path: root/doc/libnftables-json.adoc

libnftables-json(5)
===================
Phil Sutter <phil@nwl.cc>
:doctype: manpage
:compat-mode!:

== NAME
libnftables-json - Supported JSON schema by libnftables

== SYNOPSIS
*{ "nftables": [* 'OBJECTS' *] }*

'OBJECTS' := 'LIST_OBJECTS' | 'CMD_OBJECTS'

'LIST_OBJECTS' := 'LIST_OBJECT' [ *,* 'LIST_OBJECTS' ]

'CMD_OBJECTS' := 'CMD_OBJECT' [ *,* 'CMD_OBJECTS' ]

'CMD_OBJECT' := *{* 'CMD'*:* 'LIST_OBJECT' *}* | 'METAINFO_OBJECT'

'CMD' := *"add"* | *"replace"* | *"create"* | *"insert"* | *"delete"* |
         *"list"* | *"reset"* | *"flush"* | *"rename"*

'LIST_OBJECT' := 'TABLE' | 'CHAIN' | 'RULE' | 'SET' | 'MAP' | 'ELEMENT' |
		 'FLOWTABLE' | 'COUNTER' | 'QUOTA' | 'CT_HELPER' | 'LIMIT' |
		 'METAINFO_OBJECT' | 'CT_TIMEOUT'

== DESCRIPTION
libnftables supports JSON formatted input and output. This is implemented as an
alternative frontend to the standard CLI syntax parser, therefore basic
behaviour is identical and, for (almost) any operation available in standard
syntax, there should be an equivalent one in JSON.

JSON input may be provided in a single string as parameter to
*nft_run_cmd_from_buffer()* or in a file identified by the 'filename' parameter
of the *nft_run_cmd_from_filename()* function.

JSON output has to be enabled via the *nft_ctx_output_set_json()* function, turning
library standard output into JSON format. Error output remains unaffected.

== GLOBAL STRUCTURE
In general, any JSON input or output is enclosed in an object with a single
property named 'nftables'. Its value is an array containing commands (for
input) or ruleset elements (for output).

A command is an object with a single property whose name identifies the command.
Its value is a ruleset element - basically identical to output elements, apart
from certain properties which may be interpreted differently or are required
when output generally omits them.

== METAINFO OBJECT
In output, the first object in an *nftables* array is a special one containing
library information. Its content is as follows:

[verse]
*{ "metainfo": {
	"version":* 'STRING'*,
	"release_name":* 'STRING'*,
	"json_schema_version":* 'NUMBER'
*}}*

The values of *version* and *release_name* properties are equal to the package
version and release name as printed by *nft -v*. The value of the
*json_schema_version* property is an integer indicating the schema version.

If supplied in library input, the parser will verify the *json_schema_version* value
to not exceed the internally hardcoded one (to make sure the given schema is
fully understood). In future, a lower number than the internal one may activate
compatibility mode to parse outdated and incompatible JSON input.

== COMMAND OBJECTS
The structure accepts an arbitrary amount of commands which are interpreted in
order of appearance. For instance, the following standard syntax input:

----
flush ruleset
add table inet mytable
add chain inet mytable mychain
add rule inet mytable mychain tcp dport 22 accept
----

translates into JSON as such:

----
{ "nftables": [
	{ "flush": { "ruleset": null }},
	{ "add": { "table": {
			"family": "inet",
			"name": "mytable"
	}}},
	{ "add": { "chain": {
			"family": "inet",
			"table": "mytable",
			"chain": "mychain"
	}}}
	{ "add": { "rule": {
			"family": "inet",
			"table": "mytable",
			"chain": "mychain",
			"expr": [
				{ "match": {
					"left": { "payload": {
							"protocol": "tcp",
							"field": "dport"
					}},
					"right": 22
				}},
				{ "accept": null }
			]
	}}}
]}
----

=== ADD
[verse]
____
*{ "add":* 'ADD_OBJECT' *}*

'ADD_OBJECT' := 'TABLE' | 'CHAIN' | 'RULE' | 'SET' | 'MAP' | 'ELEMENT' |
                'FLOWTABLE' | 'COUNTER | QUOTA' | 'CT_HELPER' | 'LIMIT' |
		'CT_TIMEOUT'
____

Add a new ruleset element to the kernel.

=== REPLACE
[verse]
*{ "replace":* 'RULE' *}*

Replace a rule. In 'RULE', the *handle* property is mandatory and identifies the
rule to be replaced.

=== CREATE
[verse]
*{ "create":* 'ADD_OBJECT' *}*

Identical to *add* command, but returns an error if the object already exists.

=== INSERT
[verse]
*{ "insert":* 'RULE' *}*

This command is identical to *add* for rules, but instead of appending the rule
to the chain by default, it inserts at first position. If a *handle* or *index*
property is given, the rule is inserted before the rule identified by those
properties.

=== DELETE
[verse]
*{ "delete":* 'ADD_OBJECT' *}*

Delete an object from the ruleset. Only the minimal number of properties
required to uniquely identify an object is generally needed in 'ADD_OBJECT'. For
most ruleset elements, this is *family* and *table* plus either *handle* or
*name* (except rules since they don't have a name).

=== LIST
[verse]
____
*{ "list":* 'LIST_OBJECT' *}*

'LIST_OBJECT' := 'TABLE' | 'TABLES' | 'CHAIN' | 'CHAINS' | 'SET' | 'SETS' |
                 'MAP' | 'MAPS | COUNTER' | 'COUNTERS' | 'QUOTA' | 'QUOTAS' |
                 'CT_HELPER' | 'CT_HELPERS' | 'LIMIT' | 'LIMITS | RULESET' |
                 'METER' | 'METERS' | 'FLOWTABLES' | 'CT_TIMEOUT'
____

List ruleset elements. The plural forms are used to list all objects of that
kind, optionally filtered by *family* and for some, also *table*.

=== RESET
[verse]
____
*{ "reset":* 'RESET_OBJECT' *}*

'RESET_OBJECT' := 'COUNTER' | 'COUNTERS' | 'QUOTA' | 'QUOTAS'
____

Reset state in suitable objects, i.e. zero their internal counter.

=== FLUSH
[verse]
____
*{ "flush":* 'FLUSH_OBJECT' *}*

'FLUSH_OBJECT' := 'TABLE' | 'CHAIN' | 'SET' | 'MAP' | 'METER' | 'RULESET'
____

Empty contents in given object, e.g. remove all chains from given *table* or
remove all elements from given *set*.

=== RENAME
[verse]
*{ "rename":* 'CHAIN' *}*

Rename a chain. The new name is expected in a dedicated property named
*newname*.

== RULESET ELEMENTS

=== TABLE
[verse]
*{ "table": {
	"family":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'
*}}*

This object describes a table.

*family*::
	The table's family, e.g. *"ip"* or *"ip6"*.
*name*::
	The table's name.
*handle*::
	The table's handle. In input, it is used only in *delete* command as
	alternative to *name*.

=== CHAIN
[verse]
*{ "chain": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"newname":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"type":* 'STRING'*,
	"hook":* 'STRING'*,
	"prio":* 'NUMBER'*,
	"dev":* 'STRING'*,
	"policy":* 'STRING'
*}}*

This object describes a chain.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The chain's name.
*handle*::
	The chain's handle. In input, it is used only in *delete* command as
	alternative to *name*.
*newname*::
	A new name for the chain, only relevant in the *rename* command.

The following properties are required for base chains:

*type*::
	The chain's type.
*hook*::
	The chain's hook.
*prio*::
	The chain's priority.
*dev*::
	The chain's bound interface (if in the netdev family).
*policy*::
	The chain's policy.

=== RULE
[verse]
____
*{ "rule": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"chain":* 'STRING'*,
	"expr": [* 'STATEMENTS' *],
	"handle":* 'NUMBER'*,
	"index":* 'NUMBER'*,
	"comment":* 'STRING'
*}}*

'STATEMENTS' := 'STATEMENT' [*,* 'STATEMENTS' ]
____

This object describes a rule. Basic building blocks of rules are statements.
Each rule consists of at least one.

*family*::
	The table's family.
*table*::
	The table's name.
*chain*::
	The chain's name.
*expr*::
	An array of statements this rule consists of. In input, it is used in
	*add*/*insert*/*replace* commands only.
*handle*::
	The rule's handle. In *delete*/*replace* commands, it serves as an identifier
	of the rule to delete/replace. In *add*/*insert* commands, it serves as
	an identifier of an existing rule to append/prepend the rule to.
*index*::
	The rule's position for *add*/*insert* commands. It is used as an alternative to
	*handle* then.
*comment*::
	Optional rule comment.

=== SET / MAP
[verse]
____
*{ "set": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"type":* 'SET_TYPE'*,
	"policy":* 'SET_POLICY'*,
	"flags": [* 'SET_FLAG_LIST' *],
	"elem":* 'SET_ELEMENTS'*,
	"timeout":* 'NUMBER'*,
	"gc-interval":* 'NUMBER'*,
	"size":* 'NUMBER'
*}}*

*{ "map": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"type":* 'SET_TYPE'*,
	"map":* 'STRING'*,
	"policy":* 'SET_POLICY'*,
	"flags": [* 'SET_FLAG_LIST' *],
	"elem":* 'SET_ELEMENTS'*,
	"timeout":* 'NUMBER'*,
	"gc-interval":* 'NUMBER'*,
	"size":* 'NUMBER'
*}}*

'SET_TYPE' := 'STRING' | *[* 'SET_TYPE_LIST' *]*
'SET_TYPE_LIST' := 'STRING' [*,* 'SET_TYPE_LIST' ]
'SET_POLICY' := *"performance"* | *"memory"*
'SET_FLAG_LIST' := 'SET_FLAG' [*,* 'SET_FLAG_LIST' ]
'SET_FLAG' := *"constant"* | *"interval"* | *"timeout"*
'SET_ELEMENTS' := 'EXPRESSION' | *[* 'EXPRESSION_LIST' *]*
'EXPRESSION_LIST' := 'EXPRESSION' [*,* 'EXPRESSION_LIST' ]
____

These objects describe a named set or map. Maps are a special form of sets in
that they translate a unique key to a value.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The set's name.
*handle*::
	The set's handle. For input, it is used in the *delete* command only.
*type*::
	The set's datatype, see below.
*map*::
	Type of values this set maps to (i.e. this set is a map).
*policy*::
	The set's policy.
*flags*::
	The set's flags.
*elem*::
	Initial set element(s), see below.
*timeout*::
	Element timeout in seconds.
*gc-interval*::
	Garbage collector interval in seconds.
*size*::
	Maximum number of elements supported.

==== TYPE
The set type might be a string, such as *"ipv4_addr"* or an array
consisting of strings (for concatenated types).

==== ELEM
A single set element might be given as string, integer or boolean value for
simple cases. If additional properties are required, a formal *elem* object may
be used.

Multiple elements may be given in an array.

=== ELEMENT
[verse]
____
*{ "element": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"elem":* 'SET_ELEM'
*}}*

'SET_ELEM' := 'EXPRESSION' | *[* 'EXPRESSION_LIST' *]*
'EXPRESSION_LIST' := 'EXPRESSION' [*,* 'EXPRESSION' ]
____

Manipulate element(s) in a named set.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The set's name.
*elem*::
	See elem property of set object.

=== FLOWTABLE
[verse]
____
*{ "flowtable": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"hook":* 'STRING'*,
	"prio":* 'NUMBER'*,
	"dev":* 'FT_INTERFACE'
*}}*

'FT_INTERFACE' := 'STRING' | *[* 'FT_INTERFACE_LIST' *]*
'FT_INTERFACE_LIST' := 'STRING' [*,* 'STRING' ]
____

This object represents a named flowtable.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The flow table's name.
*hook*::
	The flow table's hook.
*prio*::
	The flow table's priority.
*dev*::
	The flow table's interface(s).

=== COUNTER
[verse]
*{ "counter": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"packets":* 'NUMBER'*,
	"bytes":* 'NUMBER'
*}}*

This object represents a named counter.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The counter's name.
*handle*::
	The counter's handle. In input, it is used by the *delete* command only.
*packets*::
	Packet counter value.
*bytes*::
	Byte counter value.

=== QUOTA
[verse]
*{ "quota": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"bytes":* 'NUMBER'*,
	"used":* 'NUMBER'*,
	"inv":* 'BOOLEAN'
*}}*

This object represents a named quota.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The quota's name.
*handle*::
	The quota's handle. In input, it is used by the *delete* command only.
*bytes*::
	Quota threshold.
*used*::
	Quota used so far.
*inv*::
	If true, match if the quota has been exceeded.

=== CT HELPER
[verse]
____
*{ "ct helper": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* '... '*,
	"type":* 'STRING'*,
	"protocol":* 'CTH_PROTO'*,
	"l3proto":* 'STRING'
*}}*

'CTH_PROTO' := *"tcp"* | *"udp"*
____

This object represents a named conntrack helper.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The ct helper's name.
*handle*::
	The ct helper's handle. In input, it is used by the *delete* command only.
*type*::
	The ct helper type name, e.g. *"ftp"* or *"tftp"*.
*protocol*::
	The ct helper's layer 4 protocol.
*l3proto*::
	The ct helper's layer 3 protocol, e.g. *"ip"* or *"ip6"*.

=== LIMIT
[verse]
____
*{ "limit": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"rate":* 'NUMBER'*,
	"per":* 'STRING'*,
	"burst":* 'NUMBER'*,
	"unit":* 'LIMIT_UNIT'*,
	"inv":* 'BOOLEAN'
*}}*

'LIMIT_UNIT' := *"packets"* | *"bytes"*
____

This object represents a named limit.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The limit's name.
*handle*::
	The limit's handle. In input, it is used by the *delete* command only.
*rate*::
	The limit's rate value.
*per*::
	Time unit to apply the limit to, e.g. *"week"*, *"day"*, *"hour"*, etc.
	If omitted, defaults to *"second"*.
*burst*::
	The limit's burst value. If omitted, defaults to *0*.
*unit*::
	Unit of rate and burst values. If omitted, defaults to *"packets"*.
*inv*::
	If true, match if limit was exceeded. If omitted, defaults to *false*.

=== CT TIMEOUT
[verse]
____
*{ "ct timeout": {
	"family":* 'STRING'*,
	"table":* 'STRING'*,
	"name":* 'STRING'*,
	"handle":* 'NUMBER'*,
	"protocol":* 'CTH_PROTO'*,
	"state":* 'STRING'*,
	"value:* 'NUMBER'*,
	"l3proto":* 'STRING'
*}}*

'CTH_PROTO' := *"tcp"* | *"udp"* | *"dccp"* | *"sctp"* | *"gre"* | *"icmpv6"* | *"icmp"* | *"generic"*
____

This object represents a named conntrack timeout policy.

*family*::
	The table's family.
*table*::
	The table's name.
*name*::
	The ct timeout object's name.
*handle*::
	The ct timeout object's handle. In input, it is used by *delete* command only.
*protocol*::
	The ct timeout object's layer 4 protocol.
*state*::
	The connection state name, e.g. *"established"*, *"syn_sent"*, *"close"* or
	*"close_wait"*, for which the timeout value has to be updated.
*value*::
	The updated timeout value for the specified connection state.
*l3proto*::
	The ct timeout object's layer 3 protocol, e.g. *"ip"* or *"ip6"*.

== STATEMENTS
Statements are the building blocks for rules. Each rule consists of at least
one.

=== VERDICT
[verse]
*{ "accept": null }*
*{ "drop": null }*
*{ "continue": null }*
*{ "return": null }*
*{ "jump": { "target": * 'STRING' *}}*
*{ "goto": { "target": * 'STRING' *}}*

A verdict either terminates packet traversal through the current chain or
delegates to a different one.

*jump* and *goto* statements expect a target chain name.

=== MATCH
[verse]
*{ "match": {
	"left":* 'EXPRESSION'*,
	"right":* 'EXPRESSION'*,
	"op":* 'STRING'
*}}*

This matches the expression on left hand side (typically a packet header or packet meta
info) with the expression on right hand side (typically a constant value). If the
statement evaluates to true, the next statement in this rule is considered. If not,
processing continues with the next rule in the same chain.

*left*::
	Left hand side of this match.
*right*::
	Right hand side of this match.
*op*::
	Operator indicating the type of comparison.

==== OPERATORS

[horizontal]
*&*:: Binary AND
*|*:: Binary OR
*^*:: Binary XOR
*<<*:: Left shift
*>>*:: Right shift
*==*:: Equal
*!=*:: Not equal
*<*:: Less than
*>*:: Greater than
*<=*:: Less than or equal to
*>=*:: Greater than or equal to
*in*:: Perform a lookup, i.e. test if bits on RHS are contained in LHS value

Unlike with the standard API, the operator is mandatory here. In the standard API,
a missing operator may be resolved in two ways, depending on the type of expression
on the RHS:

- If the RHS is a bitmask or a list of bitmasks, the expression resolves into a
  binary operation with the inequality operator, like this: '+LHS & RHS != 0+'.
- In any other case, the equality operator is simply inserted.

For the non-trivial first case, the JSON API supports the *in* operator.

=== COUNTER
[verse]
____
*{ "counter": {
	"packets":* 'NUMBER'*,
	"bytes":* 'NUMBER'
*}}*

*{ "counter":* 'STRING' *}*
____

This object represents a byte/packet counter. In input, no properties are
required. If given, they act as initial values for the counter.

The first form creates an anonymous counter which lives in the rule it appears
in. The second form specifies a reference to a named counter object.

*packets*::
	Packets counted.
*bytes*::
	Bytes counted.

=== MANGLE
[verse]
*{ "mangle": {
	"key":* 'EXPRESSION'*,
	"value":* 'EXPRESSION'
*}}*

This changes the packet data or meta info.

*key*::
	The packet data to be changed, given as an *exthdr*, *payload*, *meta*, *ct* or
	*ct helper* expression.
*value*::
	Value to change data to.

=== QUOTA
[verse]
____
*{ "quota": {
	"val":* 'NUMBER'*,
	"val_unit":* 'STRING'*,
	"used":* 'NUMBER'*,
	"used_unit":* 'STRING'*,
	"inv":* 'BOOLEAN'
*}}*

*{ "quota":* 'STRING' *}*
____

The first form creates an anonymous quota which lives in the rule it appears in.
The second form specifies a reference to a named quota object.

*val*::
	Quota value.
*val_unit*::
	Unit of *val*, e.g. *"kbytes"* or *"mbytes"*. If omitted, defaults to
	*"bytes"*.
*used*::
	Quota used so far. Optional on input. If given, serves as initial value.
*used_unit*::
	Unit of *used*. Defaults to *"bytes"*.
*inv*::
	If *true*, will match if quota was exceeded. Defaults to *false*.

=== LIMIT
[verse]
____
*{ "limit": {
	"rate":* 'NUMBER'*,
	"rate_unit":* 'STRING'*,
	"per":* 'STRING'*,
	"burst":* 'NUMBER'*,
	"burst_unit":* 'STRING'*,
	"inv":* 'BOOLEAN'
*}}*

*{ "limit":* 'STRING' *}*
____

The first form creates an anonymous limit which lives in the rule it appears in.
The second form specifies a reference to a named limit object.

*rate*::
	Rate value to limit to.
*rate_unit*::
	Unit of *rate*, e.g. *"packets"* or *"mbytes"*. Defaults to *"packets"*.
*per*::
	Denominator of *rate*, e.g. *"week"* or *"minutes"*.
*burst*::
	Burst value. Defaults to *0*.
*burst_unit*::
	Unit of *burst*, ignored if *rate_unit* is *"packets"*. Defaults to
	*"bytes"*.
*inv*::
	If *true*, matches if the limit was exceeded. Defaults to *false*.

=== FWD
[verse]
____
*{ "fwd": {
	"dev":* 'EXPRESSION'*,
	"family":* 'FWD_FAMILY'*,
	"addr":* 'EXPRESSION'
*}}*

'FWD_FAMILY' := *"ip"* | *"ip6"*
____

Forward a packet to a different destination.

*dev*::
	Interface to forward the packet on.
*family*::
	Family of *addr*.
*addr*::
	IP(v6) address to forward the packet to.

Both *family* and *addr* are optional, but if at least one is given, both must be present.

=== NOTRACK
[verse]
*{ "notrack": null }*

Disable connection tracking for the packet.

=== DUP
[verse]
*{ "dup": {
	"addr":* 'EXPRESSION'*,
	"dev":* 'EXPRESSION'
*}}*

Duplicate a packet to a different destination.

*addr*::
	Address to duplicate packet to.
*dev*::
	Interface to duplicate packet on. May be omitted to not specify an
	interface explicitly.

=== NETWORK ADDRESS TRANSLATION
[verse]
____
*{ "snat": {
	"addr":* 'EXPRESSION'*,
	"port":* 'EXPRESSION'*,
	"flags":* 'FLAGS'
*}}*

*{ "dnat": {
	"addr":* 'EXPRESSION'*,
	"port":* 'EXPRESSION'*,
	"flags":* 'FLAGS'
*}}*

*{ "masquerade": {
	"port":* 'EXPRESSION'*,
	"flags":* 'FLAGS'
*}}*

*{ "redirect": {
	"port":* 'EXPRESSION'*,
	"flags":* 'FLAGS'
*}}*

'FLAGS' := 'FLAG' | *[* 'FLAG_LIST' *]*
'FLAG_LIST' := 'FLAG' [*,* 'FLAG_LIST' ]
'FLAG' := *"random"* | *"fully-random"* | *"persistent"*
____

Perform Network Address Translation.

*addr*::
	Address to translate to.
*port*::
	Port to translate to.
*flags*::
	Flag(s).

All properties are optional and default to none.

=== REJECT
[verse]
*{ "reject": {
	"type":* 'STRING'*,
	"expr":* 'EXPRESSION'
*}}*

Reject the packet and send the given error reply.

*type*::
	Type of reject, either *"tcp reset"*, *"icmpx"*, *"icmp"* or *"icmpv6"*.
*expr*::
	ICMP type to reject with.

All properties are optional.

=== SET
[verse]
*{ "set": {
	"op":* 'STRING'*,
	"elem":* 'EXPRESSION'*,
	"set":* 'STRING'
*}}*

Dynamically add/update elements to a set.

*op*::
	Operator on set, either *"add"* or *"update"*.
*elem*::
	Set element to add or update.
*set*::
	Set reference.

=== LOG
[verse]
____
*{ "log": {
	"prefix":* 'STRING'*,
	"group":* 'NUMBER'*,
	"snaplen":* 'NUMBER'*,
	"queue-threshold":* 'NUMBER'*,
	"level":* 'LEVEL'*,
	"flags":* 'FLAGS'
*}}*

'LEVEL' := *"emerg"* | *"alert"* | *"crit"* | *"err"* | *"warn"* | *"notice"* |
           *"info"* | *"debug"* | *"audit"*

'FLAGS' := 'FLAG' | *[* 'FLAG_LIST' *]*
'FLAG_LIST' := 'FLAG' [*,* 'FLAG_LIST' ]
'FLAG' := *"tcp sequence"* | *"tcp options"* | *"ip options"* | *"skuid"* |
          *"ether"* | *"all"*
____

Log the packet.

*prefix*::
	Prefix for log entries.
*group*::
	Log group.
*snaplen*::
	Snaplen for logging.
*queue-threshold*::
	Queue threshold.
*level*::
	Log level. Defaults to *"warn"*.
*flags*::
	Log flags.

All properties are optional.

=== CT HELPER
[verse]
*{ "ct helper":* 'EXPRESSION' *}*

Enable the specified conntrack helper for this packet.

*ct helper*::
	CT helper reference.

=== METER
[verse]
*{ "meter": {
	"name":* 'STRING'*,
	"key":* 'EXPRESSION'*,
	"stmt":* 'STATEMENT'
*}}*

Apply a given statement using a meter.

*name*::
	Meter name.
*key*::
	Meter key.
*stmt*::
	Meter statement.

=== QUEUE
[verse]
____
*{ "queue": {
	"num":* 'EXPRESSION'*,
	"flags":* 'FLAGS'
*}}*

'FLAGS' := 'FLAG' | *[* 'FLAG_LIST' *]*
'FLAG_LIST' := 'FLAG' [*,* 'FLAG_LIST' ]
'FLAG' := *"bypass"* | *"fanout"*
____

Queue the packet to userspace.

*num*::
	Queue number.
*flags*::
	Queue flags.

=== VERDICT MAP
[verse]
*{ "vmap": {
	"key":* 'EXPRESSION'*,
	"data":* 'EXPRESSION'
*}}*

Apply a verdict conditionally.

*key*::
	Map key.
*data*::
	Mapping expression consisting of value/verdict pairs.

=== CT COUNT
[verse]
*{ "ct count": {
	"val":* 'NUMBER'*,
	"inv":* 'BOOLEAN'
*}}*

Limit the number of connections using conntrack.

*val*::
	Connection count threshold.
*inv*::
	If *true*, match if *val* was exceeded. If omitted, defaults to
	*false*.

=== CT TIMEOUT
[verse]
*{ "ct timeout":* 'EXPRESSION' *}*

Assign connection tracking timeout policy.

*ct timeout*::
	CT timeout reference.

=== XT
[verse]
*{ "xt": null }*

This represents an xt statement from xtables compat interface. Sadly, at this
point, it is not possible to provide any further information about its content.

== EXPRESSIONS
Expressions are the building blocks of (most) statements. In their most basic
form, they are just immediate values represented as a JSON string, integer or
boolean type.

=== IMMEDIATES
[verse]
'STRING'
'NUMBER'
'BOOLEAN'

Immediate expressions are typically used for constant values. For strings, there
are two special cases:

*@STRING*::
	The remaining part is taken as set name to create a set reference.
*\**::
	Construct a wildcard expression.

=== LISTS
[verse]
'ARRAY'

List expressions are constructed by plain arrays containing of an arbitrary
number of expressions.

=== CONCAT
[verse]
____
*{ "concat":* 'CONCAT' *}*

'CONCAT' := *[* 'EXPRESSION_LIST' *]*
'EXPRESSION_LIST' := 'EXPRESSION' [*,* 'EXPRESSION_LIST' ]
____

Concatenate several expressions.

=== SET
[verse]
____
*{ "set":* 'SET' *}*

'SET' := 'EXPRESSION' | *[* 'EXPRESSION_LIST' *]*
____

This object constructs an anonymous set. For mappings, an array of arrays with
exactly two elements is expected.

=== MAP
[verse]
*{ "map": {
	"key":* 'EXPRESSION'*,
	"data":* 'EXPRESSION'
*}}*

Map a key to a value.

*key*::
	Map key.
*data*::
	Mapping expression consisting of value/target pairs.

=== PREFIX
[verse]
*{ "prefix": {
	"addr":* 'EXPRESSION'*,
	"len":* 'NUMBER'
*}}*

Construct an IPv4 or IPv6 prefix consisting of address part in *addr* and prefix
length in *len*.

=== RANGE
[verse]
*{ "range": [* 'EXPRESSION' *,* 'EXPRESSION' *] }*

Construct a range of values. The first array item denotes the lower boundary,
the second one the upper boundary.

=== PAYLOAD
[verse]
____
*{ "payload": {
	"base":* 'BASE'*,
	"offset":* 'NUMBER'*,
	"len":* 'NUMBER'
*}}*

*{ "payload": {
	"protocol":* 'STRING'*,
	"field":* 'STRING'
*}}*

'BASE' := *"ll"* | *"nh"* | *"th"*
____

Construct a payload expression, i.e. a reference to a certain part of packet
data. The first form creates a raw payload expression to point at a random
number (*len*) of bytes at a certain offset (*offset*) from a given reference
point (*base*). The following *base* values are accepted:

*"ll"*::
	The offset is relative to Link Layer header start offset.
*"nh"*::
	The offset is relative to Network Layer header start offset.
*"th"*::
	The offset is relative to Transport Layer header start offset.

The second form allows to reference a field by name (*field*) in a named packet
header (*protocol*).

=== EXTHDR
[verse]
*{ "exthdr": {
	"name":* 'STRING'*,
	"field":* 'STRING'*,
	"offset":* 'NUMBER'
*}}*

Create a reference to a field (*field*) in an IPv6 extension header (*name*).
*offset* is used only for *rt0* protocol.

If the *field* property is not given, the expression is to be used as a header
existence check in a *match* statement with a boolean on the right hand side.

=== TCP OPTION
[verse]
*{ "tcp option": {
	"name":* 'STRING'*,
	"field":* 'STRING'
*}}*

Create a reference to a field (*field*) of a TCP option header (*name*).

If the *field* property is not given, the expression is to be used as a TCP option
existence check in a *match* statement with a boolean on the right hand side.

=== META
[verse]
____
*{ "meta": {
	"key":* 'META_KEY'
*}}*

'META_KEY' := *"length"* | *"protocol"* | *"priority"* | *"random"* | *"mark"* |
              *"iif"* | *"iifname"* | *"iiftype"* | *"oif"* | *"oifname"* |
	      *"oiftype"* | *"skuid"* | *"skgid"* | *"nftrace"* |
	      *"rtclassid"* | *"ibriport"* | *"obriport"* | *"ibridgename"* |
	      *"obridgename"* | *"pkttype"* | *"cpu"* | *"iifgroup"* |
	      *"oifgroup"* | *"cgroup"* | *"nfproto"* | *"l4proto"* |
	      *"secpath"*
____

Create a reference to packet meta data.

=== RT
[verse]
____
*{ "rt": {
	"key":* 'RT_KEY'*,
	"family":* 'RT_FAMILY'
*}}*

'RT_KEY' := *"classid"* | *"nexthop"* | *"mtu"*
'RT_FAMILY' := *"ip"* | *"ip6"*
____

Create a reference to packet routing data.

The *family* property is optional and defaults to unspecified.

=== CT
[verse]
____
*{ "ct": {
	"key":* 'STRING'*,
	"family":* 'CT_FAMILY'*,
	"dir":* 'CT_DIRECTION'
*}}*

'CT_FAMILY' := *"ip"* | *"ip6"*
'CT_DIRECTION' := *"original"* | *"reply"*
____

Create a reference to packet conntrack data.

Some CT keys do not support a direction. In this case, *dir* must not be
given.

=== NUMGEN
[verse]
____
*{ "numgen": {
	"mode":* 'NG_MODE'*,
	"mod":* 'NUMBER'*,
	"offset":* 'NUMBER'
*}}*

'NG_MODE' := *"inc"* | *"random"*
____

Create a number generator.

The *offset* property is optional and defaults to 0.

=== HASH
[verse]
____
*{ "jhash": {
	"mod":* 'NUMBER'*,
	"offset":* 'NUMBER'*,
	"expr":* 'EXPRESSION'*,
	"seed":* 'NUMBER'
*}}*

*{ "symhash": {
	"mod":* 'NUMBER'*,
	"offset":* 'NUMBER'
*}}*
____

Hash packet data.

The *offset* and *seed* properties are optional and default to 0.

=== FIB
[verse]
____
*{ "fib": {
	"result":* 'FIB_RESULT'*,
	"flags":* 'FIB_FLAGS'
*}}*

'FIB_RESULT' := *"oif"* | *"oifname"* | *"type"*

'FIB_FLAGS' := 'FIB_FLAG' | *[* 'FIB_FLAG_LIST' *]*
'FIB_FLAG_LIST' := 'FIB_FLAG' [*,* 'FIB_FLAG_LIST' ]
'FIB_FLAG' := *"saddr"* | *"daddr"* | *"mark"* | *"iif"* | *"oif"*
____

Perform kernel Forwarding Information Base lookups.

=== BINARY OPERATION
[verse]
*{ "|": [* 'EXPRESSION'*,* 'EXPRESSION' *] }*
*{ "^": [* 'EXPRESSION'*,* 'EXPRESSION' *] }*
*{ "&": [* 'EXPRESSION'*,* 'EXPRESSION' *] }*
*{ "+<<+": [* 'EXPRESSION'*,* 'EXPRESSION' *] }*
*{ ">>": [* 'EXPRESSION'*,* 'EXPRESSION' *] }*

All binary operations expect an array of exactly two expressions, of which the
first element denotes the left hand side and the second one the right hand
side.

=== VERDICT
[verse]
*{ "accept": null }*
*{ "drop": null }*
*{ "continue": null }*
*{ "return": null }*
*{ "jump": { "target":* 'STRING' *}}*
*{ "goto": { "target":* 'STRING' *}}*

Same as the *verdict* statement, but for use in verdict maps.

*jump* and *goto* verdicts expect a target chain name.

=== ELEM
[verse]
*{ "elem": {
	"val":* 'EXPRESSION'*,
	"timeout":* 'NUMBER'*,
	"expires":* 'NUMBER'*,
	"comment":* 'STRING'
*}}*

Explicitly set element object, in case *timeout*, *expires* or *comment* are
desired. Otherwise, it may be replaced by the value of *val*.

=== SOCKET
[verse]
____
*{ "socket": {
	"key":* 'SOCKET_KEY'
*}}*

'SOCKET_KEY' := *"transparent"*
____

Construct a reference to packet's socket.

=== OSF
[verse]
____
*{ "osf": {
	"key":* 'OSF_KEY'*,
	"ttl":* 'OSF_TTL'
*}}*

'OSF_KEY' := *"name"*
'OSF_TTL' := *"loose"* | *"skip"*
____

Perform OS fingerprinting. This expression is typically used in the LHS of a *match*
statement.

*key*::
	Which part of the fingerprint info to match against. At this point, only
	the OS name is supported.
*ttl*::
	Define how the packet's TTL value is to be matched. This property is
	optional. If omitted, the TTL value has to match exactly. A value of *loose*
	accepts TTL values less than the fingerprint one. A value of *skip*
	omits TTL value comparison entirely.