Change Cisco switches spanning-tree from PVST to RSTP.

[JelihoMagicMan]

I am a new network support person with a  little more than a year in my current position. Where I work, I have several (qty. 10) older switches to replace. They are models C2960, IE-3000, and C3560 devices. I will not be replacing them all at one time. I found that there are a couple of V-LANs on each of them. The two people in this position set up the switches before me with the PVST spanning-tree protocol, and I would like to see if I can get my questions answered about spanning-tree protocols.

1. If the switches have been in the environment for several years, can the protocol be changed to RSTP from PVST?

2. If I were to change the protocol, what kinds of things could this mess up on the network?

3. Is there a detailed process or procedure for implementing a protocol change on ten Cisco switches with multiple VLANs?

Thank you in advance for any information you could provide as it refers to my dilemma.

[balaji.bandi]

Look at the document Migration :

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/72836-rapidpvst-mig-config.html

This there help you some insight :

https://community.cisco.com/t5/switching/migrating-pvst-to-rstp-pros-n-cons/td-p/1292932

[Martin L]

ad 1. We should be running Rapid STP at all times and always; unless there is a need for MST, but never legacy STP which should be retired by now from all networks and exams!

ad 2.  no mess, RSTP  is backwards compatible with legacy STP,  Think about Rapid as improved STP version; aka STP on steroids.  You can have PVST and Rapid STP switches on the network at the same time but it is recommended to migrate to Rapid asap. In case a PVST switch connects to Rapid sw port x, such port operates in legacy STP mode while all other ports (and the whole sw) is in Rapid mode.  This is very useful for migration with almost no down-time.

ad 3.  see links shared by B.B.  in addition, when implementing a protocol change, I would make sure the good switch is the Root sw and stays that way after migration; probably start migration with the Root sw.  Change Switch VTP mode to transparent to save vlans in running config; otherwise you won't see them listed in show run.  When copy and paste conifgs from old to new sw, look for things that will be marked with ^ as some commands are not applicable in new IOS.

Don;t forget apply Portfast command on all end-user ports (it is not automatic) and Label cables before unplugging them.

You can practice migration before migration with your new switches (make a temp lab) or use free online CML via DevNet sand box option.

Best of luck!

Regards, ML
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[paul driver]

Hello

1- yes

2 -stp convergence which can and will cause network disruption 

3 - first make the stp mode change on all access layer switches fthen any distribution switches and lastly core switches 

[JelihoMagicMan]

Thank you all for the information. I appreciate the feedback very much.

As I stated earlier, I am new to this environment and unsure how to determine or identify the access layer switches, the distribution switches, and the core switches. Is this information identifiable through CLI or the WebUI?

[Martin L]

no, access, distribution, core layers are design principles of so called hierarchical topology which is more or less replaced (or mixed) with new approach called modular design topology.  You may not have core or distribution layers or have variants of them such as collapsed core, dual-layer core, etc. You must have access core as this is where end-hosts connect.

see picture and read a paragraph in section Network Diagram  https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/72836-rapidpvst-mig-config.html

You have access-layer switches and 2 distribution.  Missing is Core layer which would be on the top of distribution switches (above them) but core could be a router, not a switch. 

I would go to youtube and search for hierarchical topology design; there should be lots of videos about this.

Regards, ML
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[paul driver]

Hello

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@JelihoMagicMan wrote:

As I stated earlier, I am new to this environment and unsure how to determine or identify the access layer switches, the distribution switches, and the core switches. Is this information identifiable through CLI or the WebUI?

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.

Core layer switch = Connects the distribution switch's and other devices ( such as WAN rtrs /Firewall etc..) these devices usually run  layer 2 connections, That is connections to the distribution switches and the L3 routing for the Local Area Network (LAN) and Wide Are Network (WAN)

Distribution layer switch =  these usually are switch's that interconnect access and core switches together, ( No edge devices)

Access layer-switch =these are usually switches that have ONLY edge device's attached (pc's printers. Servers, access points etc..) but have a uplink to a distribution or distribution/core switch

Now in large sites you would mostly see something like the above, however for smaller sites they could implement a collapse Core/Distribution & access layer ( a single switch or a stack of switches or even a chassis switches for core/distribution) performing both functions of a separate core and distribution switches, And for small sites you could have a single stack of switch performing all of the above (core/distribution/access)

Please review this, it may assist you further to understand a Local Area Network (LAN) design