spanning tree pvst or rapid-pvst

Answered Question
Aug 14th, 2010

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I am in process of upgrading network configurations and performance issues .Currently we have Core / Distribution and Access Layer switches, But all are just hooked up into each other with default configurations (except they are configured with IP Addresses) .

Currently

At Core i have Cisco 3750 L3 and Cisco 3550 (disconnected )

At Distribution i have Cisco 2960 (x5) and Cisco 2950

At Access i have all Cisco 2950 (almost x 40) Switches.

I have some redundant links at Distributions and some at Access layer .Spanning tree in enabled but problem in my network is that my network is working ok some time and all of sudden some distribution or access switches goes off line and i cannot even ping or telnet them .So when i restart the specific switches then this works again but some time of day this problem raise/occur again .So i studied some switching concepts and now want to trouble shoot and upgrade my configurations with the help from all senior guys to resolve these issues .

I have many questions in mind to make clear before i continue

1- Should i go with spanning tree (pvst or rapid-pvst) currently = pvst

2- Currently root bridge is not central i trace it through sh spanning tree and found that one of access layer switch is Root Bridge,So i have to make L3 switch as root bridge .butt How ?

3- I want fast convergence and loop free ,Also want end users to activate connections rapidly instead of waiting 30 to 60 seconds .currently my core and access switch configs are

MDF.CoreSwitch.1#sh spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID                   is enabled
Portfast Default                          is disabled
PortFast BPDU Guard Default     is disabled
Portfast BPDU Filter Default        is disabled
Loopguard Default                      is disabled
EtherChannel misconfig guard     is enabled
UplinkFast                                 is disabled
BackboneFast                           is disabled
Configured Pathcost method used is short

and

Access-swtich-10#sh spanning-tree summary
Root bridge for: none.
Extended system ID                           is enabled.
PortFast BPDU Guard                        is disabled
EtherChannel misconfiguration guard   is enabled
UplinkFast                                         is disabled
BackboneFast                                    is disabled
Default pathcost method used is short

4-Should enable Portfast on switch level or port level

5-Uplink fast / Backbone fast ????? Where should i enable them at Core or Distribution or at Access .Or on all

6-If i go for rapid-pvst then still i need portfast ,uplink fast and backbone fast .

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7-All my switches are configured as switchport mode dynamic desirable . For trunking purpose this configuration is ok or I have to manually configure switchport mode trunk on all switch to switch links.

It is humble request to all the seniors to help in this regard because these problems are eating my network, Waiting for replies’

I have this problem too.
0 votes
Correct Answer by Yudong Wu about 6 years 3 months ago

See my answer in line.

1- Should i go with spanning tree (pvst or rapid-pvst) currently = pvst

[Wu] rpvst provides fast convergence. So, I would suggest rapid-pvst

[Jey]  My Access switches have IOS  Version 12.1(12c)EA1 which dont have  rapidp-pvst ,So i need IOS upgrade on all of them ,I find Latest IOS for  2950 as  12.1(22) .

Question is should i go for upgrade all ,And which i stable ver to upgrade

[Wu], Yes, If you would like to use r-pvst, you have to upgrade them. I am not sure which version is more stable. But I would like to suggest you to read the release notes of the version which you are planning to upgrade to and make sure if there is any known issue that could impact your operation.

2-   Currently root bridge is not central i trace it through sh spanning   tree and found that one of access layer switch is Root Bridge,So i have   to make L3 switch as root bridge .**** How ?

[Wu] The switch  with  lowest priority will become root. use the command "spanning-tree  vlan  priority "

[jey] If i use "spanning-tree vlan root .what is diffrence b/w two

[Wu] They actually do the same thing -- change the priority. I would say "spanning-tree vlan root" is better since it will automatically check the switch priority of the current root switch and set the priority accordingly to make sure this switch to be a root.

4-Should enable Portfast on switch level or port level

[Wu] You can enable it on switch level and it will make all non-trunk port in portfast.

[jey.1] I will prefer to go for switch level "spanning-tree portfast default" ,Now what about trunk ports which have  "switchport mode dynamic desirable" mode .When i enable portfast they also change into portfast mode ?

[Wu] I think "portfast default" is only applied to non-trunk port. If "dynamic" port does not negotiate as a trunk, portfast should be applied. When I do the implementation, I always confgure the port mode manually. So, I am not 100% sure this. You should be able to run a quick testing on this as well.

[jey.2]

What about

spanning tree portfast rootguard

spanning tree portfast bpdu guard

spanning tree portfast bpdu filter

Do i need all these in my network ,If needed = ? where core/Distb/Access

[Wu] Yes, you can enable them as well. They will provide more protection. You can enable them on all switches.

6-If i go for rapid-pvst then still i need portfast ,uplink fast and backbone fast .

[Wu] Yes

[ Jey] Answer to 5 you told me that you dont need uplink fast and backbone fast here in 6 told yes in case of rapid-pvst

Please explain

[Wu] Sorry, I don't know why I put "yes" there. You don't need them if you use r-pvst

7-All my switches are configured as switchport mode dynamic desirable . For trunking purpose this configuration is ok or I have to manually configure switchport mode trunk on all switch to switch links.

[Wu] Personally, I always like to manually configure the switchport mode instead of using "dynamic".

8  - As i told you my distribuon switches which have alternet /redundent  links goes off line some times ,How to trouble shoot them becase  spanning tree is already enable there ,Please guide me how to trace  exactly whats happening there [any flood ,brodcast storm or any Ghost  ...] Please explain

[Wu] http://www.cisco.com/en/US/partner/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

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Yudong Wu Sat, 08/14/2010 - 16:19

Answer in line

1- Should i go with spanning tree (pvst or rapid-pvst) currently = pvst

[Wu] rpvst provides fast convergence. So, I would suggest rapid-pvst

2- Currently root bridge is not central i trace it through sh spanning tree and found that one of access layer switch is Root Bridge,So i have to make L3 switch as root bridge .**** How ?

[Wu] The switch with lowest priority will become root. use the command "spanning-tree vlan priority "

3- I want fast convergence and loop free ,Also want end users to activate connections rapidly instead of waiting 30 to 60 seconds .currently my core and access switch configs are

[Wu] rpvst should provide the fast convergence. Portfast need to be enabled on the ports which connected to end user's PC.

4-Should enable Portfast on switch level or port level

[Wu] You can enable it on switch level and it will make all non-trunk port in portfast.

5-Uplink fast / Backbone fast ????? Where should i enable them at Core or Distribution or at Access .Or on all

[Wu] You don't need them if using Rpvst

6-If i go for rapid-pvst then still i need portfast ,uplink fast and backbone fast .

[Wu] Yes

7-All my switches are configured as switchport mode dynamic desirable . For trunking purpose this configuration is ok or I have to manually configure switchport mode trunk on all switch to switch links.

[Wu] Personally, I always like to manually configure the switchport mode instead of using "dynamic".

HTH

SystemAdminNet Sun, 08/15/2010 - 01:36

Dear Yudong Wu

I am thankful for your explanations it will really help me .Some more things to make clear before i will physcial change in my toplogy.

1- Should i go with spanning tree (pvst or rapid-pvst) currently = pvst

[Wu] rpvst provides fast convergence. So, I would suggest rapid-pvst

[Jey] My Access switches have IOS  Version 12.1(12c)EA1 which dont have rapidp-pvst ,So i need IOS upgrade on all of them ,I find Latest IOS for 2950 as  12.1(22) .

Question is should i go for upgrade all ,And which i stable ver to upgrade

2-  Currently root bridge is not central i trace it through sh spanning  tree and found that one of access layer switch is Root Bridge,So i have  to make L3 switch as root bridge .**** How ?

[Wu] The switch with  lowest priority will become root. use the command "spanning-tree vlan  priority "

[jey] If i use "spanning-tree vlan root .what is diffrence b/w two

4-Should enable Portfast on switch level or port level

[Wu] You can enable it on switch level and it will make all non-trunk port in portfast.

[jey.1] I will prefer to go for switch level "spanning-tree portfast default" ,Now what about trunk ports which have  "switchport mode dynamic desirable" mode .When i enable portfast they also change into portfast mode ?

[jey.2]

What about

spanning tree portfast rootguard

spanning tree portfast bpdu guard

spanning tree portfast bpdu filter

Do i need all these in my network ,If needed = ? where core/Distb/Access

6-If i go for rapid-pvst then still i need portfast ,uplink fast and backbone fast .

[Wu] Yes

[ Jey] Answer to 5 you told me that you dont need uplink fast and backbone fast here in 6 told yes in case of rapid-pvst

Please explain

7-All my switches are configured as switchport mode dynamic desirable . For trunking purpose this configuration is ok or I have to manually configure switchport mode trunk on all switch to switch links.

[Wu] Personally, I always like to manually configure the switchport mode instead of using "dynamic".

8 - As i told you my distribuon switches which have alternet /redundent links goes off line some times ,How to trouble shoot them becase spanning tree is already enable there ,Please guide me how to trace exactly whats happening there [any flood ,brodcast storm or any Ghost ...] Please explain

Correct Answer
Yudong Wu Sun, 08/15/2010 - 22:48

See my answer in line.

1- Should i go with spanning tree (pvst or rapid-pvst) currently = pvst

[Wu] rpvst provides fast convergence. So, I would suggest rapid-pvst

[Jey]  My Access switches have IOS  Version 12.1(12c)EA1 which dont have  rapidp-pvst ,So i need IOS upgrade on all of them ,I find Latest IOS for  2950 as  12.1(22) .

Question is should i go for upgrade all ,And which i stable ver to upgrade

[Wu], Yes, If you would like to use r-pvst, you have to upgrade them. I am not sure which version is more stable. But I would like to suggest you to read the release notes of the version which you are planning to upgrade to and make sure if there is any known issue that could impact your operation.

2-   Currently root bridge is not central i trace it through sh spanning   tree and found that one of access layer switch is Root Bridge,So i have   to make L3 switch as root bridge .**** How ?

[Wu] The switch  with  lowest priority will become root. use the command "spanning-tree  vlan  priority "

[jey] If i use "spanning-tree vlan root .what is diffrence b/w two

[Wu] They actually do the same thing -- change the priority. I would say "spanning-tree vlan root" is better since it will automatically check the switch priority of the current root switch and set the priority accordingly to make sure this switch to be a root.

4-Should enable Portfast on switch level or port level

[Wu] You can enable it on switch level and it will make all non-trunk port in portfast.

[jey.1] I will prefer to go for switch level "spanning-tree portfast default" ,Now what about trunk ports which have  "switchport mode dynamic desirable" mode .When i enable portfast they also change into portfast mode ?

[Wu] I think "portfast default" is only applied to non-trunk port. If "dynamic" port does not negotiate as a trunk, portfast should be applied. When I do the implementation, I always confgure the port mode manually. So, I am not 100% sure this. You should be able to run a quick testing on this as well.

[jey.2]

What about

spanning tree portfast rootguard

spanning tree portfast bpdu guard

spanning tree portfast bpdu filter

Do i need all these in my network ,If needed = ? where core/Distb/Access

[Wu] Yes, you can enable them as well. They will provide more protection. You can enable them on all switches.

6-If i go for rapid-pvst then still i need portfast ,uplink fast and backbone fast .

[Wu] Yes

[ Jey] Answer to 5 you told me that you dont need uplink fast and backbone fast here in 6 told yes in case of rapid-pvst

Please explain

[Wu] Sorry, I don't know why I put "yes" there. You don't need them if you use r-pvst

7-All my switches are configured as switchport mode dynamic desirable . For trunking purpose this configuration is ok or I have to manually configure switchport mode trunk on all switch to switch links.

[Wu] Personally, I always like to manually configure the switchport mode instead of using "dynamic".

8  - As i told you my distribuon switches which have alternet /redundent  links goes off line some times ,How to trouble shoot them becase  spanning tree is already enable there ,Please guide me how to trace  exactly whats happening there [any flood ,brodcast storm or any Ghost  ...] Please explain

[Wu] http://www.cisco.com/en/US/partner/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

SystemAdminNet Mon, 08/16/2010 - 00:01

8  - As i  told you my distribuon switches which have alternet /redundent  links  goes off line some times ,How to trouble shoot them becase  spanning  tree is already enable there ,Please guide me how to trace  exactly  whats happening there [any flood ,brodcast storm or any Ghost  ...]  Please explain

[Wu] http://www.cisco.com/en/US/partner/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

This link requires addtional Access to Cisco ,What is this link and what access should i have

Yudong Wu Mon, 08/16/2010 - 09:35

Hi Jey,

You should be able to access the document as long as you have a valid CCO account.

Anyway, I attached its PDF here.

By the way, since you are managing a network like this, I would suggest you to do some search on Cisco.com to find some related articles on spanning tree. They are very helpful.

Here are two articles of best practice for cat6k switch, you can refer to the spanning tree section there as well. The principle is the same.

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst6500/ios/12.2SX/best/practices/recommendations.html#wp1053726

http://www.cisco.com/en/US/partner/products/hw/switches/ps700/products_white_paper09186a00801b49a4.shtml

HTH

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