Root cause of the flow-selective IPv6 heartbeat loss investigated
2026-07-12/13: Ubuntu ships /usr/lib/sysctl.d/55-ipv6-privacy.conf with
use_tempaddr=2 system-wide. Nothing on wlan0 overrode it before this
morning's netplan fix, so the interface carried a rotating privacy
address alongside the stable one. hbc's long-lived flow eventually
straddled a temp-address deprecation event mid-flight, which looked
exactly like random upstream packet loss (in-transit, IPv6-only,
flow-selective) and cost a day of packet captures before the cause
turned out to be this default fighting the WAN config instead.
The netplan/NM ipv6.ip6-privacy=false fix already forces this per
connection, but that's a timing-dependent override racing a package
default. This makes it explicit and permanent: 99- loads after (and
wins over) 55- the next time sysctl --system runs.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Andreas WredeandClaude Sonnet 5
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