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Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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VLAN Stacking in Multi-Vendor Networks

The first field in the VLAN tag is the tag protocol identifier (TPID), which is 2 bytes. In a VLAN-stacking network, after the frame is double tagged, the outer tag TPID must match the TPID of the next-hop system.

While 802.1Q requires that the inner tag TPID is 0x8100, it does not require a specific value for the outer tag TPID. Systems may use any 2-byte value; the Dell Networking OS uses 0x9100 (shown in the following) while non-Dell Networking systems might use a different value.

If the next-hop system’s TPID does not match the outer-tag TPID of the incoming frame, the system drops the frame. For example, as shown in the following, the frame originating from Building A is tagged VLAN RED, and then double-tagged VLAN PURPLE on egress at R4. The TPID on the outer tag is 0x9100. R2’s TPID must also be 0x9100, and it is, so R2 forwards the frame.

Given the matching-TPID requirement, there are limitations when you employ Dell Networking systems at network edges, at which, frames are either double tagged on ingress (R4) or the outer tag is removed on egress (R3).

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