Firewall

Open and close ports, check rules, block and unblock IPs. With ufw for a quick start, nftables for full control and CrowdSec for community-maintained blocklists.

21 one-liners: 8 harmless, 11 caution, 2 destructive

firewall 15 ufw 10 ban 5 crowdsec 5 cscli 5 nftables 4 nft 4 port 3 rules 3 ssh 2 iptables 2 backup 2 logging 2

Add an IP address to an nftables blocklist

#nft add element inet filter blocklist '{ 203.0.113.25 }'

Allow a port only from a specific IP with ufw

#ufw allow from 198.51.100.0/24 to any port 22 proto tcp

Back up iptables rules to a file

#iptables-save > /root/iptables-$(date +%F-%H%M).rules

Ban an IP address manually in CrowdSec

#cscli decisions add --ip 203.0.113.25 --duration 24h --reason 'manual ban'

Block an IP address or subnet with ufw

#ufw insert 1 deny from 203.0.113.0/24

Close a port in ufw by deleting its rule

#ufw delete allow 8080/tcp

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Count IP addresses blocked by ufw

#journalctl -k --since "today" --no-pager | grep 'UFW BLOCK' | grep -o 'SRC=[^ ]*' | sort | uniq -c | sort -rn | head -20

Create an IP blocklist set in nftables

#nft add set inet filter blocklist '{ type ipv4_addr; flags interval; }' && nft insert rule inet filter input ip saddr @blocklist drop

Delete a ufw rule by number

Enable ufw logging

#ufw logging low

Enable ufw without locking yourself out

#ufw allow 22/tcp && ufw enable

List ufw rules with numbers

#ufw status numbered

Open a port with nftables

#nft insert rule inet filter input tcp dport 443 accept

Open a port with ufw

#ufw allow 443/tcp

Restore iptables rules from a backup

#iptables-restore --test < /root/iptables-2026-10-09-1200.rules && iptables-restore < /root/iptables-2026-10-09-1200.rules

Show active CrowdSec decisions and bans

#cscli decisions list

Show CrowdSec alerts

#cscli alerts list

Show CrowdSec metrics for logs, parsers and bouncers

Show detailed ufw status and default policies

#ufw status verbose

Show the complete nftables ruleset with handles

#nft -a list ruleset

Unban an IP address in CrowdSec

#cscli decisions delete --ip 198.51.100.10