Last night, my Ubuntu-based VPS updated itself to Linux smtp 5.15.0-56-generic #62-Ubuntu SMP Tue Nov 22 19:54:14 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
and since then, SLAAC seems to be unconditionally enabled.
For weird reasons, the provider decided to have static IPv6 configuration, and set up the VPS with
net.ipv6.conf.net0.accept_ra = 0
net.ipv6.conf.net0.autoconf = 0
As I understand it, this should disable SLAAC addresses.
However, since the recent update, I do see SLAAC addresses on my net0
interface. That would by itself not be a problem, but it somehow breaks IPv6 connectivity from some but not all sources.
In my log files, I can see successful IPv6 connections to the smtp service before the reboot, but not after.
I tried removing the addresses manually, but they come back after some time.
rhialto@smtp:/var/log$ ip a
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
valid_lft forever preferred_lft forever
2: net0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether xx:xx:xx:xx:26:48 brd ff:ff:ff:ff:ff:ff
altname enp0s3
altname ens3
inet xxx.xxx.xxx.129/24 brd xxx.xxx.xxx.255 scope global dynamic net0
valid_lft 60541sec preferred_lft 60541sec
inet6 2a02:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:2648/64 scope global dynamic mngtmpaddr noprefixroute
valid_lft 2591895sec preferred_lft 604695sec
inet6 2a02:xxxx:xxxx:xxxx:yyyy:xxxx:xxxx:2648/64 scope global dynamic mngtmpaddr noprefixroute
valid_lft 2591895sec preferred_lft 604695sec
inet6 2a02:zzzz:zzzz:zzzz::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::xxxx:xxxx:xxxx:2648/64 scope link
valid_lft forever preferred_lft forever
The desired address is near the bottom: 2a02:zzzz:zzzz:zzzz::1/64
Also it causes tools like traceroute6 to choose the wrong source address, and outgoing IPv6 connections use the wrong source address:
rhialto@smtp:$ ip -6 route get 2a00:1450:400e:810::2004
2a00:1450:400e:810::2004 from :: via fe80::wwww:wwww:wwww:f03d dev net0 proto ra src 2a02:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:2648 metric 1024 pref high
Are the Ubuntu people already aware of this issue and when will it be fixed?
Addendum: when I rebooted back to the previous version, all was well again, for a few minutes. That was Linux smtp 5.15.0-53-generic #59-Ubuntu SMP Mon Oct 17 18:53:30 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
. Then the SLAAC addresses came back. So maybe the problem exists for longer than I thought.