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         kernel configuration file:
               device vlan
         Alternatively, to load the driver as a module at boot time, place the
         following line in loader.conf(5):


         The vlan driver demultiplexes frames tagged according to the IEEE 802.1Q
         standard into logical vlan network interfaces, which allows rout-
         ing/bridging between multiple VLANs through a single switch trunk port.
         Each vlan interface is created at runtime using interface cloning.  This
         is most easily done with the ifconfig(8) create command or using the
         cloned_interfaces variable in rc.conf(5).
         To function, a vlan interface must be assigned a parent interface and
         numeric VLAN tag using ifconfig(8).  A single parent can be assigned to
         multiple vlan interfaces provided they have different tags.  The parent
         interface is likely to be an Ethernet card connected to a properly con-
         figured switch port.  The VLAN tag should match one of those set up in
         the switched network.
         Initially vlan assumes the same minimum length for tagged and untagged
         frames.  This mode is selected by the sysctl(8) variable set to 0 (default).  However, there are network
         devices that fail to adjust frame length, should it fall below the
         allowed minimum due to untagging.  Such devices should be able to inter-
         operate with vlan after changing the value of to
         1.  In the latter mode, vlan will pad short frames before tagging them so
         that their length stays not less than the minimum value after untagging
         by the non-compliant devices.


         The vlan driver supports efficient operation over parent interfaces that
         can provide help in processing VLANs.  Such interfaces are automatically
         recognized by their capabilities.  Depending on the level of sophistica-
         tion found in a physical interface, it may do full VLAN processing or
         just be able to receive and transmit long frames (up to 1522 bytes
         including an Ethernet header and FCS).  The capabilities may be user-con-
         trolled by the respective parameters to ifconfig(8), vlanhwtag and
         vlanmtu.  However, a physical interface is not obliged to react to them:
         It may have either capability enabled permanently without a way to turn
         it off.  The whole issue is very specific to a particular device and its
         By now, the list of physical interfaces able of full VLAN processing in
         the hardware is limited to the following devices: ae(4), age(4), alc(4),
         ale(4), bce(4), bge(4), cxgb(4), em(4), ixgb(4), jme(4), msk(4), nge(4),
         re(4), sge(4), stge(4), ti(4), txp(4), and vge(4).
         long frames for vlan use and calculates the appropriate frame MTU based
         on the capabilities of the parent interface.  Some other interfaces not
         listed above may handle long frames, but they do not advertise this abil-
         ity of theirs.  The MTU setting on vlan can be corrected manually if used
         in conjunction with such a parent interface.


         ifconfig(8), sysctl(8)


         No 802.1Q features except VLAN tagging are implemented.

    BSD April 14, 2010 BSD


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