I just spend few days debugging absolutely simple problem.
My servers wasn’t able to communicate after applying nftables rules with policy deny.
The rule was very simple:
iifname eth0 ip6 saddr @good ip6 daddr…
If by any chance you’ve lost your IPv6 link local address, a simple interface up/interface down wouldn’t restore link local address to you.
Before providing a magical code to restore that address, here is the way to loose…