ESXi hosts cannot see iSCSI storage due to incorrect VLAN mapping on Fabric Interconnects

Products

• VMware vSphere ESXi

Issue/Introduction

• ESXi hosts are unable to discover or connect to iSCSI storage targets since the iSCSI VMkernels (vmks) cannot reach them.
• Packet captures reveal that ARP requests are sent to the physical infrastructure, but no ARP replies are received, indicating packets are being dropped by the physical network.
• You are using UCS environment and while checking the mac table on the Fabric Interconnects, the traffic is seen learning on a different vLAN than the expected.

Environment

VMware vSphere ESXi

Cause

• The MAC address of the iSCSI VMkernel is being learned on an incorrect VLAN on the Fabric Interconnects.
• This can occur if the physical NICs (vmnics) used by the iSCSI vmk/s are incorrectly mapped to a VLAN intended for different traffic, leading to a mismatch between the virtual configuration and the physical fabric policy.

Resolution

To resolve this issue, you must align the vmnic mapping with the correct VLAN on the physical fabric:

1. Identify the vmnics associated with the iSCSI VMkernel interfaces.

2. Verify the MAC address table on the Fabric Interconnects to confirm which VLAN is learning the vmnic MACs in question.

3. Work with your internal networking team to ensure vmnic-to-VLAN mapping is correct on both physical and virtual levels. Please either remap the vmnics or configure the missing VLANs on the current setup.

4. Test connectivity by performing a ping from the ESXi iSCSI VMkernel to the storage target.