Older blog entries for fraggle (starting at number 57)

IPv6

IPv6 is something that I've been interested in for a while; I was even employed to do some v6 porting work a few years ago. Unfortunately, even though it's been several years and address exhaustion is rapidly approaching, uptake remains slow.

As I see it there are several problems with IPv6 adoption:
  1. Software doesn't support it
  2. Hardware doesn't support it
  3. ISPs don't provide it

As these go, (1) isn't actually that big a problem now. A lot of the most important software already supports v6. Ubuntu/Debian seems to just work with IPv6 (and presumably other Linux distributions as well), and even Windows supports it as of Vista. Software packages like Firefox work out of the box.

(2) is still a big issue for a lot of hardware but I suspect that there's a lot of hardware now that supports it, but has it turned off (routers, etc). (3) is simply a fact; I haven't heard of any ISPs supporting v6, and I suspect a lot of that is dependent on (2).

6to4


6to4 (not to be confused with
6in4 or
6over4, thanks for the clear naming, guys), is in my opinion an excellent piece of engineering and exactly what is needed to fuel IPv6 adoption. It solves the hardware/ISP problems by tunneling v6 traffic over v4; however, the clever part about it is that it does this without the need to register an account with a tunnel provider or explicitly configure it. I first became aware of 6to4 when I heard that the Apple Extreme base station has it enabled by default, which I think demonstrates its potential; it's possible to circumvent the remaining hardware/ISP problems with IPv6 just by getting manufacturers of broadband routers to adopt 6to4.

With 6to4, tunnels are made opportunistically between v4 addresses, which means that if you have two machines using 6to4, they can communicate directly, without the overhead that routing through a third party would cause (If this sounds a bit pointless, consider that it means two machines both behind NAT gateways in the v4 world can have end-to-end connectivity
in the v6 world). Any other v6 data is sent to a magic anycast address that automatically routes v6 data to the closest v6 gateway.

With 6to4, a machine has an IPv6 address range that is derived from its public IPv4 address. For example, if your IPv4 address is 1.2.3.4, your IPv6 subnet range is 2002:0102:0304::/48. IPv6 traffic for that range automatically gets sent to that IPv4 address. What really happens
is that your 6to4-enabled broadband router assigns addresses from this range to machines on your home LAN.

Setting up 6to4


My DSL router doesn't support 6to4; however, I managed to work around this. My router does support port forwarding (actually, protocol forwarding in this case), and I have a Linux machine in my lounge that I use as a media centre/server.

The first step was to set up a rule on the router to forward 6to4 data to the server machine. I have a BT
Voyager
router which is helpfully quite flexible in this respect. 6to4 data is IP traffic with a protocol number of 41. From the router's command line interface, this did the job:

create nat rule entry ruleid 41416 rdr prot num 41 lcladdrfrom 192.168.1.6 lcladdrto 192.168.1.6

It was then a case of configuring the server to do 6to4. As it is running Ubuntu, I added this to /etc/network/interfaces:
iface tun6to4 inet6 v4tunnel
	address 2002:0102:0304::1
	netmask 16
	endpoint any
	local 192.168.1.6
	ttl 255
	remote 192.88.99.1
	post-up ip -6 route add 2000::/3 via ::192.88.99.1 dev tun6to4
	post-down ip -6 route flush dev tun6to4

auto tun6to4

A simple "sudo ifup tun6to4" and the tunnel device should come up. It should then be possible to ping IPv6 addresses:
$ ping6 ipv6.google.com
PING ipv6.google.com(2001:4860:a003::68) 56 data bytes
64 bytes from 2001:4860:a003::68: icmp_seq=1 ttl=61 time=53.8 ms
64 bytes from 2001:4860:a003::68: icmp_seq=2 ttl=61 time=52.5 ms
64 bytes from 2001:4860:a003::68: icmp_seq=3 ttl=61 time=45.5 ms
64 bytes from 2001:4860:a003::68: icmp_seq=4 ttl=61 time=51.5 ms


Routing



At this point, the server has IPv6 connectivity, but what I really want is every machine on the network to have it. So the next step is to set up the server as an IPv6 router.

To do this, other machines need to know that the server is a router and acquire IPv6 addresses. In IPv4, this is usually done with a DHCP server handing out addresses from a pool. Instead, with IPv6, routers advertise their address ranges, and the clients automatically construct an address. This is possible because of the vast address range in IPv6.

A package called radvd (router advertisement daemon) sends router advertisements. It's in the Debian package repository and very easy to configure. This is my /etc/radvd.conf file:
interface eth0
{
	AdvSendAdvert on;
	prefix 2002:0102:0304:face::/64
	{
		AdvOnLink on;
		AdvAutonomous on;
		AdvRouterAddr on;
	};
};

Notice that I've defined a subnet range for clients. The address range given by 6to4 is 2002:0102:0304::/48, while radvd assigns addresses in the 2002:0102:0304:face::/64 range. Next, I statically assign an address in this range in /etc/network/interfaces by adding this:
iface eth0 inet6 static
        address 2002:0102:0304:face::1
	netmask 64

Now the router advertisements are handing out v6 addresses to other machines on the network, and the server has an address within the subnet range to communicate with them. It's then just a matter of turning on routing. Add this to /etc/sysctl.conf:
net.ipv6.conf.all.forwarding=1
net.ipv6.conf.default.forwarding=1

Or to make it take effect immediately:
sudo sysctl net.ipv6.conf.all.forwarding=1
sudo sysctl net.ipv6.conf.default.forwarding=1

That's it! Here's the output from ifconfig on another machine on my network:
wlan0     Link encap:Ethernet  HWaddr 00:1c:10:63:63:d0
          inet addr:192.168.1.25  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2002:0102:0304:face:21c:10ff:fe63:63d0/64 Scope:Global
          inet6 addr: fe80::21c:10ff:fe63:63d0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7658 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7228 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4073660 (4.0 MB)  TX bytes:903010 (903.0 KB)

And here's Google IPv6:



Note that in the examples above, I've obscured my 6to4 address range to 2002:0102:0304::, to hide my IPv4 address, for privacy. If you want to follow my instructions, this needs to be replaced with your own public IPv4 address.

Syndicated 2009-03-20 22:03:27 from fragglet

Stock photos

BBC News' obsession with filling their articles with stock photos that contain no relevant information is reaching absurd extremes.

Syndicated 2009-02-13 13:07:45 from fragglet

9 Feb 2009 (updated 30 Sep 2010 at 10:37 UTC) »

ebay

Buying things on eBay became more fun once I started getting creative with the feedback that I leave for people.

Syndicated 2009-01-20 01:15:28 from fragglet

12 inch pianist

For anyone who doesn't get today's xkcd (I did, but there seem to be quite a few people who haven't heard that joke before).

Syndicated 2009-01-19 20:17:48 from fragglet

The Buddha Lounge

The Indian restaurant opposite my house, which was called The Natraj, has reinvented itself as a trendy bar, called "The Buddha Lounge". This is ironic on multiple levels.

Firstly, the Five precepts of Buddhism forbid the consumption of alcohol or intoxicating substances. Secondly, the more strict Eight precepts encourage followers to abstain from music and dancing, and also from all sexual activity (and the main purpose of these types of bar is basically to find willing sexual partners). Finally, followers also refrain from "luxurious places for sitting or sleeping", so even the "lounge" part is out.

What's next, the Jesus Casino?

Syndicated 2008-12-23 00:11:29 from fragglet

Does this make me an Internet star?

I was reading the Wikipedia article about Ken Silverman's PNGOUT, which is a program for creating optimised versions of PNG images. However, it was the screenshot in that article that intrigued me the most. Upon further investigation, it seems that a group of Wikipedia users have been running a minor contest amongst themselves to create the most optimised version possible of an image I originally uploaded three years ago.

It's really weird when you stumble across things like this.

Syndicated 2008-09-26 01:04:47 from fragglet

c-algorithms 1.2.0

Version 1.2.0 of my C Algorithms library is up. The biggest changes in this release are the improvements to the test suite. I've written a bit about the test process that I've been using for improving the library.

Learning about coverage tools has been an interesting process. I liken writing tests without using coverage analysis to trying to optimise code without doing any profiling. With optimisation, it's easy to pick something that you think is a bottleneck and waste lots of time optimising it; in the same way, I've found that it's possible to write tests that you think are exercising the code in a satisfactory way, but actually aren't. Profiling helps to show exactly what's going on. In the course of analysing the library, I found a bug that should have been shown up in the tests, but wasn't, because the tests weren't exercising all of the code as I assumed they were.

Testing how code behaves in failure conditions is as important as testing how it behaves normally, so I wrote some code that uses #define macros to wrap the standard C allocation functions and allow the tests to simulate memory allocation failures. Again, coverage analysis is helpful here, too.

All in all, I'm not entirely sure why I'm writing a data structures and algorithms library, considering that all of these things have already been implemented hundreds of times over by different people. I originally wrote the library to remove the dependency of Irmo on GLib. Since then it's taken on a life and direction of its own, probably due to my own slightly obsessive nature. I think I just like the process of crafting something to the highest quality I possibly can.

(Also: Open source software with a test process? World coming to an end!)

Syndicated 2008-09-15 11:28:01 from fragglet

4 gigs of pain

We're rapidly reaching (or have reached?) the point where it's standard to have at least 4 gigabytes of RAM in desktop PCs. This presents an interesting dilemma, because most people run 32 bit operating systems; 32 bits doesn't allow more than 4GB of RAM to be addressed. The ideal alternative is to move to 64 bits; all modern CPUs support x86-64. Unfortunately, it requires a massive porting effort to get everything working on x86-64 (drivers from third party vendors are likely to be the biggest problem), so we're not quite there yet.

In the meantime, there's a useful feature called PAE which allows up to 64GB to be addressed by a 32 bit OS. I was surprised to see, however, that neither Windows XP or even Vista support it, although the server-based versions of Windows do!

The cynic in me wondered if this was a deliberate attempt by Microsoft to stop people from using the normal desktop version of Windows for running big servers, but this seemed a bit too much, even for them. But the Wikipedia article has the actual reason: "desktop versions of Windows (Windows XP, Windows Vista) limit physical address space to 4 GB for driver compatibility reasons".

So poor Microsoft appear to be stuck between a rock and a hard place. They cannot enable PAE, which is, in a sense, a backwards compatibility feature, because doing so would break driver backwards compatibility. This would appear to be an example of a situation where the Linux-style hatred of stable APIs wins over maintaining backwards compatibility. One part of the problem is that Microsoft relies on third-party vendors for drivers. They can't just update their platform and the drivers with it, because they don't have any control over them.

Syndicated 2008-08-04 11:59:27 from fragglet

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