STP may cause temporary loss of network connectivity when a failover or failback event occurs

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

Symptoms:
In a switched network environment which uses Spanning Tree Protocol (STP), you experience these symptoms:

• An ESXi or ESX host temporarily loses network connectivity when a failover or failback event occurs.
• Virtual machines temporarily lose network connectivity when a failover or failback event occurs.
• A VMware High Availability (HA) isolation event occurs after one of the teamed NICs of the COS is unplugged and plugged in to a different port.

Environment

ESXi 6.x, 7.x, 8.x

Cause

• When STP convergence is initiated, it compels all physical switches within the STP domain to clear their forwarding tables and re-learn the STP topology and MAC addresses.
• This process typically takes between 30 to 50 seconds.
• During this period, no user data is transmitted through the ports, which may cause some user applications to time out.
• Connectivity is restored once the STP domain completes the convergence process

Resolution

STP is used to accomplish a loop-free environment. Every time a port state goes up, STP calculation occurs. As the result of the calculation, the switch ports are either set to a forwarding or blocking state to prevent a traffic loop. STP topology convergence has four states:

• Blocking
• Listening
• Learning
• Forwarding

To prevent the 30-50 second loss of connectivity during STP convergence, perform one of these options:

• Set STP to Portfast on all switch ports that are connected to network adapters on an ESXi host
  
  Portfast allows the ports to immediately be set back to the forwarding state and prevents the link state changes that occur on ESX/ESXi hosts from affecting the STP topology. Setting STP to Portfast prevents the 30-50 second loss of network connectivity.
  
  The command to set STP to Portfast depends on the model of the switch. As the command is different from model to model and vendor to vendor, contact your physical switch vendor for more detailed information on how to configure the same.
  
  
• Disable STP
  
  VMware does not typically recommend that you disable STP. However, to prevent this issue from occurring, it may be necessary to disable STP. Before you disable STP, contact your switch vendor.
  
  The command to disable STP depends on the switch. Contact your switch vendor for more detailed information.
  
  
  

Additional Information

Contact switch vendor for more information related to switch commands

See also Understanding the BPDU Filter feature in vSphere (2047822) .

For more information, see Spanning Tree Protocol - Cisco.

 

Rapid Spanning Tree Protocol has replaced Spanning Tree Protocol. For more information, see the white paper Understand Rapid Spanning Tree protocol (802.1w) from Cisco.

 

Note: 

Sample Configuration - ESX/ESXi connecting to physical switch via VLAN access mode and External Switch VLAN Tagging (EST Mode)