2 .\" Copyright (c) 2001 Yar Tikhiy
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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 $
27 .\" $DragonFly: src/share/man/man4/vlan.4,v 1.4 2004/07/08 00:14:49 hmp Exp $
34 .Nd IEEE 802.1Q VLAN network interface
36 .Cd pseudo-device vlan Op Ar count
41 driver demultiplexes frames tagged according to
42 the IEEE 802.1Q standard into logical
44 network interfaces, which allows routing/bridging between
45 multiple VLANs through a single switch trunk port.
49 interface is created at runtime using interface cloning.
51 most easily done with the
61 interface must be assigned a parent interface and
62 numeric VLAN tag using
64 A single parent can be assigned to multiple
66 interfaces provided they have different tags.
67 The parent interface is likely to be an ethernet card connected
68 to a properly configured switch port.
69 The VLAN tag should match one of those set up in the switched
74 driver supports physical devices that do
75 the VLAN demultiplexing in firmware.
78 flag should be set on a
81 .Pq Em not on its parent
84 in that case to indicate that hardware support for
85 the 802.1Q VLANs is present in its parent.
87 .Ss "Selecting the Right Network Interface Card to Run VLANs Through"
88 By now, the only NICs that have both hardware support and proper
89 driver hooks for the 802.1Q VLAN technology in
100 The rest of the ethernet NICs supported by
103 VLANs using software emulation in the
106 However, most of them lack the capability
107 of transmitting and/or receiving oversized frames.
108 Using such a NIC as a parent interface
109 implies a reduced MTU on the corresponding
112 In the modern Internet, this is likely to cause
114 connectivity problems due to massive, inadequate
116 filtering that breaks the Path MTU Discovery mechanism.
118 The NICs that support oversized frames are as follows:
119 .Bl -tag -width ".Xr fxp 4 " -offset indent
121 supports long frames for
128 .Pa /sys/dev/netif/de/if_de.c
129 source file and rebuilding the kernel.
130 The hack works only for the 21041, 21140, and 21140A chips.
132 supports long frames for
136 supports long frames for
140 supports long frames for
144 has support for long frames.
146 supports long frames for
150 supports long frames only if the card is built on a newer chip
155 Unless marked as having native support for
157 the above drivers don't inform the
159 driver about their long frame handling capability.
160 Just increase the MTU of a
162 interface if it appears to be lower than 1500 bytes after
163 attaching to a parent known to support long frames.
167 No 802.1Q features except VLAN tagging are implemented.