FCM9002 USER MANUAL
76-02-095 Rev.B
Page 29 of 145
Ports may also be configured to act as trunk ports where they will pass frames
that ingress already containing VLAN Tags, and will discard any untagged
frames.
Ports may also be configured for mixed mode operation where they will pass
tagged frames and push a tag onto untagged frames.
A port may also operate as a QinQ access port pushing a tag onto all incoming
frames including those already tagged, as shown for C-Tag 128 above.
The action of pushing a C-Tag is shown below:
where a four byte VLAN Tag is inserted into the frame after the source address
and before the Ethertype.
A C-Tag is made up of four bytes as shown below:
Where
8100
A 2 byte Ethertype to identify IEEE 802.1q VLAN Tags
Pri
A 3 bit priority marker, 0 lowest – 7 highest
C
CFI, Canonical Form Indicator normally set to 0.
ID
A 12 bit identifier in range 1 to 4095
