Service Manual

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).
VLAN Stacking
The default TPID for the outer VLAN tag is 0x9100. The system allows you to congure both bytes of the 2 byte TPID.
Previous versions allowed you to congure the rst byte only, and thus, the systems did not dierentiate between TPIDs with a
common rst byte. For example, 0x8100 and any other TPID beginning with 0x81 were treated as the same TPID, as shown in the
following illustration. Dell Networking OS Versions 8.2.1.0 and later dierentiate between 0x9100 and 0x91XY, also shown in the
following illustration.
You can congure the rst 8 bits of the TPID using the vlan-stack protocol-type command.
The TPID is global. Ingress frames that do not match the system TPID are treated as untagged. This rule applies for both the outer
tag TPID of a double-tagged frame and the TPID of a single-tagged frame.
For example, if you congure TPID 0x9100, the system treats 0x8100 and untagged trac the same and maps both types to the
default VLAN, as shown by the frame originating from Building C. For the same trac types, if you congure TPID 0x8100, the
system is able to dierentiate between 0x8100 and untagged trac and maps each to the appropriate VLAN, as shown by the
packet originating from Building A.
Therefore, a mismatched TPID results in the port not dierentiating between tagged and untagged trac.
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Service Provider Bridging