Hi,
PVST==> per vlan spanning-tree
Say if you are having 100 vlans, there will be 100 spanning-tree instances.
As you know STP process utilizes CPU cycles and 100 spanning-tree instances will consume more CPU Cycles than that of a protocol which runs less no of STP instances.
++ Per-VLAN Spanning Tree (PVST) maintains a spanning tree instance for each VLAN configured in the network.
++ It uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs.
++ Since PVST treats each VLAN as a separate network, it has the ability to load balance traffic (at layer-2) by forwarding some VLANs on one trunk and other Vlans on another trunk without causing a Spanning Tree loop.
MST=> Multiple spanning-tree
We can group the vlans and we can run MST accordingly.
For example for 100 Vlans, you can group 10 vlans in 1 mst instance... So you will run 10 STP instances.
So STP instances are far less in MST compared to PVST.
MST:
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Distribution2#show spanning-tree mst 1
##### MST1 vlans mapped: 10,30,100
Bridge address 0015.c6c1.3000 priority 28673 (28672 sysid 1)
Root address 0015.63f6.b700 priority 24577 (24576 sysid 1)
port Gi2/0/23 cost 200000 rem hops 1
useful links - MST:
==============
http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml
PVST:
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http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080136673.shtml
Hope this helps
Cheers
Somu
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