MSTP instance 0 and 1

Unanswered Question
Mar 7th, 2009


I have a question regarding a topology of 3 switches :

1. When i configure cisco switch 3750 IOS(12.2) to work with MSTP instance 0 , is it mean that i work RSTP ? or MSTP ?

2.Why i needed to define portfast for fast convergence to the Host ports for Instance 0 (otherwise convegence time was 30 sec)

but when i configured the switch instance 1 i did not have to do so.

The convegence time was less than 1 sec ?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Sun, 03/08/2009 - 00:26

Hello Yoram,

1) MST 802.1s supports multiple RSTP 802.1W instances

2) In RSTP it is very important to define the edge ports (with spanning-tree portfast) in order to improve convergence time: each edge port is excluded from the handshake and sync process it is not an optional part.



Actually MST doesn't send out distinct BPDUs for each instance: a single set of BPDUs is sent out with sections about other instances.


Hope to help


yoram12345 Sun, 03/08/2009 - 01:26

hi Giuseppe,

Thanks for the info.

Actually i would like to test interop between cisco MSTP to other switch RSTP.

So teh question is if i should define the vlan on CISCO on instance 0 or different than 0 ?

Or it does not matter.


Giuseppe Larosa Sun, 03/08/2009 - 06:03

Hello Yoram,

I report here a link to a thread with an answer from Francois Tallet one of greatest experts in STP in the forums :


It should be fine with instance 0, and probably also with instance 1

Hope to help



This Discussion