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vlan(4) [netbsd man page]

VLAN(4) 						   BSD 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. This is particularly useful on routers or on hosts which must be connected to many different networks through a single physical interface. To use a vlan interface, the administrator must first create the interface and then specify the VID (VLAN identifier, the first 12 bits from a 16-bit integer which distinguishes each VLAN from any others) and 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. To be compatible with other IEEE 802.1Q devices, the vlan interface supports a 1500 byte MTU, which means that the parent interface will have to handle packets that are 4 bytes larger than the original Ethernet standard. Drivers supporting this increased MTU are: - drivers using the DP8390 core (such as ec(4), ne(4), we(4), and possibly others) - bge(4) - bnx(4) - ea(4) - eb(4) - epic(4) - etherip(4) - ex(4) - fxp(4) - gem(4) - hme(4) - le(4) - sip(4) - ste(4) - stge(4) - ti(4) - tl(4) - tlp(4) - vge(4) - vr(4) - wm(4) - xi(4) 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 transmitted through vlan0. The same VLAN can be created at system startup time by placing the following in /etc/ifconfig.vlan0: create vlan 6 vlanif tlp0 SEE ALSO
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. BSD
December 16, 2010 BSD

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VLAN(4) 						   BSD Kernel Interfaces Manual 						   VLAN(4)

NAME
vlan -- IEEE 802.1Q VLAN network interface SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file: device vlan Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): if_vlan_load="YES" DESCRIPTION
The vlan driver demultiplexes frames tagged according to the IEEE 802.1Q standard into logical vlan network interfaces, which allows rout- ing/bridging between multiple VLANs through a single switch trunk port. Each vlan interface is created at runtime using interface cloning. This is most easily done with the ifconfig(8) create command or using the cloned_interfaces variable in rc.conf(5). To function, a vlan interface must be assigned a parent interface and numeric VLAN tag using ifconfig(8). A single parent can be assigned to multiple vlan interfaces provided they have different tags. The parent interface is likely to be an Ethernet card connected to a properly configured switch port. The VLAN tag should match one of those set up in the switched network. Initially vlan assumes the same minimum length for tagged and untagged frames. This mode is selected by the sysctl(8) variable net.link.vlan.soft_pad set to 0 (default). However, there are network devices that fail to adjust frame length, should it fall below the allowed minimum due to untagging. Such devices should be able to interoperate with vlan after changing the value of net.link.vlan.soft_pad to 1. In the latter mode, vlan will pad short frames before tagging them so that their length stays not less than the minimum value after untagging by the non-compliant devices. HARDWARE
The vlan driver supports efficient operation over parent interfaces that can provide help in processing VLANs. Such interfaces are automati- cally recognized by their capabilities. Depending on the level of sophistication found in a physical interface, it may do full VLAN process- ing or just be able to receive and transmit long frames (up to 1522 bytes including an Ethernet header and FCS). The capabilities may be user-controlled by the respective parameters to ifconfig(8), vlanhwtag and vlanmtu. However, a physical interface is not obliged to react to them: It may have either capability enabled permanently without a way to turn it off. The whole issue is very specific to a particular device and its driver. By now, the list of physical interfaces able of full VLAN processing in the hardware is limited to the following devices: ae(4), age(4), alc(4), ale(4), bce(4), bge(4), cxgb(4), em(4), ixgb(4), jme(4), msk(4), nge(4), re(4), sge(4), stge(4), ti(4), txp(4), and vge(4). The rest of the Ethernet interfaces can run VLANs using software emulation in the vlan driver. However, some of them lack the capability of transmitting and receiving long frames. Assigning such an interface as the parent to vlan will result in a reduced MTU on the corresponding vlan interfaces. In the modern Internet, this is likely to cause tcp(4) connectivity problems due to massive, inadequate icmp(4) filtering that breaks the Path MTU Discovery mechanism. The following interfaces support long frames for vlan natively: bfe(4), cas(4), dc(4), fwe(4), fxp(4), gem(4), hme(4), le(4), nfe(4), nve(4), rl(4), sf(4), sis(4), sk(4), ste(4), tl(4), tx(4), vr(4), and xl(4). The vlan driver automatically recognizes devices that natively support long frames for vlan use and calculates the appropriate frame MTU based on the capabilities of the parent interface. Some other interfaces not listed above may handle long frames, but they do not advertise this ability of theirs. The MTU setting on vlan can be corrected manually if used in conjunction with such a parent interface. SEE ALSO
ifconfig(8), sysctl(8) BUGS
No 802.1Q features except VLAN tagging are implemented. BSD
April 14, 2010 BSD
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