# nftables

Related articles

- Firewalls
- iptables

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Reason: nftables is an entirely new utility, and lacks sufficient documentation on this wiki. (Discuss in Talk:Nftables#)

nftables is a netfilter project that aims to replace the existing ip-, ip6-, arp-, and ebtables framework. It provides a new packet filtering framework, a new user-space utility (nft), and a compatibility layer for ip- and ip6tables. It uses the existing hooks, connection tracking system, user-space queueing component, and logging subsystem of netfilter.

You can also visit the official nftables wiki page for more information.

The first release is available in Linux 3.13, which is in the core repository (linux), and nftables (the user-space components) is available in the extra repository (nftables), and on the AUR in package nftables-gitAUR.

## Overview

nftables consists of three main components: a kernel implementation, the libnl netlink communication and the nftables user-space front-end. The kernel provides a netlink configuration interface, as well as run-time rule-set evaluation using a small classification language interpreter. libnl contains the low-level functions for communicating with the kernel; the nftables front-end is what the user interacts with.

## nft

nftables' user-space utility `nft` now performs most of the rule-set evaluation before handing rule-sets to the kernel. Because of this, nftables provides no default tables or chains; although, a user can emulate an iptables-like setup.

Note: nftables contains `/etc/nftables.conf` which has a "filter" table. Rules in this table are designed to allow some protocols and reject everything else.

It works in a fashion similar to ifconfig or iproute2. The commands are a long, structured sequence rather than using argument switches like in iptables. For example:

    nft add rule ip6 filter input ip6 saddr ::1 accept

`add` is the command. `rule` is a subcommand of `add`. `ip6` is an argument of `rule`, telling it to use the ip6 family. `filter` and `input` are arguments of `rule` specifying the table and chain to use, respectively. The rest that follows is a rule definition, which includes matches (`ip`), their parameters (`saddr`), parameter arguments (`::1`), and jumps (`accept`).

The following is an incomplete list of the commands available in nft:

    list
      tables [family]
      table [family] <name>
      chain [family] <table> <name>

    add
      table [family] <name>
      chain [family] <table> <name> [chain definitions]
      rule [family] <table> <chain> <rule definition>

    table [family] <name> (shortcut for `add table`)

    insert
      rule [family] <table> <chain> <rule definition>

    delete
      table [family] <name>
      chain [family] <table> <name>
      rule [family] <table> <handle>

    flush
      table [family] <name>
      chain [family] <table> <name>

`family` is optional, but it will default to `ip`.

## Tables

The purpose of tables is to hold chains. Unlike tables in iptables, there are no built-in tables in nftables. Tables can have one of five families specified, which unifies the various iptables utilities into one:

nftables family | iptables utility
--- | ---
ip | iptables
ip6 | ip6tables
inet | iptables and ip6tables
arp | arptables
bridge | ebtables

`ip` is the default family. `inet` requires Linux >=3.15 and allows for the unification of the ip and ip6 families to make defining rules for both easier.

### Listing

You can list the current tables in a family with the `nft list` command.

    # nft list tables
    # nft list tables ip6

You can list a full table definition by specifying a table name:

    # nft list table foo
    # nft list table ip6 foo

### Creation

Tables can be added via two commands — one just being a shortcut for the other. Here is an example of how to add an ip table called foo and an ip6 table called foo:

    # nft add table foo
    # nft table ip6 foo

You can have two tables with the same name as long as they are in different families.

### Deletion

Tables can only be deleted if there are no chains in them.

    # nft delete table foo
    # nft delete table ip6 foo

## Chains

The purpose of chains is to hold rules. Unlike chains in iptables, there are no built-in chains in nftables. This means that if no chain uses any types or hooks in the netfilter framework, packets that would flow through those chains will not be touched by nftables, unlike iptables.

### Listing

The `nft list table foo` command will list all the chains in the foo table. You can also list rules from an individual chain.

    # nft list chain foo bar
    # nft list chain ip6 foo bar

These commands will list the `bar` chains in the ip and ip6 `foo` tables.

### Creation

Chains can be added when a table is created in a file definition or one at time via the `nft add chain` command.

    # nft add chain foo bar
    # nft add chain ip6 foo bar

These commands will add a chain called `bar` to the ip and ip6 `foo` tables.

#### Properties

Because nftables has no built-in chains, it allows chains to access certain features of the netfilter framework.

    # nft add chain filter input \{ type filter hook input priority 0\; \}

This command tells nftables to add a chain called `input` to the `filter` table and defines its type, hook, and priority. These properties essentially replace the built-in tables and chains in iptables.

##### Types

There are three types a chain can have and they correspond to the tables used in iptables:

- filter
- nat
- route (mangle)

##### Hooks

There are five hooks a chain can use and they correspond to the chains used in iptables:

- input
- output
- forward
- prerouting
- postrouting

##### Priorities

Note: Priorities do not currently appear to have any effect on which chain sees packets first.
Note: Since the priority seems to be an unsigned integer, negative priorities will be converted into very high priorities.

Priorities tell nftables which chains packets should pass through first. They are integers, and the higher the integer, the higher the priority.

### Deletion

Chains can only be deleted if there are no rules in them.

    # nft delete chain foo bar
    # nft delete chain ip6 foo bar

These commands delete the `bar` chains from the ip and ip6 `foo` tables.

## Rules

The purpose of rules is to identify packets (match) and carry out tasks (jump). Like in iptables, there are various matches and jumps available, though not all of them are feature-complete in nftables.

### Listing

You can list the current rules in a table with the `nft list` command, using the same method as listing a table. You can also list rules from an individual chain.

    # nft list chain foo bar
    # nft list chain ip6 foo bar

These commands will list the rules in the `bar` chains in the ip and ip6 `foo` tables.

### Creation

Rules can be added when a table is created in a file definition or one at time via the `nft add rule` command.

    # nft add rule foo bar ip saddr 127.0.0.1 accept
    # nft add rule ip6 foo bar ip saddr ::1 accept

These commands will add a rule to the `bar` chains in the ip and ip6 `foo` tables that matches an `ip` packet when its `saddr` (source address) is 127.0.0.1 (IPv4) or ::1 (IPv6) and accepts those packets.

#### Matches

There are various matches available in nftables and, for the most part, coincide with their iptables counterparts. The most noticeable difference is that there are no generic or implicit matches anymore. A generic match was one that was always available, such as `--protocol` or `--source`. Implicit matches were protocol-specific, such as `--sport` when a packet was determined to be TCP.

The following is an incomplete list of the matches available:

- meta (meta properties, e.g. interfaces)
- icmp (ICMP protocol)
- icmpv6 (ICMPv6 protocol)
- ip (IP protocol)
- ip6 (IPv6 protocol)
- tcp (TCP protocol)
- udp (UDP protocol)
- sctp (SCTP protocol)
- ct (connection tracking)

The following is an incomplete list of match arguments (for a more complete list, see `man 8 nft`):

    meta:
      oif <output interface INDEX>
      iif <input interface INDEX>
      oifname <output interface NAME>
      iifname <input interface NAME>

      (oif and iif accept string arguments and are converted to interface indexes)
      (oifname and iifname are more dynamic, but slower because of string matching)

    icmp:
      type <icmp type>

    icmpv6:
      type <icmpv6 type>

    ip:
      protocol <protocol>
      daddr <destination address>
      saddr <source address>

    ip6:
      daddr <destination address>
      saddr <source address>

    tcp:
      dport <destination port>
      sport <source port>

    udp:
      dport <destination port>
      sport <source port>

    sctp:
      dport <destination port>
      sport <source port>

    ct:
      state <new | established | related | invalid>

#### Jumps

Jumps work the same as they do in iptables, except multiple jumps can now be used in one rule.

    # nft add rule filter input tcp dport 22 log accept

The following is an incomplete list of jumps:

- accept (accept a packet)
- reject (reject a packet)
- drop (drop a packet)
- snat (perform source NAT on a packet)
- dnat (perform destination NAT on a packet)
- log (log a packet)
- counter (keep a counter on a packet; counters are optional in nftables)
- return (stop traversing the chain)
- jump <chain> (jump to another chain)
- goto <chain> (jump to another chain, but do not return)

### Insertion

Rules can be prepended to chains with the `nft insert rule` command.

    # nft insert rule filter input ct state established,related accept

### Deletion

Individual rules can only be deleted by their handles. The `nft --handle list` command must be used to determine rule handles. Note the `--handle` switch, which tells `nft` to list handles in its output.

The following determines the handle for a rule and then deletes it. The `--number` argument is useful for viewing some numeric output, like unresolved IP addresses.

    # nft --handle --numeric list chain filter input

    table ip fltrTable {
         chain input {
              type filter hook input priority 0;
              ip saddr 127.0.0.1 accept # handle 10
         }
    }

    # nft delete rule fltrTable input handle 10

All the chains in a table can be flushed with the `nft flush table` command. Individual chains can be flushed using either the `nft flush chain` or `nft delete rule` commands.

    # nft flush table foo
    # nft flush chain foo bar
    # nft delete rule ip6 foo bar

The first command flushes all of the chains in the ip `foo` table. The second flushes the `bar` chain in the ip `foo` table. The third deletes all of the rules in `bar` chain in the ip6 `foo` table.

### Atomic Reloading

Flush the current ruleset :

    # echo "flush ruleset" > /tmp/nftables

Dump the current ruleset:

    # nft list ruleset >> /tmp/nftables

Now you can edit /tmp/nftables and apply your changes with:

    # nft -f /tmp/nftables

## File Definitions

File definitions can be used by the `nft -f` command, which acts like the `iptables-restore` command. However, unlike `iptables-restore`, this command does not flush out your existing ruleset, to do so you have to prepend the flush command.

    /etc/nftables/filter.rules

    flush table ip filter
    table ip filter {
         chain input {
              type filter hook input priority 0;
              ct state established,related accept
              ip saddr 127.0.0.1 accept
              tcp dport 22 log accept
              reject
         }
    }

To export your rules (like `iptables-save`):

    # nft list ruleset

## Getting Started

The below example shows nft commands to configure a basic IPv4 only firewall. If you want to filter both IPv4 and IPv6 you should look at the other examples in `/usr/share/nftables` or just start with the default provided in `/etc/nftables.conf` which already works with IPv4/IPv6.

To get an iptables-like chain set up, you will first need to use the provided IPv4 filter file:

    # nft -f /usr/share/nftables/ipv4-filter

To list the resulting chain:

    # nft list table filter

Drop output to a destination:

    # nft add rule ip filter output ip daddr 1.2.3.4 drop

Drop packets destined for local port 80:

    # nft add rule ip filter input tcp dport 80 drop

Delete all rules in a chain:

    # nft delete rule filter output

## Samples

### Simple IP/IPv6 Firewall

    firewall.rules

    # A simple firewall

    flush ruleset

    table firewall {
      chain incoming {
        type filter hook input priority 0;

        # established/related connections
        ct state established,related accept

        # invalid connections
        ct state invalid drop

        # loopback interface
        iifname lo accept

        # icmp
        icmp type echo-request accept

        # open tcp ports: sshd (22), httpd (80)
        tcp dport {ssh, http} accept

        # everything else
        drop
      }
    }

    table ip6 firewall {
      chain incoming {
        type filter hook input priority 0;

        # established/related connections
        ct state established,related accept

        # invalid connections
        ct state invalid drop

        # loopback interface
        iifname lo accept

        # icmp
        # routers may also want: mld-listener-query, nd-router-solicit
        icmpv6 type {echo-request,nd-neighbor-solicit} accept

        # open tcp ports: sshd (22), httpd (80)
        tcp dport {ssh, http} accept

        # everything else
        drop
      }
    }

### Limit rate IP/IPv6 Firewall

    firewall.2.rules

    table firewall {
        chain incoming {
            type filter hook input priority 0;

            # no ping floods:
            ip protocol icmp limit rate 10/second accept
            ip protocol icmp drop

            ct state established,related accept
            ct state invalid drop

            iifname lo accept

    	# avoid brute force on ssh:
            tcp dport ssh limit rate 15/minute accept

            reject
        }
    }

    table ip6 firewall {
        chain incoming {
            type filter hook input priority 0;

            # no ping floods:
            ip6 nexthdr icmpv6 limit rate 10/second accept
            ip6 nexthdr icmpv6 drop

            ct state established,related accept
            ct state invalid drop

            # loopback interface
            iifname lo accept

    	# avoid brute force on ssh:
            tcp dport ssh limit rate 15/minute accept

            reject
        }
    }

### Jump

When using jumps in config file, it is necessary to define the target chain first. Otherwise one could end up with `Error: Could not process rule: No such file or directory`.

    jump.rules

    table inet filter {
        chain web {
            tcp dport http accept
            tcp dport 8080 accept
        }
        chain input {
            type filter hook input priority 0;
            ip saddr 10.0.2.0/24 jump web
            drop
        }
    }

## Loading rules at boot

To automatically load rules on system boot, simply enable the nftables systemd service by executing `systemctl enable nftables`

The rules will be loaded from `/etc/nftables.conf` by default.

Note: You may have to create `/etc/modules-load.d/nftables.conf` with all of the nftables related modules you require as entries for the systemd service to work correctly. You can get a list of modules using this command:

    lsmod | grep nf

Otheriwse, you could end up with the dreaded `Error: Could not process rule: No such file or directory` error.

## Logging to Syslog

If you use a Linux kernel < 3.17, you have to modprobe `xt_LOG` to enable logging.

## See also

- netfilter nftables wiki
- First release of nftables
- nftables quick howto
- The return of nftables

Category:

- Firewalls