Backups (port 902 (tcp) failed: Connection refused)

Products

• VMware vSphere ESXi

Issue/Introduction

ESXi vmkernel configured for backup, the pings succeed. However, when running netcat for port 902 to the ESXi host, it fails with a "connection refused" error.

Environment

vSphere ESXi 7.x
vSphere ESXi 8.x
vSphere vCenter Server 6.x
vSphere vCenter Server 7.x
vSphere vCenter Server 8.x

Cause

 ARP table on the Backup appliance, noticed two MAC addresses bound to the same IP. One MAC belongs to VMware vmkernel3 (00:50), and the other is a Network interface card  MAC address, which corresponds to the IP of the backup appliance .

The Backup appliance is pinging the IP, but the physical network is routing that traffic to the duplicate IP and its associated MAC. As a result, it's receiving a connection refused message on TCP/902 because the duplicate IP isn't listening for communications on that port.

When someone pings out from the ESXi host, the physical switches learn the "correct" MAC of the host's vmkernel, and traffic functions properly again—until the duplicate MAC is learned once more, causing further interference.

Resolution

Assign a new IP on same subnet to the ESXi vmkernel and refreshed the nodes. This will allow you to successfully ping the ESXi host, responding with a single MAC address.