Allied Telesis AT-S62 - Manual (Page 468)

Chapter 30: IGMP Snooping Commands
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❑ Deleted untagged ports are returned to the Default_VLAN as
untagged.
❑ You can delete ports from only one group at a time.
Examples
The following command uses syntax 1 to delete untagged port 12 from
the InternetGroups VLAN:
delete vlan=InternetGroups port=12 frame=untagged
The following command accomplishes the same thing using syntax 2:
delete vlan=InternetGroups untagged=12