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| == Configuration File Processing ==
| | {{Delete|All wikilinks on the entire wiki have already been changed to point to the awall guide on git. Nothing points to this article, nor should it}} |
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| [[Alpine Wall]] (awall) reads its configuration from multiple
| | The current Alpine Wall User's Guide is available [https://git.alpinelinux.org/awall/about/ here]. |
| JSON-formatted files, called ''policy files''. The processing starts
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| from directory <tt>/usr/share/awall/mandatory</tt>, which contains
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| mandatory policy files shipped with APK packages. After that,
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| installation-specific policy files in <tt>/etc/awall</tt> are
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| processed.
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| The latter directory may also contain symbolic links to policy files
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| located in <tt>/usr/share/awall/optional</tt>. These are optional
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| policies, which can be enabled on need basis. Such symbolic links are
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| easily created and destroyed using the <tt>awall enable</tt> and
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| <tt>awall disable</tt> commands. <tt>awall list</tt> shows which
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| optional policies are enabled and disabled. The command also prints
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| the description of the optional policy if defined in the file using
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| a top-level attribute named '''description'''.
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| Sometimes a policy file depends on other policy files. In this case,
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| the policy file must have a top-level attribute '''import''', the
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| value of which is a list of policy names, which correspond to the file
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| names without the <tt>.json</tt> suffix. The policies listed there are
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| always processed before the importing policy. The order of the
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| generated iptables rules generally reflects the processing order of
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| their corresponding awall policies.
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| As the import directive does not require the path name to be
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| specified, awall expects policies to have unique names, even if
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| located in different directories. It is allowed to import optional
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| policies that are not explicitly enabled by the user. Such policies
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| show up with the <tt>required</tt> status in the output of <tt>awall
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| list</tt>.
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| == List Parameters ==
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| Several awall parameters are defined as lists of values. In order to
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| facilitate manual editing of policy files, awall also accepts single
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| values in place of lists. Such values are semantically equivalent to
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| lists containing one element.
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| == Variable Expansion ==
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| Awall allows variable definitions in policy files. The top-level
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| attribute '''variable''' is a dictionary containing the
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| definitions. The value of a variable can be of any type (string,
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| integer, list, or dictionary).
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| A variable is referenced in policy files by a string which equals the
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| variable name prepended with the '''$''' character. If the value of
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| the variable is a string, the reference can be embedded into a longer
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| string in order to substitute some part of that string (in shell
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| style). Variable references can be used when defining other variables,
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| as long as the definitions are not circular.
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| Policy files can reference variables defined in other policy
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| files. Policy files can also override variables defined elsewhere by
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| redefining them. In this case, the new definition affects all policy
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| files, also those processed before the overriding policy. Awall
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| variables are in fact simple macros, since each variable remains
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| constant thoughout a single processing round. If multiple files define
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| the same variable, the definition in the file processed last takes
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| effect.
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| If defined as an empty string, all non-embedded references to a
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| variable evaluate as if the attribute in question was not present in
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| the configuration. This is also the case when a string containing
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| embedded variable references finally evaluates to an empty string.
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| == Configuration Objects ==
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| Configuration objects can be divided into two main types.
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| ''Auxiliary objects'' model high-level concepts such as services and
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| zones. ''Rule objects'' translate into one or more iptables rules, and
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| are often defined with the help of some auxiliary objects.
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| === Services ===
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| A ''service'' represents a set of network protocols. A top-level
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| attribute '''service''' is a dictionary that maps service names to
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| service definition objects, or lists thereof in more complex cases.
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| A service definition object contains an attribute named '''proto''',
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| which corresponds to the <tt>--protocol</tt> option of iptables. The
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| protocol can be defined as a numerical value or string as defined in
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| <tt>/etc/protocols</tt>. If the protocol is '''tcp''' or '''udp''',
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| the scope of the service definition may be constrained by defining an
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| attribute named '''port''', which is a list of TCP or UDP port
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| numbers. If the protocol is '''icmp''' or '''icmpv6''', an analogous
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| '''icmp-type''' attribute may be used. In addition, the scope of the
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| rule is also automatically limited to IPv4 or IPv6, respectively.
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| === Zones ===
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| A ''zone'' represents a set of network hosts. A top-level attribute
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| '''zone''' is a dictionary that maps zone names to zone objects. A
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| zone object has an attribute named '''iface''', '''addr''', or
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| both. '''iface''' is a list of network interfaces and '''addr''' is a
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| list of IPv4/IPv6 host and network addresses (CIDR
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| notation). '''addr''' may also contain domain names, which are
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| expanded to IP addresses using DNS resolution. If not defined,
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| '''addr''' defaults to the entire address space and '''iface''' to all
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| interfaces.
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| Rule objects contain two attributes, '''in''' and '''out''', which are
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| lists of zone names. These attributes control whether a packet matches
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| the rule or not. If a particular zone is referenced by the '''in'''
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| attribute, the rule applies to packets whose ingress interface and
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| source address are covered by the zone definition. Correspondingly, if
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| a zone is referenced by the '''out''' attribute, the rule applies to
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| packets whose egress interface and destination address are included in
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| the zone. If both '''in''' and '''out''' are defined, the packet must
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| fulfill both criteria in order to match the rule.
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| === Rules ===
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| There are three types of rule objects: ''policies'', ''filters'', and
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| ''NAT rules''.
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| All rule objects can have the '''in''' and '''out''' attributes
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| referring to zones as described in the previous section. In addition,
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| the scope of the rule can be further constrained with the following
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| attributes:
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| {|
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| !Attribute!!Value format!!Effect
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| |-
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| |'''src'''
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| |Similar to '''addr''' attribute of zone objects
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| |Packet's source address matches the value
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| |-
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| |'''dest'''
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| |Similar to '''addr''' attribute of zone objects
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| |Packet's destination address matches the value
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| |-
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| |'''ipset'''
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| |Object containing two attributes: '''name''' referring to an IP set and '''args''', which is a list of strings '''in''' and '''out'''
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| |Packet matches the IP set referred here when the match arguments are taken from the source ('''in''') and destination ('''out''') address or port in the order specified by '''args'''
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| |-
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| |'''ipsec'''
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| |'''in''' or '''out'''
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| |IPsec decapsulation perfomed on ingress ('''in''') or encapsulation performed on egress ('''out''')
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| |}
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| Rule objects must have an attribute named '''action''', the value of
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| which can be one of the following:
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| {|
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| !Value!!Action
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| |-
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| |'''accept'''
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| |Accept the packet
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| |-
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| |'''reject'''
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| |Reject the packet with an ICMP error message
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| |-
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| |'''drop'''
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| |Silently drop the packet
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| |-
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| |'''logreject'''
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| |Similar to '''reject''' but with kernel logging
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| |-
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| |'''logdrop'''
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| |Similar to '''drop''' but with kernel logging
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| |}
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| Rule objects are declared in type-specific top-level dictionaries in
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| awall policy files. If a packet matches multiple rules, the one
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| appearing earlier in the list takes precedence. If the matching rules
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| are defined in different policy files, the one that was processed
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| earlier takes precedence in the current implementation, but this may
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| change in future versions.
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| ==== Filters ====
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| Filter objects specify an action for packets fulfilling certain
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| criteria. The top-level attribute '''filter''' is a list of filter
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| objects. The precedence rules are similar to those of policy objects.
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| In addition to the common rule attributes, filter objects can have a
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| '''service''' attribute constraining the scope to specific services
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| only. This attribute is a list of service names, referring to the
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| keys of the top-level '''service''' dictionary.
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| Filter objects may also contain limits for packet flow or new
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| connections. These are specified with the '''flow-limit''' and
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| '''conn-limit''' attributes, respectively. The values of these
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| attributes are limit objects that have two attributes: '''count''' and
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| '''interval'''. '''count''' specifies how many new connections or
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| packets are allowed within the time frame specified by '''interval'''
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| (in seconds). The '''logdrop''' action is applied to the packets
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| exceeding the limit.
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| Filter objects may have an attribute named '''dnat''', the value of
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| which is an IPv4 address. If defined, this enables destination NAT for
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| all IPv4 packets matching the rule, such that the specified address
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| replaces the original destination address. This option has no effect
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| on IPv6 packets.
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| ==== Policies ====
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| Policy objects describe the default action for packets that did not
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| match any filter. The top-level attribute '''policy''' is a list of
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| policy objects. Policy objects do not have other attributes than those
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| common to all rule objects.
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| ==== NAT Rules ====
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| NAT rules come in two flavors: ''source NAT rules'' and
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| ''destination NAT rules''. These are contained in two top-level lists
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| named '''snat''' and '''dnat''', respectively.
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| Each NAT rule must have an attribute named '''ip-range''' that
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| specifies the IPv4 address range to which the original source or
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| destinatinon address is mapped. The value can be a single IPv4 address
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| or a range specified by two addresses, separated with the '''-'''
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| character.
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| Optionally, a NAT rule can specify the TCP and UDP port range to which
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| the original source or destination port is mapped. The attribute is
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| named '''port-range''', and the value can be a single port number or a
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| range specified by two numbers, separated with the '''-'''
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| character. If '''port-range''' is not specified, the original port
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| number is kept intact.
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| Like filters, NAT rules can have a '''service''' attribute
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| constraining their scope to specific services.
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| === IP Sets ===
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| Any IP set referenced by rule objects should be created by
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| awall. Auxiliary ''IP set'' objects are used to defined them in awall
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| policy files. The top-level attribute '''ipset''' is a dictionary, the
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| keys of which are IP set names. The values are IP set objects, which
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| have two mandatory attributes. The attribute named '''type'''
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| corresponds to the type argument of the <tt>ipset create</tt>
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| command. '''family''' specifies whether the set is for IPv4 or IPv6
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| addresses, and the possible values are '''inet''' and '''inet6''',
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| correspondingly.
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| == Command Line Syntax ==
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| === Translating Policy Files to Firewall Configuration Files ===
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| '''awall translate''' ['''-o'''|'''--output''' DIRECTORY] ['''-V'''|'''--verify''']
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| The <tt>--verify</tt> option makes awall verify the configuration
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| using the test mode of iptables-restore before overwriting the old
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| files.
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| Specifying the output directory allows testing awall policies without
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| overwriting the current iptables and ipset configuration files. By
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| default, awall generates the configuration to <tt>/etc/iptables</tt>
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| and <tt>/etc/ipset.d</tt>, which are read by the init scripts.
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| === Run-Time Activation of New Firewall Configuration ===
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| '''awall activate'''
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| This command genereates firewall configuration from the policy files
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| and enables it. If the user confirms the new configuration by hitting
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| the Return key within 10 seconds, the configuration is saved to the
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| files. Otherwise, the old configuration is restored.
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| === Optional Policies ===
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| Optional policies can be enabled or disabled using this command:
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| '''awall''' {'''enable'''|'''disable'''} POLICY...
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| Optional policies can be listed using this command:
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| '''awall list'''
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| The '''enabled''' status means that the policy has been enabled by the
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| user. The '''disabled''' status means that the policy is not in
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| use. The '''required''' status means that the policy has not been
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| enabled by the user but is in use because it is required by another
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| policy which is in use.
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| [[Category:Networking]]
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