In addition to matching an exact value, a VID filter mask allows masking any set of bits. The masking operation is ((value and vid-mask) = = (tag and vid-mask)). For example: A value of 6 and a mask of 7 would match all VIDs with the lower 3 bits set to 6. VID filters allow explicit matching of VIDs and matching of any bit pattern within the VID tag.
When using VID filters on SAPs, only VID filters are allowed on this SAP. Filters of type normal and ISID are not allowed.
An additional check for the ‟0” VID tag may be required when using specific wild card operations. For example, frames with no tags on null encapsulated ports match a value of 0 in outer tag and inner tag because there are no tags in the frame for matching. If a zero tag is possible but not wanted, it can be explicitly filtered using exact match on ‟0” before testing other bits for ‟0”.
config>system>ethernet>new-qinq-untagged-sap is a special QinQ function for single tagged QinQ frames with a null second tag. Using this in combination with VID filters is not recommended. The outer tag is the only tag available for filtering on egress for frames arriving from MPLS SDPs or from PBB services, even though additional tags may be carried transparently.