IPv6 is like a zombie apocalypse.

You can kill it, but if you're not paying close attention, it will come back to haunt you.

A little background: I have IPv6 turned off in my main router because it creates more problems than it solves for me at this point in time.

While investigating the source of some odd behavior on BugPi (Pi4), I ran "journalctl -k". Here is a screenshot of what I found at the bottom of that log:

The Internet provided a hint that it might be related to IPv6. I thought I was done with IPv6, but then realized no, I had not disabled it on this particular device. Verification came by way of my favorite quick route to IP data: "ip addr".

NOTE: This screenshot is of Renegade's "ip addr" output. I had already finished fixing BugPi, so I couldn't show IPv6 on it. Ironically, doing this showed me I had not turned it off on Renegade either.

On the Pi, I was able to use "sudo nmtui" to turn IPv6 off on the current interface (the one showing "UP").

Issuing "ip addr" again showed IPv6 was gone. It held true after a reboot as well. And revisiting "journalctl" a couple of days later showed the earlier error was gone. So was the odd behavior that started all this in the first place.

greg@bugpi:~ $ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether e4:5f:01:32:f9:42 brd ff:ff:ff:ff:ff:ff
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether e4:5f:01:32:f9:43 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.17/24 brd 192.168.1.255 scope global dynamic noprefixroute wlan0
       valid_lft 52934sec preferred_lft 52934sec

OOPS. I have not disabled it on Renegade.

While writing this missive, I noticed IPv6 was active on my Mint laptop. Well that's no good. So I set about fixing that too.

However: IPv6 support is now in the Linux kernel

Using "sudo nmtui" (Network Manager) did not work on my Mint laptop. I discovered that is because IPv6 support is now baked into the kernel. So now we have to use "sudo sysctl net.ipv6.conf.all.disable_ipv6=1" to turn it off. That did work, and for now, the evil genie is back in the bottle.

2: wls8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 58:fb:84:73:a9:01 brd ff:ff:ff:ff:ff:ff
    altname wlp1s0
    inet 192.168.1.65/24 brd 192.168.1.255 scope global dynamic noprefixroute wls8
       valid_lft 84215sec preferred_lft 84215sec

I'm sure at some point IPv6 will be ready for prime time, but not just yet. I'll keep support for it turned off until it becomes a thing that works.