IPv6: No NAT Is Good NAT

Curtis Franklin Jr., Executive Editor | 6/8/2011 | 9 comments

Curtis Franklin Jr.
Welcome to World IPv6 Day. I hope yours is going better than mine -- I have a UTM from a vendor that's lagging woefully behind the IPv6 curve -- but I've yet to hear of any major problems due to the global testing taking place. That's a good thing, but I don't come here today to praise IPv6, but to worry about it. That's because the transition from IPv4 to IPv6 has some potentially serious security "gotchas," and they start with three little letters: NAT.

Network Address Translation (NAT) is the crutch that has kept IPv4 hobbling along as well as it has for the last few years. With NAT, a single IP address on the outside interface of the router is matched to a whole network's worth of IP addresses on the inside interface. Translating requests and traffic between the one and the many is handled by the router itself. It's a decent way to magnify the address space of the Internet, but some folks have decided it's good for more than addressing -- it's also a security feature. That has led to the opening line of many a Router Guy's speech to the masses: NAT is NOT Security.

There are a surprising number of folks who will tell you that a NAT network is inherently more secure because the address of each machine is not directly exposed on the Internet. That's true, if you assume that anyone attacking your network is lazy, stupid, and incompetent. Think of it as the electronic equivalent of hanging one of those fake "security system installed" decals in your car window, and you're on the right track. Reaching through the router to a machine on the inside is trivial once you've installed a piece of software delivered via email or web application, so you're really only stopping some fairly basic port scans. But that doesn't stop a lot of companies from including it as part of the "security program."

The security aspect of NAT, such as it is, may disappear completely with IPv6. Why? Since IPv6 has a sufficiently large address space to give every user about as many addresses as exist on the Internet today, NAT just isn't necessary. That means network designers won't be able to include it as part of their security designs (that's a good thing) and will have to deal with each machine having an address that's exposed to the Internet as a whole.

It would be easy, or at least easier, to be confident in the brave new world of NAT-less security if we could be confident in the IPv6 implementations themselves. Unfortunately, there are indications that many of the networking stacks (the software that binds the addressing to the physical interface) for IPv6 and IPv6 transition are not as robust as we might hope. The combination of new internal/external network dynamic and immature network stacks could lead to serious security issues for companies making the transition, if they don't pay special attention to the issues.

The big news in this for IT shops is two-fold. First, if you're depending on NAT for any sort of security, stop it -- now. Next, when you're planning the transition to IPv6, be sure to prepare for vulnerabilities in networking components you've come to think of as stable -- components like the TCP/IP stack. Those two actions alone will go a long way toward keeping your network more security during the long transition to IPv6.

View Comments: Newest First | Oldest First | Threaded View
CurtisFranklin   IPv6: No NAT Is Good NAT   6/9/2011 3:39:03 PM
Re: No NAT Is Good NAT
@Sane, you're right: organizations large enough to employ a decent router jockey will be in good shape. I think that this is going to wreak havoc in the mid-market, the kind of shop that has an IT staff of four or five generalists to handle everything. They're either going to have to up their game on the routing and directory administration front, get a good contractor in to change their address-space architecture, or become roadkill.
SaneIT   IPv6: No NAT Is Good NAT   6/9/2011 3:00:21 PM
Re: No NAT Is Good NAT
@Curtis - Most companies big enough to worry about NAT are proxying traffic for things like web surfing from desktops so I'm not sure why they would think that IPv6 means that they have to make things like desktops accessable from outside their own network.  Anyone working at a level that is comfortable talking about routing will instintively know just how easy it is to blackhole inbound traffic for an entire subnet and I don't suspect that outbound proxies will vanish either.  Personally I'm looking forward to the day that I can assign 50 publically accessable addresses to a single web server instead of everything depending on host headers.
CurtisFranklin   IPv6: No NAT Is Good NAT   6/9/2011 12:48:45 PM
Re: No NAT Is Good NAT
@SaneIT, one of the things that many people feel is that the only choices are NAT and every device open to the Internet. More discussion about the advantages (necessity?) of directory systems and intelligent gateways is necessary before we see wide-spread adoption of IPv6 at the medium-sized business level. There are a lot of reasons to like IPv6, but a lot of mis-information to cut through before it's embraced by everyone.
CurtisFranklin   IPv6: No NAT Is Good NAT   6/9/2011 12:41:59 PM
Re: NAT-less
@Gigi, you're right: device traceability is one of the things that has privacy proponents very worried, indeed. There has been a great deal of discussion about how IPv6 will affect networks down around layers 2 and 3, but relatively little discussion about the impact the change will have farther up the ISO stack. As we get closer to large-scale implementation, those discussions must happen if we're to avoid some truly unfortunate consequences.
SaneIT   IPv6: No NAT Is Good NAT   6/9/2011 8:53:13 AM
Re: No NAT Is Good NAT
I have to agree, NAT is handy but it's rarely 100% necessary and IPv6 will put an end to those rare cases where it's the best option.  One thing that I haven't heard much is how IPv6 will affect network security as a whole.  I highly doubt that any company out there is going to open the flood gates and allow bi-directional traffic to every address on their network, but I do wonder if companies are going to start auditing route tables a little more closely now.  In the long term I think it will make well managed networks more secure since it removes a layer of complexity on most networks.
Gigi   IPv6: No NAT Is Good NAT   6/9/2011 3:47:51 AM
Re: NAT-less
In IPv 6 we have to enable the Privacy extensions manually, other than Windows platform. Since it’s not happening as default, system administrators have to take acre about this; otherwise the unique MAC address will exposed to internet and makes devices traceable. From one of the analysis report it seems that because of this issue, migration from IPV4 to 6 caused criticism of data privacy in various countries.
Gigi   IPv6: No NAT Is Good NAT   6/9/2011 3:47:47 AM
Re: NAT-less
In IPv 6 we have to enable the Privacy extensions manually, other than Windows platform. Since it’s not happening as default, system administrators have to take acre about this; otherwise the unique MAC address will exposed to internet and makes devices traceable. From one of the analysis report it seems that because of this issue, migration from IPV4 to 6 caused criticism of data privacy in various countries.
LadyIT   IPv6: No NAT Is Good NAT   6/8/2011 8:07:08 PM
Re: NAT-less
@cvargas: but with the advent of Active Directory this should have been on the table for removal.

Couldn't agree more. And even though I've been away from day to day network security for a bit, must admit I'm surprised that some admins would still be relying on NAT for security. This was a bit of an eye-opener, and makes me wonder how many orgs are still doing so...
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cvargas   IPv6: No NAT Is Good NAT   6/8/2011 5:38:49 PM
Anyone who has been responsible for network security should have gotten rid of NAT years ago. This is especially true for Windows domain structures. In the days of peer to peer networking for small environments, NAT was a godsend because it allowed for easy connectivity between computers, but with the advent of Active Directory this should have been on the table for removal. By continuing to run NAT, admins basically were not thinking security and were thinking ease. There will always be a need for name to IP translation. DNS is not only quicker and has less security concerns but is far more easy to maintain. My vote is to say NAT should not be considered in any size network.

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