After some searching I’ve uncovered this gem.

“Cisco’s implementation of spanning-tree is done, by default, at the VLAN level. Each VLAN runs its own instance of spanning-tree. This is called PVST (per-vlan spanning-tree). To support this, Cisco modified the bridge ID to include a 12-bit VLAN ID field in the bridge ID which is called the Extended System ID. The rationale for this was that the priority field did not need the granularity provided by a 16-bit field, but instead could get by with the top four bits of the field, leaving 12 bits to express a VLAN ID. This is consistent with the VLAN ID field in a dot1q frame, which also has a 12-bit VLAN ID field. This means then, that the priority bits have decimal values of 4096, 8192, 16384, and 32768. Using this form of the bridge ID means that priorities are always expressed as some multiple of 4096.”

This hopefully answers your question.

Deon

cheers

Thanks for taking the time to comment, I really appreciate it.

Will look into the error. Thanks for pointing it out (big oops)! When I get some time again will load up a fixed image with the correction.

Hope you have a good day and weekend on your side

Deon

STP 802.1D BPDU Flags (1 Byte)
Bits
7 TC-Ack (TCA)
0 Topology Change (TC)

7 6 5 4 3 2 1 0
+—+-+-+-+-+-+-+–+
msb |TCA| | | | | | |TC| lsb
+—+-+-+-+-+-+-+–+

RSTP 802.1w BPDU Flags (1 Byte)
Bits
7 TC-Ack (TCA)
6 Proposal
5 Port Role
4 Port Role
3 Learning
2 Forwarding
1 Agreement
0 Topology Change (TC)

Re your comment about plugging in and out of RSTP I had same problem with IP phones moving from port to port on an switch causing TCN and outage to all ports in vlan. Inserted “(config-if)# spanning-tree portfast” on all access ports and problem disappeared.
Portfast is required to define an edge port in RSTP.

From my BCMSN notes.
Nice notes.
Thanks

I value all visitors and input. The content on these pages is after all only study notes.

I know as a web content creator though that I can’t make everyone happy and serve pages to everyone through their preferred browsers.

My main concern is to serve pages that at least remain readable to the following browsers:

1. Firefox
2. Internet Explorer
3. Chrome
4. Opera
5. Safari
6. Mozilla
7. Konqueror
8. Playstation 3

Your choice web browser (Amaya) is to be honest not featuring at all in my top listed browsers (which is what my visitors use to access the network ninja) and as such not really on my radar of compatibility development.

Sorry to disappoint.

Deon Botha