Author: Martin

Recently, I’ve been traveling with a Dual-SIM smartphone, which I also use for Wi-Fi tethering my notebook. I can use both SIM cards from different network operators for Internet connectivity and can switch back and forth while Wi-Fi tethering remains active. This is particularly useful while roaming, as the SIM cards are usually connected to different local networks in the roaming country (VPLMNs in 3GPP parlance). If the signal of one network is weak at one location, there’s a good chance the other is better, so no manual network reselection is required. Both home network operators support IPv6, so I was wondering how the smartphone manufacturer has implemented the notification to the notebook that the IPv6 prefix and the IPv6 DNS server address have changed when I switch between the SIM cards!?

Continue reading Changing IPv6 Backhaul While Tethering

Today, I realized that the mobile Internet while on the move has become fast enough to allow backing-up data residing on servers at home to an external hard drive connected to my notebook while traveling. This is a bit of a strange scenario, but let me explain:

Continue reading The Reverse Home Server Backup

Yes, I’m an IPv6 fan and I strive to reach a good balance between running my self-hosted services on an IPv4 / IPv6 dual-stack and simplicity of configuration and maintenance. One service that had some issues in the past with IPv6 was OpenVPN. Perhaps things have gotten better but when I first installed the service many years ago, getting IPv6 through the tunnel just didn’t work. So I have an IPv4-only OpenVPN server at home and I have to make sure there is no IPv6 ‘leakage’ outside the tunnel if the local connectivity offers IPv6.

The answer to the problem was to install the bind9 DNS server and send configuration information to client devices during the VPN tunnel establishment to only use this DNS server. To prevent IPv6 leakage, I configured that DNS server to send empty responses to AAAA DNS requests. The fun part: This seems to be an ‘unloved’ feature in bind9 and so the way this is configured has changed every time I made an Ubuntu OS upgrade. So here’s how to configure bind9 to send empty answers to IPv6 AAAA requests:

Continue reading Bind9 DNS: Follow the IPv6 Filter

It’s the time of the year again before autumn sets full sail for another Vintage Computing Festival in Berlin. It’s taking place this weekend (8 + 9. Oct. 2022) and should you just happen to be in Berlin and interested in the topic, come by and enjoy!

I’ve been part of the ‘orga team’ for a few years know and I’m very happy that this year around, we’ve moved from a virtual event back into the real world! There’s both tons of exhibitions and talks again. While you obviously have to come on site to see the exhibits, the talks are streamed live on media.ccc.de, starting at 10:15 am today (Saturday) and Sunday. Note: Most talks are in German, and you can find an overview of the talks here.

Should you come by and want to have a chat, just ask where I am at the information desk at the entrance.

Recently, I’ve spent a week on vacation in Vienna, and I used a bit of that time while walking around and spending time in cafés to have a look at the performance of the LTE and 5G networks in the city. With the EU’s ‘roam like at home’ rules, I didn’t need a local SIM card for this, and as long as the backhaul between the visited network (in Austria) and the home network (in Germany) is properly dimensioned and configured. In effect, this home network detour only adds a few milliseconds of delay. And indeed, while I was in Vienna, I could easily exceed 1 Gbit/s downlink throughput. So while it is good to see that such high speeds are achievable even while roaming, it’s availability and capacity that are the main differentiators these days from my point of view.

Continue reading Vienna Network Notes

In a previous post, I’ve been looking at my “technical debt” of having a couple of services running in virtual machines that are still based on Ubuntu 18.04 which will be End-of-Live in April 2023. In the meantime I’ve started the upgrade process, which, to my surprise ended up in a kernel panic after rebooting.

Continue reading Ubuntu 22.04 Kernel Bloat

Internet access over Starlink is definitely an interesting topic and has me captivated ever since first reports appeared of individuals who got themselves a dish when the public beta test first started in 2020. While their reports are often impressive, there is relatively little information of the overall capacity of the system today and its potential in the future. But when digging a bit deeper, some interesting numbers can be found.

Continue reading Starlink – Let’s Play With Numbers

Despite running a lot of services in my cloud at home and in a data center, I am very positively surprised that unless I want to actively add, remove or change anything, there is very little intervention required on a day to day basis. That’s because apart from very few exceptions, my security updates are automated or semi-automated with Ansible scripts. But I have noticed that over time, some technical debt has crept up that needs to be dealt with now.

That’s mostly because some of the services I host simply break when updating the underlying operating system from Ubuntu 18.04 to 20.04 (or now perhaps 22.04). Fortunately, all services in question run in virtual machines, so going back to a sane state after a broken update is easy by creating a VM snapshot before the update.

While I don’t mind running some of my services on an older but still supported Ubuntu variant, the lifecycle of Ubuntu 18.04 is coming to an end in 2023. So it’s time to think about what to do for those cases. While that’s of course a bit of a pain point, it also triggers the healthy process of deciding whether its worth to reinstall that service on a new OS version, retire it for good or to look for an alternative.

Continue reading Technical Debt – Renew or Retire?

I must have had one of the oldest cars in Cologne. In 2001, I bought a used Toyota Paseo from 1998 and have driven it until now. That’s 22 years, and for the past decade, people were already strangely looking at me whenever I showed up with my old and quirky car that had so fallen out of time. But I didn’t care much. It was a great car, and it didn’t ever let me down when it really counted, not for a single of those 265.000 km that were finally on the odometer. If you think about it, that’s almost the distance to the moon. Not quite, but almost. However, I’ve come to a point at which I would have had to invest a significant sum to keep it going. So with a sad heart, I finally had to say good bye. Yes, with a sad heart, because over the time, I’ve developed a personal relationship with that car that just never let me down and has served me so well. So here’s an epitaph and some musings why this ending will also be an interesting new beginning. That’s because I intend not to buy another car and instead switch to alternative mobility options. So here’s the story:

Continue reading Going Car-Less After 22 Years – A Journey Ends, a New One Begins

Here’s a quick online lecture talk announcement for this Saturday evening, 10. September 2022, 19:00 CEST (Central European Time) that I have received today and which I will definitely attend:

Jan-Daniel Kaplanski of the German Red Cross will talk about his efforts to bring Internet connectivity to large refugee homes in Germany. I’ve been looking at such efforts in the past already and I’m looking forward to hear about Jan-Daniel’s experiences, what kind of technology was rolled out and how the system is used.

The talk is part of a lecture seriesof the Update computer club in Uppsala, Sweden and they’ll use their own BBB server for the event. Click here to join at 19:00 CEST on Saturday.

And here’s the announcement in full:

With increased refugee numbers, an unprecedented high demand for the possibility of communication with the remaining family members left home arose, rendering the previous solution insufficient. That previous solution was based on one WiFi AP and one repeater each per building, connected to a 50 Mbit/s DL/UL synchronous optical fibre network via an external VPN provider to ensure network separation with the company’s staff network. The aim of this project was to provide a new fast solution with its separate external connection, by building a separate network from the ground up. This is an ongoing endeavour, which has currently reached its test phase with three operational APs across two buildings and eight network switches across six buildings, more to follow.

Jan-Daniel Kaplanski (German Red Cross)

The lecture is free and open to everyone.