I've been reading the MAC address reduction feature of the extended system ID command. I understood that enabling this command will change the priority bit allocation inside the bridge ID. Traditional 2 byte priority will be changed to 4 bits with the remaining 12 bit reserved for VLAN ID.
I would like to know if this command has any infulence on the priority field (port priority) of port ID??
As per my understanding, the port ID is 16bit with 6 bit for priority and 10 bit for port index, 128 being the default priority (range 0 to 240) as a multiple of 16. If priority really have 6 bits, then why it's a multiple of 16??
Hope someone can help me..
Thanks, Ameen Ahmed.
802.1t standards re-define the Port ID and Bridge ID field in STP BPDU's.
16 bith Port ID is divided into 4 bits of Port Priority and 12 bits of Port Number.
So with 4 bits for Port Priority, the value has to be multiples of 16 (just binary to decimal conversion).
Moreover this Port ID is not related to Bridge ID as there are separate fields in BPDU.
You can refer to the below URL's:
There is no field for VLAN while mentioning Port ID. You have to mention the VLAN's along with Port prioirty value when you want to modify it in the switches.
spanning-tree vlan 100 port-priority
Hope this answers your question.
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