VTP and STP

[krishnateja1]

Hey all,

I have few questions in lan switching, Please help me with this.

1.What happens when the server fails in vtp version 2 and also when it comes back to online?

2.What happens when the primary server comes back to online when secondary is acting as a primary in vtp version 3?

3.What happens when STP root bridge goes down?

4.What happens when MST and RSTP primary root bridges come back to online after any failure occurs?

[Flavio Miranda]

Hello @krishnateja1,

 Here is my interpretation:

1.What happens when the server fails in vtp version 2 and also when it comes back to online?

Not much. When it comes back, it will see that its revision number is lower than the client revision number and will use the updated information in the VTP advertisement from Client to update to its VLAN database.

2.What happens when the primary server comes back to online when secondary is acting as a primary in vtp version 3?

A former primary server that is reconnected to a domain after a reload will revert automatically to secondary server mode.

3.What happens when STP root bridge goes down?

In a 'natural' process, a new bridge will elected based on the currently Switches priority. I mean 'natural' considetring the automatic process considering an admin can intervain on the process anytime.

4.What happens when MST and RSTP primary root bridges come back to online after any failure occurs?

Although MST is much more complex, the basic idea remains. When the bridges comes online it also proclaim itself as root, then, I new election is necessary.

 Detailed explanation can be found here:

https://www.cisco.com/c/en/us/td/docs/routers/7600/ios/15S/configuration/guide/7600_15_0s_book/spantree.html#53908

-If I helped you somehow, please, rate it as useful.-

[Julio E. Moisa]

Hi

1.What happens when the server fails in vtp version 2 and also when it comes back to online?

Basically and by experiences, if the vtp server fails and it is located on the root bridge, all the traffic will be moved to the back root switch (lowest priority than the primary root switch), it could generate a minor impact. 

2.What happens when the primary server comes back to online when secondary is acting as a primary in vtp version 3?

It should have the same behavior, if the root switch is reestablished it will take the role and VTP will be established as well. 

3.What happens when STP root bridge goes down?

All the TCN will be sent to the back up root bridge (switch with lowest priority) because it will take the primary root. if you have not selected the root and back root manually, all the switches will be sending BPDUs in order to claim the root, this BPDUs include the Root Brigde ID and Sender Bridge ID, the switches will compare this information and will select the switch with lowest Bridge priority and a tie breaker is the lowest MAC address. I always recommend configure the root and backup root manually. 

4.What happens when MST and RSTP primary root bridges come back to online after any failure occurs?

They will have quick convergence but It could generate a minor impact, but the traffic will be pointing to the primary root. 

Hope it is useful.