Difference between revisions of "Nftables"

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[[es:Nftables]]
 
[[es:Nftables]]
 
[[ja:Nftables]]
 
[[ja:Nftables]]
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[[ru:Nftables]]
 
[[zh-hans:Nftables]]
 
[[zh-hans:Nftables]]
 
{{Related articles start}}
 
{{Related articles start}}
 
{{Related|iptables}}
 
{{Related|iptables}}
 
{{Related articles end}}
 
{{Related articles end}}
[http://netfilter.org/projects/nftables/ nftables] is a netfilter project that aims to replace the existing {ip,ip6,arp,eb}tables framework. It provides a new packet filtering framework, a new user-space utility (nft), and a compatibility layer for {ip,ip6}tables. It uses the existing hooks, connection tracking system, user-space queueing component, and logging subsystem of netfilter.
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{{Style|Pseudo-variables should not be words that are part of the nft syntax, like "table", "chain" and "handle" (e.g {{ic|nft add '''table''' ''family'' '''table'''}}, {{ic|nft add rule ''family'' ''table'' ''chain'' '''handle ''handle''''' ''statement''}}). They make the examples very confusing.}}
 +
[https://netfilter.org/projects/nftables/ nftables] is a netfilter project that aims to replace the existing {ip,ip6,arp,eb}tables framework. It provides a new packet filtering framework, a new user-space utility (nft), and a compatibility layer for {ip,ip6}tables. It uses the existing hooks, connection tracking system, user-space queueing component, and logging subsystem of netfilter.
  
It consists of three main components: a kernel implementation, the libnl netlink communication and the nftables user-space front-end.
+
It consists of three main components: a kernel implementation, the libnl [[Wikipedia:Netlink|netlink]] communication and the nftables user-space front-end.
 
The kernel provides a netlink configuration interface, as well as run-time rule-set evaluation, libnl contains the low-level functions for communicating with the kernel, and the nftables front-end is what the user interacts with via nft.
 
The kernel provides a netlink configuration interface, as well as run-time rule-set evaluation, libnl contains the low-level functions for communicating with the kernel, and the nftables front-end is what the user interacts with via nft.
  
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== Usage ==
 
== Usage ==
  
''nftables'' makes a distinction between temporary rules made in the commandline and permanent ones loaded from or saved to a file.
+
'''nftables''' makes '''no''' distinction between temporary rules made in the command line and permanent ones loaded from or saved to a file.
The default file is {{ic|/etc/nftables.conf}} which already contains a simple ipv4/ipv6 firewall table named "inet filter".
 
  
To use it [[start/enable]] the {{ic|nftables.service}}.
+
All rules have to be created or loaded using {{ic|nft}} command line utility.
  
You can check the ruleset with
+
Refer to [[#Configuration]] section on how to use.
 +
 
 +
Current ruleset can be printed with:
  
 
  # nft list ruleset
 
  # nft list ruleset
  
{{Note|You may have to create {{ic|/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: {{bc|$ grep -Eo '^nf\w+' /proc/modules}}
+
=== Simple firewall ===
  
Otherwise, you could end up with the dreaded {{ic|Error: Could not process rule: No such file or directory}} error.}}
+
{{Pkg|nftables}} comes with simple and secure firewall configuration stored in {{ic|/etc/nftables.conf}} file.
 +
 
 +
The {{ic|nftables.service}} will load rules from that file when [[start/enable|started or enabled]].
  
 
== Configuration ==
 
== Configuration ==
  
nftables' user-space utility ''nft'' performs most of the rule-set evaluation before handing rule-sets to the kernel. Rules are stored in chains, which in turn are stored in tables. The following sections indicate how to create and modify these constructs.
+
nftables user-space utility {{ic|nft}} performs most of the rule-set evaluation before handing rule-sets to the kernel. Rules are stored in chains, which in turn are stored in tables. The following sections indicate how to create and modify these constructs.
 
 
All changes below are temporary. To make changes permanent, save your ruleset to {{ic|/etc/nftables.conf}} which is loaded by {{ic|nftables.service}}:
 
# nft -s list ruleset > /etc/nftables.conf
 
 
 
{{Note|{{ic|nft list}} does not output variable definitions, if you have any in {{ic|/etc/nftables.conf}} they will be lost. Any variables used in rules will be replaced by their value.}}
 
  
 
To read input from a file use the {{ic|-f}}/{{ic|--file}} option:
 
To read input from a file use the {{ic|-f}}/{{ic|--file}} option:
  
  # nft -f ''filename''
+
  # nft --file ''filename''
  
Note that any rules already loaded are not automatically flushed.
+
Note that any rules already loaded are '''not''' automatically flushed.
  
 
See {{man|8|nft}} for a complete list of all commands.
 
See {{man|8|nft}} for a complete list of all commands.
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To create one rule that applies to both IPv4 and IPv6, use {{ic|inet}}. {{ic|inet}} allows for the unification of the {{ic|ip}} and {{ic|ip6}} families to make defining rules for both easier.
 
To create one rule that applies to both IPv4 and IPv6, use {{ic|inet}}. {{ic|inet}} allows for the unification of the {{ic|ip}} and {{ic|ip6}} families to make defining rules for both easier.
  
See the section {{ic|ADDRESS FAMILIES}} in {{man|8|nft}} for a complete description of address families.
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See {{man|8|nft|ADDRESS FAMILIES}} for a complete description of address families.
  
In all of the following, {{ic|''family''}} is optional, and if not specified is set to {{ic|ip}}.
+
In all of the following, {{ic|''family_type''}} is optional, and if not specified is set to {{ic|ip}}.
  
 
==== Create table ====
 
==== Create table ====
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The following adds a new table:
 
The following adds a new table:
  
  # nft add table ''family'' ''table''
+
  # nft add table ''family_type'' ''table_name''
  
 
==== List tables ====
 
==== List tables ====
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To list all chains and rules of a specified table do:
 
To list all chains and rules of a specified table do:
  
  # nft list table ''family'' ''table''
+
  # nft list table ''family_type'' ''table_name''
  
For example, to list all the rules of the {{ic|filter}} table of the {{ic|inet}} family:
+
For example, to list all the rules of the {{ic|my_table}} table of the {{ic|inet}} family:
  
  # nft list table inet filter
+
  # nft list table inet my_table
  
 
==== Delete table ====
 
==== Delete table ====
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To delete a table do:
 
To delete a table do:
  
  # nft delete table ''family'' ''table''
+
  # nft delete table ''family_type'' ''table_name''
  
Tables can only be deleted if there are no chains in them.
+
This will destroy all chains in the table.
  
 
==== Flush table ====
 
==== Flush table ====
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To flush all rules from a table do:
 
To flush all rules from a table do:
  
  # nft flush table ''family'' ''table''
+
  # nft flush table ''family_type'' ''table_name''
  
 
=== Chains ===
 
=== Chains ===
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Chains have two types. A ''base'' chain is an entry point for packets from the networking stack, where a hook value is specified. A ''regular'' chain may be used as a jump target for better organization.
 
Chains have two types. A ''base'' chain is an entry point for packets from the networking stack, where a hook value is specified. A ''regular'' chain may be used as a jump target for better organization.
  
In all of the following {{ic|''family''}} is optional, and if not specified is set to {{ic|ip}}.
+
In all of the following {{ic|''family_type''}} is optional, and if not specified is set to {{ic|ip}}.
  
 
==== Create chain ====
 
==== Create chain ====
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===== Regular chain =====
 
===== Regular chain =====
  
The following adds a regular chain named {{ic|''chain''}} to the table named {{ic|''table''}}:
+
The following adds a regular chain named {{ic|''chain_name''}} to the table named {{ic|''table_name''}}:
  
  # nft add chain ''family'' ''table'' ''chain''
+
  # nft add chain ''family_type'' ''table_name'' ''chain_name''
  
For example, to add a regular chain named {{ic|tcpchain}} to the {{ic|filter}} table of the {{ic|inet}} address family do:
+
For example, to add a regular chain named {{ic|my_tcp_chain}} to the {{ic|my_table}} table of the {{ic|inet}} address family do:
  
  # nft add chain inet filter tcpchain
+
  # nft add chain inet my_table my_tcp_chain
  
 
===== Base chain =====
 
===== Base chain =====
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To add a base chain specify hook and priority values:
 
To add a base chain specify hook and priority values:
  
  # nft add chain ''family'' ''table'' ''chain'' '{ type ''type'' hook ''hook'' priority ''priority'' ; }'
+
  # nft add chain ''family_type'' ''table_name'' ''chain_name'' '{ type ''chain_type'' hook ''hook_type'' priority ''priority_value'' ; }'
  
{{ic|''type''}} can be {{ic|filter}}, {{ic|route}}, or {{ic|nat}}.
+
{{ic|''chain_type''}} can be {{ic|filter}}, {{ic|route}}, or {{ic|nat}}.
  
For IPv4/IPv6/Inet address families {{ic|''hook''}} can be {{ic|prerouting}}, {{ic|input}}, {{ic|forward}}, {{ic|output}}, or {{ic|postrouting}}. See {{man|8|nft}} for a list of hooks for other families.
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For IPv4/IPv6/Inet address families {{ic|''hook_type''}} can be {{ic|prerouting}}, {{ic|input}}, {{ic|forward}}, {{ic|output}}, or {{ic|postrouting}}. See {{man|8|nft|ADDRESS FAMILIES}} for a list of hooks for other families.
  
{{ic|''priority''}} takes an integer value. Chains with lower numbers are processed first and can be negative. [https://wiki.nftables.org/wiki-nftables/index.php/Configuring_chains#Base_chain_types]
+
{{ic|''priority_value''}} takes either a priority name or an its integer value. See {{man|8|nft|CHAINS}} for a list of standard priority names and values. Chains with lower numbers are processed first and can be negative. [https://wiki.nftables.org/wiki-nftables/index.php/Configuring_chains#Base_chain_types]
  
 
For example, to add a base chain that filters input packets:
 
For example, to add a base chain that filters input packets:
  
  # nft add chain inet filter input '{ type filter hook input priority 0; }'
+
  # nft add chain inet mt_table my_chain '{ type filter hook input priority 0; }'
  
 
Replace {{ic|add}} with {{ic|create}} in any of the above to add a new chain but return an error if the chain already exists.
 
Replace {{ic|add}} with {{ic|create}} in any of the above to add a new chain but return an error if the chain already exists.
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The following lists all rules of a chain:
 
The following lists all rules of a chain:
  
  # nft list chain ''family'' ''table'' ''chain''
+
  # nft list chain ''family_type'' ''table_name'' ''chain_name''
  
For example, the following lists the rules of the chain named {{ic|output}} in the {{ic|inet}} table named {{ic|filter}}:
+
For example, the following lists the rules of the chain named {{ic|my_output}} in the {{ic|inet}} table named {{ic|my_table}}:
  
  # nft list chain inet filter output
+
  # nft list chain inet my_table my_output
  
 
==== Edit a chain ====
 
==== Edit a chain ====
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To edit a chain, simply call it by its name and define the rules you want to change.
 
To edit a chain, simply call it by its name and define the rules you want to change.
  
  # nft chain ''family table chain'' '{ [ type ''type'' hook ''hook'' device ''device'' priority ''priority'' ; policy ''policy'' ; ] }'
+
  # nft chain ''family_type table_name chain_name'' '{ [ type ''chain_type'' hook ''hook_type'' device ''device_name'' priority ''priority_value'' ; policy ''policy_type'' ; ] }'
  
For example, to change the input chain policy of the default table from {{ic|accept}} to {{ic|drop}}
+
For example, to change the {{ic|my_input}} chain policy of the default table from {{ic|accept}} to {{ic|drop}}
  
  # nft chain inet filter input '{ policy drop ; }'
+
  # nft chain inet my_table my_input '{ policy drop ; }'
  
 
==== Delete a chain ====
 
==== Delete a chain ====
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To delete a chain do:
 
To delete a chain do:
  
  # nft delete chain ''family'' ''table'' ''chain''
+
  # nft delete chain ''family_type'' ''table_name'' ''chain_name''
  
 
The chain must not contain any rules or be a jump target.
 
The chain must not contain any rules or be a jump target.
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To flush rules from a chain do:
 
To flush rules from a chain do:
  
  # nft flush chain ''family'' ''table'' ''chain''
+
  # nft flush chain ''family_type'' ''table_name'' ''chain_name''
  
 
=== Rules ===
 
=== Rules ===
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To add a rule to a chain do:
 
To add a rule to a chain do:
  
  # nft add rule ''family'' ''table'' ''chain'' handle ''handle'' ''statement''
+
  # nft add rule ''family_type'' ''table_name'' ''chain_name'' handle ''handle_value'' ''statement''
  
The rule is appended at {{ic|''handle''}}, which is optional. If not specified, the rule is appended to the end of the chain.
+
The rule is appended at {{ic|''my_handle''}}, which is optional. If not specified, the rule is appended to the end of the chain.
  
 
To prepend the rule to the position do:
 
To prepend the rule to the position do:
  
  # nft insert rule ''family'' ''table'' ''chain'' handle ''handle'' ''statement''
+
  # nft insert rule ''family_type'' ''table_name'' ''chain_name'' handle ''handle_value'' ''statement''
  
If {{ic|''handle''}} is not specified, the rule is prepended to the chain.
+
If {{ic|''handle_value''}} is not specified, the rule is prepended to the chain.
  
 
===== Expressions =====
 
===== Expressions =====
  
Typically a {{ic|''statement''}} includes some expression to be matched and then a verdict statement. Verdict statements include {{ic|accept}}, {{ic|drop}}, {{ic|queue}}, {{ic|continue}}, {{ic|return}}, {{ic|jump ''chain''}}, and {{ic|goto ''chain''}}. Other statements than verdict statements are possible. See {{man|8|nft}} for more information.
+
Typically a {{ic|''statement''}} includes some expression to be matched and then a verdict statement. Verdict statements include {{ic|accept}}, {{ic|drop}}, {{ic|queue}}, {{ic|continue}}, {{ic|return}}, {{ic|jump ''chain_name''}}, and {{ic|goto ''chain_name''}}. Other statements than verdict statements are possible. See {{man|8|nft}} for more information.
  
 
There are various expressions 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. A generic match was one that was always available, such as {{ic|--protocol}} or {{ic|--source}}. Implicit matches were protocol-specific, such as {{ic|--sport}} when a packet was determined to be TCP.
 
There are various expressions 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. A generic match was one that was always available, such as {{ic|--protocol}} or {{ic|--source}}. Implicit matches were protocol-specific, such as {{ic|--sport}} when a packet was determined to be TCP.
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Individual rules can only be deleted by their handles. The {{ic|nft --handle list}} command must be used to determine rule handles. Note the {{ic|--handle}} switch, which tells {{ic|nft}} to list handles in its output.
 
Individual rules can only be deleted by their handles. The {{ic|nft --handle list}} command must be used to determine rule handles. Note the {{ic|--handle}} switch, which tells {{ic|nft}} to list handles in its output.
  
The following determines the handle for a rule and then deletes it. The {{ic|--number}} argument is useful for viewing some numeric output, like unresolved IP addresses.
+
The following determines the handle for a rule and then deletes it. The {{ic|--numeric}} argument is useful for viewing some numeric output, like unresolved IP addresses.
  
{{hc|# nft --handle --numeric list chain inet filter input|2=<nowiki>
+
{{hc|# nft --handle --numeric list chain inet my_table my_input|2=<nowiki>
table inet fltrTable {
+
table inet my_table {
 
     chain input {
 
     chain input {
 
           type filter hook input priority 0;
 
           type filter hook input priority 0;
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</nowiki>}}
 
</nowiki>}}
  
  # nft delete rule inet fltrTable input handle 10
+
  # nft delete rule inet my_table my_input handle 10
  
 
All the chains in a table can be flushed with the {{ic|nft flush table}} command. Individual chains can be flushed using either the {{ic|nft flush chain}} or {{ic|nft delete rule}} commands.
 
All the chains in a table can be flushed with the {{ic|nft flush table}} command. Individual chains can be flushed using either the {{ic|nft flush chain}} or {{ic|nft delete rule}} commands.
  
  # nft flush table foo
+
  # nft flush table ''table_name''
  # nft flush chain foo bar
+
  # nft flush chain ''family_type'' ''table_name'' ''chain_name''
  # nft delete rule ip6 foo bar
+
  # nft delete rule ''family_type'' ''table_name'' ''chain_name''
  
The first command flushes all of the chains in the ip {{ic|foo}} table. The second flushes the {{ic|bar}} chain in the ip {{ic|foo}} table. The third deletes all of the rules in {{ic|bar}} chain in the ip6 {{ic|foo}} table.
+
The first command flushes all of the chains in the ip {{ic|''table_name''}} table. The second flushes the {{ic|''chain_name''}} chain in the ip {{ic|foo}} table. The third deletes all of the rules in {{ic|''chain_name''}} chain in the {{ic|''family_type''}} {{ic|''table_name''}} table.
  
 
=== Atomic reloading ===
 
=== Atomic reloading ===
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{{hc|/etc/nftables.conf|2=<nowiki>
 
{{hc|/etc/nftables.conf|2=<nowiki>
#!/usr/bin/nft -f
 
 
 
flush ruleset
 
flush ruleset
  
table inet filter {
+
table inet my_table {
chain input {
+
chain my_input {
 
type filter hook input priority 0; policy drop;
 
type filter hook input priority 0; policy drop;
  
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ct state established,related accept comment "Accept traffic originated from us"
 
ct state established,related accept comment "Accept traffic originated from us"
  
ip6 nexthdr icmpv6 icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
+
meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
ip protocol icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
+
meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
 
ip protocol igmp accept comment "Accept IGMP"
 
ip protocol igmp accept comment "Accept IGMP"
  
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}
 
}
  
chain forward {
+
chain my_forward {
 
type filter hook forward priority 0; policy drop;
 
type filter hook forward priority 0; policy drop;
 +
# Drop everything forwarded to us. We do not forward. That is routers job.
 
}
 
}
  
chain output {
+
chain my_output {
 
type filter hook output priority 0; policy accept;
 
type filter hook output priority 0; policy accept;
 +
# Accept every outbound connection
 
}
 
}
  
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{{hc|/etc/nftables.conf|2=<nowiki>
 
{{hc|/etc/nftables.conf|2=<nowiki>
#!/usr/bin/nft -f
 
 
 
flush ruleset
 
flush ruleset
  
table inet filter {
+
table inet my_table {
chain input {
+
chain my_input {
 
type filter hook input priority 0; policy drop;
 
type filter hook input priority 0; policy drop;
  
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ct state established,related accept comment "Accept traffic originated from us"
 
ct state established,related accept comment "Accept traffic originated from us"
  
ip6 nexthdr icmpv6 icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
+
meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
ip protocol icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
+
meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
 
ip protocol igmp accept comment "Accept IGMP"
 
ip protocol igmp accept comment "Accept IGMP"
  
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}
 
}
  
chain forward {
+
chain my_forward {
 
type filter hook forward priority 0; policy drop;
 
type filter hook forward priority 0; policy drop;
 +
# Drop everything forwarded to us. We do not forward. That is routers job.
 
}
 
}
  
chain output {
+
chain my_output {
 
type filter hook output priority 0; policy accept;
 
type filter hook output priority 0; policy accept;
 +
# Accept every outbound connection
 
}
 
}
  
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{{bc|1=<nowiki>
 
{{bc|1=<nowiki>
table inet filter {
+
table inet my_table {
chain input {
+
chain my_input {
 
type filter hook input priority 0; policy drop;
 
type filter hook input priority 0; policy drop;
  
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ct state invalid drop comment "Drop invalid connections"
 
ct state invalid drop comment "Drop invalid connections"
  
ip protocol icmp icmp type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"
+
meta l4proto icmp icmp type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"
ip6 nexthdr icmpv6 icmpv6 type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"
+
meta l4proto ipv6-icmp icmpv6 type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"
  
 
ct state established,related accept comment "Accept traffic originated from us"
 
ct state established,related accept comment "Accept traffic originated from us"
  
ip6 nexthdr icmpv6 icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
+
meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
ip protocol icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
+
meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
 
ip protocol igmp accept comment "Accept IGMP"
 
ip protocol igmp accept comment "Accept IGMP"
  
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{{bc|1=<nowiki>
 
{{bc|1=<nowiki>
table inet filter {
+
table inet my_table {
 
     chain web {
 
     chain web {
 
         tcp dport http accept
 
         tcp dport http accept
 
         tcp dport 8080 accept
 
         tcp dport 8080 accept
 
     }
 
     }
     chain input {
+
     chain my_input {
 
         type filter hook input priority 0;
 
         type filter hook input priority 0;
 
         ip saddr 10.0.2.0/24 jump web
 
         ip saddr 10.0.2.0/24 jump web
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=== Different rules for different interfaces ===
 
=== Different rules for different interfaces ===
  
If your box has more than one network interface, and you would like to use different rules for different interfaces, you may want to use a "dispatching" filter chain, and then interface-specific filter chains. For example, let us assume your box acts as a home router, you want to run a web server accessible over the LAN (interface enp3s0), but not from the public internet (interface enp2s0), you may want to consider a structure like this:
+
If your box has more than one network interface, and you would like to use different rules for different interfaces, you may want to use a "dispatching" filter chain, and then interface-specific filter chains. For example, let us assume your box acts as a home router, you want to run a web server accessible over the LAN (interface {{ic|enp3s0}}), but not from the public internet (interface {{ic|enp2s0}}), you may want to consider a structure like this:
  
 
{{bc|<nowiki>
 
{{bc|<nowiki>
table inet filter {
+
table inet my_table {
   chain input { # this chain serves as a dispatcher
+
   chain my_input { # this chain serves as a dispatcher
 
     type filter hook input priority 0;
 
     type filter hook input priority 0;
  
 
     iif lo accept # always accept loopback
 
     iif lo accept # always accept loopback
     iifname enp2s0 jump input_enp2s0
+
     iifname enp2s0 jump my_input_public
     iifname enp3s0 jump input_enp3s0
+
     iifname enp3s0 jump my_input_private
  
     reject with icmp type port-unreachable # refuse traffic from all other interfaces
+
     reject with icmpx type port-unreachable # refuse traffic from all other interfaces
 
   }
 
   }
   chain input_enp2s0 { # rules applicable to public interface interface
+
   chain my_input_public { # rules applicable to public interface interface
 
     ct state {established,related} accept
 
     ct state {established,related} accept
 
     ct state invalid drop
 
     ct state invalid drop
 
     udp dport bootpc accept
 
     udp dport bootpc accept
 
     tcp dport bootpc accept
 
     tcp dport bootpc accept
     reject with icmp type port-unreachable # all other traffic
+
     reject with icmpx type port-unreachable # all other traffic
 
   }
 
   }
   chain input_enp3s0 {
+
   chain my_input_private {
 
     ct state {established,related} accept
 
     ct state {established,related} accept
 
     ct state invalid drop
 
     ct state invalid drop
Line 482: Line 482:
 
     tcp port http accept
 
     tcp port http accept
 
     tcp port https accept
 
     tcp port https accept
     reject with icmp type port-unreachable # all other traffic
+
     reject with icmpx type port-unreachable # all other traffic
 
   }
 
   }
   chain ouput { # we let everything out
+
   chain my_output { # we let everything out
 
     type filter hook output priority 0;
 
     type filter hook output priority 0;
 
     accept
 
     accept
Line 495: Line 495:
 
=== Masquerading ===
 
=== Masquerading ===
  
nftables has a special keyword {{ic|masquerade}} "where the source address is automagically set to the address of the output interface" ([http://wiki.nftables.org/wiki-nftables/index.php/Performing_Network_Address_Translation_%28NAT%29#Masquerading source]). This is particularly useful for situations in which the IP address of the interface is unpredictable or unstable, such as the upstream interface of routers connecting to many ISPs. Without it, the Network Address Translation rules would have to be updated every time the IP address of the interface changed.
+
nftables has a special keyword {{ic|masquerade}} "where the source address is automagically set to the address of the output interface" ([https://wiki.nftables.org/wiki-nftables/index.php/Performing_Network_Address_Translation_%28NAT%29#Masquerading source]). This is particularly useful for situations in which the IP address of the interface is unpredictable or unstable, such as the upstream interface of routers connecting to many ISPs. Without it, the Network Address Translation rules would have to be updated every time the IP address of the interface changed.
  
 
To use it:
 
To use it:
Line 506: Line 506:
  
 
{{bc|<nowiki>
 
{{bc|<nowiki>
table inet nat {
+
table inet my_nat {
   chain prerouting {
+
   chain my_masquerade {
    type nat hook prerouting priority 0;
 
  }
 
  chain postrouting {
 
 
     type nat hook postrouting priority 100;
 
     type nat hook postrouting priority 100;
 
     oifname "enp2s0" masquerade
 
     oifname "enp2s0" masquerade
Line 516: Line 513:
 
}
 
}
 
</nowiki>}}
 
</nowiki>}}
 +
 +
Since the table type is {{ic|inet}} both IPv4 and IPv6 packets will be masqueraded. If you want only ipv4 packets to be masqueraded (since extra adress space of IPv6 makes NAT not required) {{ic|meta nfproto ipv4}} expression can be used infront of {{ic|oifname "enp2s0" masquerade}} or the table type can be changed to {{ic|ip}}.
 +
 +
=== NAT with port forwarding ===
 +
 +
{{Accuracy|I think {{ic|my_postrouting}} chain will cause the destination computer see that connections are made by router rather than from some global IP. Also this does not masquerade outbound traffic.}}
 +
 +
This example will forward ports 22 and 80 to {{ic|''destination_ip''}}. You will need to set {{ic|net.ipv4.ip_forward}} and {{ic|net.ipv4.conf.''wan_interface''.forwarding}} to {{ic|1}} via [[sysctl]].
 +
 +
{{bc|
 +
table ip my_nat {
 +
  chain my_prerouting {
 +
    type nat hook prerouting priority -100;
 +
 +
    tcp dport { ssh, http } dnat to ''destination_ip''
 +
  }
 +
 +
  chain my_postrouting {
 +
    type nat hook postrouting priority 100;
 +
 +
    ip daddr ''destination_ip'' masquerade
 +
  }
 +
}
 +
}}
  
 
== Tips and tricks ==
 
== Tips and tricks ==
 +
 +
=== Saving current rule set ===
 +
 +
The output of {{ic|nft list ruleset}} command is a valid input file for it as well. Current rule set can be saved to file and later loaded back in.
 +
 +
$ nft -s list ruleset | tee ''filename''
 +
 +
{{Note|{{ic|nft list}} does not output variable definitions, if you had any in your original file they will be lost. Any variables used in rules will be replaced by their value.}}
  
 
=== Simple stateful firewall ===
 
=== Simple stateful firewall ===
 +
 +
{{Accuracy|This is not a very simple firewall. I would consider what Arch Linux ships in /etc/nftables.conf simple. Recommend replacing this section with that script and give some directions on how to expand it for specific needs.}}
  
 
See [[Simple stateful firewall]] for more information.
 
See [[Simple stateful firewall]] for more information.
Line 531: Line 562:
 
Add a table:
 
Add a table:
  
  # nft add table inet filter
+
  # nft add table inet my_table
  
 
Add the input, forward, and output base chains. The policy for input and forward will be to drop. The policy for output will be to accept.
 
Add the input, forward, and output base chains. The policy for input and forward will be to drop. The policy for output will be to accept.
  
  # nft add chain inet filter input '{ type filter hook input priority 0 ; policy drop ; }'
+
  # nft add chain inet my_table my_input '{ type filter hook input priority 0 ; policy drop ; }'
  # nft add chain inet filter forward '{ type filter hook forward priority 0 ; policy drop ; }'
+
  # nft add chain inet my_table my_forward '{ type filter hook forward priority 0 ; policy drop ; }'
  # nft add chain inet filter output '{ type filter hook output priority 0 ; policy accept ; }'
+
  # nft add chain inet my_table my_output '{ type filter hook output priority 0 ; policy accept ; }'
  
 
Add two regular chains that will be associated with tcp and udp:
 
Add two regular chains that will be associated with tcp and udp:
  
  # nft add chain inet filter TCP
+
  # nft add chain inet my_table my_tcp_chain
  # nft add chain inet filter UDP
+
  # nft add chain inet my_table my_udp_chain
  
 
Related and established traffic will be accepted:
 
Related and established traffic will be accepted:
  
  # nft add rule inet filter input ct state related,established accept
+
  # nft add rule inet my_table my_input ct state related,established accept
  
 
All loopback interface traffic will be accepted:
 
All loopback interface traffic will be accepted:
  
  # nft add rule inet filter input iif lo accept
+
  # nft add rule inet my_table my_input iif lo accept
  
 
Drop any invalid traffic:
 
Drop any invalid traffic:
  
  # nft add rule inet filter input ct state invalid drop
+
  # nft add rule inet my_table my_input ct state invalid drop
  
 
Accept ICMP and IGMP:
 
Accept ICMP and IGMP:
  
  # nft add rule inet filter input ip6 nexthdr icmpv6 icmpv6 type '{ destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report }' accept
+
  # nft add rule inet my_table my_input meta l4proto ipv6-icmp icmpv6 type '{ destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report }' accept
  # nft add rule inet filter input ip protocol icmp icmp type '{ destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem }' accept
+
  # nft add rule inet my_table my_input meta l4proto icmp icmp type '{ destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem }' accept
  # nft add rule inet filter input ip protocol igmp accept
+
  # nft add rule inet my_table my_input ip protocol igmp accept
  
 
New udp traffic will jump to the UDP chain:
 
New udp traffic will jump to the UDP chain:
  
  # nft add rule inet filter input ip protocol udp ct state new jump UDP
+
  # nft add rule inet my_table my_input meta l4proto udp ct state new jump my_udp_chain
  
 
New tcp traffic will jump to the TCP chain:
 
New tcp traffic will jump to the TCP chain:
  
  # nft add rule inet filter input 'ip protocol tcp tcp flags & (fin|syn|rst|ack) == syn ct state new jump TCP'
+
  # nft add rule inet my_table my_input 'meta l4proto tcp tcp flags & (fin|syn|rst|ack) == syn ct state new jump my_tcp_chain'
  
 
Reject all traffic that was not processed by other rules:
 
Reject all traffic that was not processed by other rules:
  
  # nft add rule inet filter input ip protocol udp reject
+
  # nft add rule inet my_table my_input meta l4proto udp reject
  # nft add rule inet filter input ip protocol tcp reject with tcp reset
+
  # nft add rule inet my_table my_input meta l4proto tcp reject with tcp reset
  # nft add rule inet filter input counter reject with icmp type prot-unreachable
+
  # nft add rule inet my_table my_input counter reject with icmpx type port-unreachable
  
 
At this point you should decide what ports you want to open to incoming connections, which are handled by the TCP and UDP chains. For example to open connections for a web server add:
 
At this point you should decide what ports you want to open to incoming connections, which are handled by the TCP and UDP chains. For example to open connections for a web server add:
  
  # nft add rule inet filter TCP tcp dport 80 accept
+
  # nft add rule inet my_table my_tcp_chain tcp dport 80 accept
  
 
To accept HTTPS connections for a webserver on port 443:
 
To accept HTTPS connections for a webserver on port 443:
  
  # nft add rule inet filter TCP tcp dport 443 accept
+
  # nft add rule inet my_table my_tcp_chain tcp dport 443 accept
  
 
To accept SSH traffic on port 22:
 
To accept SSH traffic on port 22:
  
  # nft add rule inet filter TCP tcp dport 22 accept
+
  # nft add rule inet my_table my_tcp_chain tcp dport 22 accept
  
 
To accept incoming DNS requests:
 
To accept incoming DNS requests:
  
  # nft add rule inet filter TCP tcp dport 53 accept
+
  # nft add rule inet my_table my_tcp_chain tcp dport 53 accept
  # nft add rule inet filter UDP udp dport 53 accept
+
  # nft add rule inet my_table my_udp_chain udp dport 53 accept
  
 
Be sure to make your changes permanent when satisifed.
 
Be sure to make your changes permanent when satisifed.
Line 609: Line 640:
 
#:{{bc|<nowiki>
 
#:{{bc|<nowiki>
 
chain forward {
 
chain forward {
   type filter hook forward priority security; policy drop
+
   type filter hook forward priority security; policy drop;
 
   mark 1 accept
 
   mark 1 accept
 
</nowiki>}}
 
</nowiki>}}
Line 631: Line 662:
 
* [https://home.regit.org/netfilter-en/nftables-quick-howto/ nftables quick howto]
 
* [https://home.regit.org/netfilter-en/nftables-quick-howto/ nftables quick howto]
 
* [https://lwn.net/Articles/564095/ The return of nftables]
 
* [https://lwn.net/Articles/564095/ The return of nftables]
* [http://developers.redhat.com/blog/2016/10/28/what-comes-after-iptables-its-successor-of-course-nftables/ What comes after ‘iptables’? Its successor, of course: `nftables`]
+
* [https://developers.redhat.com/blog/2016/10/28/what-comes-after-iptables-its-successor-of-course-nftables/ What comes after ‘iptables’? Its successor, of course: `nftables`]

Latest revision as of 07:11, 20 March 2020

Tango-edit-clear.pngThis article or section needs language, wiki syntax or style improvements. See Help:Style for reference.Tango-edit-clear.png

Reason: Pseudo-variables should not be words that are part of the nft syntax, like "table", "chain" and "handle" (e.g nft add table family table, nft add rule family table chain handle handle statement). They make the examples very confusing. (Discuss in Talk:Nftables#)

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

It 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, libnl contains the low-level functions for communicating with the kernel, and the nftables front-end is what the user interacts with via nft.

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

Installation

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Mention iptables-nft.[1] (Discuss in Talk:Nftables#)

Install the userspace utilities package nftables or the git version nftables-gitAUR.

Tip: Most iptables front-ends feature no direct or indirect support of nftables, but may introduce it.[2] One graphical front-end that supports both, nftables and iptables, is firewalld.[3]

Usage

nftables makes no distinction between temporary rules made in the command line and permanent ones loaded from or saved to a file.

All rules have to be created or loaded using nft command line utility.

Refer to #Configuration section on how to use.

Current ruleset can be printed with:

# nft list ruleset

Simple firewall

nftables comes with simple and secure firewall configuration stored in /etc/nftables.conf file.

The nftables.service will load rules from that file when started or enabled.

Configuration

nftables user-space utility nft performs most of the rule-set evaluation before handing rule-sets to the kernel. Rules are stored in chains, which in turn are stored in tables. The following sections indicate how to create and modify these constructs.

To read input from a file use the -f/--file option:

# nft --file filename

Note that any rules already loaded are not automatically flushed.

See nft(8) for a complete list of all commands.

Tables

Tables hold #Chains. Unlike tables in iptables, there are no built-in tables in nftables. The number of tables and their names is up to the user. However, each table only has one address family and only applies to packets of this family. Tables can have one of five families specified:

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

ip (i.e. IPv4) is the default family and will be used if family is not specified.

To create one rule that applies to both IPv4 and IPv6, use inet. inet allows for the unification of the ip and ip6 families to make defining rules for both easier.

See nft(8) for a complete description of address families.

In all of the following, family_type is optional, and if not specified is set to ip.

Create table

The following adds a new table:

# nft add table family_type table_name

List tables

To list all tables:

# nft list tables

List chains and rules in a table

To list all chains and rules of a specified table do:

# nft list table family_type table_name

For example, to list all the rules of the my_table table of the inet family:

# nft list table inet my_table

Delete table

To delete a table do:

# nft delete table family_type table_name

This will destroy all chains in the table.

Flush table

To flush all rules from a table do:

# nft flush table family_type table_name

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.

Chains have two types. A base chain is an entry point for packets from the networking stack, where a hook value is specified. A regular chain may be used as a jump target for better organization.

In all of the following family_type is optional, and if not specified is set to ip.

Create chain

Regular chain

The following adds a regular chain named chain_name to the table named table_name:

# nft add chain family_type table_name chain_name

For example, to add a regular chain named my_tcp_chain to the my_table table of the inet address family do:

# nft add chain inet my_table my_tcp_chain
Base chain

To add a base chain specify hook and priority values:

# nft add chain family_type table_name chain_name '{ type chain_type hook hook_type priority priority_value ; }'

chain_type can be filter, route, or nat.

For IPv4/IPv6/Inet address families hook_type can be prerouting, input, forward, output, or postrouting. See nft(8) for a list of hooks for other families.

priority_value takes either a priority name or an its integer value. See nft(8) for a list of standard priority names and values. Chains with lower numbers are processed first and can be negative. [4]

For example, to add a base chain that filters input packets:

# nft add chain inet mt_table my_chain '{ type filter hook input priority 0; }'

Replace add with create in any of the above to add a new chain but return an error if the chain already exists.

List rules

The following lists all rules of a chain:

# nft list chain family_type table_name chain_name

For example, the following lists the rules of the chain named my_output in the inet table named my_table:

# nft list chain inet my_table my_output

Edit a chain

To edit a chain, simply call it by its name and define the rules you want to change.

# nft chain family_type table_name chain_name '{ [ type chain_type hook hook_type device device_name priority priority_value ; policy policy_type ; ] }'

For example, to change the my_input chain policy of the default table from accept to drop

# nft chain inet my_table my_input '{ policy drop ; }'

Delete a chain

To delete a chain do:

# nft delete chain family_type table_name chain_name

The chain must not contain any rules or be a jump target.

Flush rules from a chain

To flush rules from a chain do:

# nft flush chain family_type table_name chain_name

Rules

Rules are either constructed from expressions or statements and are contained within chains.

Add rule

Tip: The iptables-translate utility translates iptables rules to nftables format.

To add a rule to a chain do:

# nft add rule family_type table_name chain_name handle handle_value statement

The rule is appended at my_handle, which is optional. If not specified, the rule is appended to the end of the chain.

To prepend the rule to the position do:

# nft insert rule family_type table_name chain_name handle handle_value statement

If handle_value is not specified, the rule is prepended to the chain.

Expressions

Typically a statement includes some expression to be matched and then a verdict statement. Verdict statements include accept, drop, queue, continue, return, jump chain_name, and goto chain_name. Other statements than verdict statements are possible. See nft(8) for more information.

There are various expressions 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. 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 nft(8)):

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>

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 --numeric argument is useful for viewing some numeric output, like unresolved IP addresses.

# nft --handle --numeric list chain inet my_table my_input
table inet my_table {
     chain input {
          type filter hook input priority 0;
          ip saddr 127.0.0.1 accept # handle 10
     }
}
# nft delete rule inet my_table my_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 table_name
# nft flush chain family_type table_name chain_name
# nft delete rule family_type table_name chain_name

The first command flushes all of the chains in the ip table_name table. The second flushes the chain_name chain in the ip foo table. The third deletes all of the rules in chain_name chain in the family_type table_name table.

Atomic reloading

Flush the current ruleset:

# echo "flush ruleset" > /tmp/nftables 

Dump the current ruleset:

# nft -s list ruleset >> /tmp/nftables

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

# nft -f /tmp/nftables

Examples

Workstation

/etc/nftables.conf
flush ruleset

table inet my_table {
	chain my_input {
		type filter hook input priority 0; policy drop;

		iif lo accept comment "Accept any localhost traffic"
		ct state invalid drop comment "Drop invalid connections"
		ct state established,related accept comment "Accept traffic originated from us"

		meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
		meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
		ip protocol igmp accept comment "Accept IGMP"

		udp dport mdns ip6 daddr ff02::fb accept comment "Accept mDNS"
		udp dport mdns ip daddr 224.0.0.251 accept comment "Accept mDNS"

		udp sport 1900 udp dport >= 1024 ip6 saddr { fd00::/8, fe80::/10 } meta pkttype unicast limit rate 4/second burst 20 packets accept comment "Accept UPnP IGD port mapping reply"
		udp sport 1900 udp dport >= 1024 ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } meta pkttype unicast limit rate 4/second burst 20 packets accept comment "Accept UPnP IGD port mapping reply"

		udp sport netbios-ns udp dport >= 1024 meta pkttype unicast ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept Samba Workgroup browsing replies"
		udp sport netbios-ns udp dport >= 1024 meta pkttype unicast ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept Samba Workgroup browsing replies"

		counter comment "Count any other traffic"
	}

	chain my_forward {
		type filter hook forward priority 0; policy drop;
		# Drop everything forwarded to us. We do not forward. That is routers job.
	}

	chain my_output {
		type filter hook output priority 0; policy accept;
		# Accept every outbound connection
	}

}

Server

/etc/nftables.conf
flush ruleset

table inet my_table {
	chain my_input {
		type filter hook input priority 0; policy drop;

		iif lo accept comment "Accept any localhost traffic"
		ct state invalid drop comment "Drop invalid connections"
		ct state established,related accept comment "Accept traffic originated from us"

		meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
		meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
		ip protocol igmp accept comment "Accept IGMP"

		udp dport mdns ip6 daddr ff02::fb accept comment "Accept mDNS"
		udp dport mdns ip daddr 224.0.0.251 accept comment "Accept mDNS"

		tcp dport ssh accept comment "Accept SSH on port 22"

		tcp dport { http, https, 8008, 8080 } accept comment "Accept HTTP (ports 80, 443, 8008, 8080)"

		meta l4proto { tcp, udp } th dport 2049 ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept NFS"
		meta l4proto { tcp, udp } th dport 2049 ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept NFS"

		udp dport netbios-ns ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept NetBIOS Name Service (nmbd)"
		udp dport netbios-ns ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept NetBIOS Name Service (nmbd)"
		udp dport netbios-dgm ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept NetBIOS Datagram Service (nmbd)"
		udp dport netbios-dgm ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept NetBIOS Datagram Service (nmbd)"
		tcp dport netbios-ssn ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept NetBIOS Session Service (smbd)"
		tcp dport netbios-ssn ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept NetBIOS Session Service (smbd)"
		tcp dport microsoft-ds ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept Microsoft Directory Service (smbd)"
		tcp dport microsoft-ds ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept Microsoft Directory Service (smbd)"

		udp sport bootpc udp dport bootps ip saddr 0.0.0.0 ip daddr 255.255.255.255 accept comment "Accept DHCPDISCOVER (for DHCP-Proxy)"
		udp sport { bootpc, 4011 } udp dport { bootps, 4011 } ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept PXE"
		udp dport tftp ip6 saddr { fd00::/8, fe80::/10 } accept comment "Accept TFTP"
		udp dport tftp ip saddr { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 } accept comment "Accept TFTP"

	}

	chain my_forward {
		type filter hook forward priority 0; policy drop;
		# Drop everything forwarded to us. We do not forward. That is routers job.
	}

	chain my_output {
		type filter hook output priority 0; policy accept;
		# Accept every outbound connection
	}

}

Limit rate

table inet my_table {
	chain my_input {
		type filter hook input priority 0; policy drop;

		iif lo accept comment "Accept any localhost traffic"
		ct state invalid drop comment "Drop invalid connections"

		meta l4proto icmp icmp type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"
		meta l4proto ipv6-icmp icmpv6 type echo-request limit rate over 10/second burst 4 packets drop comment "No ping floods"

		ct state established,related accept comment "Accept traffic originated from us"

		meta l4proto ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report } accept comment "Accept ICMPv6"
		meta l4proto icmp icmp type { destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem } accept comment "Accept ICMP"
		ip protocol igmp accept comment "Accept IGMP"

		tcp dport ssh ct state new limit rate 15/minute accept comment "Avoid brute force on SSH"

	}

}

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.

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

Different rules for different interfaces

If your box has more than one network interface, and you would like to use different rules for different interfaces, you may want to use a "dispatching" filter chain, and then interface-specific filter chains. For example, let us assume your box acts as a home router, you want to run a web server accessible over the LAN (interface enp3s0), but not from the public internet (interface enp2s0), you may want to consider a structure like this:

table inet my_table {
  chain my_input { # this chain serves as a dispatcher
    type filter hook input priority 0;

    iif lo accept # always accept loopback
    iifname enp2s0 jump my_input_public
    iifname enp3s0 jump my_input_private

    reject with icmpx type port-unreachable # refuse traffic from all other interfaces
  }
  chain my_input_public { # rules applicable to public interface interface
    ct state {established,related} accept
    ct state invalid drop
    udp dport bootpc accept
    tcp dport bootpc accept
    reject with icmpx type port-unreachable # all other traffic
  }
  chain my_input_private {
    ct state {established,related} accept
    ct state invalid drop
    udp dport bootpc accept
    tcp dport bootpc accept
    tcp port http accept
    tcp port https accept
    reject with icmpx type port-unreachable # all other traffic
  }
  chain my_output { # we let everything out
    type filter hook output priority 0;
    accept
  }
}

Alternatively you could choose only one iifname statement, such as for the single upstream interface, and put the default rules for all other interfaces in one place, instead of dispatching for each interface.

Masquerading

nftables has a special keyword masquerade "where the source address is automagically set to the address of the output interface" (source). This is particularly useful for situations in which the IP address of the interface is unpredictable or unstable, such as the upstream interface of routers connecting to many ISPs. Without it, the Network Address Translation rules would have to be updated every time the IP address of the interface changed.

To use it:

  • make sure masquerading is enabled in the kernel (true if you use the default kernel), otherwise during kernel configuration, set CONFIG_NFT_MASQ=m.
  • the masquerade keyword can only be used in chains of type nat.
  • masquerading is a kind of source NAT, so only works in the output path.

Example for a machine with two interfaces: LAN connected to enp3s0, and public internet connected to enp2s0:

table inet my_nat {
  chain my_masquerade {
    type nat hook postrouting priority 100;
    oifname "enp2s0" masquerade
  }
}

Since the table type is inet both IPv4 and IPv6 packets will be masqueraded. If you want only ipv4 packets to be masqueraded (since extra adress space of IPv6 makes NAT not required) meta nfproto ipv4 expression can be used infront of oifname "enp2s0" masquerade or the table type can be changed to ip.

NAT with port forwarding

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: I think my_postrouting chain will cause the destination computer see that connections are made by router rather than from some global IP. Also this does not masquerade outbound traffic. (Discuss in Talk:Nftables#)

This example will forward ports 22 and 80 to destination_ip. You will need to set net.ipv4.ip_forward and net.ipv4.conf.wan_interface.forwarding to 1 via sysctl.

table ip my_nat {
  chain my_prerouting {
    type nat hook prerouting priority -100;

    tcp dport { ssh, http } dnat to destination_ip
  }

  chain my_postrouting {
    type nat hook postrouting priority 100;

    ip daddr destination_ip masquerade
  }
}

Tips and tricks

Saving current rule set

The output of nft list ruleset command is a valid input file for it as well. Current rule set can be saved to file and later loaded back in.

$ nft -s list ruleset | tee filename
Note: nft list does not output variable definitions, if you had any in your original file they will be lost. Any variables used in rules will be replaced by their value.

Simple stateful firewall

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: This is not a very simple firewall. I would consider what Arch Linux ships in /etc/nftables.conf simple. Recommend replacing this section with that script and give some directions on how to expand it for specific needs. (Discuss in Talk:Nftables#)

See Simple stateful firewall for more information.

Single machine

Flush the current ruleset:

# nft flush ruleset

Add a table:

# nft add table inet my_table

Add the input, forward, and output base chains. The policy for input and forward will be to drop. The policy for output will be to accept.

# nft add chain inet my_table my_input '{ type filter hook input priority 0 ; policy drop ; }'
# nft add chain inet my_table my_forward '{ type filter hook forward priority 0 ; policy drop ; }'
# nft add chain inet my_table my_output '{ type filter hook output priority 0 ; policy accept ; }'

Add two regular chains that will be associated with tcp and udp:

# nft add chain inet my_table my_tcp_chain
# nft add chain inet my_table my_udp_chain

Related and established traffic will be accepted:

# nft add rule inet my_table my_input ct state related,established accept

All loopback interface traffic will be accepted:

# nft add rule inet my_table my_input iif lo accept

Drop any invalid traffic:

# nft add rule inet my_table my_input ct state invalid drop

Accept ICMP and IGMP:

# nft add rule inet my_table my_input meta l4proto ipv6-icmp icmpv6 type '{ destination-unreachable, packet-too-big, time-exceeded, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert, mld2-listener-report }' accept
# nft add rule inet my_table my_input meta l4proto icmp icmp type '{ destination-unreachable, router-solicitation, router-advertisement, time-exceeded, parameter-problem }' accept
# nft add rule inet my_table my_input ip protocol igmp accept

New udp traffic will jump to the UDP chain:

# nft add rule inet my_table my_input meta l4proto udp ct state new jump my_udp_chain

New tcp traffic will jump to the TCP chain:

# nft add rule inet my_table my_input 'meta l4proto tcp tcp flags & (fin|syn|rst|ack) == syn ct state new jump my_tcp_chain'

Reject all traffic that was not processed by other rules:

# nft add rule inet my_table my_input meta l4proto udp reject
# nft add rule inet my_table my_input meta l4proto tcp reject with tcp reset
# nft add rule inet my_table my_input counter reject with icmpx type port-unreachable

At this point you should decide what ports you want to open to incoming connections, which are handled by the TCP and UDP chains. For example to open connections for a web server add:

# nft add rule inet my_table my_tcp_chain tcp dport 80 accept

To accept HTTPS connections for a webserver on port 443:

# nft add rule inet my_table my_tcp_chain tcp dport 443 accept

To accept SSH traffic on port 22:

# nft add rule inet my_table my_tcp_chain tcp dport 22 accept

To accept incoming DNS requests:

# nft add rule inet my_table my_tcp_chain tcp dport 53 accept
# nft add rule inet my_table my_udp_chain udp dport 53 accept

Be sure to make your changes permanent when satisifed.

Prevent brute-force attacks

Sshguard is program that can detect brute-force attacks and modify firewalls based on IP addresses it temporarily blacklists. See Sshguard#nftables on how to set up nftables to be used with it.

Troubleshooting

Working with Docker

Using nftables can interfere with Docker networking (and probably other container runtimes as well). In particular the drop policy for the forward chain will block packets originating in docker containers. If you want to keep the forward rule in your inet table, you can use the following:

  1. Install iptables-nft to provide an iptables compatible interface for nftables that docker can use.
  2. Use the following for the forward chain in your inet table:
    chain forward {
      type filter hook forward priority security; policy drop;
      mark 1 accept
    
  3. Add a rule to the DOCKER-USER chain in the ip filter table to mark packets if docker is running:
    table ip filter {
      chain DOCKER-USER {
        mark set 1
      }
    }
    

This works by marking packets if docker is active, and accepting the packets in this case, since docker has already filtered them (the forward chain defined by docker uses a drop policy).

See also