I hope IPv6 *never* catches on
(Temporal note: this article was written a few days ago and then
This year, like every year, will be the year we finally run out of IPv4
addresses. And like every year before it, you won't be affected, and you
won't switch to IPv6.
I was first inspired to write about IPv6 after I read an article by Daniel
J. Bernstein (the qmail/djbdns/redo guy) called The IPv6 Mess. Now, that
article appears to be from 2002 or 2003, if you can trust its HTTP
Last-Modified date, so I don't know if he still agrees with it or not. (If
you like trolls, check out the recent reddit
commentary about djb's article.) But 8 years later, his article still
strikes me as exactly right.
Now, djb's commentary, if I may poorly paraphrase, is really about why it's
impossible (or perhaps more precisely, uneconomical, in the
sense that there's a chicken-and-egg problem preventing adoption) for IPv6
to catch on without someone inventing something fundamentally new. His
point boils down to this: if I run an IPv6-only server, people with IPv4
can't connect to it, and at least one valuable customer is *surely* on IPv4.
So if I adopt IPv6 for my server, I do it in addition to IPv4, not in
exclusion. Conversely, if I have an IPv6-only client, I can't talk to
IPv4-only servers. So for my IPv6 client to be useful, either *all* servers
have to support IPv6 (not likely), or I *must* get an IPv4 address, perhaps
one behind a NAT.
In short, any IPv6 transition plan involves *everyone* having an IPv4
address, right up until *everyone* has an IPv6 address, at which point we
can start dropping IPv4, which means IPv6 will *start* being useful. This
is a classic chicken-and-egg problem, and it's unsolvable by brute force;
it needs some kind of non-obvious insight. djb apparently hadn't seen any
such insight by 2002, and I haven't seen much new since then.
(I'd like to meet djb someday. He would probably yell at me. It would be
Still, djb's article is a bit limiting, because it's all about why IPv6
physically can't become popular any time soon. That kind of argument
isn't very convincing on today's modern internet, where people solve
impossible problems all day long using the unstoppable power of "not SQL",
Ruby on Rails, and Ajax to-do list applications (ones used by breakfast
No, allow me to expand on djb's argument using modern Internet discussion
Top 10 reasons I hope IPv6 never catches on
Just kidding. No, we're going to do this apenwarr-style:
What I hate about IPv6
Really, there's only one thing that makes IPv6 undesirable, but it's a
doozy: the addresses are just too annoyingly long. 128 bits: that's
16 bytes, four times as long as an IPv4 address. Or put another way, IPv4
contains almost enough addresses to give one to each human on earth;
IPv6 has enough addresses to give 39614081257132168796771975168 (that's
2**95) to every human on earth, plus a few extra if you really must.
Of course, you wouldn't really do that; you would waste addresses to make
subnetting and routing easier. But here's the horrible ironic part of it:
all that stuff about making routing easier... that's from 20 years ago!
Way back in the IETF dark ages when they were inventing IPv6 (you know it
was the dark ages, because they invented the awful will-never-be-popular
IPsec at the same time), people were worried about the complicated hardware
required to decode IPv4 headers and route packets. They wanted to build the
fastest routers possible, as cheaply as possible, and IPv4 routing tables
are annoyingly complex. It's pretty safe to assume that someday, as the
Internet gets more and more crowded, nearly every single /24 subnet in IPv4
will be routed to a different place. That means - hold your breath - an
astonishing 2**24 routes in every backbone router's routing table! And
those routes might have 4 or 8 or even 16 bytes of information each! Egads!
That's... that's... 256 megs of RAM in every single backbone router!
Oh. Well, back in 1995, putting 256 megs of RAM in a router sounded like a
big deal. Nowadays, you can get a $99 Sheevaplug with twice that. And let
me tell you, the routers used on Internet backbones cost a lot more than
It gets worse. IPv6 is much more than just a change to the address length;
they totally rearranged the IPv4 header format (which means you have to
rewrite all your NAT and firewall software, mostly from scratch). Why?
Again, to try to reduce the cost of making a router. Back then, people were
seriously concerned about making IPv6 packets "switchable" in the same way
ethernet packets are: that is, using pure hardware to read the first few
bytes of the packet, look it up in a minimal routing table, and forward it
on. IPv4's variable-length headers and slightly strange option fields made
this harder. Some would say impossible. Or rather, they would, if it were
Since then, FPGAs and ASICs and DSPs and microcontrollers have gotten a
whole lot cheaper and faster. If Moore's Law calls for a doubling of
transistor performance every 18 months, then between 1995 and 2011 (16
years), that's 10.7 doublings, or 1663 times more performance for the price.
So if your $10,000 router could route 1 gigabit/sec of IPv4 in 1995 - which
was probably pretty good for 1995 - then nowadays it should be able to route
1663 gigabits/sec. It probably can't, for various reasons, but you know
what? I sincerely doubt that's IPv4's fault.
If it were still 1995 and you had to route, say, 10 gigabits/sec for the
same price as your old 1 gigabit/sec router using the same hardware
technology, then yeah, making a more hardware-friendly packet format might
be your only option. But the router people somehow forgot about Moore's
Law, or else they thought (indications are that they did) that IPv6 would
catch on much faster than it has.
Well, it's too late now. The hardware-optimized packet format of IPv6 is
worth basically zero to us on modern technology. And neither is the
simplified routing table. But if we switch to IPv6, we still have to pay
the software cost of those things, which is extremely high. (For
example, Linux IPv6 iptables rules are totally different from IPv4 iptables
rules. So every Linux user would need to totally change their firewall
So okay, the longer addresses don't fix anything technologically, but we're
still running out of addresses, right? I mean, you can't argue with the
fact that 2**32 is less than the number of people on earth. And everybody
needs an IP address, right?
Well, no, they don't:
The rise of NAT
NAT is Network Address Translation, sometimes called IP Masquerading.
Basically, it means that as a packet goes through your router/firewall, the
router transparently changes your IP address from a private one - one reused
by many private subnets all over the world and not usable on the "open
internet" - to a public one. Because of the way TCP and UDP work, you can
safely NAT many, many private addresses onto a single public address.
So no. Not everybody in the world needs a public IP address. In fact,
*most* people don't need one, because most people make only outgoing
connections, and you don't need your own public IP address to make an
By the way, the existence of NAT (and DHCP) has largely eliminated another
big motivation behind IPv6: automatic network renumbering. Network
renumbering used to be a big annoying pain in the neck; you'd have to go
through every computer on your network, change its IP address, router, DNS
server, etc, rewrite your DNS settings, and so on, every time you changed
ISPs. When was the last time you heard about that being a problem? A long,
long time ago, because once you switch to private IP subnets, you virtually
never have to renumber again. And if you use DHCP, even the rare mandatory
renumbering (like when you merge with another company and you're both using
192.168.1.0/24) is rolled out automatically from a central server.
Okay, fine, so you don't need more addresses for client-only machines. But
every server needs its own public address, right? And with the rise of
peer-to-peer networking, everyone will be a server, right?
Well, again, no, not really. Consider this for a moment:
Every HTTP Server on Earth Could Be Sharing a Single IP Address and You Wouldn't Know The Difference
That's because HTTP/1.1 (which is what *everyone* uses now... speaking of
avoiding chicken/egg problems) supports "virtual hosts." You can connect to
an IP address on port 80, and you provide a Host: header at the beginning of
the connection, telling it which server name you're looking for. The IP you
connect to can then decide to route that request anywhere it wants.
In short, HTTP is IP-agnostic. You could run HTTP over IPv4 or IPv6 or IPX
or SMS, if you wanted, and you wouldn't need to care which IP address your
server had. In a severely constrained world, Linode or Slicehost or Comcast
or whoever could simply proxy all the incoming HTTP requests to their
network, and forward the requests to the right server.
(See the very end of this article for discussion of how this applies to
Would it be a pain? Inefficient? A bit expensive? Sure it would. So was
setting up NAT on client networks, when it first arrived. But we got used
to it. Nowadays we consider it no big deal. The same could happen to
What I'd expect to happen is that as the IPv4 address space gets more
crowded, the cost of a static IP address will go up. Thus, fewer and fewer
public IP addresses will be dedicated to client machines, since clients
won't want to pay extra for something they don't need. That will free up
more and more addresses for servers, who will have to pay extra.
It'll be a *long* time before we reach 4 billion (2**32) server IPs,
particularly given the long-term trend toward more and more (infinitely
proxyable) HTTP. In fact, you might say that HTTP/1.1 has successfully
positioned itself as the winning alternative to IPv6.
So no, we are obviously not going to run out of IPv4 addresses. Obviously.
The world will change, as it did when NAT changed from a clever idea to a
worldwide necessity (and earlier, when we had to move from static IPs to
dynamic IPs) - but it certainly won't grind to a halt.
It is possible do do peer-to-peer when both peers are behind a NAT.
Another argument against widespread NATting is that you can't
run peer-to-peer protocols if both ends are behind a NAT. After all, how
would they figure out how to connect to each other? (Let's assume
peer-to-peer is a good idea, for purposes of this article. Don't
just think about movie piracy; think about generally improved distributed
database protocols, peer-to-peer filesystem backups, and such.)
I won't go into this too much, other than to say that there are already
traversal protocols out there, and as NAT gets more and more annoyingly
mandatory, those protocols and implementations are going to get much better.
Note too that NAT traversal protocols don't have a chicken-and-egg problem
like IPv6 does, for the same reason that dynamic IP addresses don't, and NAT
itself doesn't. The reason is: if one side of the equation uses it, but
the other doesn't, you might never know. That, right there, is the
one-line description of how you avoid chicken-and-egg adoption problems.
And how IPv6 didn't.
IPv6 addresses are as bad as GUIDs
So here's what I really hate about IPv6: 16-byte (32 hex digit) addresses
are impossible to memorize. Worse, auto-renumbering of networks,
facilitated by IPv6, mean that anything I memorize today might be totally
IPv6 addresses are like GUIDs (which also got really popular in the 1990s
dark ages, notably, although luckily most of us have learned our lessons
since then). The problem with GUIDs are now well-known: that is, although
they're globally unique, they're also totally unrecognizable.
If GUIDs were a good idea, we would use them instead of URLs. Are URLs
perfect? Does anyone love Network Solutions? No, of course not. But it's
1000x better than looking at http://b05d25c8-ad5c-4580-9402-106335d558fe and
trying to guess if that's *really* my bank's web site or not.
The counterargument, of course, is that DNS is supposed to solve this
problem. Give each host a
GUID IPv6 address, and then just
map a name to that address, and you can have the best of both worlds.
Sounds good, but isn't actually. First of all, go look around in the
Windows registry sometime, specifically the HKEY_CLASSES_ROOT section. See
how super clean and user-friendly it isn't? Barf. But furthermore, DNS on
the Internet is still a steaming pile of hopeless garbage. When I bring my
laptop to my friend's house and join his WLAN, why can't he ping it by name?
Because DNS sucks. Why doesn't it show up by name in his router control
panel so he knows which box is using his bandwidth? Because DNS sucks. Why
can the Windows server browse list see it by name (sometimes, after a random
delay, if you're lucky), even though DNS can't? Because they got sick of
DNS and wrote something that works. Why do we still send co-workers
hyperlinks with IP addresses in them instead of hostnames? Because the
fascist sysadmin won't add a DNS entry for the server Bob set up on his
DNS is, at best, okay. It will get better over time, as necessity dictates.
All the problems I listed above are mostly solved already, in one form or
another, in different DNS, DHCP, and routing products. It's certainly not
the DNS *protocol* that's to blame, it's just how people use it.
But still, if you had to switch to IPv6, you'd discover that those
DNS problems that were a nuisance yesterday are suddenly a giant fork
stabbing you in the face today. I'd rather they fixed DNS *before* making
me switch to something where I can't possibly remember my IP addresses
Server-side NAT could actually make the world a better place
So that's my IPv6 rant. I want to leave you with some good news, however: I
think the increasing density of IPv4 addresses will actually make the
Internet a better place, not a worse one.
Client-side NAT had an unexpected huge benefit: security. NAT is like
"newspeak" in Orwell's 1984: we remove nouns and verbs to make certain
things inexpressible. For example, it is not possible for a hacker in Outer
Gronkstown to even express to his computer the concept of connecting
to the Windows File Sharing port on your laptop, because from where he's
standing, there is no name that unambiguously identifies that port. There
is no packet, IPv4 or IPv6 or otherwise, that he can send that will arrive
at that port.
A NAT can be unbelievably simple-minded, and just because of that one
limitation, it will vastly, insanely, unreasonably increase your security.
As a society of sysadmins, we now understand this. You could give us all
the IPv6 addresses in the world, and we'd still put our corporate networks
behind a NAT. No contest.
Server-side NAT is another thing that could actually make life better, not
worse. First of all, it gives servers the same security benefits as clients -
if I accidentally leave a daemon running on my server, it's not
automatically a security hole. (I actually get pretty
scared about the vhosts I run, just because of those accidental holes.)
But there's something else, which I would be totally thrilled to see fixed.
You see, IPv4 addresses aren't really 32-bits. They're actually 48
bits: a 32-bit IP address plus a 16-bit port number. People treat them as
separate things, but what NAT teaches us is that they're really two parts of
the same whole: the flow identifier, and you can break them up any way you
The address of my personal apenwarr.ca server isn't 220.127.116.11; it's
18.104.22.168:80. As a user of my site, you didn't have to type the IP
(which was provided by DNS) or the port number (which is a hardcoded default
in your web browser), but if I started another server, say on port 8042,
then you *would* have to enter the port. Worse, the port number would be a
weird, meaningless, magic number, akin to memorizing an IP address (though
mercifully, only half as long).
So here's my proposal to save the Internet from IPv6: let's extend DNS to
give out not only addresses, but port numbers. So if I go to
www2.apenwarr.ca, it could send me straight to 22.214.171.124:8042. Or if I
ask for ssh.apenwarr.ca, I get 126.96.36.199:22.
Someday, when IPv4 addresses get too congested, I might have to share that
IP address with five other people, but that'll be fine, because each of us
can run our own web server on something other than port 80, and DNS would
transparently give out the right port number.
This also solves the problem with HTTPS. Alert readers will have noticed,
in my comments above, that HTTPS can't support virtual hosts the same way
HTTP does, because of a terrible flaw in its certificate handling.
someone might make a new version of the HTTPS standard without this terrible
flaw, but in the meantime, transparently supporting multiple HTTPS servers
via port numbers on the same machine eliminates the problem; each port can
have its own certificate.
(Update 2011/03/28: zillions of people wrote to remind me about SNI, an HTTPS
extension that allows it to work with vhosts. Thanks! Now, some of those
people seemed to think this refutes my article somehow, which is not true.
In fact, the existence of an HTTPS vhosting standard makes IPv6 even *less*
necessary. Then again, the standard doesn't work with IE6.)
This proposal has very minor chicken-and-egg problems. Yes, you'll have to
update every operating system and every web browser before you can safely
use it for *everything*. But for private use - for example, my personal ssh
or VPN or testing web server - at least it'll save me remembering stupid
port numbers. Like the original DNS, it can be adopted incrementally, and
everyone who adopts it sees a benefit. Moreover, it's layered on top of
existing standards, and routable over the existing Internet, so enabling
it has basically zero admin cost.
Of course, I can't really take credit for this idea. It's already been invented and
is being used in a few places.
Embrace IPv4. Love it. Appreciate the astonishing long-lasting simplicity
and resilience of a protocol that dates back to the 1970s. Don't let people
pressure you into stupid, awful, pain-inducing, benefit-free IPv6. Just
relax and have fun.
You're going to be enjoying IPv4 for a long, long time.
Syndicated 2011-03-27 02:00:38 (Updated 2011-03-29 02:13:30) from apenwarr - Business is Programming