what if Rapid Spanning Tree is enabled in non redundant network

[shyamradhe]

Hi 

My question is staright, as Title, let me show you an example

  As you can see there is no redundancy in the network, and Root bridge is last L2 switch,and Using "Spanning tree mode rapid pvst" so in this case may question is., 

- Will this can cause a poor data flow over LAN, ? I  have 100 switches total in my envoiroment and some of them are old as- cisco CE500 models, and they are elected as Root Bridge (Default).

but in my network no dual uplinks or redundancy formed. so will this cause any issue in network performance. ?????

[chrihussey]

Probably not as you won't have any interfaces blocking. However it couldn't hurt designating a switch as root that was more centralized.

[shyamradhe]

Thanks chrihussey, for clarification,

Actually I am facing a mistrious LAN disconnection issue in my Office network, There are 30 VLANs in my network, one core switch, without any redundancy !

and users are facing lan disconnection issue for 3-4 seconds , and this happens randomly only for one VLAN at a time. i checked a lot, switch ports are fine, intervaln routing is working , no packet drops etc..

no hardware issue, that time i noticed that each VLAN has different root bridge, thats why i asked, 

[paul driver]

Hello

Has suggested designate a the root switch manually via the priority 

spanning-tree vlan 1-4092 priority 0

Also to make sure that unnecessary stp recalculations don't occur for your access ports have them portfast enabled

Lasty if your vlans don't need span all the switches then manually prune the unwarranted vlans off the switch interconnects 

res

paul

[shyamradhe]

Hi Paul

As I said there is no Dual Uplinks in my topology, but still i make core as root bridge, and will do all recomonded settings like you said pruning any unwanted VLANs etc., but still root cause not indentified why this is happening in my network. :( .

Lets see what happens when i put all recomonded settings..!!

[chrihussey]

Even with your topology it does sound like there may be a spanning tree issue. I'd follow up with Mr. Driver's comments in this thread to define the spanning tree topology as well as limit the VLANs spanning throughout your network. That would be a very good start.

Also, with over 100 switches, I'd check to make sure there wasn't a loop that you weren't aware of. It would also not be out of the realm of possibility to have a faulty switch causing issues. Tough to track down, but getting familiar with the output of the "show spanning-tree detail" CLI command would be a good start. Specifically paying close attention to topology changes and associated ports.

VLAN0622 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 622, address 5017.ffaf.6b80
  Configured hello time 2, max age 20, forward delay 15
  We are the root of the spanning tree
  Topology change flag not set, detected flag not set
  Number of topology changes 7 last change occurred 42w5d ago
          from GigabitEthernet1/0/46

[A.Swinnen]

I'd also configure some switch deterministically as root, else you cannot exclude the fact that the STP must be reculculated when a new switch is added or removed.

[Joseph W. Doherty]

In addition to the other posters suggestions, what's the diameter of your L2 topology? (STP has limitations on how "broad" a topology it supports. With 100 switches, might you have a long daisy chain segment?)

Also, you may want to check if there's anything going on that could delay the BPDUs, such as a flapping link, a saturated link, broadcast storm, etc.

[shyamradhe]

Hi 

yes  Joseph , I have some long hand from core (daisy chain segment over 300+ meters ) , which are fiber copper mix.

I checked packet drops, and other counters on uplink ports , but every things looks fine.

My suspected issue is change in STP topology, because it doesn't happens periodically , but it hit's one VLAN traffic in 2-3 days(disconnects and connects automatically within 3-4 seconds) however on the same time other vlans traffic works fine..

Please suggest some usefull troubleshooting area on which i can work ...

[shyamradhe]

Hi

Checked TCN logs from core switch and found this... as I said i have no redundant Uplinks in my network. also using Rpvst

then why these counts are there ?

CINSUR01CORESW01#sho spanning-tree detail | inc iee|occurr|from|is exec
VLAN0001 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 180460 last change occurred 00:00:34 ago
from GigabitEthernet1/6
VLAN0010 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40701 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0020 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40688 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0025 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40609 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0040 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40573 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0041 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40573 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0042 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40575 last change occurred 00:00:33 ago
from GigabitEthernet1/6
VLAN0043 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40576 last change occurred 00:00:33 ago
CINSUR01CORESW01#sho spanning-tree detail | inc iee|occurr|from|is exec
VLAN0001 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 180460 last change occurred 00:00:39 ago
from GigabitEthernet1/6
VLAN0010 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40701 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0020 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40688 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0025 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40609 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0040 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40573 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0041 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40573 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0042 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40575 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0043 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40576 last change occurred 00:00:38 ago
from GigabitEthernet1/6
VLAN0044 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40576 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0045 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40576 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0050 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40702 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0055 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40576 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0056 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40573 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0060 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40824 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0070 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 44800 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0080 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 41125 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0090 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 41720 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0100 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43033 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0110 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40570 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0150 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40706 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0200 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43203 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0250 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40983 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0300 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43180 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0350 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 52511 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0400 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 44453 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0450 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43619 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0500 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40604 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0550 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 42952 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0600 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 42882 last change occurred 00:00:40 ago
from GigabitEthernet1/6
VLAN0700 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40843 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0750 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 42688 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0777 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40551 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0800 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43920 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0850 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 66679 last change occurred 00:00:05 ago
from GigabitEthernet6/3
VLAN0860 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 66637 last change occurred 00:00:29 ago
from GigabitEthernet6/11
VLAN0900 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 41472 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0950 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 40537 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN0999 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 1383 last change occurred 00:00:41 ago
from GigabitEthernet1/6
VLAN1000 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 43311 last change occurred 00:00:41 ago
from GigabitEthernet1/6

[chrihussey]

Looks like you need to follow the trail. Check the switch off of G1/6, run the same command and see where it leads.

[Joseph W. Doherty · Accepted solution]

Ok, understand you daisy chain some switches because of distance limitations, but you need to analyze the maximum diameter of your network.

You might also double check all your switches are running RSTP and not STP (the two can work together, but you really don't want to run any with STP).

As Paul suggested, you should also insure edge ports have portfast enabled.

As for troubleshooting suggestions, you might start with: https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/28943-170.html?dtid=osscdc000283