Considerations for using software iSCSI port binding in ESXi

Products

• VMware vSphere ESXi

Issue/Introduction

This article provides information on when to use and when not to use iSCSI port binding.

Environment

VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

Resolution

Port Binding

Port binding is used in iSCSI when multiple VMkernel ports for iSCSI reside in the same broadcast domain and IP subnet to allow multiple paths to an iSCSI array that broadcasts a single IP address. When using port binding, you must remember that:

• All VMkernel ports used for iSCSI connectivity must reside in the same broadcast domain and IP subnet.
• All VMkernel ports used for iSCSI connectivity must reside in the same vSwitch.
• There must be a one-to-one mapping between vmkernel (vmk) ports and physical (vmnic) NIC ports.
• If you are using multiple VLANs for iSCSI traffic, use separate vSwitches for each VLAN.

When not to use port binding

Port binding should not be used when:
 

• Array Target iSCSI ports are in a different broadcast domain and IP subnet.
• VMkernel ports used for iSCSI connectivity exist in a different broadcast domain, IP subnet and/or vSwitch.
• Routing is required to reach the iSCSI array if using prior version of vSphere 6.5.
• Do not use LACP or any other link aggregation for iSCSI software multipathing. iSCSI software mulitpathing requires just one uplink per vmkernel, and link aggregation gives it more than one. See Host requirements for link aggregation (etherchannel, port channel, or LACP) in ESXi for more information.​​​​​​​

• Example

  
  
  In this sample scenario, there are multiple VMkernel ports in on different IP subnets and broadcast domains and the target ports also reside in a different IP subnet and broadcast domain. In this case, you should not use port binding. If you configure port binding in this configuration, you may experience these issues:

  • Rescan times take longer than usual.
  • Incorrect number of paths are seen per device.
  • Unable to see any storage from the storage device.

  
  When to use port binding

  Example

  
  
  
  In this scenario, there are multiple VMkernel ports, all residing in the same IP subnet and broadcast domain. In this case, you must use port binding. If you do not configure port binding in this configuration, you may experience these symptoms:

  • Unable to see storage presented to the ESXi/ESX host.
  • Paths to the storage report as Dead.
  • Loss of path redundancy messages in vCenter Server.

  Note: To configure multiple Network Adapters in iSCSI or iSER, see Multiple Network Adapters in iSCSI or iSER Configuration

Additional Information

• 
  
  • Cannot reach iSCSI target after enabling iSCSI port binding on ESXi
  • Rescanning takes a long time when using multiple VMkernel ports with port binding to access two or more storage arrays on different broadcast domains
  • Multihoming on ESXi
  • Unbinding physical network cards from the iSCSI VMKernel using the command line