Rules

OPNsense contains a stateful packet filter, which can be used to restrict or allow traffic from and/or to specific networks as well as influence how traffic should be forwarded (see also policy based routing in “Multi WAN”).

The rules section shows all policies that apply on your network, grouped by interface.

Overview

Our overview shows all the rules that apply to the selected interface (group) or floating section. For every rule some details are provided and when applicable you can perform actions, such as move, edit, copy, delete.

../_images/Firewall_overview.png

Below you will find some highlights about this screen.

  1. Interface name
    The name of the interface is part of the normal menu breadcrumb
  2. Category
    If categories are used in the rules, you can select which one you will show here.
  3. Toggle inspection
    You can toggle between inspection and rule view here, when in inspection mode, statistics of the rule are shown. (such as packet counters, number of active states, …)
  4. Show / hide automatic rules
    Some rules are automatically generated, you can toggle here to show the details. If a magnifying glass is shown you can also browse to its origin (The setting controlling this rule).
  5. Automatic rules
    The contents of the automatic rules
  6. User rules
    All user defined rules

The basics

Before creating rules, it’s good to know about some basics which apply to all rules.

States

By default rules are set to stateful (you can change this, but it has consequences), which means that the state of a connection is saved into a local dictionary which will be resolved when the next packet comes in. The consequence of this is that when a state exists, the firewall doesn’t need to process all its rules again to determine the action to apply, which has huge performance advantages.

The use of states can also improve security particularly in case of tcp type traffic, since packet sequence numbers and timestamps are also checked in order to pass traffic, it’s much harder to spoof traffic.

Note

When changing rules, sometimes its necessary to reset states to assure the new policies are used for existing traffic. You can do this in Firewall ‣ Diagnostics ‣ States Reset or Firewall ‣ Diagnostics ‣ States Dump to reset specific states.

Note

In order to keep states, the system need to reserve memory. By default 10% of the system memory is reserved for states, this can be configured in Firewall ‣ Settings ‣ Firewall Maximum States. (The help text shows the default number of states on your platform)

Action

Rules can be set to three different action types:

  • Pass –> allow traffic
  • Block –> deny traffic and don’t let the client know it has been dropped (which is usually advisable for untrusted networks)
  • Reject –> deny traffic and let the client know about it. (only tcp and udp support rejecting packets, which in case of TCP means a RST is returned, for UDP ICMP UNREACHABLE is returned).

For internal networks it can be practical to use reject, so the client does not have to wait for a time-out when access is not allowed. When receiving packets from untrusted networks, you usually don’t want to communicate back if traffic is not allowed.

Processing order

Firewall rules are processed in sequence, first evaluating the Floating rules section followed by all rules which belong to interface groups and finally all interface rules.

Internal (automatic) rules are usually registered first.

Rules can either be set to quick or not set to quick, the default is to use quick. When set to quick, the rule is handled on “first match” basis, which means that the first rule matching the packet will take precedence over rules following in sequence.

When quick is not set, last match wins. This can be useful for rules which define standard behaviour. Our default deny rule uses this property for example (if no rule applies, drop traffic).

Note

Internally rules are registered using a priority, floating uses 200000, groups use 300000 and interface rules land on 400000 combined with the order in which they appear. Automatic rules are usually registered at a higher priority (lower number).

Tip

The interface should show all rules that are used, when in doubt, you can always inspect the raw output of the ruleset in /tmp/rules.debug

Direction

Traffic can be matched on in[coming] or out[going] direction, our default is to filter on incoming direction. In which case you would set the policy on the interface where the traffic originates from.

For example, if you want to allow https traffic coming from any host on the internet, you would usually set a policy on the WAN interface allowing port 443 to the host in question.

Note

Traffic leaving the firewall is accepted by default (using a non-quick rule), when Disable force gateway in Firewall ‣ Settings ‣ Advanced is not checked, the connected gateway would be enforced as well.

Settings

Traffic that is flowing through your firewall can be allowed or denied using rules, which define policies. This section of the documentation describe the different settings, grouped by usage.

Descriptive settings

Some settings help to identify rules, without influencing traffic flow.


Category The category this rule belongs to, can be used as a filter in the overview
Description Descriptive text

Basic settings

Below are the settings most commonly used:


Action The action to perform.
Disabled Disable a rule without removing it, can be practical for testing purposes and to support easy enablement of less frequently used policies.
Interface Interface[s] this rule applies on. You can easily copy rules between interfaces and change this field to the new target interface. (remember to check the order before applying)
TCP/IP Version Does this rule apply on IPv4, IPv6 or both.
Protocol Protocol to use, most common are TCP and UDP
Source Source network or address, when combining IPv4 and IPv6 in one rule, you can use aliases which contain both address families.
Source / Invert Invert source selection (for example not 192.168.0.0/24)
Destination Destination network or address, like source you can use aliases here as well.
Destination / Invert When the filter should be inverted, you can mark this checkbox
Destination port range For TCP and/or UDP you can select a service by name (http, https) or number (range), you can also use aliases here to simplify management.
Log Create a log entry when this rule applies, you can use Firewall ‣ Log Files ‣ Live View to monitor if your rule applies.

Tip

The use of descriptive names help identify traffic in the live log view easily.

Tip

With the use of the eye button in the right top corner of the screen you can find statistics about the rule in question (number of evaluations, number of active states and traffic counters).

Less commonly used

Some settings are usually best left default, but can also be set in the normal rule configuration.


Source port range In case of TCP and/or UDP, you can also filter on the source port (range) that is used by the client. Since in most cases you can’t influence the source port, this setting is usually kept default (any).
Quick If a packet matches a rule specifying quick, the first matching rule wins. When not set to quick the last matching rule wins. When not sure, best use quick rules and interpret the ruleset from top to bottom.
Direction Direction of the traffic, see also Direction.

High Availability

The following options are specifically used for HA setups.


No XMLRPC Sync Disable configuration sync for this rule, when Firewall Rules sync is enabled in System ‣ High Availability ‣ Settings
State Type / NO pfsync Prevent states created by this rule to be synced to the other node

Schedule

Rules can also be scheduled to be active at specific days or time ranges, you can create schedules in Firewall ‣ Advanced ‣ Schedules and select one in the rule.

Policy based routing

This feature can be used to forward traffic to another gateway based on more fine grained filters than static routes could (OSI layer 4 verses OSI layer 3) and can be used to build multi-wan scenario’s using gateway groups.

More information about Multi-Wan can be found in the “Multi WAN” chapter.


Gateway When a gateway is specified, packets will use policy based routing using the specified gateway or gateway group. Usually this option is set on the receiving interface (LAN for example), which then chooses the gateway specified here. (This ignores default routing rules)
disable reply-to By default traffic is always send to the connected gateway on the interface. If for some reason you don’t want to force traffic to that gateway, you can disable this behaviour.

Note

When using policy based routing, don’t forget to exclude local traffic which shouldn’t be forwarded. You can do so by creating a rule with a higher priority, using a default gateway.

Connection limits

The advanced options contains some settings to limit the use of a rule or specify specific timeouts for the it. Most generic (default) settings for these options can be found under Firewall ‣ Settings ‣ Advanced


Max states Limits the number of concurrent states the rule may create. When this limit is reached, further packets that would create state will not match this rule until existing states time out.
Max source nodes Limits the maximum number of source addresses which can simultaneously have state table entries.
Max established Limits the maximum number of simultaneous TCP connections which have completed the 3-way handshake that a single host can make.
Max source states Limits the maximum number of simultaneous state entries that a single source address can create with this rule.
Max new connections Limit the rate of new connections over a time interval. The connection rate is an approximation calculated as a moving average. (number of connections / seconds) Only applies on TCP connections
State timeout State Timeout in seconds (applies to TCP only)

Advanced

Some less common used options are defined below.


Source OS Operating systems can be fingerprinted based on some tcp fields from the originating connection. These fingerprints can be used as well to match traffic on. (more detailed information can be found in the pf.os man page)
allow options By default the firewall blocks IPv4 packets with IP options or IPv6 packets with routing extension headers set. If you have an application that requires such packets (such as multicast or IGMP) you can enable this option.
TCP flags If specific TCP flags need to be set or unset, you can specify those here.
Set priority Packets matching this rule will be assigned a specific queueing priority. If the packet is transmitted on a VLAN interface, the queueing priority will be written as the priority code point in the 802.1Q VLAN header. If two priorities are given, packets which have a TOS of lowdelay and TCP ACKs with no data payload will be assigned to the second one.
Match priority Only match packets which have the given queueing priority assigned.
Set local tag Packets matching this rule will be tagged with the specified string. The tag acts as an internal marker that can be used to identify these packets later on. This can be used, for example, to provide trust between interfaces and to determine if packets have been processed by translation rules. Tags are “sticky”, meaning that the packet will be tagged even if the rule is not the last matching rule. Further matching rules can replace the tag with a new one but will not remove a previously applied tag. A packet is only ever assigned one tag at a time.
Match local tag Match packets that are tagged earlier (using set local tag)
State Type

Influence the state tracking mechanism used, the following options are available. When in doubt, it’s usually best to preserve the default keep state

  • Keep state is used for stateful connection tracking.
  • Sloppy state works like keep state, but it does not check sequence numbers. Use it when the firewall does not see all packets.
  • Synproxy state proxies incoming TCP connections to help protect servers from spoofed TCP SYN floods. This option includes the functionality of keep state and modulate state combined.
  • None Do not use state mechanisms to keep track.