RSTP Questions

vinodbharwani · ‎02-16-2008

Hi Friend

Few questions:

1) Is RSTP operation is depend on BPDU same as Normal STP operation ( TCN) ?

2) How RSTP topology change detect and stablize it self ?

Istvan_Rabai · ‎02-16-2008

Hi Vinod,

The answer for your 1st question is: Yes, and No.

Yes, it depends on BPDUs, but the use of BPDUs is not the same:

In RSTP switches send BPDUs even if the root switch doesn't. In RSTP there is a proposal- agreement mechanism during which proposal and agreement BPDUs are sent between neighboring switches to decide about port roles and states.

The answer to your 2nd question:

A switch sends a TC notification as one of its ports goes to the Forwarding state.

TC notifications are sent throughout the layer2 domain as soon as they are initiated.

It is not necessary to send it to the root switch first and for the root to send the TC BPDU to other switches.

Mac-address tables are immediately flushed, as the TC notification is received by any switch.

For the detailed description of RSTP operation look at this site:

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swmstp.html#wp1043798

Cheers:

Istvan