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Routing & Switching · Intermediate

Extended System ID

The 12-bit field in the STP bridge priority that carries the VLAN ID, allowing a unique bridge ID per VLAN with one MAC.

Definition

Introduced with 802.1t, it lets switches use one MAC address for all VLAN instances. It forces configurable priority to multiples of 4096.

Example

show spanning-tree shows 'priority 32769 (priority 32768 sys-id-ext 1)'.

Exam tip

The displayed priority equals configured priority plus VLAN number.

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