vlan [{set | clear}] [ifname]

[root@sylixos:/root]# help vlan           
show | set | clear net interface VLAN ID.
eg. vlan               show all vlan id.
    vlan set en0 3     set netif:en0 VLAN ID 3.
    vlan clear en0     clear netif:en0 VLAN ID.
vlan [{set | clear}] [ifname]
[root@sylixos:/root]# 

[root@sylixos:/root]# vlan          

IFACE  VLAN ID   TAG  PRI
----- --------- ----- ---
[root@sylixos:/root]# vlan set en1 1
[root@sylixos:/root]# vlan

IFACE  VLAN ID   TAG  PRI
----- --------- ----- ---
en1           1     1   0
[root@sylixos:/root]# vlan clear en1
[root@sylixos:/root]# vlan          

IFACE  VLAN ID   TAG  PRI
----- --------- ----- ---