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426 lines
23 KiB
ReStructuredText
===========================
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Rules
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===========================
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OPNsense contains a stateful packet filter, which can be used to restrict or allow traffic from and/or to specific networks
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as well as influence how traffic should be forwarded (see also policy based routing in ":doc:`/manual/how-tos/multiwan`").
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The rules section shows all policies that apply on your network, grouped by interface.
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--------------------
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Overview
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--------------------
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Our overview shows all the rules that apply to the selected interface (group) or floating section.
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For every rule some details are provided and when applicable you can perform actions, such as move, edit, copy, delete.
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.. image:: images/Firewall_overview.png
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:width: 600px
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:align: center
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Below you will find some highlights about this screen.
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1. Interface name
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The name of the interface is part of the normal menu breadcrumb
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2. Category
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If categories are used in the rules, you can select which one you will show here.
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3. Toggle inspection
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You can toggle between inspection and rule view here, when in inspection mode, statistics of the rule are shown.
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(such as packet counters, number of active states, ...)
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4. Show / hide automatic rules
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Some rules are automatically generated, you can toggle here to show the details. If a magnifying glass
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is shown you can also browse to its origin (The setting controlling this rule).
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5. Automatic rules
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The contents of the automatic rules
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6. User rules
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All user defined rules
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--------------------
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The basics
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--------------------
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Before creating rules, it's good to know about some basics which apply to all rules.
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....................
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States
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....................
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By default rules are set to stateful (you can change this, but it has consequences), which means that the state of
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a connection is saved into a local dictionary which will be resolved when the next packet comes in.
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The consequence of this is that when a state exists, the firewall doesn't need to process all its rules again to determine
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the action to apply, which has huge performance advantages.
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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
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to pass traffic, it's much harder to spoof traffic.
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.. Note::
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When changing rules, sometimes its necessary to reset states to assure the new policies are used for existing traffic.
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You can do this in :menuselection:`Firewall --> Diagnostics --> States`.
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.. Note::
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In order to keep states, the system need to reserve memory. By default 10% of the system memory is reserved for states,
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this can be configured in :menuselection:`Firewall --> Settings --> Firewall Maximum States`.
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(The help text shows the default number of states on your platform)
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States can also be quite convenient to find the active top users on your firewall at any time, as of 21.7 we added
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an easy to use "session" browser for this purpose. You can find it under :menuselection:`Firewall --> Diagnostics --> Sessions`.
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....................
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Action
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....................
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.. _Firewall_Rule_Action:
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Rules can be set to three different action types:
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* Pass --> allow traffic
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* Block --> deny traffic and don't let the client know it has been dropped (which is usually advisable for untrusted networks)
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* Reject --> deny traffic and let the client know about it. (only tcp and udp support rejecting packets, which in case of TCP means a :code:`RST` is returned, for UDP :code:`ICMP UNREACHABLE` is returned).
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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.
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When receiving packets from untrusted networks, you usually don't want to communicate back if traffic is not allowed.
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Processing order
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.. _Firewall_Rule_Processing_Order:
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Firewall rules are processed in sequence per section, first evaluating the **Floating** rules section followed by all rules which
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belong to **interface groups** and finally all **interface** rules.
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Internal (automatic) rules are usually registered first.
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.. blockdiag::
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:desctable:
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blockdiag {
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System [label="System defined", style = dotted];
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Floating [label="Floating rules"];
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Groups [label="Interface groups"];
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Interfaces [label="Interfaces"];
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System -> Floating -> Groups -> Interfaces;
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}
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Rules can either be set to :code:`quick` or not set to quick, the default is to use quick. When set to quick, the rule is
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handled on "first match" basis, which means that the first rule matching the packet will take precedence over rules following in sequence.
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When :code:`quick` is not set, last match wins. This can be useful for rules which define standard behaviour.
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Our default deny rule uses this property for example (if no rule applies, drop traffic).
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.. Note::
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Internally rules are registered using a priority, floating uses :code:`200000`,
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groups use :code:`300000` and interface rules land on :code:`400000` combined with the order in which they appear.
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Automatic rules are usually registered at a higher priority (lower number).
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.. Tip::
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The interface should show all rules that are used, when in doubt, you can always inspect the raw output of the ruleset in :code:`/tmp/rules.debug`
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....................
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Rule sequence
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.. _Firewall_Rule_Sequence:
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The sequence in which the rules are displayed and processed can be customized per section:
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* Select one or more rules using the checkbox on the left side of the rule.
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* Use the arrow button in the action menu on the right side of a rule in order to move selected rules before the rule where the action button is pressed.
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* Or you can use the arrow button on the top in the heading row to move the selected rules to the end.
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......................
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Direction
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.. _Firewall_Rule_Direction:
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.. blockdiag::
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:desctable:
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blockdiag {
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source [label="Source"];
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firewall [label="Firewall"];
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destination [label="Destination"];
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source -> firewall [label="in"]
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firewall -> destination [label="out"];
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}
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Traffic can be matched on :code:`in[coming]` or :code:`out[going]` direction, our default is to filter on incoming direction.
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In which case you would set the policy on the interface where the traffic originates from.
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For example, if you want to allow :code:`https` traffic coming from any host on the internet,
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you would usually set a policy on the WAN interface allowing port :code:`443` to the host in question.
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.. Note::
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Traffic leaving the firewall is accepted by default (using a non-quick rule), when **Disable force gateway** in
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:menuselection:`Firewall --> Settings --> Advanced` is not checked, the connected gateway would be enforced as well.
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--------------------
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Settings
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--------------------
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Traffic that is flowing through your firewall can be allowed or denied using rules, which define policies.
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This section of the documentation describe the different settings, grouped by usage.
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.......................
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Descriptive settings
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.......................
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Some settings help to identify rules, without influencing traffic flow.
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=====================================================================================================================
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==================================== ===============================================================================
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Category The category this rule belongs to, can be used as a filter in the overview
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Description Descriptive text
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==================================== ===============================================================================
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.................
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Basic settings
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.................
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Below are the settings most commonly used:
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=====================================================================================================================
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==================================== ===============================================================================
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Action The :ref:`action <Firewall_Rule_Action>` to perform.
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Disabled Disable a rule without removing it, can be practical for testing purposes and
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to support easy enablement of less frequently used policies.
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Interface Interface[s] this rule applies on. You can easily copy rules between interfaces
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and change this field to the new target interface.
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(remember to check the order before applying)
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TCP/IP Version Does this rule apply on IPv4, IPv6 or both.
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Protocol Protocol to use, most common are TCP and UDP
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Source Source network or address, when combining IPv4 and IPv6 in one rule, you can use
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aliases which contain both address families.
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Source / Invert Invert source selection (for example not 192.168.0.0/24)
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Destination Destination network or address, like source you can use aliases here as well.
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Destination / Invert When the filter should be inverted, you can mark this checkbox
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Destination port range For TCP and/or UDP you can select a service by name (http, https)
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or number (range), you can also use aliases here to simplify management.
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Log Create a log entry when this rule applies, you can use
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:menuselection:`Firewall --> Log Files --> Live View` to monitor if your rule
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applies.
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==================================== ===============================================================================
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.. Tip::
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The use of descriptive names help identify traffic in the live log view easily.
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.. Tip::
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.. raw:: html
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<i class="fa fa-eye"></i>
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With the use of the eye button in the right top corner of the screen you can find statistics about the rule in
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question (number of evaluations, number of active states and traffic counters).
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.....................
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Less commonly used
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Some settings are usually best left default, but can also be set in the normal rule configuration.
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=====================================================================================================================
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==================================== ===============================================================================
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Source port range In case of TCP and/or UDP, you can also filter on the source port (range) that is
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used by the client. Since in most cases you can't influence the source port,
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this setting is usually kept default (:code:`any`).
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Quick If a packet matches a rule specifying quick, the first matching rule wins.
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When not set to quick the last matching rule wins. When not sure, best use
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quick rules and interpret the ruleset from top to bottom.
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Direction Direction of the traffic,
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see also :ref:`Direction <Firewall_Rule_Direction>`.
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==================================== ===============================================================================
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High Availability
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The following options are specifically used for HA setups.
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=====================================================================================================================
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==================================== ===============================================================================
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No XMLRPC Sync Disable configuration sync for this rule, when **Firewall Rules** sync is
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enabled in :menuselection:`System --> High Availability --> Settings`
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State Type / NO pfsync Prevent states created by this rule to be synced to the other node
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==================================== ===============================================================================
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Schedule
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Rules can also be scheduled to be active at specific days or time ranges, you can create schedules in
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:menuselection:`Firewall --> Advanced --> Schedules` and select one in the rule.
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Policy based routing
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This feature can be used to forward traffic to another gateway based on more fine grained filters than static routes
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could (`OSI layer 4 verses OSI layer 3 <https://en.wikipedia.org/wiki/OSI_model>`__) and can be used to build multi-wan scenario's using gateway groups.
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More information about Multi-Wan can be found in the ":doc:`/manual/how-tos/multiwan`" chapter.
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=====================================================================================================================
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==================================== ===============================================================================
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Gateway When a gateway is specified, packets will use policy based routing using
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the specified gateway or gateway group. Usually this option is set on the
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receiving interface (LAN for example), which then chooses the gateway
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specified here. (This ignores default routing rules). Only packets flowing in
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the same direction of the rule are affected by this parameter, the opposite
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direction (replies) are not affected by this option.
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reply-to By default traffic is always send to the connected gateway on the interface.
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If for some reason you don't want to force traffic to that gateway, you
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can disable this behaviour or enforce an alternative target here.
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==================================== ===============================================================================
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.. Note::
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When using policy based routing, don't forget to exclude local traffic which shouldn't be forwarded.
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You can do so by creating a rule with a higher priority, using a :code:`default` gateway.
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.. Tip::
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In our experience the packet capture function (:menuselection:`Interfaces --> Diagnostics --> Packet capture`) can
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be a valuable tool to inspect if traffic is really heading the direction you would expect it to go, just
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choose a host to monitor and try to exchange some packets. When selecting all interfaces, it's easy to see
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where traffic headed.
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Connection limits
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The advanced options contains some settings to limit the use of a rule or specify specific timeouts for
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the it. Most generic (default) settings for these options can be found under :menuselection:`Firewall --> Settings --> Advanced`
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=====================================================================================================================
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==================================== ===============================================================================
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Max states Limits the number of concurrent states the rule may create.
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When this limit is reached, further packets that would create state will
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not match this rule until existing states time out.
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Max source nodes Limits the maximum number of source addresses which can simultaneously
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have state table entries.
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Max established Limits the maximum number of simultaneous TCP connections which have
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completed the 3-way handshake that a single host can make.
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Max source states Limits the maximum number of simultaneous state entries that
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a single source address can create with this rule.
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Max new connections Limit the rate of new connections over a time interval. The
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connection rate is an approximation calculated as a moving average.
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(number of connections / seconds) Only applies on TCP connections
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State timeout State Timeout in seconds (applies to TCP only)
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==================================== ===============================================================================
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Advanced
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Some less common used options are defined below.
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=====================================================================================================================
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==================================== ===============================================================================
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Source OS Operating systems can be fingerprinted based on some tcp fields from
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the originating connection. These fingerprints can be used as well
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to match traffic on. (more detailed information can be found in the
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`pf.os <https://www.freebsd.org/cgi/man.cgi?query=pf.os>`__ man page)
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allow options By default the firewall blocks IPv4 packets with IP options or IPv6
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packets with routing extension headers set.
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If you have an application that requires such packets
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(such as multicast or IGMP)
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you can enable this option.
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TCP flags If specific TCP flags need to be set or unset, you can specify those here.
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Set priority Packets matching this rule will be assigned a specific queueing priority.
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If the packet is transmitted on a VLAN interface, the queueing priority
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will be written as the priority code point in the 802.1Q VLAN
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header. If two priorities are given, packets which have a TOS of
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lowdelay and TCP ACKs with no data payload will be assigned to the second one.
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Match priority Only match packets which have the given queueing priority assigned.
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Set local tag Packets matching this rule will be tagged with the specified string.
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The tag acts as an internal marker that can be used to identify these
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packets later on. This can be used, for example, to provide trust between
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interfaces and to determine if packets have been processed by translation rules.
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Tags are “sticky”, meaning that the packet will be tagged even
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if the rule is not the last matching rule.
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Further matching rules can replace the tag with a new one but will not
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remove a previously applied tag. A packet is only ever assigned
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one tag at a time.
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Match local tag Match packets that are tagged earlier (using set local tag)
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State Type Influence the state tracking mechanism used, the following options are available.
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When in doubt, it's usually best to preserve the default :code:`keep state`
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* Keep state :menuselection:`-->` is used for stateful connection tracking.
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* Sloppy state :menuselection:`-->` works like keep state,
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but it does not check sequence numbers.
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Use it when the firewall does not see all packets.
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* Synproxy state :menuselection:`-->` proxies incoming TCP connections to help
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protect servers from spoofed TCP SYN floods.
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This option includes the functionality of keep state
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and modulate state combined.
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* None :menuselection:`-->` Do not use state mechanisms to keep track.
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==================================== ===============================================================================
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--------------------
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Troubleshooting
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--------------------
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While building your ruleset things can go wrong, it's always good to know where to look for signs of an issue.
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One of the most common mistakes is traffic doesn't match the rule and/or the order of the rule doesn't make sense
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for whatever reason.
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With the use of the "inspect" button, one can easily see if a rule is being evaluated and traffic did pass using
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this rule. As of 21.7 it's also possible to jump directly into the attached states to see if your host is in the list
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as expected.
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Another valuable tool is the live log viewer, in order to use it, make sure to provide your rule with an easy to
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read description and enable the "log" option.
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If your using source routing (policy based routing), debugging can sometimes get a bit more complicated. Since the normal
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system routing table may not apply, it helps to know which flow the traffic actually followed. The packet capture is a useful
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tool in that case.
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Common issues in this area include return traffic using a different interface than the one it came into, since traffic
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follows the normal routing table on it's way out (reply-to issue), or traffic leaving the wrong interface due to overselection
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(matching internal traffic and forcing a gateway).
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Inspecting used netmasks is also a good idea, intending to match a host but providing a subnet is a mistake easily made
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(e.g. :code:`192.168.1.1/32` vs :code:`192.168.1.1/24` is in reality all of :code:`192.168.1.x`).
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Last but not least, remember rules are matched in order and the default (inbound) policy is :code:`block` if nothing else
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is specified, since we match traffic on :code:`inbound`, make sure to add rules where traffic originates from
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(e.g. :code:`lan` for traffic leaving your network, the return should normally be allowed by state).
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--------------------
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API access
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--------------------
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Partial API access is provided with the :code:`os-firewall` plugin, which is described in more detail in
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the :doc:`firewall <../development/api/plugins/firewall>` api reference manual.
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