Tailscale ports: what to open on your firewall
Tailscale needs no inbound port in most setups. See the outbound ports it uses, why 41641 is not 51820, and the ufw and firewalld rules that help on a VPS.
#ufw
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List the active firewall rules on Ubuntu
Three views of one ruleset on Ubuntu: nft list ruleset, iptables -L -n -v and ufw status. Find shadowed rules with counters and see why Docker skips ufw.
Docker bypasses UFW: why and how to fix it
Docker publishes container ports with iptables rules that skip UFW, so a denied port still answers the internet. See the mechanism and the fixes that work.
Recover from a broken ufw ruleset
Locked out by ufw? Get back in through the provider console, disable the firewall, read the rules that actually applied, and stop it happening again.
UFW and IPv6: the open door on your VPS
Your cloud firewall or handwritten iptables may only cover IPv4, leaving services wide open on IPv6. See why it happens on a VPS and how to close the gap.
UFW firewall basics: set up a VPS firewall
UFW is the simple way to run a firewall on a VPS. Set a default-deny policy, allow only the ports you need, and turn it on without locking out SSH.