diff options
| -rw-r--r-- | doc/nft.txt | 234 |
1 files changed, 183 insertions, 51 deletions
diff --git a/doc/nft.txt b/doc/nft.txt index e317cfd8..d33d01cc 100644 --- a/doc/nft.txt +++ b/doc/nft.txt @@ -15,7 +15,10 @@ SYNOPSIS DESCRIPTION ----------- -nft is the command line tool used to set up, maintain and inspect packet filtering and classification rules in the Linux kernel, in the nftables framework. The Linux kernel subsystem is known as nf_tables, and `nft' stands for Netfilter. +nft is the command line tool used to set up, maintain and inspect packet +filtering and classification rules in the Linux kernel, in the nftables +framework. The Linux kernel subsystem is known as nf_tables, and `nft' stands +for Netfilter. OPTIONS ------- @@ -80,22 +83,40 @@ INPUT FILE FORMATS ------------------ LEXICAL CONVENTIONS ~~~~~~~~~~~~~~~~~~~ -Input is parsed line-wise. When the last character of a line, just before the newline character, is a non-quoted backslash (\), the next line is treated as a continuation. Multiple commands on the same line can be separated using a semicolon (;). + +Input is parsed line-wise. When the last character of a line, just before the +newline character, is a non-quoted backslash (\), the next line is treated as a +continuation. Multiple commands on the same line can be separated using a +semicolon (;). + -A hash sign (#) begins a comment. All following characters on the same line are ignored. + +A hash sign (#) begins a comment. All following characters on the same line are +ignored. + -Identifiers begin with an alphabetic character (a-z,A-Z), followed zero or more alphanumeric characters (a-z,A-Z,0-9) and the characters slash (/), backslash (\), underscore (_) and dot (.). Identifiers using different characters or clashing with a keyword need to be enclosed in double quotes ("). +Identifiers begin with an alphabetic character (a-z,A-Z), followed zero or more +alphanumeric characters (a-z,A-Z,0-9) and the characters slash (/), backslash +(\), underscore (_) and dot (.). Identifiers using different characters or +clashing with a keyword need to be enclosed in double quotes ("). INCLUDE FILES ~~~~~~~~~~~~~ [verse] *include* 'filename' -Other files can be included by using the *include* statement. The directories to be searched for include files can be specified using the *-I*/*--includepath* option. You can override this behaviour either by prepending `./' to your path to force inclusion of files located in the current working directory (i.e. relative path) or / for file location expressed as an absolute path. + +Other files can be included by using the *include* statement. The directories to +be searched for include files can be specified using the *-I*/*--includepath* +option. You can override this behaviour either by prepending `./' to your path +to force inclusion of files located in the current working directory (i.e. +relative path) or / for file location expressed as an absolute path. + -If *-I*/*--includepath* is not specified, then nft relies on the default directory that is specified at compile time. You can retrieve this default directory via *-h*/*--help* option. + +If *-I*/*--includepath* is not specified, then nft relies on the default +directory that is specified at compile time. You can retrieve this default +directory via *-h*/*--help* option. + -Include statements support the usual shell wildcard symbols (\*,?,[]). Having no matches for an include statement is not an error, if wildcard symbols are used in the include statement. This allows having potentially empty include directories for statements like **include "/etc/firewall/rules/"**. The wildcard matches are loaded in alphabetical order. Files beginning with dot (.) are not matched by include statements. +Include statements support the usual shell wildcard symbols (\*,?,[]). Having no +matches for an include statement is not an error, if wildcard symbols are used +in the include statement. This allows having potentially empty include +directories for statements like **include "/etc/firewall/rules/"**. The wildcard +matches are loaded in alphabetical order. Files beginning with dot (.) are not +matched by include statements. SYMBOLIC VARIABLES ~~~~~~~~~~~~~~~~~~ @@ -103,7 +124,9 @@ SYMBOLIC VARIABLES *define* variable 'expr' *$variable* -Symbolic variables can be defined using the *define* statement. Variable references are expressions and can be used initialize other variables. The scope of a definition is the current block and all blocks contained within. +Symbolic variables can be defined using the *define* statement. Variable +references are expressions and can be used initialize other variables. The scope +of a definition is the current block and all blocks contained within. .Using symbolic variables --------------------------------------- @@ -117,7 +140,9 @@ filter input iif $int_ifs accept [[ADDRESS_FAMILIES]] ADDRESS FAMILIES ---------------- -Address families determine the type of packets which are processed. For each address family the kernel contains so called hooks at specific stages of the packet processing paths, which invoke nftables if rules for these hooks exist. +Address families determine the type of packets which are processed. For each +address family the kernel contains so called hooks at specific stages of the +packet processing paths, which invoke nftables if rules for these hooks exist. [horizontal] ip:: IPv4 address family. @@ -127,18 +152,24 @@ arp:: ARP address family, handling IPv4 ARP packets. bridge:: Bridge address family, handling packets which traverse a bridge device. netdev:: Netdev address family, handling packets from ingress. -All nftables objects exist in address family specific namespaces, therefore all identifiers include an address family. If an identifier is specified without an address family, the *ip* family is used by default. +All nftables objects exist in address family specific namespaces, therefore all +identifiers include an address family. If an identifier is specified without an +address family, the *ip* family is used by default. IPV4/IPV6/INET ADDRESS FAMILIES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The IPv4/IPv6/Inet address families handle IPv4, IPv6 or both types of packets. They contain five hooks at different packet processing stages in the network stack. +The IPv4/IPv6/Inet address families handle IPv4, IPv6 or both types of packets. +They contain five hooks at different packet processing stages in the network +stack. .IPv4/IPv6/Inet address family hooks [options="header"] |================== |Hook | Description |prerouting | -All packets entering the system are processed by the prerouting hook. It is invoked before the routing process and is used for early filtering or changing packet attributes that affect routing. +All packets entering the system are processed by the prerouting hook. It is +invoked before the routing process and is used for early filtering or changing +packet attributes that affect routing. |input | Packets delivered to the local system are processed by the input hook. |forward | @@ -179,7 +210,8 @@ The Netdev address family handles packets from ingress. |================= |Hook | Description |ingress | -All packets entering the system are processed by this hook. It is invoked before layer 3 protocol handlers and it can be used for early filtering and policing. +All packets entering the system are processed by this hook. It is invoked before +layer 3 protocol handlers and it can be used for early filtering and policing. |================= RULESET @@ -188,18 +220,26 @@ RULESET {list | flush} *ruleset* ['family'] \{export\} [*ruleset*] {'format'} -The *ruleset* keyword is used to identify the whole set of tables, chains, etc. currently in place in kernel. The following *ruleset* commands exist: +The *ruleset* keyword is used to identify the whole set of tables, chains, etc. +currently in place in kernel. The following *ruleset* commands exist: [horizontal] *list*:: Print the ruleset in human-readable format. -*flush*:: Clear the whole ruleset. Note that unlike iptables, this will remove all tables and whatever they contain, effectively leading to an empty ruleset - no packet filtering will happen anymore, so the kernel accepts any valid packet it receives. +*flush*:: Clear the whole ruleset. Note that unlike iptables, this will remove +all tables and whatever they contain, effectively leading to an empty ruleset - +no packet filtering will happen anymore, so the kernel accepts any valid packet +it receives. -*export*:: Print the ruleset in machine readable format. The mandatory 'format' parameter may be either *xml* or *json*. +*export*:: Print the ruleset in machine readable format. The mandatory 'format' +parameter may be either *xml* or *json*. -It is possible to limit *list* and *flush* to a specific address family only. For a list of valid family names, see <<ADDRESS_FAMILIES>> above. +It is possible to limit *list* and *flush* to a specific address family only. +For a list of valid family names, see <<ADDRESS_FAMILIES>> above. -Note that contrary to what one might assume, the output generated by *export* is not parseable by *nft -f*. Instead, the output of *list* command serves well for that purpose. +Note that contrary to what one might assume, the output generated by *export* is +not parseable by *nft -f*. Instead, the output of *list* command serves well for +that purpose. TABLES ------ @@ -208,7 +248,15 @@ TABLES {delete | list | flush} *table* ['family'] 'table' delete *table* ['family'] handle 'handle' -Tables are containers for chains, sets and stateful objects. They are identified by their address family and their name. The address family must be one of *ip*, *ip6*, *inet*, *arp*, *bridge*, *netdev*. The *inet* address family is a dummy family which is used to create hybrid IPv4/IPv6 tables. The *meta expression nfproto* keyword can be used to test which family (ipv4 or ipv6) context the packet is being processed in. When no address family is specified, *ip* is used by default. The only difference between add and create is that the former will not return an error if the specified table already exists while *create* will return an error. +Tables are containers for chains, sets and stateful objects. They are identified +by their address family and their name. The address family must be one of *ip*, +*ip6*, *inet*, *arp*, *bridge*, *netdev*. The *inet* address family is a dummy +family which is used to create hybrid IPv4/IPv6 tables. The *meta expression +nfproto* keyword can be used to test which family (ipv4 or ipv6) context the +packet is being processed in. When no address family is specified, *ip* is used +by default. The only difference between add and create is that the former will +not return an error if the specified table already exists while *create* will +return an error. .Table flags [options="header"] @@ -253,10 +301,14 @@ CHAINS delete *chain* ['family'] 'table' handle 'handle' rename *chain* ['family'] 'table' 'chain' 'newname' -Chains are containers for rules. They exist in two kinds, base chains and regular chains. A base chain is an entry point for packets from the networking stack, a regular chain may be used as jump target and is used for better rule organization. +Chains are containers for rules. They exist in two kinds, base chains and +regular chains. A base chain is an entry point for packets from the networking +stack, a regular chain may be used as jump target and is used for better rule +organization. [horizontal] -*add*:: Add a new chain in the specified table. When a hook and priority value are specified, the chain is created as a base chain and hooked up to the networking stack. +*add*:: Add a new chain in the specified table. When a hook and priority value +are specified, the chain is created as a base chain and hooked up to the networking stack. *create*:: Similar to the *add* command, but returns an error if the chain already exists. *delete*:: Delete the specified chain. The chain must not contain any rules or be used as jump target. *rename*:: Rename the specified chain. @@ -283,15 +335,23 @@ new route lookup is performed if relevant parts of the IP header have changed. This allows to e.g. implement policy routing selectors in nftables. |================= -Apart from the special cases illustrated above (e.g. *nat* type not supporting *forward* hook or *route* type only supporting *output* hook), there are two further quirks worth noticing: +Apart from the special cases illustrated above (e.g. *nat* type not supporting +*forward* hook or *route* type only supporting *output* hook), there are two +further quirks worth noticing: -* netdev family supports merely a single combination, namely *filter* type and *ingress* hook. Base chains in this family also require the *device* parameter to be present since they exist per incoming interface only. -* arp family supports only *input* and *output* hooks, both in chains of type *filter*. +* netdev family supports merely a single combination, namely *filter* type and + *ingress* hook. Base chains in this family also require the *device* parameter + to be present since they exist per incoming interface only. +* arp family supports only *input* and *output* hooks, both in chains of type + *filter*. -The *priority* parameter accepts a signed integer value which specifies the order in which chains with same *hook* value are traversed. The ordering is +The *priority* parameter accepts a signed integer value which specifies the +order in which chains with same *hook* value are traversed. The ordering is ascending, i.e. lower priority values have precedence over higher ones. -Base chains also allow to set the chain's *policy*, i.e. what happens to packets not explicitly accepted or refused in contained rules. Supported policy values are *accept* (which is the default) or *drop*. +Base chains also allow to set the chain's *policy*, i.e. what happens to packets +not explicitly accepted or refused in contained rules. Supported policy values +are *accept* (which is the default) or *drop*. RULES ----- @@ -300,16 +360,30 @@ RULES replace *rule* ['family'] 'table' 'chain' handle 'handle' 'statement'... delete *rule* ['family'] 'table' 'chain' handle 'handle' -Rules are added to chain in the given table. If the family is not specified, the ip family is used. Rules are constructed from two kinds of components according to a set of grammatical rules: ex‐ pressions and statements. +Rules are added to chain in the given table. If the family is not specified, the +ip family is used. Rules are constructed from two kinds of components according +to a set of grammatical rules: ex‐ pressions and statements. -The add and insert commands support an optional location specifier, which is either a 'handle' of an existing rule or an 'index' (starting at zero). Internally, rule locations are always identified by 'handle' and the translation from 'index' happens in userspace. This has two potential implications in case a concurrent ruleset change happens after the translation was done: The effective rule index might change if a rule was inserted or deleted before the referred one. If the referred rule was deleted, the command is rejected by the kernel just as if an invalid 'handle' was given. +The add and insert commands support an optional location specifier, which is +either a 'handle' of an existing rule or an 'index' (starting at zero). +Internally, rule locations are always identified by 'handle' and the translation +from 'index' happens in userspace. This has two potential implications in case a +concurrent ruleset change happens after the translation was done: The effective +rule index might change if a rule was inserted or deleted before the referred +one. If the referred rule was deleted, the command is rejected by the kernel +just as if an invalid 'handle' was given. *add*:: -Add a new rule described by the list of statements. The rule is appended to the given chain unless a position is specified, in which case the rule is appended to the rule given by the 'handle'. The alternative name position is deprecated and should not be used anymore. +Add a new rule described by the list of statements. The rule is appended to the +given chain unless a position is specified, in which case the rule is appended +to the rule given by the 'handle'. The alternative name position is deprecated +and should not be used anymore. -*insert*:: Similar to the *add* command, but the rule is prepended to the beginning of the chain or before the rule at the given position. +*insert*:: Similar to the *add* command, but the rule is prepended to the +beginning of the chain or before the rule at the given position. -*replace*:: Similar to the add command, but the rule replaces the specified rule. +*replace*:: Similar to the add command, but the rule replaces the specified +rule. *delete*:: Delete the specified rule. @@ -335,21 +409,30 @@ table inet filter { SETS ---- -nftables offers two kinds of set concepts. Anonymous sets are sets that have no specific name. The set members are enclosed in curly braces, with commas to separate elements when creating the rule the set is used in. Once that rule is removed, the set is removed as well. They cannot be updated, i.e. once an anonymous set is declared it cannot be changed anymore except by removing/altering the rule that uses the anonymous set. +nftables offers two kinds of set concepts. Anonymous sets are sets that have no +specific name. The set members are enclosed in curly braces, with commas to +separate elements when creating the rule the set is used in. Once that rule is +removed, the set is removed as well. They cannot be updated, i.e. once an +anonymous set is declared it cannot be changed anymore except by +removing/altering the rule that uses the anonymous set. .*Using anonymous sets to accept particular subnets and ports* ---------- nft add rule filter input ip saddr { 10.0.0.0/8, 192.168.0.0/16 } tcp dport { 22, 443 } accept ---------- -Named sets are sets that need to be defined first before they can be referenced in rules. Unlike anonymous sets, elements can be added to or removed from a named set at any time. Sets are referenced from rules using an @ prefixed to the sets name. +Named sets are sets that need to be defined first before they can be referenced +in rules. Unlike anonymous sets, elements can be added to or removed from a +named set at any time. Sets are referenced from rules using an @ prefixed to the +sets name. .*Using named sets to accept addresses and ports* ------------------ nft add rule filter input ip saddr @allowed_hosts tcp dport @allowed_ports accept ------------------ -The sets allowed_hosts and allowed_ports need to be created first. The next section describes nft set syntax in more detail. +The sets allowed_hosts and allowed_ports need to be created first. The next +section describes nft set syntax in more detail. [verse] add *set* ['family'] 'table' 'set' { type 'type' ; [flags 'flags' ;] [timeout 'timeout' ;] [gc-interval 'gc-interval' ;] [elements = { 'element'[,...] @@ -358,7 +441,9 @@ add *set* ['family'] 'table' 'set' { type 'type' ; [flags 'flags' ;] [timeout 't delete *set* ['family'] 'table' handle 'handle' {add | delete} *element* ['family'] 'table' 'set' { 'element'[,...] } -Sets are elements containers of an user-defined data type, they are uniquely identified by an user-defined name and attached to tables. Their behaviour can be tuned with the flags that can be specified at set creation time. +Sets are elements containers of an user-defined data type, they are uniquely +identified by an user-defined name and attached to tables. Their behaviour can +be tuned with the flags that can be specified at set creation time. [horizontal] *add*:: Add a new set in the specified table. See the Set specification table below for more information about how to specify a sets properties. @@ -444,7 +529,19 @@ FLOWTABLES {add | create} *flowtable* ['family'] 'table' 'flowtable' { hook 'hook' priority 'priority' ; devices = { 'device'[,...] } ; } {delete | list} *flowtable* ['family'] 'table' 'flowtable' -Flowtables allow you to accelerate packet forwarding in software. Flowtables entries are represented through a tuple that is composed of the input interface, source and destination address, source and destination port; and layer 3/4 protocols. Each entry also caches the destination interface and the gateway address - to update the destination link-layer address - to forward packets. The ttl and hoplimit fields are also decremented. Hence, flowtables provides an alternative path that allow packets to bypass the classic forwarding path. Flowtables reside in the ingress hook, that is located before the prerouting hook. You can select what flows you want to offload through the flow offload expression from the forward chain. Flowtables are identified by their address family and their name. The address family must be one of ip, ip6, inet. The inet address family is a dummy family which is used to create hybrid IPv4/IPv6 tables. When no address family is specified, ip is used by default. +Flowtables allow you to accelerate packet forwarding in software. Flowtables +entries are represented through a tuple that is composed of the input interface, +source and destination address, source and destination port; and layer 3/4 +protocols. Each entry also caches the destination interface and the gateway +address - to update the destination link-layer address - to forward packets. +The ttl and hoplimit fields are also decremented. Hence, flowtables provides an +alternative path that allow packets to bypass the classic forwarding path. +Flowtables reside in the ingress hook, that is located before the prerouting +hook. You can select what flows you want to offload through the flow offload +expression from the forward chain. Flowtables are identified by their address +family and their name. The address family must be one of ip, ip6, inet. The inet +address family is a dummy family which is used to create hybrid IPv4/IPv6 +tables. When no address family is specified, ip is used by default. [horizontal] *add*:: Add a new flowtable for the given family with the given name. @@ -458,7 +555,9 @@ STATEFUL OBJECTS {add | delete | list | reset} type ['family'] 'table' 'object' delete type ['family'] 'table' handle 'handle' -Stateful objects are attached to tables and are identified by an unique name. They group stateful information from rules, to reference them in rules the keywords "type name" are used e.g. "counter name". +Stateful objects are attached to tables and are identified by an unique name. +They group stateful information from rules, to reference them in rules the +keywords "type name" are used e.g. "counter name". [horizontal] *add*:: Add a new stateful object in the specified table. @@ -470,10 +569,15 @@ include::stateful-objects.txt[] EXPRESSIONS ------------ -Expressions represent values, either constants like network addresses, port numbers etc. or data gathered from the packet during ruleset evaluation. -Expressions can be combined using binary, logical, relational and other types of expressions to form complex or relational (match) expressions. They are also used as arguments to certain types of operations, like NAT, packet marking etc. + +Expressions represent values, either constants like network addresses, port +numbers etc. or data gathered from the packet during ruleset evaluation. +Expressions can be combined using binary, logical, relational and other types of +expressions to form complex or relational (match) expressions. They are also +used as arguments to certain types of operations, like NAT, packet marking etc. ++ -Each expression has a data type, which determines the size, parsing and representation of symbolic values and type compatibility with other expressions. +Each expression has a data type, which determines the size, parsing and +representation of symbolic values and type compatibility with other expressions. DESCRIBE COMMAND ~~~~~~~~~~~~~~~~ @@ -501,17 +605,26 @@ cwr 0x80 DATA TYPES ---------- -Data types determine the size, parsing and representation of symbolic values and type compatibility of expressions. A number of global data types exist, in addition some expression types define further data types specific to the expression type. Most data types have a fixed size, some however may have a dynamic size, f.i. the string type. + +Data types determine the size, parsing and representation of symbolic values +and type compatibility of expressions. A number of global data types exist, in +addition some expression types define further data types specific to the +expression type. Most data types have a fixed size, some however may have a +dynamic size, f.i. the string type. + -Types may be derived from lower order types, f.i. the IPv4 address type is derived from the integer type, meaning an IPv4 address can also be specified as an integer value. + +Types may be derived from lower order types, f.i. the IPv4 address type is +derived from the integer type, meaning an IPv4 address can also be specified as +an integer value. + -In certain contexts (set and map definitions) it is necessary to explicitly specify a data type. Each type has a name which is used for this. +In certain contexts (set and map definitions) it is necessary to explicitly +specify a data type. Each type has a name which is used for this. include::data-types.txt[] PRIMARY EXPRESSIONS ------------------- -The lowest order expression is a primary expression, representing either a constant or a single datum from a packet's payload, meta data or a stateful module. +The lowest order expression is a primary expression, representing either a +constant or a single datum from a packet's payload, meta data or a stateful +module. include::primary-expression.txt[] @@ -523,9 +636,16 @@ include::payload-expression.txt[] STATEMENTS ---------- -Statements represent actions to be performed. They can alter control flow (return, jump to a different chain, accept or drop the packet) or can perform actions, such as logging, rejecting a packet, etc. + +Statements represent actions to be performed. They can alter control flow +(return, jump to a different chain, accept or drop the packet) or can perform +actions, such as logging, rejecting a packet, etc. + -Statements exist in two kinds. Terminal statements unconditionally terminate evaluation of the current rule, non-terminal statements either only conditionally or never terminate evaluation of the current rule, in other words, they are passive from the ruleset evaluation perspective. There can be an arbitrary amount of non-terminal statements in a rule, but only a single terminal statement as the final statement. +Statements exist in two kinds. Terminal statements unconditionally terminate +evaluation of the current rule, non-terminal statements either only +conditionally or never terminate evaluation of the current rule, in other words, +they are passive from the ruleset evaluation perspective. There can be an +arbitrary amount of non-terminal statements in a rule, but only a single +terminal statement as the final statement. include::statements.txt[] @@ -535,7 +655,10 @@ These are some additional commands included in nft. MONITOR ~~~~~~~~ -The monitor command allows you to listen to Netlink events produced by the nf_tables subsystem, related to creation and deletion of objects. When they occur, nft will print to stdout the monitored events in either XML, JSON or native nft format. + +The monitor command allows you to listen to Netlink events produced by the +nf_tables subsystem, related to creation and deletion of objects. When they +occur, nft will print to stdout the monitored events in either XML, JSON or +native nft format. + To filter events related to a concrete object, use one of the keywords 'tables', 'chains', 'sets', 'rules', 'elements', 'ruleset'. + @@ -570,9 +693,14 @@ Hit ^C to finish the monitor operation. ERROR REPORTING --------------- -When an error is detected, nft shows the line(s) containing the error, the position of the erroneous parts in the input stream and marks up the erroneous parts using carets (^). If the error results from the combination of two expressions or statements, the part imposing the constraints which are violated is marked using tildes (~). + +When an error is detected, nft shows the line(s) containing the error, the +position of the erroneous parts in the input stream and marks up the erroneous +parts using carets (^). If the error results from the combination of two +expressions or statements, the part imposing the constraints which are violated +is marked using tildes (~). + -For errors returned by the kernel, nft can't detect which parts of the input caused the error and the entire command is marked. +For errors returned by the kernel, nft can't detect which parts of the input +caused the error and the entire command is marked. .Error caused by single incorrect expression -------------------------------------------- @@ -597,7 +725,9 @@ filter output oif wlan0 EXIT STATUS ----------- -On success, nft exits with a status of 0. Unspecified errors cause it to exit with a status of 1, memory allocation errors with a status of 2, unable to open Netlink socket with 3. +On success, nft exits with a status of 0. Unspecified errors cause it to exit +with a status of 1, memory allocation errors with a status of 2, unable to open +Netlink socket with 3. SEE ALSO -------- @@ -614,6 +744,8 @@ COPYRIGHT --------- Copyright © 2008-2014 Patrick McHardy <kaber@trash.net> Copyright © 2013-2018 Pablo Neira Ayuso <pablo@netfilter.org> + -nftables is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation. + +nftables is free software; you can redistribute it and/or modify it under the +terms of the GNU General Public License version 2 as published by the Free +Software Foundation. + This documentation is licensed under the terms of the Creative Commons Attribution-ShareAlike 4.0 license, CC BY-SA 4.0 ⟨http://creativecommons.org/licenses/by-sa/4.0/⟩. |