2.4. Creating and managing nftables tables, chains, and rules

Procedure

1. Create a table named nftables_svc with the inet address family so that the table can process both IPv4 and IPv6 packets:

   # nft add table inet nftables_svc

2. Add a base chain named INPUT, that processes incoming network traffic, to the inet nftables_svc table:

   # nft add chain inet nftables_svc INPUT { type filter hook input priority filter \; policy accept \; }

   To avoid that the shell interprets the semicolons as the end of the command, escape the semicolons using the \ character.

3. Add rules to the INPUT chain. For example, allow incoming TCP traffic on port 22 and 443, and, as the last rule of the INPUT chain, reject other incoming traffic with an Internet Control Message Protocol (ICMP) port unreachable message:

   # nft add rule inet nftables_svc INPUT tcp dport 22 accept
   # nft add rule inet nftables_svc INPUT tcp dport 443 accept
   # nft add rule inet nftables_svc INPUT reject with icmpx type port-unreachable

   If you enter the nft add rule commands as shown, nft adds the rules in the same order to the chain as you run the commands.

4. Display the current rule set including handles:

   # nft -a list table inet nftables_svc
   table inet nftables_svc { # handle 13
     chain INPUT { # handle 1
       type filter hook input priority filter; policy accept;
       tcp dport 22 accept # handle 2
       tcp dport 443 accept # handle 3
       reject # handle 4
     }
   }

5. Insert a rule before the existing rule with handle 3. For example, to insert a rule that allows TCP traffic on port 636, enter:

   # nft insert rule inet nftables_svc INPUT handle 3 tcp dport 636 accept

6. Append a rule after the existing rule with handle 3. For example, to insert a rule that allows TCP traffic on port 80, enter:

   # nft add rule inet nftables_svc INPUT handle 3 tcp dport 80 accept

7. Display the rule set again with handles. Verify that the later added rules have been added to the specified positions:

   # nft -a list table inet nftables_svc
   table inet nftables_svc { # handle 13
     chain INPUT { # handle 1
       type filter hook input priority filter; policy accept;
       tcp dport 22 accept # handle 2
       tcp dport 636 accept # handle 5
       tcp dport 443 accept # handle 3
       tcp dport 80 accept # handle 6
       reject # handle 4
     }
   }

8. Remove the rule with handle 6:

   # nft delete rule inet nftables_svc INPUT handle 6

   To remove a rule, you must specify the handle.

9. Display the rule set, and verify that the removed rule is no longer present:

   # nft -a list table inet nftables_svc
   table inet nftables_svc { # handle 13
     chain INPUT { # handle 1
       type filter hook input priority filter; policy accept;
       tcp dport 22 accept # handle 2
       tcp dport 636 accept # handle 5
       tcp dport 443 accept # handle 3
       reject # handle 4
     }
   }

10. Remove all remaining rules from the INPUT chain:

    # nft flush chain inet nftables_svc INPUT

11. Display the rule set, and verify that the INPUT chain is empty:

    # nft list table inet nftables_svc
    table inet nftables_svc {
      chain INPUT {
        type filter hook input priority filter; policy accept
      }
    }

12. Delete the INPUT chain:

    # nft delete chain inet nftables_svc INPUT

    You can also use this command to delete chains that still contain rules.

13. Display the rule set, and verify that the INPUT chain has been deleted:

    # nft list table inet nftables_svc
    table inet nftables_svc {
    }

14. Delete the nftables_svc table:

    # nft delete table inet nftables_svc

    You can also use this command to delete tables that still contain chains.

    注意

    To delete the entire rule set, use the nft flush ruleset command instead of manually deleting all rules, chains, and tables in separate commands.