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33 .Nd "IEEE 802.1Q VLAN network interface"
35 To compile this driver into the kernel,
36 place the following lines in your
37 kernel configuration file:
38 .Bd -ragged -offset indent
43 Alternatively, to load the driver as a
44 module at boot time, place the following line in
46 .Bd -literal -offset indent
52 driver demultiplexes frames tagged according to
53 the IEEE 802.1Q standard into logical
55 network interfaces, which allows routing/bridging between
56 multiple VLANs through a single switch trunk port.
60 interface is created at runtime using interface cloning.
62 most easily done with the
72 interface must be assigned a parent interface and
73 numeric VLAN tag using
75 A single parent can be assigned to multiple
77 interfaces provided they have different tags.
78 The parent interface is likely to be an Ethernet card connected
79 to a properly configured switch port.
80 The VLAN tag should match one of those set up in the switched
85 assumes the same minimum length for tagged and untagged frames.
86 This mode is selected by the
89 .Va net.link.vlan.soft_pad
91 However, there are network devices that fail to adjust frame length,
92 should it fall below the allowed minimum due to untagging.
93 Such devices should be able to interoperate with
95 after changing the value of
96 .Va net.link.vlan.soft_pad
100 will pad short frames before tagging them
101 so that their length stays not less than the minimum value
102 after untagging by the non-compliant devices.
106 driver supports efficient operation over parent interfaces that can provide
107 help in processing VLANs.
108 Such interfaces are automatically recognized by their capabilities.
109 Depending on the level of sophistication found in a physical
110 interface, it may do full VLAN processing or just be able to
111 receive and transmit long frames (up to 1522 bytes including an Ethernet
113 The capabilities may be user-controlled by the respective parameters to
118 However, a physical interface is not obliged to react to them:
119 It may have either capability enabled permanently without
120 a way to turn it off.
121 The whole issue is very specific to a particular device and its driver.
123 By now, the list of physical interfaces able of full VLAN processing
124 in the hardware is limited to the following devices:
143 The rest of the Ethernet interfaces can run
144 VLANs using software emulation in the
147 However, some of them lack the capability
148 of transmitting and receiving long frames.
149 Assigning such an interface as the parent to
151 will result in a reduced MTU on the corresponding
154 In the modern Internet, this is likely to cause
156 connectivity problems due to massive, inadequate
158 filtering that breaks the Path MTU Discovery mechanism.
160 The following interfaces support long frames for
185 driver automatically recognizes devices that natively support long frames
188 use and calculates the appropriate frame MTU based on the
189 capabilities of the parent interface.
190 Some other interfaces not listed above may handle long frames,
191 but they do not advertise this ability of theirs.
194 can be corrected manually if used in conjunction with such a parent interface.
201 No 802.1Q features except VLAN tagging are implemented.
206 interface will be sent through
208 only if the parent interface uses
210 for link state notification.