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Deadwood update

 

March 20 2012

In today's blog entry, I describe this month's Deadwood update, as well as discuss why IPv6 should have NAT66 support.

Deadwood update

When looking at the source code of DwCompress.c, I discovered that input validation was not always done. I have updated DwCompress.c to have more input validation.

It can be downloaded here:

http://www.maradns.org/deadwood/snap/
I plan to work on MaraDNS/Deadwood again one day next month, after the 20th, unless a critical security bug is found.

NAT66 will be needed

There is a religious belief among some proponents of IPv6 (a proposed method of increasing the network numbers the internet has, which we will undoubtedly make standard during the 2010s because we're running out of numbers in the current internet) that NAT--the process of converting a single routable IP like 199.167.196.104 in to multiple local private IPs like 192.168.1.196--should never be done.

Indeed, the expansion of IPs that IPv6 gives us removes one reason to have NAT. But people who dismiss NAT as being "evil" ignore some of the other benefits of NAT:

  • NAT causes a network to have a built-in firewall. Yes, it is possible to have a firewall without NAT. However, NAT's natural default configuration is one where computers on an internal network are invisible from the big bad internet.

  • NAT hides the network topology from external attackers.

  • NAT allows one to add as many IPs as needed to one's internal network without needing to get IPs from one's ISP. Anti-NAT fanatics claim that ISPs will always give customers a generous number of ISPs (keep in mind that a /96 in IPv6 is as big as all of today's internet; IPv6 is huge); these claims ignore the fact that, without NAT, you can only have a large internal network if your ISP lets you. Indeed, low-cost hosting providers with IPv6 today sometimes only give their customers 16 IPv6 IPs.

  • NAT allows one to change ISPs or use multiple ISPs at the same time without needing to revise the numbering of their internal network. Changing IPs on even a small network is non-trivial; I had to spend a good part of Sunday afternoon revising my home network to use a /16 (65,000 IPs) instead of a /24 (256 IPs), and this network only has a handful of computers on it. (Since you asked: I use a lot of virtual machines for my work and it's logistically simpler to give each computer their own /24 than to split up a single /24).

I am not ignoring the disadvantages of NAT: It makes peer-to-peer applications, such as Skype, harder to implement. However, implementing peer-to-peer through NAT is a solved problem, and making services on an internal network available to the external internet is trivial with most NAT firewalls.

LWN recently had an interesting discussion about IPv6 and NAT.

(NAT44, for the record, is the technology used in most of today's internet, allowing a single IPv4 IP to represent a number of internal machines on a network. I remember when NAT44 was called "IP masquerade". NAT66 is the technology to allow a small pool of IPv6 IPs to represent a large number of internal machines on a network. NAT64 and NAT46 are something else entirely.)

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