Removing or adding switches cause connection loss

[Harjeet1408]

We have been facing issue of network / connection loss to clients since months and had narrowed it down to when we remove or add a switch in our network then the connection to all clients is lost for few seconds.

Our Network is like this:

Switch-1(Root) -> Switch-2 -> Switch-4 and so on

Switch-1(Root) -> Switch-3 -> Switch-5 and so on

Other Information:

1. all switches in the network are SG300
2. 10-12 switches in the network
3. root switch bridge priority - 4096
4. STP operation mode - rapid stp
5. all switches have an average of 100 clients
6. access port have edge port setting enabled

Does any one know about this ? how can i prevent it ?

Thanks in advance

Harjeet

[pwwiddicombe]

Are you sure switch-1 truly is the root bridge?  sh spanning-tree on that switch and see if it truly is root.

Plus, is the same rapid-stp being used consistently on all switches?

[Harjeet1408]

Hi pwwiddicombe,

Below is the outcome of sh spanning-tree and yes all the switches are configured rapid-stp.

switche67fdc#sh spanning-tree


Spanning tree enabled mode RSTP
Default port cost method:  long
Loopback guard:   Disabled



  Root ID    Priority    4096
             Address     04:6c:9d:e6:7f:dc
             This switch is the root
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Number of topology changes 56 last change occurred 04:42:45 ago
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15

Interfaces
  Name     State   Prio.Nbr    Cost    Sts   Role PortFast       Type
--------- -------- --------- -------- ------ ---- -------- -----------------
   gi1    enabled   128.49   2000000   Dsbl  Dsbl    No            -
   gi2    enabled   128.50    20000    Frw   Desg   Yes       P2P (RSTP)
   gi3    enabled   128.51    20000    Frw   Desg   Yes       P2P (RSTP)
   gi4    enabled   128.52   2000000   Dsbl  Dsbl    No            -
   gi5    enabled   128.53   2000000   Dsbl  Dsbl    No            -
   gi6    enabled   128.54    20000    Frw   Desg   Yes       P2P (RSTP)
   gi7    enabled   128.55    20000    Frw   Desg    No       P2P (RSTP)
   gi8    enabled   128.56    200000   Frw   Desg   Yes       P2P (RSTP)
   gi9    enabled   128.57    20000    Frw   Desg    No       P2P (RSTP)
  gi10    enabled   128.58   2000000   Dsbl  Dsbl    No            -
  gi11    enabled   128.59   2000000   Dsbl  Dsbl    No            -
  gi12    enabled   128.60   2000000   Dsbl  Dsbl    No            -
  gi13    enabled   128.61   2000000   Dsbl  Dsbl    No            -
  gi14    enabled   128.62    20000    Frw   Desg   Yes       P2P (RSTP)
  gi15    enabled   128.63   2000000   Dsbl  Dsbl    No            -
  gi16    enabled   128.64   2000000   Dsbl  Dsbl    No            -
  gi17    enabled   128.65    20000    Frw   Desg    No       P2P (RSTP)
  gi18    enabled   128.66    20000    Frw   Desg    No       P2P (RSTP)
  gi19    enabled   128.67   2000000   Dsbl  Dsbl    No            -
  gi20    enabled   128.68    20000    Frw   Desg    No       P2P (RSTP)
  gi21    enabled   128.69   2000000   Dsbl  Dsbl    No            -
  gi22    enabled   128.70   2000000   Dsbl  Dsbl    No            -
  gi23    enabled   128.71   2000000   Dsbl  Dsbl    No            -
  gi24    enabled   128.72   2000000   Dsbl  Dsbl    No            -
  gi25    enabled   128.73   2000000   Dsbl  Dsbl    No            -
  gi26    enabled   128.74   2000000   Dsbl  Dsbl    No            -
  gi27    enabled   128.75   2000000   Dsbl  Dsbl    No            -
  gi28    enabled   128.76   2000000   Dsbl  Dsbl    No            -

[pwwiddicombe]

I don't normally configure portfast on links to other switches...

"Because the purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to converge, it is effective only when used on interfaces connected to end stations. If you enable Port Fast on an interface connecting to another switch, you risk creating a spanning-tree loop."

[Harjeet1408]

Edge Port is configured to auto so port fast showing "YES" here is either the directly connected system or any wireless router or wireless access points (about 20-25 clients connected to it).

Switches are connected to ports where the Port Fast status is "NO" ( cross checked this )

[Tuan Phuong Dung]

Very good, thank you so much!