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Nick Andrew News

2016-05-10 - Installing a StartSSL identity certificate in Google Chrome

StartSSL provides free SSL/TLS certificates for web servers, and it also installs a Class 1 Client certificate into your browser to authenticate yourself to its own site.

This article is all about how to install the Class 1 Client certificate into Google Chrome, especially when Chrome does not accept the certificate automatically, as happened to me when an old certificate expired.

I'll be signing up under the dummy address website@nick-andrew.net to demonstrate the process.

Step 1, Sign Up

  • Visit https://startssl.com/
  • Enter your email address, website@nick-andrew.net
  • Click on "Send Verification Code"

StartSSL signup box

  • Wait for the email from validation@startssl.com
  • Enter the supplied code into "Verification Code", then click "Sign Up"

At this point, Chrome is supposed to import your client certificate and you can be on your way. Certainly at this point if I was using Firefox, then Firefox has installed the certificate, and a box appears with a "Login Now" button. But it doesn't happen for me, on Chrome version 50.

So I'm going to set it up the hard way.

Step 2, Generate a private key

At a shell prompt, do this:

$ openssl req -newkey rsa:2048 -keyout website.key -out website.csr
Generating a 2048 bit RSA private key
writing new private key to 'website.key'
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:website@nick-andrew.net
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
$ cat website.csr | xclip -in

Make sure you enter website@nick-andrew.net in the Common Name field.

  • Click on "Certificates Wizard"
  • Select "Client S/MIME and Authentication Certificate"
  • Enter email address website@nick-andrew.net
  • Select "Generated by Myself (.cer PEM format certificate)
  • Middle-click the mouse button to paste in the .csr file contents
  • Click "here" to download the certificate
$ unzip website%40nick-andrew.net.zip                              
Archive:  website%40nick-andrew.net.zip                                                             
  inflating: 1_Intermediate.crt      
  inflating: 2_website@nick-andrew.net.crt

To import a certificate, Chrome needs a file in PKCS12 format. The magic command to make that is:

$ openssl pkcs12 -export -inkey website.key -in 2_website@nick-andrew.net.crt -out certificate.pkcs12 -name "StartSSL cert for website@nick-andrew.net" -certfile 1_Intermediate.crt
Enter pass phrase for website.key:
Enter Export Password:
Verifying - Enter Export Password:

Finally, you can import the certificate.pkcs12 file into Google Chrome. Go to chrome://settings and click on "Show advanced settings". Then click on "Manage certificates..."

Chrome Certificate manager

In the "Your Certificates" tab, select "Import..."

Select "certificate.pkcs12" and enter the Export password you used.

Enter your export password

At this point, Google Chrome has successfully imported the certificate, and it can be used to authenticate to StartSSL the next time you visit the site.

Certificate manager after installation

2014-10-06 - Testing tsuru PaaS system

Installing my app:

vagrant@tsuru:~/GIT/tsuru-demo$ git commit -m 'Add basic app'
[master 57ffb34] Add basic app
 3 files changed, 29 insertions(+)
 create mode 100644 .buildpacks
 create mode 100644 Procfile
 create mode 100755 app.psgi
vagrant@tsuru:~/GIT/tsuru-demo$ git remote -v
vagrant@tsuru:~/GIT/tsuru-demo$ git remote add tsuru git@
vagrant@tsuru:~/GIT/tsuru-demo$ git push tsuru master
Counting objects: 8, done.
Compressing objects: 100% (6/6), done.
Writing objects: 100% (8/8), 1.00 KiB | 0 bytes/s, done.
Total 8 (delta 0), reused 0 (delta 0)
remote: tar: Removing leading `/' from member names
remote: BUILDPACK: 
remote:        Multipack app detected
remote: =====> Downloading Buildpack: https://github.com/miyagawa/heroku-buildpack-perl.git
remote: =====> Detected Framework: Perl/PSGI
remote: -----> Bootstrapping cpanm
remote:        Successfully installed App-cpanminus-1.7012
remote:        1 distribution installed
remote: -----> Installing dependencies
remote:        ! Configuring . failed. See /home/ubuntu/.cpanm/work/1412583687.168/build.log for details.
remote: -----> Installing Starman
remote:        Successfully installed ExtUtils-Config-0.008
remote:        Successfully installed ExtUtils-InstallPaths-0.010
remote:        Successfully installed ExtUtils-Helpers-0.022
remote:        Successfully installed Test-Harness-3.33
remote:        Successfully installed Module-Build-Tiny-0.038
remote:        Successfully installed HTTP-Date-6.02
remote:        Successfully installed File-ShareDir-Install-0.09
remote:        Successfully installed Test-SharedFork-0.29
remote:        Successfully installed Test-TCP-2.06
remote:        Successfully installed URI-1.64
remote:        Successfully installed LWP-MediaTypes-6.02
remote:        Successfully installed Encode-Locale-1.03
remote:        Successfully installed IO-HTML-1.001
remote:        Successfully installed HTTP-Message-6.06
remote:        Successfully installed HTTP-Body-1.19
remote:        Successfully installed Try-Tiny-0.22
remote:        Successfully installed POSIX-strftime-Compiler-0.40
remote:        Successfully installed Apache-LogFormat-Compiler-0.32
remote:        Successfully installed Filesys-Notify-Simple-0.12
remote:        Successfully installed Class-Inspector-1.28
remote:        Successfully installed File-ShareDir-1.102
remote:        Successfully installed HTTP-Tiny-0.050 (upgraded from 0.025)
remote:        Successfully installed Hash-MultiValue-0.15
remote:        Successfully installed Devel-StackTrace-1.34
remote:        Successfully installed Devel-StackTrace-AsHTML-0.14
remote:        Successfully installed Stream-Buffered-0.03
remote:        Successfully installed Plack-1.0032
remote:        Successfully installed Net-Server-2.008
remote:        Successfully installed Data-Dump-1.22
remote:        Successfully installed HTTP-Parser-XS-0.16
remote:        Successfully installed Starman-0.4010
remote:        31 distributions installed
remote: Using release configuration from last framework (Perl/PSGI).
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:        Default process types for Multipack -> web
remote: ---- Building application image ----
remote:  ---> Sending image to repository (22.28MB)
remote:  ---> Cleaning up
remote: ---- Starting 1 new unit ----
remote:  ---> Started unit 63ba717632...
remote: ---- Adding routes to 1 new units ----
remote:  ---> Added route to unit 63ba717632
remote: OK
To git@
 * [new branch]      master -> master

So far, so good!

vagrant@tsuru:~/GIT/tsuru-demo$ tsuru app-list 
| Application     | Units State Summary     | Address                             | Ready? |
| helloworld      | 0 of 1 units in-service | helloworld.      | Yes    |
| tsuru-dashboard | 1 of 1 units in-service | tsuru-dashboard. | Yes    |

This looks very nice. At this point, 2 tsuru apps should be ready to run, at the hostnames shown, which both resolve to, the address of my cluster.

2014-10-05 - Running perl web apps in Flynn

Flynn is a new PaaS (Platform as a Service) project intended to manage a cluster of servers running applications inside containers. Applications are deployed using a simple 'git push' and behind the scenes the application is built in a container and the container is then started on one or more nodes within the cluster.

Current version is v20140817, classed as Pre-release. In other words, it's still bleeding edge.

I tried it out under a VMWare ESXi client, an LXC container and inside a Vagrant Virtualbox VM (all running Ubuntu 14.04 Trusty).

First, the two failures. Trying it in the LXC container failed utterly because the container wasn't able to itself run containers. I could have probably fixed that by messing with the LXC container configuration, but there are only so many hours in a day (and I use all of them already).

I couldn't get Flynn running under the ESXi client. I doubt it was an unfixable problem, i.e. there's nothing inherent in the ESXi client which would stop Flynn from working.

I did get it going under Vagrant Virtualbox, by following the steps listed under "Manual Ubuntu Deployment" very carefully(*). Those steps were (presented as a script):

#  Install Flynn on this host

apt-get update
apt-get -y upgrade
apt-get -y install apt-transport-https curl patch

apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv BC79739C507A9B53BB1B0E7D820A5489998D827B
echo deb https://dl.flynn.io/ubuntu flynn main > /etc/apt/sources.list.d/flynn.list
apt-get update
apt-get -y install linux-image-extra-$(uname -r) flynn-host

if [ ! -f token ] ; then
        curl -k https://discovery.etcd.io/new > token

        patch <<EOF /etc/init/flynn-host.conf
--- a   2014-10-04 08:15:09.380249566 +0000
+++ b   2014-10-04 04:33:20.135872045 +0000
@@ -1,5 +1,7 @@
 description "Flynn layer 0"

+env ETCD_DISCOVERY=$(cat token)
 #start on (started libvirt-bin and started networking)
 respawn limit 1000 60


flynn-release download /etc/flynn/version.json
start flynn-host

Don't forget to install the correct linux-image-extra package, as I did - else you won't have aufs and Flynn will emit unhelpful errors. Don't forget to run the flynn-release command, as I did - else flynn-host will not be able to run anything and it will respawn forever by upstart.

In fact it's a good idea to change the respawn limit 1000 60 line to respawn limit 5 300 and add a line post-stop exec sleep 10 to ensure that if Flynn doesn't start up properly, it won't thrash your VM.

After this it's necessary to run flynn-bootstrap, and that must be done after setting up some wildcard DNS resources to point to your cluster host(s). Flynn's load-balancing (?) router uses the hostname in the HTTP request to distribute your traffic to the apps running in the containers listening on some ports other than 80 or 443.

When I did eventually get Flynn running, it more or less did what the sparse documentation indicated it should.

I was able to get a simple perl web app running in containers. An app is developed in a git repository and is deployed by pushing a branch to Flynn's git server. Flynn then builds the app into a container and deploys it accordingly. Building the app requires some machine-readable build and execution instructions. Documentation for doing this for perl was nonexistent so I had to figure it out.

Here's my application in its repository.

==> .buildpacks <==

==> cpanfile <==
requires 'Mojolicious';
requires 'Sys::Hostname';

==> app.psgi <==
#!/usr/bin/env perl
use Mojolicious::Lite;
use Sys::Hostname qw();

# Documentation browser under "/perldoc"
plugin 'PODRenderer';

get '/' => sub {
  my $c = shift;
  $c->stash('hostname', Sys::Hostname::hostname());


@@ index.html.ep
% layout 'default';
% title 'Welcome';
Welcome to the Mojolicious real-time web framework! Hello, world! <%= $hostname %>

@@ layouts/default.html.ep
<!DOCTYPE html>
  <head><title><%= title %></title></head>
  <body><%= content %></body>

==> Procfile <==
web: 'perl -Mlib=$PWD/local/lib/perl5 ./local/bin/starman --preload-app --port $PORT'

Did I mention there is no documentation for running a perl app?

Flynn apps can (must?) be defined in a Heroku buildpack compatible manner. The included flynn/slugbuilder component has some preset buildpacks, and one of the buildpacks allows additional buildpacks (such as the perl one) to be specified in a .buildpacks file. So that's what .buildpacks is for, to pull in Miyagawa's buildpack for a Perl/PSGI application.

The cpanfile says what perl modules need to be installed. I used Mojolicious and generated a sample application with a very small amount of customisation.

For Miyagawa's buildpack, the perl script has to be named app.psgi (that's how it detects if the buildpack should be used).

Finally the Procfile is a YAML file and it specifies how the command should be started to run in 'web' (flynn scale web=5 scales the application to 5 concurrent instances).

I could have omitted the Procfile, and Flynn would have started the application according to instructions in a .release file generated by the buildpack.

That's how far I got before something broke and I couldn't get Flynn working again. Bear in mind, Flynn is still bleeding edge but it shows some promise.


  • Flynn's still beta but the system shows promise. The company has a lot of sponsors and a good theoretical base ("service discovery inspired by the Google Omega paper").
  • More documentation is needed, indeed the lack of explanation for running a perl app inspired this blog post.
  • I was looking for something with a simple interface and Flynn was the first thing I tried. I just wanted to (a) be able to push my repo to have it deployed, and (b) not have to care where it's actually running. Flynn satisfied those two requirements.
  • Flynn's error messages are painfully inadequate. "driver not supported" means the aufs kernel module couldn't be loaded. Other messages were even less useful.
  • It's hard to debug applications running in containers (and by this I mean Flynn's own components) to find out what's going wrong
  • Flynn writes heaps of logs under /tmp/flynn-host-logs and, while they helped in debugging a little, I wonder if they'll ever be cleaned up. I couldn't run Flynn in production with such a profusion of log files growing forever.
  • Docker images seem a bit fragile. Running the flynn-release command broke because a docker image was partly downloaded and I had to clear it myself out of the /var/lib/docker directory before Flynn could download the rest of its code.

Next up I'll be testing Tsuru.

2010-04-25 - No sound after upgrading to Ubuntu 9.10 (Karmic Koala)

This affected my EEE 901. The symptoms were:

  • No sound output on the laptop's built-in device (snd-hda-intel)
  • When I plugged in a USB sound device (snd-usb-audio), it also didn't produce any sound
  • Pulseaudio showed only a "dummy" output device. No hardware devices shown
  • "cat /proc/asound/cards" showed the sound cards were recognised by the kernel

The problem turned out to be with my $HOME/.asoundrc and $HOME/.asoundrc.asoundconf files. I found this:

  • "alsamixer" failed to run, complaining of problems with the above files


  • I removed .asoundrc and .asoundrc.asoundconf
  • I killed and restarted pulseaudio
    • pulseaudio -k
    • pulseaudio --start

Then sound worked. I assume that pulseaudio couldn't get the ALSA device information due to the problems with the config file(s). It was probably only .asoundrc.asoundconf with a problem but I had nothing special in the other file so I removed that too.

2010-04-16 - GPT, Grub and RAID

GPT is the Generalised Partition Table which is a new standard for partitioning a hard disk. Its advantages over the MSDOS partition table used since the 1980s are:

  • larger devices (over 2T)
  • more partitions per device
  • extended set of partition types

Grub 2 (versions 1.96 and later) can boot disks which use GPT, but there are some considerations which are detailed below.

What's the MSDOS partition table?

The MSDOS partition table was invented when disk drive capacities were around 5-20 megabytes and sectors were addressed using a (C,H,S) 3-tuple: Cylinder, Head and Sector numbers. This addressing scheme has been obsolete for a very long time now, and has been kludged several times to cope. Firstly disk drive capacities increased enormously - and we started to use geometries with large numbers of heads (63) and sectors (255) to cope. Secondly disk drives no longer have a fixed geometry: although the number of heads is fixed (up to twice the number of physical platters the drive has), there is a varying number of sectors per track, as more data is stored on the outside of each platter. Disk drives store an approximately constant amount of data per square millimetre of disk surface. Thirdly, modern drives provide internal error correction by relocating sectors away from disk areas with physical defects.

The MSDOS partition table uses CHS and also provides an LBA representation of each partition. LBA is a linear numbering of sectors independent of the physical drive geometry in which sectors are numbered starting from zero and going to a very high number (depending on device listed capacity) and we have relied on this for some years now - as the size of devices exceeded the capacity of CHS to describe, operating systems started ignoring the CHS values and using only LBA. But LBA's capacity is about to run out; it has a hard limit of 2 TB (1 terabyte = 2^40 bytes) and we will soon surpass that capacity.

What's GPT?

GPT uses an LBA system with a much larger capacity. It has provision for more partitions per device (although in my experience, with larger device sizes we make larger partitions, not more partitions). MSDOS was limited to 4 so-called "primary" partitions and one of these could be used as a pointer to further "extended" partitions. It was a kludge, and GPT eliminates this kludge.

MSDOS also used a single byte to describe the contents of each partition. This was troublesome as almost all of the 256 possibilities have been used at various times (the linux fdisk utility contains a list). So GPT extends that with UUID based partition types - an almost limitless set.

Linux supports GPT partition tables (also called disk labels). A tool called 'gdisk' can create and edit them, and other partitioning tools have varying levels of support.

Grub 2 can boot disks partitioned with GPT. But there are some interactions between Grub, GPT and RAID, which is the reason for the existence of this article.

GPT, Grub2 and RAID considerations

  • GPT partitions can be made with 'gdisk'. Some of the tools are still immature.

  • Grub2 can boot GPT partitioned disks, but it needs a so-called "BIOS Boot Partition" of at least 32 Mbytes. That's where Grub2 stores some of its low level boot code.

  • Grub2 cannot boot off a RAID partition which uses version 1.0, 1.1 or 1.2 metadata. The RAID must have been created using version 0.90 metadata.

4K sector disks

Storage manufacturers are now shipping 4K sector disks. Why 4K not the previous standard of 512 bytes? 4K sectors are more efficient for such large devices: the drive can pick up more data with each read operation; the number of physical sectors on the device is reduced by 8 times (which reduces the size of relocation tables, for instance); 4K matches the page size used in the x86 architecture. There are a lot of good reasons why.

The first Western Digital 4K drives were released with a compatibility mode enabled in which the drive simulates 512 byte sectors. This can affect performance quite a lot. The installer should ensure that all partitions are a multiple of 8 sectors in size. This affects GPT partitioning as well as MSDOS. It's a bit easier to ensure this in GPT because there's no geometry baggage, unlike MSDOS.

2010-04-09 - LS-30 GSM interface

The LS-30 can notify an alert via its internal PSTN interface. There is also an optional GSM interface (pictured), which takes a SIM card and can be used instead of or in addition to the PSTN notification.

LS-30 optional GSM interface

Alerts are notified via SMS message at first, and this is followed by a voice call. Five numbers can be configured for GSM. The SMS message looks like this:

Burglar       01-03 19:19 2010/04/02

The "01-03" refers to the device which triggered.

My monitoring software can detect a Burglary message and SMS me directly. I get the impression that it takes a couple of minutes for the LS-30 to get around to sending an SMS. It may be that the LS-30 takes time to check the PSTN line for a dial tone. The LS-30 seems to try to alert via PSTN first, and tries GSM second.

My monitoring system sends an SMS of this form:

Burglary at Fri Apr 9 10:48:50 EST 2010 zone 500 group 00

The zone and group numbers would correspond (on a real burglary) to the "01-03" shown above.

2010-04-04 - Reverse-Engineering the LS-30

In February 2010, after long investigation, I purchased an LS-30 Alarm System From Securepro Security. Having moved recently, I needed an alarm system. I'd had many years experience with the Solution 16 (PDF) range of alarms, originally designed and manufactured by EDM (a Zeta Internet customer) and now owned by Bosch. But I thought perhaps technology has improved in the meantime, and I wanted something more powerful, configurable, ... more geeky. That's the LS-30.

View of LS-30 from the front

The LS-30 is an alarm system designed for self-installation in a home or business. It communicates wirelessly with its devices, which include:

  • PIR (Passive Infra-Red) burglar sensors
  • Remote control key fobs
  • Solar powered outdoors siren
  • Magnetic reed switch door sensors
  • Smoke detectors
  • And more.

It is very configurable, and according to the vendor has "more features than any other system available". Except perhaps for very expensive commercial systems. What appealed to me though, was the ethernet interface - I can plug it into my network and (hopefully) configure it remotely.

I have begun to reverse-engineer the LS-30 communications protocol. Furthermore, I have released my code under the GNU General Public License (Version 3) so others in the community can benefit from this effort (and help me finish the job). See the links in the left column to my GitHub project.

2009-06-13 - dnscache fixed

I was able to solve the problem with dnscache. Basically, before sending each new request to a nameserver (for a particular query), dnscache would close the socket used for the last request. So any late response would not reach dnscache.

The code flow was roughly this:

+->  close socket
|    open socket()
|    bind() local end of socket to random port
|    connect() socket to next destination
|    send() request packet
+-<  poll with timeout for a response

The fix turned out to be fairly simple. Open a socket before sending the first request packet for a particular query, do not connect it to the destination, and use sendto() to specify each destination instead of send(). So the fixed code flow now looks like this:

     open socket()
     bind() local end of socket to random port
+->  sendto() request packet to next destination
+-<  poll with timeout for a response
     close() socket

The improvement on performance is extreme. I'm testing on a virtual machine using the 'netem' module to artificially create network latency of 5000ms. Before patching, dnscache took 310 seconds to lookup 'A www.telstra.net' - much longer than I had calculated in the previous post, because in fact dnscache had to send more requests than expected due to missing nameserver glue, perhaps for the net domain. After patching, dnscache was able to resolve 'www.telstra.net' in only 16 seconds. It sends 6 queries then receives the response to the first, and closes the socket so subsequent responses are ignored (they're not needed anyway).

You might think this patch is not necessary because 5000ms network latency is an extreme test and most internet hosts will have much lower latency (it's usually a leaf-node problem) but I experienced it on a modern HSDPA network. Also I have seen saturated dialup and ISDN connections with very high latencies (over 3000ms for ISDN). Also dnscache's timeouts start at 1 second so performance will start to degrade as soon as average request latency exceeds 1000ms. The more nameservers a domain has, the longer it will take to lookup because dnscache sends a request to every nameserver with a 1-second timeout before changing to 3 seconds (then 11, then 45).

I've made the patch available on github.com in a new repository I made called djbdns. The url is:


This repository also contains all public releases of djbdns to date: version 1.01 through 1.05. DJB has put djbdns into the public domain so it is OK for me to do this. There are also some patches written by other people, linked from tinydns.org. Feel free to clone, fork and submit further patches to this djbdns repository on github.

2009-06-08 - dnscache fails spectacularly on high latency connections

Like most people I use dnscache extensively for name resolution within my network. All this worked fine until recently when my DSL link broke (with the telephone line) and I had to use HSDPA for external connectivity.

My HSDPA provider is supposed to provide a maximum speed of at least 1.8 Mbit/sec - of course this can be lower due to network congestion, poor signal strength, low capacity network links and so on. I don't think I have ever received the full 1800 kbit/sec from my provider, maybe nothing over 300 kbit/sec in fact.

Anyway this particular outage was particularly troublesome because I was getting only 50 kbit/sec through HSDPA ... slower than a dialup modem. It was slow in another respect too, the packet round-trip time was between 5 and 7 seconds. That's over 200 times more than a typical RTT on DSL of 25 ms.

I don't know what caused the extremely high latency, but I do know what its effect was. Dnscache failed almost completely. It would send out requests to nameservers on the internet, and not receiving any response in a reasonable time, would go on to try the next nameserver, and the next, and so on. The responses came back at some later time ... after dnscache had given up on the request (and dnscache would ignore the response). So the net effect was a storm of DNS packets sent and received, as well as ICMP port-unreachable packets when responses were received after dnscache had stopped listening.

Now that the DSL is working I am testing dnscache (from djbdns 1.05) to see the exact nature of this problem and if it can be fixed. I am using Linux's Traffic Control subsystem (see lartc.org for documentation) and specifically the 'netem' queue discipline module to simulate various amounts of latency to a virtual host.

I setup the variable latency using this script:

#  Setup network delay for testing dnscache on high latency links
#  Outbound traffic on eth0 is delayed by several seconds if
#    - ip dst is

set -x

tc qdisc del dev eth0 root 2>/dev/null

# Setup root class and base rates
tc qdisc add dev eth0 root handle 1: htb default 99

tc class add dev eth0 parent 1: classid 1:1 htb rate 100mbit
# all traffic
tc class add dev eth0 parent 1:1 classid 1:10 htb rate 100mbit
# delayed traffic
tc class add dev eth0 parent 1:1 classid 1:11 htb rate 2mbit
# default
tc class add dev eth0 parent 1:1 classid 1:99 htb rate 3500kbit

tc qdisc add dev eth0 parent 1:10 handle 10: sfq
tc qdisc add dev eth0 parent 1:11 handle 11: netem delay 5000ms
tc qdisc add dev eth0 parent 1:99 handle 99: sfq

# Move selected traffic into 1:11
tc filter add dev eth0 parent 1: protocol ip prio 1 u32 match ip dst flowid 1:11

This script is run on my gateway and it uses the HTB queue discipline on device eth0 and some classes beneath that to filter outbound packets on that interface. Packets sent to are delayed (by the 'netem' qdisc) by exactly 5000 msec, which is more than enough time to give dnscache a headache.

Next up I hacked dnscache to (a) run as an ordinary user, (b) listen on port 5300, and (c) show me what it is doing. Dnscache implements exponential timeouts on sent requests for 1, 3, 11 and 45 seconds. I don't know why djb chose those particular numbers. I started the server and sent a single request to lookup an 'A' record for telstra.net:

dig -p 5300 @ A telstra.net +tries=1

This is what dnscache output at first:

$ ./dnscache
query 1 7f000001:e4d2:6114 1 telstra.net.
tx 0 1 telstra.net. . 803f0235 c03a801e c0249411 c6290004 c707532a 80080a5a c0702404 c0cbe60a ca0c1b21 c0e44fc9 c00505f1 c021040c c1000e81
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1
dns_transmit to, timeout set to 1

What seems to be happening here is that dnscache is looking up the root nameservers ('.') for 'telstra.net'. The hex numbers are the IPv4 addresses of each root nameserver. Dnscache tries them in order (at least, in the same order as they appear on the 'tx' line). There are 13 root nameservers and these requests appear to be issued once per second - so this process has taken 13 seconds so far. With a 5000 msec delay on the interface, 8 of those 13 requests have been replied-to, but dnscache apparently stops listening for a response as soon as its timeout expires (1 second here) and it sends the next request.

Continuing on:

dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3
dns_transmit to, timeout set to 3

Dnscache sends to the same set of 13 nameservers, but with a 3 second timeout on each. That takes 39 seconds (for a total time spent so far of 52 seconds, and we still don't know what are the nameservers for telstra.net). Continuing:

dns_transmit to, timeout set to 11
rr 803f0235 172800 1 a.gtld-servers.net. c005061e
rr 803f0235 172800 1 b.gtld-servers.net. c0210e1e
rr 803f0235 172800 1 c.gtld-servers.net. c01a5c1e
rr 803f0235 172800 1 d.gtld-servers.net. c01f501e
rr 803f0235 172800 1 e.gtld-servers.net. c00c5e1e
rr 803f0235 172800 1 f.gtld-servers.net. c023331e
rr 803f0235 172800 1 g.gtld-servers.net. c02a5d1e
rr 803f0235 172800 1 h.gtld-servers.net. c036701e
rr 803f0235 172800 1 i.gtld-servers.net. c02bac1e
rr 803f0235 172800 1 j.gtld-servers.net. c0304f1e
rr 803f0235 172800 1 k.gtld-servers.net. c034b21e
rr 803f0235 172800 1 l.gtld-servers.net. c029a21e
rr 803f0235 172800 1 m.gtld-servers.net. c037531e
rr 803f0235 172800 ns net. a.gtld-servers.net.
rr 803f0235 172800 ns net. b.gtld-servers.net.
rr 803f0235 172800 ns net. c.gtld-servers.net.
rr 803f0235 172800 ns net. d.gtld-servers.net.
rr 803f0235 172800 ns net. e.gtld-servers.net.
rr 803f0235 172800 ns net. f.gtld-servers.net.
rr 803f0235 172800 ns net. g.gtld-servers.net.
rr 803f0235 172800 ns net. h.gtld-servers.net.
rr 803f0235 172800 ns net. i.gtld-servers.net.
rr 803f0235 172800 ns net. j.gtld-servers.net.
rr 803f0235 172800 ns net. k.gtld-servers.net.
rr 803f0235 172800 ns net. l.gtld-servers.net.
rr 803f0235 172800 ns net. m.gtld-servers.net.
rr 803f0235 172800 28 a.gtld-servers.net. 20010503a83e00000000000000020030
stats 1 945 1 0
cached 1 a.gtld-servers.net.
cached 1 b.gtld-servers.net.
cached 1 c.gtld-servers.net.
cached 1 d.gtld-servers.net.
cached 1 e.gtld-servers.net.
cached 1 f.gtld-servers.net.
cached 1 g.gtld-servers.net.
cached 1 h.gtld-servers.net.
cached 1 i.gtld-servers.net.
cached 1 j.gtld-servers.net.
cached 1 k.gtld-servers.net.
cached 1 l.gtld-servers.net.
cached 1 m.gtld-servers.net.

Dnscache has finally increased its timeout to 11 and after another 5 seconds (total time elapsed now 57 seconds) it receives a response. Now it knows the nameservers for the 'net' top-level domain. There are 13 of them and so it's going to take another 57 seconds before it learns the 4 nameservers for 'telstra.net', and then another 21 seconds to learn that there is actually no 'A' record for 'telstra.net'. That's 135 seconds total time. I don't know how long clients typically wait for a response but it's a lot less than that.

Clearly dnscache should implement two timeouts per request: one for sending a second request (to another nameserver) for the same information, and one to give up waiting for a response from the first request. The 2nd timeout should be much longer than the first.

If dnscache was modified to wait up to 10 seconds for a response but try each successive nameserver after 1 second, then it should be possible for dnscache to answer the query within 15 seconds, which is reasonable in this context. In these calculations I'm assuming that dnscache has no existing cache (other than the list of root nameservers) because that makes dnscache's behaviour predictable, and it shows us the worst case performance.

The next step for me is to work out if dnscache can have multiple outstanding requests to nameservers for the same client request. Obviously dnscache can handle multiple concurrent client requests and must query many different nameservers concurrently, but the question is whether it can query multiple nameservers for the same information, at more or less the same time, and use the first response that is received.

2008-08-25 - Configuring IPv6 using AARNet's free broker

You can obtain IPv6 connectivity in Australia using the AARNet IPv6 Migration Broker if your ISP does not already provide IPv6. As at August 2008, only Internode is known to provide consumer level IPv6 access.

For Australian users who cannot obtain IPv6 through your ISP, the AARNet IPv6 tunnel is probably the next lowest latency choice. These instructions describe setting up IPv6 with linux over a consumer DSL connection with a dynamic IPv4 address (i.e. every time you connect you get a different IP address) and NAT (Network Address Translation) on the DSL modem.

With IPv6 you can get a static address (well, 2^64 or more static addresses) and it's quite useful if you run a home network and want to provide access to devices within the network, from outside. That is, so long as the outside client has IPv6 (the chicken-and-egg problem).

Certain assumptions are made in this document - like installed software or an IPv6 enabled kernel. If these instructions don't work for you, drop me an email at nick at nick-andrew.net.

Preparation - Kernel and Software

Make sure your kernel has IPv6 support. Do "ifconfig eth0" and check for a line like this in the output:

          inet6 addr: fe80::212:34ff:fe56:789a/64 Scope:Link

You may need to load the "ipv6" module.

Check that you have the commands "ip6tables" and "ip".

Preparation - Firewall

It's good for security to setup the IPv6 firewall before you even start configuring it. Although you may have an IPv4 firewall already in place, that won't stop any IPv6 packets. I'll assume you want to make connections out, but block all connections in, which is the standard functionality you get with NAT, and useful for a client. For a server you will need to allow connections in for the server ports.

ip6tables setup

I use a shell script with a function alias, to set the firewall.
#    Simple IPv6 firewall rules

doCmd6() {
        /sbin/ip6tables $*
        if [ $rc != 0 ] ; then
                echo Error $rc doing ip6tables $*


doCmd6 -F
doCmd6 -X

doCmd6 -N 6_log_drop
doCmd6 -N 6_icmp
doCmd6 -N 6_tcp

doCmd6 -A 6_log_drop -j LOG --log-prefix "ipv6:"
doCmd6 -A 6_log_drop -j DROP

#enable ssh in   doCmd6 -A 6_tcp -p tcp -d ::/0 --dport 22 -j ACCEPT
doCmd6 -A 6_tcp -j 6_log_drop

doCmd6 -F 6_icmp
doCmd6 -A 6_icmp -j ACCEPT

doCmd6 -A INPUT -i lo -j ACCEPT
doCmd6 -A INPUT -p ALL -m state --state ESTABLISHED,RELATED -j ACCEPT
doCmd6 -A INPUT -p icmpv6 -j 6_icmp
doCmd6 -A INPUT -p tcp -j 6_tcp
doCmd6 -A INPUT -j 6_log_drop

This set of rules will allow you to make outbound IPv6 connections and will block inbound except for ICMP (your address can be pinged) and you can uncomment a line to enable ssh connections in.

Preparation - DSL modem

Assuming your DSL modem has a firewall, you will need to enable two things:

  • Outbound UDP connections to port 3653
  • Protocol 41 inbound/outbound

UDP port 3653 is used by the AARNet tunnel broker. Protocol 41 is used by 6to4 tunneling, which I will describe now.

Alternate access - 6to4 tunnel

Although this document is about obtaining IPv6 through AARNet's migration broker, there's a quicker way to get started on IPv6 using your dynamic IPv4 address. You will need the "curl" command installed. Run this script:

#  Sets up an ipv6 tunnel through the nearest public gateway.
#  Automatically learns current ipv4 address.

ipv4=$(curl -s http://www.whatismyip.com/automation/n09230945.asp)
ipv6=$(printf "2002:%02x%02x:%02x%02x::1" $(echo $ipv4 | tr "." " " ) )

echo ipv4 is $ipv4 and ipv6 is $ipv6

ifconfig sit0 up
ifconfig sit0 add $ipv6/16
route -A inet6 add 2000::/3 gw :: dev sit0 is an address which routes to the nearest public IPv6 gateway. Unfortunately for us Australians, that's probably in the USA. But it's easy to setup, as you can see.

This technique has some advantages and disadvantages. On the positive side, you have 2^80 addresses to use. That should be enough for anyone. On the negative side, these addresses are as dynamic as your IPv4 address because they are derived from it. Also, you may be able to make outbound connections but not accept inbound connections, depending on what functionality your DSL modem provides. My DSL modem allows me to open up protocol 41 traffic, but it doesn't provide a configuration option to forward all incoming protocol 41 connections to my linux box. So my box can only accept inbound connections while there's a working outbound connection (this is standard NAT functionality).

So 6to4 is a good technique to get started with IPv6 if you want to, say, browse ipv6 websites. But it's not so useful for servers.

Testing - IPv6 using commands

"ping6" and "telnet" are your friends.

$ ping6 ipv6.l.google.com
PING ipv6.l.google.com(2001:4860:0:2001::68) 56 data bytes
64 bytes from 2001:4860:0:2001::68: icmp_seq=1 ttl=52 time=308 ms
64 bytes from 2001:4860:0:2001::68: icmp_seq=2 ttl=52 time=335 ms
64 bytes from 2001:4860:0:2001::68: icmp_seq=3 ttl=52 time=321 ms
$ telnet luyer.net 80
Trying 2001:470:1f05:14d::1...
Connected to luyer.net.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.1 200 OK
Date: Mon, 25 Aug 2008 00:38:50 GMT
Server: Apache/2.2.3 (Debian) PHP/4.4.4-8+etch6 mod_ssl/2.2.3
[ ... etc ... ]

You can also install the netcat6 package (the command is "nc6") to connect out or listen for incoming connections. To test if your web browser is using IPv6 correctly, try these sites:

  • www.kame.net - on IPv6 you will see a swimming turtle, on IPv4 the turtle will not move
  • luyer.net and it will tell you if you connected through IPv4 or IPv6
  • www.sixxs.net will show your originating address and protocol at the bottom of the page.

Registering with AARNet

You'll need to create a username on the AARNet IPv6 Migration Broker and then associate that username with a tunnel.

  1. Create User Account
  2. Request Tunnel

The "Request Tunnel" CGI hangs for me, I don't know why. I assume it created a tunnel correctly because I'm getting one.

Installation of TSPC

Install the "tspc" package. I'm using Debian, so it's just "apt-get install tspc".

When Debian installs tspc, it automatically configures it to obtain an anonymous IPv6 tunnel from freenet6.net. Although that's great and easy, it's not what we need in Australia. So after installation, stop the daemon with "/etc/init.d/tspc stop".

Configuring the AARNet tunnel broker

To be continued ... no time to write the rest of the document today.

In brief, you need to use the v6udpv4 method and all traffic will be tunneled through a UDP connection. 30 second keepalive messages (I believe it's an ipv6 ping?) will keep NAT working. Your config file should look like this:






Note that AARNet assigns a /56 even though this config asks for a /64.

Monitoring the IPv6 tunnel

AARNet's broker seems a bit flaky. It sometimes ignores the UDP packets so you may need to start the daemon a few times before it connects properly. As I mentioned, the CGI to request a tunnel hangs for me. If it doesn't hang, it may return a shell script, which you can ignore.

It's possible you don't even need to use the "Request Tunnel" CGI, maybe it will assign a permanent tunnel when tspc connects for the first time.

Also AARNet reboot the server at 03:00 every morning. The tspc daemon will try to reconnect if the tunnel fails, but perhaps not forever.

In any case, you want IPv6 to be always available, which means monitoring it. If the tspc daemon stops, you will need to restart it manually. I wrote this simple perl script which just logs whenever IPv6 stops working. It doesn't monitor the process or interface at all (you'd want to monitor the process itself if you change the script to restart a failed process).

#!/usr/bin/perl -w
#       @(#) $Id$
#       vim:sw=4:ts=4:

use Date::Format qw(time2str);
use Getopt::Std qw(getopts);

use vars qw($opt_h);

$| = 1;

$opt_h || die "Need option -h hostname";

# Initial and current state
my $state = 'down';

while (1) {
        my $now = time();
        my $newstate = getPingState($opt_h);

        if ($newstate ne $state) {
                open(OF, ">>ipv6-state.log");
                my $ts = time2str('%Y-%m-%d %T', $now);
                print OF "$ts $opt_h $newstate\n";

                $state = $newstate;

        my $to_wait = 60 - ($now % 60);
        print '.';


# ------------------------------------------------------------------------
# ping6 a host, and figure out if it is up
# ------------------------------------------------------------------------

sub getPingState {
        my $host = shift;

        my $rc = system("ping6 -c 2 -q -W 8 $host >/dev/null");
        if ($rc == 0) {
                return 'up';

        return 'down';

I just run it like this: "check-ipv6.pl ipv6.l.google.com" and it pings once a minute (on the minute) and logs whenever the calculated state of the IPv6 connectivity changes.

For production use you'd want to change the 'sleep' to sleep(60) since it's not friendly to google for many sites to ping in synchronisation (i.e. always at :00). Of course you could always ping6 to broker.aarnet.net.au instead ...

64 bytes from 2001:388:1:5001:2a0:a5ff:fe4b:ae3: icmp_seq=1 ttl=64 time=52.8 ms
64 bytes from 2001:388:1:5001:2a0:a5ff:fe4b:ae3: icmp_seq=2 ttl=64 time=51.6 ms
64 bytes from 2001:388:1:5001:2a0:a5ff:fe4b:ae3: icmp_seq=3 ttl=64 time=51.1 ms