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
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
*Pls rate all helpfull post
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?
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
HTH,please rate if it does.
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?
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.
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.
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.....???