Yesterday I read this toot (German) over on mastodon which starts with “IPv6 is hard.”

No it’s not. It’s different.

I ran across this multiple times: There is an A and an AAAA-record for a FQDN, but the web server is only reachable via IPv4. You can easily test this with curl

$ curl -4  https://github.com -o /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  273k    0  273k    0     0  3417k      0 --:--:-- --:--:-- --:--:-- 3553k
$ curl -6  https://github.com -o /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (7) Couldn't connect to server

When using IPv4 273k are “saved” to /dev/null, using IPv6 we get an error message “Couldn’t connect to server”

• CLAT in Linux Networkmanager
• DNS delegation
• jc - Convert command output to json
• Stratoshark - Analyse syscalls
• curl from start to end
• Security Bingo
• Linux Routing Fundamentals
• Packet where are you
• nftable-tracer

• https://github.com/ipinfo/cli
• [https://blog.sdn.clinic/2025/03/wireguard-and-vrfs/9(https://blog.sdn.clinic/2025/03/wireguard-and-vrfs/]
• https://github.com/girishji/pythondoc.vim

Some time ago I asked on Mastodon if someone would be interested in a series of videos about IPv6. Some people are, so I’ll give it a try. Each video will be accompanied by a blog post. This blog post and other materials will be available on gitlab.

Starting in January 2025, videos will come out every Tuesday evening (CET) and I’ll try to keep them between 10 and 20 minutes.

Last week I talked about ContainerLab at our admin meetup in Berlin.

Containerlab provides a CLI for orchestrating and managing container-based networking labs. It starts the containers, builds a virtual wiring between them to create lab topologies of users choice and manages labs lifecycle.

As allways the presentation was streamed and recorded.

Talk was in German, slides are in English:

• Recording
• Slides