Port Binding

• 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.

When not to use port binding

• 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 (1001938) 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: There have been limitations in the past when using software iSCSI when the iSCSI initiator and target had to be on the same subnet. With vSphere 6.5, the software iSCSI initiator and target can be on different subnets, but not when using software iSCSI port binding. For more information, see What’s New in VMware vSphere 6.5 and Requirements for iSCSI Port Binding.

• VMware Skyline Health Diagnostics for vSphere - FAQ
• Cannot reach iSCSI target after enabling iSCSI port binding on ESX/ESXi 4.x and ESXi 5.0 (1009524)
• Rescanning takes a long time when using multiple VMkernel ports with port binding to access two or more storage arrays on different broadcast domains (2017084)
• Multi-homing on ESX/ESXi (2010877)
• Unbinding physical network cards from the iSCSI VMKernel using the command line (1030674)