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Block an IP address or subnet with ufw

caution rootFirewalldebian, ubuntu

Caution: This command changes the system. Understand what it does before you run it.

Adjust the values, the command updates live
root@server
ufw insert 1 deny from 203.0.113.0/24

Inserts a deny rule at position 1 so it is checked before all allow rules. ufw evaluates rules from top to bottom, so a plain ufw deny at the end would be overridden by an existing port rule. The rule survives reboots and is removed with ufw delete deny from <quelle>.

Note: insert 1 fails if no rule exists yet, in that case simply use ufw deny from <quelle>. IPv6 addresses are sorted in separately before the first IPv6 rules.

Also searched as

  • ufw block ip address
  • ufw deny from subnet
  • ufw insert deny rule first

Related one-liners

All in Firewall

Allow a port only from a specific IP with ufw

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

Close a port in ufw by deleting its rule

#ufw delete allow 8080/tcp
cautionFirewall

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
harmlessFirewall

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
cautionFirewall

Delete a ufw rule by number

#ufw delete 3
cautionFirewall

Enable ufw logging

#ufw logging low
cautionFirewall

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