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MST and RSTP

Antonio_1_2
Level 1
Level 1

Hello,

I have switched network in MST. When I connect Catalyst 2950 to that network (2950 is not in the MST region) that runs RSTP, convergention time is 40 seconds?

Why, the MST region and RSTP switch, are not using rapid spannig tree?

Thanks in advance

1 Accepted Solution

Accepted Solutions

Francois Tallet
Level 7
Level 7

Hi!

The problem is that the 2950 is not really running RSTP but Rapid-PVST. This is PVST with each vlan running an RSTP instance. MST was designed to interact with the IEEE version of RSTP, that only feature a single instance for all the vlans.

When doing MST/Rapid-PVST interaction, we have to fall back to plain PVST mode of operation (i.e. STP convergence type). I can explain the technical reason for that, but I'm not sure this is really interesting to your point.

If you want RSTP operation between the 2950 and the MST region you can:

- run MST on the 2950, even with no configuration (a bridge running MST with no configuration is almost exactly an RSTP bridge).

- Another solution is to avoid trunking between the Rapid-PVST and the MST region (we can run RSTP between a Rapid-PVST bridge and an MST region on an access port).

Regards,

Francois

View solution in original post

2 Replies 2

Francois Tallet
Level 7
Level 7

Hi!

The problem is that the 2950 is not really running RSTP but Rapid-PVST. This is PVST with each vlan running an RSTP instance. MST was designed to interact with the IEEE version of RSTP, that only feature a single instance for all the vlans.

When doing MST/Rapid-PVST interaction, we have to fall back to plain PVST mode of operation (i.e. STP convergence type). I can explain the technical reason for that, but I'm not sure this is really interesting to your point.

If you want RSTP operation between the 2950 and the MST region you can:

- run MST on the 2950, even with no configuration (a bridge running MST with no configuration is almost exactly an RSTP bridge).

- Another solution is to avoid trunking between the Rapid-PVST and the MST region (we can run RSTP between a Rapid-PVST bridge and an MST region on an access port).

Regards,

Francois

Thank you very much.

A

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