lines of "whatever makes me right and you wrong".

A statefull SNAT implementation itself has most of the characteristics of a "firewall".

> SNAT absolutely has intrinsic features that are utilized for security purposes.

Yes, but those features aren't there because they're security features. They're incidental to how NAT functions. It's not inherently secure. The intention of the design is to permit hosts on a network that is not Internet-routable to be able to send traffic that is Internet-routable. That's not a security feature. That's allowing traffic to pass that would ordinarily get black-holed.

> A statefull SNAT implementation itself has most of the characteristics of a "firewall".

Sure, but you should recognize that that's the same as saying a stateful SNAT implementation is an incomplete stateful firewall.

If your goal is to use private addresses, you should use NAT. The point is that if your goal is security, then you should configure a firewall.

Don't expect software that isn't designed to provide you security to provide you with any security.

SNAT is often a feature built on a network stack that also provides other "firewall" functionalities like filtering packets. Configuring SNAT is configuring a firewall? Or is only dropping packets a firewall? Or does the device need "firewall" printed on it? Does a device that has "firewall" printed on it still count as a firewall if it's not configured to filter packets? What type of filtering makes it a firewall? If an SNAT implementation drops packets is it a firewall? Is a linux/windows/bsd box with multiple interfaces a firewall? What if I slap "firewall" label on the box; a firewall now?

SNAT can be used to mask source IP and that can absolutely be utilized strategically as a layer of "security".

If your ISP delivered you a packet with a destination address of 192.168.0.5, there's a good chance your router would deliver it to that device without consulting the port forwarding table. In this way, NAT isn't a firewall and you're relying on your ISP's routing policy as your actual firewall.

If my ISP sent me a billion dollars I would be a billionaire.

What's represents a "good chance" the router is so grossly misconfigured as to allow inbound traffic no destined for the IP assigned to the WAN interface to be routed to one of the internal interfaces? I wouldn't be surprised, but what's a "good chance"? Is there data on this?

A typical, correctly configured SNAT implementation would most likely have the characteristics commonly attributed to a "firewall". An incorrectly configured network device may not have the characteristics commonly attributed to a "firewall", regardless of its ability to actually inspect and drop packets(which just about every commonly used OS network stack can do out of the box).

But even an SNAT implementation without typical "firewall" characteristics has intrinsic characteristics related to security; such as source IP masking. Which doesn't even need to be private.

> when NAT is overwhelmingly a feature built into firewalls

This is just not correct. NAT and firewall are simply orthogonal concepts and can and often are deployed separately. A simple example is your average small SOHO router, which usually has NAT but quite a lot of them lack a firewall.

> if the firewall is misconfigued, then your NAT may not be working either.

But in that case, it's very obvious because your access to the WAN side of your router won't work from anywhere except the router itself.

I like this "fail-secure" nature of NAT. If your firewall fails on a network with globally-routable IPv6 addresses, it might not be so obvious as traffic might still flow through.

It provides no security by itself. There have been (and still are) countless vulnerable Internet reachable NAT routers which can easily be exploited to provide access to the whole private network behind it. NAT by itself can't be relied on to provide any security – you need correctly configured firewalls for that. An ISP provider might provide a sensibly configured firewall with the home router, but they may also be operating an easily exploitable backdoor into your private network.

Practically speaking, even without any firewall, NAT provides some level of security. If I can't route to your network, I can't access it. Yes, theoretically someone may establish a route to an RFC-1918 address block across the Internet or within your ISP, but doing so without ISP cooperation is unlikely. To say it is "easily" exploitable is an over-exaggeration.

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