xref: /dragonfly/share/man/man4/vlan.4 (revision 71126e33) 
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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 1.4 2004/07/08 00:14:49 hmp Exp $
28.\"
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 physical devices that do
75the VLAN demultiplexing in firmware.
76The
77.Cm link0
78flag should be set on a
79.Nm
80interface
81.Pq Em not on its parent
82using
83.Xr ifconfig 8
84in that case to indicate that hardware support for
85the 802.1Q VLANs is present in its parent.
86.\"
87.Ss "Selecting the Right Network Interface Card to Run VLANs Through"
88By now, the only NICs that have both hardware support and proper
89driver hooks for the 802.1Q VLAN technology in
90.Dx
91are
92.Xr bge 4 ,
93.Xr em 4 ,
94.Xr gx 4 ,
95.Xr nge 4 ,
96.Xr ti 4 ,
97and
98.Xr txp 4 .
99.Pp
100The rest of the ethernet NICs supported by
101.Dx
102can run
103VLANs using software emulation in the
104.Nm
105driver.
106However, most of them lack the capability
107of transmitting and/or receiving oversized frames.
108Using such a NIC as a parent interface
109implies a reduced MTU on the corresponding
110.Nm
111interfaces.
112In the modern Internet, this is likely to cause
113.Xr tcp 4
114connectivity problems due to massive, inadequate
115.Xr icmp 4
116filtering that breaks the Path MTU Discovery mechanism.
117.Pp
118The NICs that support oversized frames are as follows:
119.Bl -tag -width ".Xr fxp 4 " -offset indent
120.It Xr dc 4
121supports long frames for
122.Nm
123natively.
124.It Xr de 4
125requires defining
126.Dv BIG_PACKET
127in the
128.Pa /sys/dev/netif/de/if_de.c
129source file and rebuilding the kernel.
130The hack works only for the 21041, 21140, and 21140A chips.
131.It Xr fxp 4
132supports long frames for
133.Nm
134natively.
135.It Xr sis 4
136supports long frames for
137.Nm
138natively.
139.It Xr ste 4
140supports long frames for
141.Nm
142natively.
143.It Xr tl 4
144has support for long frames.
145.It Xr tx 4
146supports long frames for
147.Nm
148natively.
149.It Xr xl 4
150supports long frames only if the card is built on a newer chip
151(Cyclone and above).
152.El
153.Pp
154Note:
155Unless marked as having native support for
156.Nm ,
157the above drivers don't inform the
158.Nm
159driver about their long frame handling capability.
160Just increase the MTU of a
161.Nm
162interface if it appears to be lower than 1500 bytes after
163attaching to a parent known to support long frames.
164.Sh SEE ALSO
165.Xr ifconfig 8
166.Sh BUGS
167No 802.1Q features except VLAN tagging are implemented.
168