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when should we use PVST or RPVST

Posted on 2016-08-25
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when should we use RPVST or RPVST

If I understand with PVST or RPVST, you can assign a separate Root bridge for each VLAN on the switch.
However in real wordl, the Core Switches are usually configured as Root Bridges, one switch as the primary and the other one a sthe backup in case the primary fails. So there is no such Root Bridge per VLAN.

Any clarifications ?

Thank you
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Question by:jskfan
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by:Akinsd
Akinsd earned 230 total points
ID: 41770787
I think you meant RSTP vs RPVST
Your real world assumption is subjective as it all depends on your preference.
RPVST is the defualt on many modern switches if not all
If your core is your only exit and it is centrally located to all your switches (fastest and shortest path), then RSTP is all you need and you'll make your core the root bridge.
If you have multiple exit (Multiple sites in a mesh topology), then you should definitely consider RPVST and have multiple root bridges per vlan

RSTP is easier to manage and troubleshoot.
For granular functionality, RPVST would be your choice

Check out these articles
https://www.experts-exchange.com/articles/11315/Root-Port-Election-STP-or-RSTP.html

http://www.learncisco.net/courses/icnd-2/vlans-and-spanning-tree/stp-protocol-types.html
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by:jskfan
ID: 41770811
I meant why configure Root bridge for each separate VLANs, instead of configuring one Root Bridge for all Vlans since all VLANs will end up at the same Core Switches.

I know when you have on each location Access Switches connected to Distribution Switches then Distribution Switches on each location are connected to Core Switches in the main Data Center, in this scenario you configure on Each Location the Distribution Switches as Root bridges (Primary and secondary) for all Vlans in that location., not each VLAN will have it is own Root Bridge.
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by:Akinsd
ID: 41770832
Yes, you're basically echoing what I mentioned above.
In your case, it looks like you only have 1 exit point and you don't have a mesh topology. In that case, RSTP may be all you need
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by:Jan Springer
Jan Springer earned 40 total points
ID: 41770839
If you have the option, you should use MST and be compatible with other vendors.
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by:jskfan
ID: 41770875
So following the design below, we do not need  PVST ?

Swicth.PNG
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Author Comment

by:jskfan
ID: 41770877
I meant we do not need to configure Root Bridge for each Vlan ?
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by:Akinsd
ID: 41770883
I just realized that the other switches are distribution switches.
You do have a Mesh Topology and definitely need RPVST
In this case, you want the distribution switch that host the interface vlan to be the root bridge for that vlan
Hence you RPVST is your best bet in this case
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by:Predrag Jovic
ID: 41771566
You should always use RSTP even if not all devices support RSTP (sure - if all devices are Cisco devices). RSTP is backward compatible with STP, so there is no harm there. With Per VLAN STP you can have separate root bridges per VLAN to have better link utilization in your network, but only if you do not have too much VLANs or mixed vendors. If you have too much VLANs (possible high CPU utilization) or mixed vendors then you can go with MST as Jan Springer suggested.
However in real wordl, the Core Switches are usually configured as Root Bridges, one switch as the primary and the other one a sthe backup in case the primary fails.
Only in the case of collapsed core core switches are Root Bridges, but not in 3 layer hierarchical network design. In 3 layer hierarchical model typically distribution is where STP is used. The reason is simple - you want to use all links and load balance traffic across all links in the core (so, there should be no blocked links in the core). Between core and distribution layer should be implemented routing with equal cost paths per link so traffic can be load balanced over all links.
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Author Comment

by:jskfan
ID: 41771683
well, if you look at the above Diagram :
At the Access Switches where the Clients are plugged into, will see there 3 separate locations, each location has Access switches and 2 Distribution Switches.
On each location I do not see why we would configure Per VLAN Spanning Tree, seeing that the Distribution Switch will be the Root Bridge anyway (one Primary the other Secondary).

**If I understand the meaning of per VLAN Spanning Tree, is different Switches can be Root Bridges per Different VLANS. In the Diagram above, I guess it makes sense to have one Distribution Switch as Root Bridge (Primary and Seconday).

The same will Apply to the Access/Distribution Switches where the Servers are Connected to
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Predrag Jovic earned 230 total points
ID: 41771777
Here is the difference.
Only one root bridge for all VLANs example - Traffic will be forwarded only through red links. Other links are not used at all (gray once).
All VLANs have the same root bridgeDifferent root bridges for 2 groups of VLANs  -
For VLANS 10, 20, 30, 40 traffic will be forwarded only through red links.
For VLANS 50, 60, 70, 80 traffic will be forwarded only through green links.
Different root bridges for groups of VLANWhat STP suppose to do is disable some links so network loops will not be present.
That means that you can't utilize some of the links. By using PVSTP or MSTP you can use all links since you can have different root bridges for group of VLANs (even if group is only one VLAN).
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Author Closing Comment

by:jskfan
ID: 41772061
Clear now
Thank you for your Help Guys
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