Spanning-tree Best practices with vPC

[j.eduardog]

Hello,

I am looking for best practices for spanning-tree features in an entire vPC network, read a cisco doc where it says to do not use bridge assurance in a vPC environment. Is there any other spanning-tree feature that we need to look further before applying with vPC, like loopguard or root-guard. Should I take care before applying those features with or without peer-switch vPC feature

Thanks in advance

[Reza Sharifi]

Hi,

Yes, there specific recommendation when using spanning-tree with VPC.

Have a look at this link under:

Special Considerations for Spanning Tree with vPCs

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572834-00_STDG_NX-OS_vPC_DG.pdf

HTH

[sajid_m123]

Reza,

Is there any impact on hardware resources on switches if I enable RSTP in an environment?

[Reza Sharifi]

For the Nexus Series, the default is Rapid PVST+.  If you don't have a whole a lot of vlans, I would stay with RSTP.  If you have a lots of vlans, then MST probably scales better.

MST Compared to Rapid PVST+

MST allows you to assign two or more VLANs to a spanning

-

tree instance. MST is not the default spanning

-

tree

mode; Rapid PVST+ is the default mode on Cisco

®

switches.

MST instances with the same

name, revision number, and VLAN

-

to

-

instance mapping combine to form an MST

region. The MST region appears as a single bridge to spanning

-

tree configurations outside the region.

The advantages of MST over Rapid PVST+ are as follows:

●

MST is an IEE

E standard.

●

MST is more resource efficient. In particular, the number of BPDUs transmitted by MST does not depend on

the number of VLANs, as Rapid PVST+ does.

●

MST decouples the creation of VLANs from the definition for forwarding the topology.

●

MST simplifies the depl

oyment of stretched Layer 2 networks, because of its ability to define regions.

For all these reasons, it is advisable for many deployments to migrate to an MST

-

based topology.

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572834-00_STDG_NX-OS_vPC_DG.pdf

HTH

[sajid_m123]

Reza,

Thanks for the good info. My question is that is there any impact on network performance due resource consumption if I enable RSTP on all the switches in a network?

[Reza Sharifi]

Usually, there is not, but how large is the network?  What type of devices are you using and how many vlans?

[sajid_m123]

Around 50 Vlans with overall 60 switches. Switches range from 3550, 3560, 3750, 3760, 4500, 6500

[j.eduardog]

Better open another topic for you sir, thanks

[j.eduardog]

Thanks for the link you provided, but what about using or not using loopguard in the access switches, is that a best practice using it even with vPC or no need to use it?

Thanks

[Reza Sharifi]

It is usually a good practice to enable loop guard on both sides of your link:

Loop Guard

Loop Guard provides additional protection against Layer 2 forwarding  loops. Loop Guard should be enabled on root and alternate ports in the  spanning tree topology. When Loop Guard detects that BPDUs are no longer  being received on a non-designated port, the port is moved into a  loop-inconsistent state instead of transitioning to the  listening/learning/forwarding state. This prevents a Layer 2 loop from  occurring in the event that a link becomes unidirectional or a node  stops transmitting BPDUs for some reason. Loop Guard may also be  configured globally, but port-specific configuration is preferred to  ensure that it is only enabled where specifically necessary. An  illustration of where to enable Loop Guard, Root Guard, and BPDU Guard  spanning tree enhancements is shown in Figure 6.

more info here:

http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/nx_7000_dc.html

HTH

[j.eduardog]

There is no specific recommendation about STP features with a full vPC environment in those links

Thanks anyway