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125 lines
4.1 KiB
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125 lines
4.1 KiB
ReStructuredText
VLAN Keywords
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=============
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.. role:: example-rule-action
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.. role:: example-rule-header
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.. role:: example-rule-options
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.. role:: example-rule-emphasis
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vlan.id
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-------
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Suricata has a ``vlan.id`` keyword that can be used in signatures to identify
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and filter network packets based on Virtual Local Area Network IDs. By default,
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it matches all layers if a packet contains multiple VLAN layers. However, if a
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specific layer is defined, it will only match that layer.
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Syntax::
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vlan.id: [op]id[,layer];
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The id can be matched exactly, or compared using the ``op`` setting::
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vlan.id:300 # exactly 300
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vlan.id:<300,0 # smaller than 300 at layer 0
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vlan.id:>=200,1 # greater or equal than 200 at layer 1
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vlan.id uses :ref:`unsigned 16-bit integer <rules-integer-keywords>`.
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The valid range for VLAN id values is ``0 - 4095``.
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This keyword also supports ``all`` and ``any`` as arguments for ``layer``.
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``all`` matches only if all VLAN layers match and ``any`` matches with any layer.
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.. table:: **Layer values for vlan.id keyword**
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=============== ================================================
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Value Description
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=============== ================================================
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[default] Match with any layer
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0 - 2 Match specific layer
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``-3`` - ``-1`` Match specific layer with back to front indexing
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all Match only if all layers match
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any Match with any layer
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=============== ================================================
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This small illustration shows how indexing works for vlan.id::
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[ethernet]
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[vlan 666 (index 0 and -2)]
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[vlan 123 (index 1 and -1)]
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[ipv4]
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[udp]
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Examples
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^^^^^^^^
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Example of a signature that would alert if any of the VLAN IDs is equal to 300:
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.. container:: example-rule
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alert ip any any -> any any (msg:"Vlan ID is equal to 300"; :example-rule-emphasis:`vlan.id:300;` sid:1;)
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Example of a signature that would alert if the VLAN ID at layer 1 is equal to 300:
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.. container:: example-rule
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alert ip any any -> any any (msg:"Vlan ID is equal to 300 at layer 1"; :example-rule-emphasis:`vlan.id:300,1;` sid:1;)
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Example of a signature that would alert if the VLAN ID at the last layer is equal to 400:
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.. container:: example-rule
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alert ip any any -> any any (msg:"Vlan ID is equal to 400 at the last layer"; :example-rule-emphasis:`vlan.id:400,-1;` sid:1;)
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Example of a signature that would alert only if all the VLAN IDs are greater than 100:
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.. container:: example-rule
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alert ip any any -> any any (msg:"All Vlan IDs are greater than 100"; :example-rule-emphasis:`vlan.id:>100,all;` sid:1;)
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It is also possible to use the vlan.id content as a fast_pattern by using the ``prefilter`` keyword, as shown in the following example.
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.. container:: example-rule
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alert ip any any -> any any (msg:"Vlan ID is equal to 200 at layer 1"; :example-rule-emphasis:`vlan.id:200,1; prefilter;` sid:1;)
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vlan.layers
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-----------
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Matches based on the number of layers.
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Syntax::
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vlan.layers: [op]number;
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It can be matched exactly, or compared using the ``op`` setting::
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vlan.layers:3 # exactly 3 vlan layers
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vlan.layers:<3 # less than 3 vlan layers
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vlan.layers:>=2 # more or equal to 2 vlan layers
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vlan.layers uses :ref:`unsigned 8-bit integer <rules-integer-keywords>`.
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The minimum and maximum values that vlan.layers can be are ``0`` and ``3``.
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Examples
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^^^^^^^^
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Example of a signature that would alert if a packet has 0 VLAN layers:
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.. container:: example-rule
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alert ip any any -> any any (msg:"Packet has 0 vlan layers"; :example-rule-emphasis:`vlan.layers:0;` sid:1;)
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Example of a signature that would alert if a packet has more than 1 VLAN layers:
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.. container:: example-rule
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alert ip any any -> any any (msg:"Packet has more than 1 vlan layer"; :example-rule-emphasis:`vlan.layers:>1;` sid:1;)
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It is also possible to use the vlan.layers content as a fast_pattern by using the ``prefilter`` keyword, as shown in the following example.
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.. container:: example-rule
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alert ip any any -> any any (msg:"Packet has 2 vlan layers"; :example-rule-emphasis:`vlan.layers:2; prefilter;` sid:1;) |