ESXi Host Fails to Add to vCenter with error "Host is Already Connected"

Products

VMware vSphere ESX 8.x VMware vCenter Server 8.0

Issue/Introduction

When attempting to add an ESXi host to the vCenter Server inventory, the process fails with the following error message:

The host <hostname or IP> is already connected to this vCenter Server.
Or
"Cannot connect <hostname or IP> in <Cluster_Name>: incorrect username or password"

From /var/run/log/vobd.log, reports a duplicate IP address detection.

[esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for ##.###.##.### on interface vmk0

From /var/run/log/vpxa.log

warning vpxa[#######] Failed to bind heartbeat socket; '##.###.##.###', e: 99(Cannot assign requested address)

Cause

This error typically occurs even if the host is not visible in the current inventory. It indicates that vCenter detects an IP address conflict or a stale registration entry, blocking the addition of the host.

When a host is removed from vCenter, some configuration details—specifically the associated vCenter Server IP—may persist in the ESXi ConfigStore. When you attempt to re-add the host (or a new host using a recycled IP), the ESXi host still believes it is managed by a vCenter instance, leading to a "Duplicate IP" or "Already Connected" misidentification.

Resolution

To resolve this issue, the stale vpxa configuration must be manually cleared from the ESXi host's internal configuration store

Log in to the ESXi host via SSH as root and run the following command to confirm the presence of the IP

configstorecli config current get -c esx -g services -k vpxa_solution_user_config | grep -i server_ip

Delete the vpxa solution user configuration from the store:

configstorecli config current delete -c esx -g services -k vpxa_solution_user_config

Restart the vCenter Agent service to initialize the change:
```
/etc/init.d/vpxa stop && /etc/init.d/vpxa start
```
Return to the vSphere Client and attempt to add the ESXi host to the inventory again.