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26 .\" $FreeBSD: src/share/man/man4/vlan.4,v 1.1.2.6 2002/08/30 11:53:56 yar Exp $
33 .Nd IEEE 802.1Q VLAN network interface
35 .Cd pseudo-device vlan Op Ar count
40 driver demultiplexes frames tagged according to
41 the IEEE 802.1Q standard into logical
43 network interfaces, which allows routing/bridging between
44 multiple VLANs through a single switch trunk port.
48 interface is created at runtime using interface cloning.
50 most easily done with the
60 interface must be assigned a parent interface and
61 numeric VLAN tag using
63 A single parent can be assigned to multiple
65 interfaces provided they have different tags.
66 The parent interface is likely to be an ethernet card connected
67 to a properly configured switch port.
68 The VLAN tag should match one of those set up in the switched
73 driver supports physical devices that do
74 the VLAN demultiplexing in firmware.
77 flag should be set on a
80 .Pq Em not on its parent
83 in that case to indicate that hardware support for
84 the 802.1Q VLANs is present in its parent.
86 .Ss "Selecting the Right Network Interface Card to Run VLANs Through"
87 By now, the only NICs that have both hardware support and proper
88 driver hooks for the 802.1Q VLAN technology in
99 The rest of the ethernet NICs supported by
102 VLANs using software emulation in the
105 However, most of them lack the capability
106 of transmitting and/or receiving oversized frames.
107 Using such a NIC as a parent interface
108 implies a reduced MTU on the corresponding
111 In the modern Internet, this is likely to cause
113 connectivity problems due to massive, inadequate
115 filtering that breaks the Path MTU Discovery mechanism.
117 The NICs that support oversized frames are as follows:
118 .Bl -tag -width ".Xr fxp 4 " -offset indent
120 supports long frames for
127 .Pa /usr/src/sys/pci/if_de.c
128 source file and rebuilding the kernel.
129 The hack works only for the 21041, 21140, and 21140A chips.
131 supports long frames for
135 supports long frames for
139 supports long frames for
143 has support for long frames.
145 supports long frames for
149 supports long frames only if the card is built on a newer chip
154 Unless marked as having native support for
156 the above drivers don't inform the
158 driver about their long frame handling capability.
159 Just increase the MTU of a
161 interface if it appears to be lower than 1500 bytes after
162 attaching to a parent known to support long frames.
166 No 802.1Q features except VLAN tagging are implemented.