xref: /dragonfly/share/man/man4/vlan.4 (revision 3f5e28f4)
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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 1.6 2007/03/11 11:15:33 swildner Exp $
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29.Dd July 25, 2001
30.Dt VLAN 4
31.Os
32.Sh NAME
33.Nm vlan
34.Nd IEEE 802.1Q VLAN network interface
35.Sh SYNOPSIS
36.Cd pseudo-device vlan Op Ar count
37.\"
38.Sh DESCRIPTION
39The
40.Nm
41driver demultiplexes frames tagged according to
42the IEEE 802.1Q standard into logical
43.Nm
44network interfaces, which allows routing/bridging between
45multiple VLANs through a single switch trunk port.
46.Pp
47Each
48.Nm
49interface is created at runtime using interface cloning.
50This is
51most easily done with the
52.Xr ifconfig 8
53.Cm create
54command or using the
55.Va cloned_interfaces
56variable in
57.Xr rc.conf 5 .
58.Pp
59To function, a
60.Nm
61interface must be assigned a parent interface and
62numeric VLAN tag using
63.Xr ifconfig 8 .
64A single parent can be assigned to multiple
65.Nm
66interfaces provided they have different tags.
67The parent interface is likely to be an ethernet card connected
68to a properly configured switch port.
69The VLAN tag should match one of those set up in the switched
70network.
71.Pp
72The
73.Nm
74driver supports efficient operation over parent interfaces that can provide
75help in processing VLANs.
76Such interfaces are automatically recognized by their capabilities.
77Depending on the level of sophistication found in a physical
78interface, it may do full VLAN processing or just be able to
79receive and transmit frames exceeding the maximum Ethernet frame size
80by the length of a 802.1Q header.
81The capabilities may be user-controlled by the respective parameters to
82.Xr ifconfig 8 ,
83.Cm vlanhwtag
84and
85.Cm vlanmtu .
86However, a physical interface is not obliged to react to them:
87It may have either capability enabled permanently without
88a way to turn it off.
89The whole issue is very specific to a particular device and its driver.
90.\"
91.Ss "Selecting the Right Network Interface Card to Run VLANs Through"
92By now, the only NICs that have both hardware support and proper
93driver hooks for the 802.1Q VLAN technology in
94.Dx
95are
96.Xr bge 4 ,
97.Xr em 4 ,
98.Xr gx 4 ,
99.Xr nge 4 ,
100.Xr re 4 ,
101.Xr stge 4 ,
102.Xr ti 4 ,
103.Xr txp 4 ,
104and
105.Xr vge 4 .
106.Pp
107The rest of the ethernet NICs supported by
108.Dx
109can run
110VLANs using software emulation in the
111.Nm
112driver.
113However, most of them lack the capability
114of transmitting and/or receiving oversized frames.
115Using such a NIC as a parent interface
116implies a reduced MTU on the corresponding
117.Nm
118interfaces.
119In the modern Internet, this is likely to cause
120.Xr tcp 4
121connectivity problems due to massive, inadequate
122.Xr icmp 4
123filtering that breaks the Path MTU Discovery mechanism.
124.Pp
125The NICs that support oversized frames are as follows:
126.Bl -tag -width ".Xr fxp 4 " -offset indent
127.It Xr dc 4
128supports long frames for
129.Nm
130natively.
131.It Xr de 4
132requires defining
133.Dv BIG_PACKET
134in the
135.Pa /sys/dev/netif/de/if_de.c
136source file and rebuilding the kernel.
137The hack works only for the 21041, 21140, and 21140A chips.
138.It Xr fxp 4
139supports long frames for
140.Nm
141natively.
142.It Xr sis 4
143supports long frames for
144.Nm
145natively.
146.It Xr ste 4
147supports long frames for
148.Nm
149natively.
150.It Xr tl 4
151has support for long frames.
152.It Xr tx 4
153supports long frames for
154.Nm
155natively.
156.It Xr xl 4
157supports long frames only if the card is built on a newer chip
158(Cyclone and above).
159.El
160.Pp
161Note:
162Unless marked as having native support for
163.Nm ,
164the above drivers don't inform the
165.Nm
166driver about their long frame handling capability.
167Just increase the MTU of a
168.Nm
169interface if it appears to be lower than 1500 bytes after
170attaching to a parent known to support long frames.
171.Sh SEE ALSO
172.Xr ifconfig 8
173.Sh BUGS
174No 802.1Q features except VLAN tagging are implemented.
175