Each line in configuration section is a single rule. Single rule contains optional matching parts and statement part.

Matches TCP / UDP / ICMP / ICMPv6 traffic. This matcher is usually followed by port number. For example tcp 443 matches TCP traffic to port 443 (https). Without port number all traffic is matched. See protocol how to match other protocols.

Instead of using tcp 443 it is recommended to use pre-defined https macro. All known macros can be listed with foomuuri list macro command.

Matches source / destination port, followed by port number. dport matcher is usually optional: tcp 443 is equal to tcp dport 443.

Port number can be:

• Single number 443
• Multiple numbers 80 443, matching 80 or 443
• Range 8880-9000
• Range and number 80 443 8880-9000
• Negative number -443, matching all but 443
• Multiple negative numbers -80 -443, matching all but 80 or 443

Matches source / destination IPv4 or IPv6 address.

Address can be

• Single IPv4 address 10.0.0.1
• Single IPv6 address fd00:f00::1
• Address with netmask 10.0.0.0/8 or fd00:f00::/32
• IPv6 address with suffix netmask ::10:0:0:f00/-64 to match with netmask ::ffff:ffff:ffff:ffff
• Interval 10.0.0.10-10.0.0.20 or fd00:f00::10-fd00:f00::20
• Multiple addresses 10.0.0.1 10.0.0.10-10.0.0.20 fd00:f00::/32. You can list both IPv4 and IPv6 addresses in same rule. Foomuuri will split them automatically to correct traffic chains.
• Negative address -10.0.0.1 or -fd00:f00::1, meaning all other addresses.
• Negative IPv6 address with suffix netmask -::10:0:0:f00/-64
• Multiple negative addresses -10.0.0.1 -fd00:f00::1
• Iplist set name @listname
• Negative iplist set name -@listname

This matcher is usually combined with tcp port matcher to allow traffic from specific source IP only, tcp 443 saddr 10.0.0.1, or to specific destination IP.

Matches source / destination MAC address for incoming traffic [new in version 0.24]. This doesn't work for outgoing traffic.

Address can be:

• Single MAC address 01:23:45:67:89:ab
• Multiple MAC addresses 01:23:45:67:89:ab 01:23:45:67:89:cc
• Negative MAC address -01:23:45:67:89:ab, meaning all other addresses.
• Multiple negative MAC addresses -01:23:45:67:89:ab -01:23:45:67:89:cc

Example:

internal-localhost {
  # drop spoofed traffic from 10.0.0.3
  saddr 10.0.0.3 mac_saddr -12:00:27:00:00:ce drop log "MAC-SPOOF"
  ...
}

Matches incoming / outgoing interface name. This is used mostly on snat, dnat and zonemap sections. For example in snat saddr 10.0.0.0/8 oifname eth0 masquerade will match all traffic coming from 10.0.0.0/8, going to eth0, and masquerades it.

Multiple interface names can be specified. Negative interface name(s) works too, meaning all but specified name(s).

Single rule will apply to both IPv4 and IPv6 traffic. Adding ipv4 or ipv6 matcher to rule will limit it to IPv4 or IPv6 only.

Matches multicast or broadcast traffic. Foomuuri will silently drop all incoming multicast and broadcast traffic unless explicitly accepted by rule.

Linux kernel can match multicast/broadcast only in incoming traffic. Therefore Foomuuri generates outgoing nft rule without multicast/broadcast matcher even if one was specified in the rule. This makes it easy to use same rule or macro for all traffic, no matter if it's incoming or outgoing.

Rule broadcast udp 11430 allows incoming broadcast messages to UDP port 11430, or all outgoing traffic to UDP port 11430. Rule multicast allows all incoming multicasts, nothing for outgoing. It is highly recommended to always specify daddr for multicast rules.

Example:

public-localhost {
  # Allow all incoming multicasts
  multicast
  ...
}

localhost-public {
  # Allow some outgoing multicast addresses. This rule can also be written
  # without "multicast" matcher as it will be omitted.
  multicast daddr 224.0.0.0/8 239.0.0.0/8 ff00::/8
  ...
}

It is much better to accept specific multicast/broadcast only, not everything. For example macro ssdp is defined as:

macro {
  ssdp    multicast udp 1900 daddr 239.255.255.250 ff02::c; udp sport 1900
}

public-localhost {
  # Allow incoming ssdp
  ssdp
  ...
}

localhost-public {
  # Allow outgoing ssdp
  ssdp
  ...
}

Above macro allows incoming traffic to specific multicast addresses and UDP port 1900, outgoing traffic to same addresses and port, and finally unicast from same port.

Matches specific protocol traffic [new in version 0.22]. For example protocol gre will match all GRE traffic and protocol sctp 22 will match SCTP traffic to port 22.

For TCP, UDP, ICMP and ICMPv6 protocols it is recommended to use shortcut matchers.

Matches incoming / outgoing IPsec traffic. These are useful if you want to allow traffic from/to IPsec without creating a new vpn zone for them. Example:

public-localhost {
  ssh              # Allow SSH with and without IPsec
  tcp 1234 sipsec  # Allow TCP 1234 with IPsec only
  ...
}

To split IPsec and non-IPsec traffic to vpn and public zones you can use these matchers in zonemap section. Usually it is not necessary to create separate zone for that.

Negative matchers -sipsec and -dipsec can also be used. They match non-IPsec traffic. These are useful in snat and dnat sections.

Matches traffic generated by uid / gid user. This works only for traffic from localhost. For example tcp 2703 uid amavis in localhost-public section allows outgoing TCP 2703 traffic from user amavis.

Multiple uid / gid names or numbers can be specified. Negative value(s) works too, meaning all but specified value(s).

Matches packet's mark. Argument can be:

• Number 42 or 0x2a
• Number with mask 0x100/0xff00, meaning check if mark and 0xff00 is equal to 0x100
• Negative number -42, meaning all other marks than 42
• Negative number with mask -0x0000/0xff00 for non-equal check

Set packet's mark. Argument can be:

• Number 42 or 0x2a
• Number with mask 0x100/0xff00, meaning set bits 0xff00 to 0x100. In other words, this keeps lower 8 bits as they are and sets upper 8 bits.

This is not normal matcher as it matches everything. Usually some other matcher should be used first. Example:

prerouting {
  iifname eth0 mark_set 0x100/0xff00  # Mark traffic from eth0 and accept it
  iifname eth1 mark_set 0x200/0xff00  # Mark traffic from eth1 and accept it
  mark_set 0x300/0xff00               # Mark all other traffic
}

Matches packet's traffic control class id. Argument can be:

• Class id 1:ff01 or 1:0xff01 (0x is optional)
• Text none for no priority set

Set packet's traffic control class id.

This is not normal matcher as it matches everything. Usually some other matcher should be used first. Example:

forward {
  daddr 192.168.0.0/16 priority_match none priority_set 1:ff01
  saddr 192.168.0.0/16 priority_match none priority_set 1:ff01
  priority_match none priority_set 1:2
}

Matches packet's conntrack status, mostly used with SNAT or DNAT [new in version 0.24]. Valid arguments are: expected, seen-reply, assured, confirmed, snat, dnat, dying.

Matches cgroup id or cgroupv2 name. Argument can be:

• Single number 1234
• Multiple numbers 1234 1244
• Range 4000-5000
• Range and number 1234 1244 4000-5000
• Negative number -1234, matching all but 1234
• Multiple negative numbers -1234 -1244, matching all but 1234 or 1244
• cgroupv2 name user.slice or system.slice/sshd.service

Warning: cgroupv2 must exist before starting Foomuuri. As Foomuuri starts very early on boot using this feature incorrectly can break your firewall startup.

Matches current time, date and day of the week [new in version 0.24]. Argument can be:

• Time hh:mm or hh:mm:ss
• Time interval hh:mm-hh:mm
• Date yyyy-mm-dd
• Day of the week: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
• Compare function: == (equal, the default), != (not equal), <, >, <=, >=
• Combination of above

Example:

public-localhost {
  # Allow until year 2025
  tcp 1234 time "< 2025-01-01"

  # Kids, go to bed! Reject traffic at night time.
  saddr @kids time "23:00-07:00" reject

  # Strange combination: Allow traffic on Mondays at 16-22, until year 2025
  tcp 5001 time "Monday 16:00-22:00 < 2025-01-01"
}

Matches packet's differentiated services code point (DSCP) value [new in version 0.28]. Example:

internal-public {
  saddr 10.0.0.4 dscp 10
  dscp af13
}

Accepts, drops or rejects traffic. Default statement for single rule is to accept matched traffic: tcp 443 is equal to tcp 443 accept.

You should always add explicit final statement as last rule to every zone-zone section in your configuration.

• For incoming traffic from internet to localhost/intranet the recommended statement is drop log.
• For outgoing traffic from localhost/intranet to internet the recommended statement is reject log.

Continues to next rule [new in version 0.24]. This is used mostly to debug rules. For example rule saddr 10.0.0.4 counter log continue counts and logs traffic from 10.0.0.4 and continues to next rule.

This is a special statement to return from current nftables chain to caller chain. Not normally used.

These statements are used in snat and dnat sections to mangle traffic source or destination IP address.

Forward packet to userspace for example for IPS/IDS inspection [new in version 0.25]. Optional flags and target can be specified. Example:

forward {
   # Forward all packets to userspace for IPS inspection
   queue flags fanout,bypass to 3-5

   # Forward matching packets only
   iifname eth0 oifname eth1 queue
}

Add byte and packet counter to rule. All traffic matching this rule will be counted. Counter can be named or anonymous. To name a counter add name after counter, for example counter my_counter.

Example:

localhost-public {
  # Add named counter to count all outgoing traffic
  counter outgoing_traffic continue -conntrack

  # Accept ssh and add anonymous counter for it
  ssh counter

  # Accept http + https and add named counter
  http counter web_traffic
  https counter web_traffic

  # Reject SMTP with named counter
  smtp reject counter smtp_blocked
}

Named counter values can be listed with foomuuri list counter. Anonymous counters can be listed with foomuuri list.

Write log entry (journal / syslog) when traffic matches this rule. Optional log prefix can be added. Default prefix is "szone-dzone STATEMENT", for example "localhost-public REJECT".

Following variables are supported in log prefix [new in version 0.29]:

• $(szone)
• $(dzone)
• $(statement)

More text to default log prefix can be added with log + "my text" [new in version 0.29].

Example:

public-localhost {
  # Use default log prefix "public-localhost DROP"
  ssh drop log

  # Drop and log incoming http with custom prefix
  http drop log "incoming-http dropped"

  # Drop and log https with custom prefix with variables. This results to
  # prefix "public => localhost: DROP"
  https drop log "$(szone) => $(dzone): $(statement)"

  # Drop telnet with prefix "public-localhost DROP:telnet"
  telnet drop log + ":telnet"

  # Use default log prefix "public-localhost DROP"
  drop log
}

Foomuuri will limit logging to log_rate rate. Default value is to log first three entries per source IP and then one additional entry per second.

This overrides global foomuuri { log_level ... } logging level for this single rule [new in version 0.22].

Possible values are:

• level emerg
• level alert
• level crit
• level err
• level warn
• level notice
• level info
• level debug

Optionally flags can be appended:

• flags tcp sequence,options enables logging of TCP sequence and options
• flags ip options enables IP options
• flags skuid enables socket UID
• flags ether enables ethernet link layer address
• flags all enables all flags

To use nflog infrastructure instead of syslog specify value group 0 (or any other number) instead of level x. Nflog options can be appended:

• snaplen 256 specifies length of packet payload to include
• queue-threshold 20 will queue packets inside the kernel before sending them to userspace

Example:

public-localhost {
  # Drop and log incoming http requests with critical level, all flags
  http drop log log_level "level crit flags all"
  ...
}

Defines global rate limit without source or destination IP address check. For example https global_rate "10/second burst 20" allows https traffic with rate:

• First 20 new connections are allowed without limit.
• After burst is filled, up to 10 new connections per second are allowed.
• This rate is "global", meaning that one single source IP can use all allowed slots, or 20 sources can use one slot each.
• Here "connection" means new connection, not total number of established, active connections (see ct count below).

There are three types of rates:

• New connection rates (x/time burst y), ignoring if some of them have already been closed.

  • "5/second"
  • "7/second burst 30"
  • "30/minute"
  • "50/minute burst 200"
  • "100/hour"
  • "100/hour burst 100"
  • "over 8/second burst 10"

• Bandwidth rates (x bytes/time burst y bytes) [new in version 0.28]:

  • "10 mbytes/second"
  • "10 mbytes/second burst 12000 kbytes"
  • "over 10 mbytes/second"
  • "over 10 mbytes/second burst 12000 kbytes"

• Conntrack rates (ct count x) counting total number of established, active connections:

  • "ct count 5"
  • "ct count over 6"

New connection rate limit can be visualized as leaking water bucket. burst 10 specifies the bucket size as 10 units. 3/minute specifies how much it leaks, 3 units per minute, or 1 unit per every 20 seconds. Every new connection adds one unit of water to it. If it fits, rule matches (usually: connection is accepted). If the bucket overflows, rule doesn't match.

If burst is not specified, value 5 is assumed for it.

Some examples:

• 5/minute burst 1 allows one new connection (burst 1) and new connection every 12 second (5/minute).
• 3/minute burst 5 allows up to 5 new connections and new connection every 20 second after those 5 connections are used.

Bandwidth rate can be used as simple traffic limiter. This can be specified per service, or total for all. Example:

public-localhost {
  # Limit all incoming traffic to 30 MiB/s, total for all traffic
  global_rate "over 30 mbytes/second" drop -conntrack

  # Limit incoming SSH traffic to 2 MiB/s, per service traffic
  ssh global_rate "over 2 mbytes/second" drop -conntrack

  # Allow incoming SSH connections
  ssh
  ...
}

Rate ct count 5 matches if there are up to 5 established connections, including current one. So rule ssh global_rate "ct count 2" allows two SSH connections (one old + current).

Rate ct count over 6 matches if there are more than 6 established connections. This is usually used with drop statement: ssh global_rate "ct count over 6" drop.

Source / destination IP address specific rate limit is similar to global_rate.

saddr_rate allows limited amount of connections or bandwidth from single source IP address, but there is no total (global) limit.

daddr_rate allows limited amount of connections or bandwidth for single destination IP address, which is usually some host in dmz zone.

Both saddr_rate and daddr_rate can be specified for single rule. For example https saddr_rate "10/second" daddr_rate "1000/second" specifies:

• Single IP can open 10 new connections per second.
• Total of 1000 connection per second from all IPs are allowed.

Normally full IPv4 or IPv6 addresses are considered when counting saddr_rate or daddr_rate. This can be changed with netmask: ping saddr_rate "5/second burst 20" saddr_rate_mask 24 56 uses /24 and /56 instead of full IP address when counting limits.

If you want to share same rate limit with two different rules you must specify a name for it. For example:

  http  saddr_rate "30/second burst 50" saddr_rate_name http_limit
  https saddr_rate "30/second burst 50" saddr_rate_name http_limit

This counts both http and https traffic as single, allowing total of 30 connections per IP per second. Without name it would allow 30 + 30 connections per IP per second.

This is special form of saddr_rate + daddr_rate, usable when you have multiple destination IPs per service (DNS round-robin). In this rule both source and destination address are counted as check key, instead of only source or destination.

Template is very similar to macro. It's just another way to define list of rules. Usually macro refers to single service (like domain or facetime) while template refers to list of different services. Example:

template my_own_name {  # Define template called "my_own_name"
  domain
  https
  ssh
}

localhost-public {
  template my_own_name  # Include template's content here
  ping
  reject log
}

See host firewall for real life example.

These can be specified in zonemap section to match original source or destination zone, and to change it to a new zone. These are used to branch out some specific traffic to its own zone, for example to split vpn and public (non-VPN) traffic.

Linux kernel provides conntrack helper functionality to some services with multiple ports, like ftp (tcp 21). You can enable this functionality by appending helper kernelname-port after matcher. For example tcp 21 helper ftp-21.

Linux has following helpers: amanda, ftp, h323, irc, netbios_ns, pptp, sane, sip, snmp, tftp

Sets maximum segment size (MSS clamping) to all traffic in zone-zone section. Some connections, like IPsec, might require this. Example:

localhost-vpn {
  mss 1390
  ssh
  reject log
}

Rules are processed after conntrack check (flag conntrack, default value). Flag -conntrack [new in version 0.24] can be added to process rule before conntrack. Conntrack will accept established and related traffic so normal rule will see only new traffic.

This can be used to count all traffic instead of new connections only, or to accept traffic without adding it to conntrack. For example high load DNS server might accept DNS traffic without conntrack.

Example:

public-localhost {
  # Count all incoming traffic
  counter incoming_traffic continue -conntrack

  # Count incoming HTTP(S) traffic in web server
  tcp dport 80 443 counter web_traffic_in continue -conntrack
  ...
}

localhost-public {
  # Count outgoing HTTP(S) traffic in web server
  tcp sport 80 443 counter web_traffic_out continue -conntrack
  ...
}

Raw nftables rule can written with nft "raw rule here". This works in zone-zone, zonemap, snat and dnat sections. For example, https macro can be written as:

  nft "tcp dport 443 accept"
  nft "udp dport 443 accept"

nft can also be used as part of rule:

  # Jump to my-custom-chain for UDP traffic to ports 1000-2000
  udp dport 1000-2000 nft "jump my-custom-chain"

See nftables web page for more information about nftables syntax.