Long-term Memory

When hosts have a dynamic IP, it’s very convenient to have its DNS-name follow that dynamic IP. There are several services on the net that do this. However, the regular DNS already provides this feature. The nsupdate tool (comes with BIND) allows you to send an update to the DNS servers. By default, a DNS server does not allow updates for security reasons.

To keep the whole world from updating your zone, there are several possibilities to restrict who can update what. The easiest to setup is an IP restriction: specify from which IPs updates are to be accepted. In my setup, however, I’d like the host to update its own record. Since the host’s IP is dynamic, this is not an option.

Continue reading ‘Secure dynamic DNS updates’ »

Place: Halle

Raptor
Tanks flown: 2
Time flown: 0h27 (cumulative model timer: 31h19)
Rx battery recharged with: mAh
Tx battery recharged with: 559 mAh
Glow heater battery recharged with: 1300 mAh
Starter battery recharged with: 1250 mAh

miniTitan
Flights: 2
Time flown: 0h21 (cumulative model timer: 3h17)
Heli battery recharged with: (1) balanced 1934 mAh; (2) balanced 2137 mAh;
Tx battery recharged with: see above

Comments:
Went flying after work. It was fairly windy, but the wind was fairly constant. I practiced the maneuvers I’ve been doing in the sim lately: autorotation and inverted flight, both successful!

Inverted flight worked out fairly well. I started by doing backflips. Next I stopped halfway through the backflip and tried to keep it stable. I only need to work on my reflexes to get me out of inverted trouble. Obviously pushing the throttle/pitch up is not the best idea… Luckily I had (just) enough height to correct my peculiar situation.

The miniTitan held up fairly well in the winds, although I was more busy fighting the wind than flying. I increased the CCMP-mixing from 50% to 75% on the elevator and ailerons. Now it is more vivid, just like my raptor. I tried some backflips as well, but the wind made this a challange.

Continue reading ‘Flight log – 2009-04-23’ »

When doing some research on the different tables in iptables, I was trying to figure out in what order what tables are traversed. Obviously PREROUTING happens before POSTROUTING, but it becomes more difficult to figure out if mangle happens before are after nat.

I found a post which links to this overview (local copy):

Recent tests on kernel 3.13.0 (Ubuntu Trusty 14.04) show that tcpdump captures before mange-PREROUTING and after nat-POSTROUTING.

Everyone that has used the Cisco IOS command line knows this problem. When you mistype a command, the router tries to resolve the “hostname” and you have to wait for 24 very long seconds:

Router#conft
Translating "conft"...domain server (255.255.255.255)
 (255.255.255.255)
Translating "conft"...domain server (255.255.255.255)
% Unknown command or computer name, or unable to find computer address
Router#

Until recently I used the “no ip domain-lookup” configuration entry to counter this. This disables DNS-lookups altogether, which might not always be what you want. I recently found the proper solution to fix this:

Continue reading ‘Avoiding the typo penalty in Cisco IOS’ »

When I’m debugging serial communications, it’s very useful to run the standard application inside a VM. This allows me to connect the virtual RS232 port to the physical one with socat, which provides me with a detailed log of every byte.

The VMware products under Windows and linux have the option to connect their serial port to a “named pipe“, although it’s more a socket, since they allow bidirectional communication. Strangely enough, VMware Fusion, the Mac product, does not have this option.

Continue reading ‘Connecting a serial port from VMware Fusion to a unix socket’ »

At my parents place, we installed photovoltaic cells. The produced electricity is converted to AC power and is coupled with the normal grid: if we produce too little, the grid provides the remaining power; overproduction is given to the grid.

The inverter (the device that converts DC into AC) is a SolarMax C-series. It has a 2-line LCD display that gives out some basic information: current, voltage, power; produced energy today, this month, this year, … This is very useful information, but is a bit hard to access. The instruction manual reveals that there is a computer interface available to read out its data. Naturally, I wanted to explore this!

Continue reading ‘SolarMax MaxTalk protocol reverse engineered’ »

I was bored of constantly looking for updates on a website. A little googling turned up this nice site. It turns (a part of) a webpage into an RSS feed. Here are the ones I created:

• Cisco Catalyst 2960 Series Switches – Release Notes
• Cisco Catalyst 3560 Series Switches – Release Notes
• Cisco Catalyst 3560-E Series Switches – Release Notes
• Cisco Catalyst 3750 Series Switches – Release Notes
• Cisco Catalyst 3750-E Series Switches – Release Notes

When I was updating my GPG/OpenPGP key, I did some research on the internals of the keys. There appear to be very nice tools to explore the internals of a key. You can also manipulate this key in different aspects: use multiple passwords on a single key, remove part of a secret key for enhanced security; you can even move subkeys between master-keys.

Continue reading ‘The internals of an OpenPGP key’ »

When troubleshooting a network performance problem today, I discovered some strange behavior when using an internet connection over a cellular network (GSM in my case):

When the line was idle for half a minute or so, the connection seems to hang a few seconds before working again. I verified this with our mobile provider Proximus and got the following interesting response: (liberally translated by me)
Continue reading ‘Setup delay on wireless data networks’ »