vlan(4) - NetBSD Manual Pages

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VLAN(4)                 NetBSD Kernel Interfaces Manual                VLAN(4)


NAME

     vlan -- IEEE 802.1Q Virtual LAN network device


SYNOPSIS

     pseudo-device vlan


DESCRIPTION

     The vlan interface provides support for IEEE 802.1Q Virtual Local Area
     Networks (VLAN).  This supports the trunking of more than one network on
     a single network interface by using 802.1Q tagged and untagged frames.

     To use a vlan interface, the administrator must first create the inter-
     face and then specify the VID (VLAN identifier, the first 12 bits from a
     16-bit integer which distinguishes each VLAN from any others) and
     (parent) physical interface associated with the VLAN.  This can be done
     by using the ifconfig(8) create, vlan, and vlanif subcommands from a
     shell command line or script.  From within a C program, use the ioctl(2)
     system call with the SIOCSIFCREATE and SIOCSIFVLAN arguments.

     Packets sent through a vlan interface are tagged with the VID and passed
     to the parent interface for transmission.  Tagged packets received on the
     parent interface are passed to the vlan interface with the corresponding
     VID associated with the parent interface.  Packets sent directly through
     the parent interface are transmitted as untagged frames.  Untagged frames
     received on the parent interface are handled by the parent interface.
     Tagged frames received on the parent interface with a VID of 0 and an
     EtherType of IP or IPv6 are processed on the parent interface.  Tagged
     frames received on the parent interface for which no vlan interface with
     a matching VID exists are dropped and counted as ``unknown protocol''.
     (These are displayed by the ifconfig(8) -v option.)

     If the vlan pseudo-device is not configured in the kernel only packets
     tagged with a VID of 0 are processed.

     To be compatible with other IEEE 802.1Q devices, the vlan interface sup-
     ports a 1500 byte MTU, which means that the parent interface will have to
     handle packets that are 4 bytes larger than the original Ethernet stan-
     dard.

     vlan can be used with devices not supporting the IEEE 802.1Q MTU, but
     then the MTU of the vlan interface will be 4 bytes too small and will not
     interoperate properly with other IEEE 802.1Q devices, unless the MTU of
     the other hosts on the VLAN are also lowered to match.


EXAMPLES

     The following will create interface vlan0 with VID six, on the Ethernet
     interface tlp0:

           ifconfig vlan0 create
           ifconfig vlan0 vlan 6 vlanif tlp0

     After this set up, IP addresses (and/or other protocols) can be assigned
     to the vlan0 interface.  All other hosts on the Ethernet connected to
     tlp0 which configure a VLAN and use VID six will see all traffic trans-
     mitted through vlan0.

     The same VLAN can be created at system startup time by placing the fol-
     lowing in /etc/ifconfig.vlan0:

           create
           vlan 6 vlanif tlp0


SEE ALSO

     bridge(4), ifconfig(8)


HISTORY

     The vlan device first appeared in NetBSD 1.5.1, and was derived from a
     VLAN implementation that appeared in FreeBSD and OpenBSD.


BUGS

     The vlan interfaces do not currently inherit changes made to the physical
     interfaces' MTU.

NetBSD 9.0                       May 29, 2017                       NetBSD 9.0