Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

PVST and MST difference

What is difference between PVST and MST?

  • WAN Routing and Switching
2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: PVST and MST difference

You would change the bridge priority for the MST instance and not vlan4 in MST setup. Hence, it would affect all 3 vlans in this case.

HTH

Sundar

Re: PVST and MST difference

In PVST mode the bridge priority is configured individually for every VLAN. In MST mode the bridge priority is set for the MST instance, which can include multiple VLANs, and any change to the bridge priority of an MST instance should make all the VLANs that are part of the MST group inherit the same attribute(s).

Here's a small capture from my lab switch that I hope helps.

SW1-3550(config)#spanning-tree vlan ?

WORD vlan range, example: 1,3-5,7,9-11

SW1-3550(config)#spanning-tree vlan 10 priority 32768

SW1-3550(config)#spanning-tree mst ?

WORD MST instance range, example: 0-3,5,7-9

configuration Enter MST configuration submode

forward-time Set the forward delay for the spanning tree

hello-time Set the hello interval for the spanning tree

max-age Set the max age interval for the spanning tree

max-hops Set the max hops value for the spanning tree

SW1-3550(config)#spanning-tree mst 1 ?

priority Set the bridge priority for the spanning tree

root Configure switch as root

SW1-3550(config)#spanning-tree mst 1 priority ?

<0-61440> bridge priority in increments of 4096

SW1-3550(config)#spanning-tree mst 1 priority 32768

HTH

Sundar

14 REPLIES
Cisco Employee

Re: PVST and MST difference

Hi Dangal,

In very simple terms as the name states PVST is only capable of running spanning tree per vlan but MST has the capability of running spanning tree for group of vlans for eg: vlan 1,2,3 can run one single instance of spanning tree as compared to PVST where each vlan will have its own spanning tree instance.

Have a look at this link and the section where to use MST will clear your views

http://www.cisco.com/warp/public/473/147.html#where

HTH

Ankur

*Pls rate all helpfull post

New Member

Re: PVST and MST difference

You mean to say i can have multiple VLAN in single instance of MST but for PVST i must have to go for the seperate instance for seperate VLAN, right!!!!! what are the other difference?

and what is difference between PVST and PVST+?

other question about tunneling ISL in 802.1Q can i have it in deployment? I mean to say as we are doing Q in Q tunneling then can we have tunneling of ISL in dot1Q, vice versa?

Cisco Employee

Re: PVST and MST difference

The major difference between PVST and PVST+ is that, PVST+ is backward compatible with IEEE 802.1d CST spanning-tree. Another difference is that PVST only supports ISL trunking while PVST+ support 802.1Q trunk.

Q in Q tunneling only works with 802.1Q encapsulation its not supported on ISL trunks.

Since all VLANs in an MSTP instance share the same STP topology, a topology change in one VLAN will affect all VLANs within that particular instance.While a topology change in PVST will not effect the other vlans.

Please see the link below for more understanding

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml#pvst

HTH,please rate if it does.

-amit singh

New Member

Re: PVST and MST difference

Amit,

will you please explain me this in detail:

"Since all VLANs in an MSTP instance share the same STP topology, a topology change in one VLAN will affect all VLANs within that particular instance.While a topology change in PVST will not effect the other vlans. "

I am not getting properly how MST will use single VTP topology?

Hall of Fame Super Blue

Re: PVST and MST difference

Hi

MST uses a single STP topology or more correctly MST groups together multiple vlans into one STP instance and MST can contain multiple instances.

Key thing here is that any topology change in one of the vlans has an effect on all the vlans within that instance.

PVST however runs an instance of STP for every single vlan so a change in one vlan is isolated to that vlan.

HTH

Jon

Re: PVST and MST difference

Hope this helps.

CST - One STP instance for all VLANs

MST - One STP instance for a group of VLANs

PVST - One STP instance for every VLAN

As you can see STP topology change in one of the VLANs that make up the MST instance would affect the whole MST instance.

HTH

Sundar

New Member

Re: PVST and MST difference

sundar you mean to say is:

Lets say we have vlan 2,3 and 4. if we change the root bridge for vlan 4 then root bridge for vlan 2 and 3 will also change.....???

Re: PVST and MST difference

You would change the bridge priority for the MST instance and not vlan4 in MST setup. Hence, it would affect all 3 vlans in this case.

HTH

Sundar

New Member

Re: PVST and MST difference

sundar will you please explain me in little bit detail about the same?

5411
Views
20
Helpful
14
Replies