vSphere Replication fails with the error "No connection to VR server: Unknown" shown on the replication VMs.

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

When a replication sync operation is kicked off from the vSphere Replication GUI, the following error is seen on the VMs being replicated :

In the vmkernel logs of the ESXi Host hosting the replication VMs, the following snippets are seen :

2025-12-29T04:43:12.016Z cpu74:6226347)WARNING: Hbr: 5093: Failed to establish connection to [10.xx.xx.xx]:31031 (groupID=GID-39ce####-####-####-####-####58d5): Failure
2025-12-29T04:44:42.025Z cpu62:6226347)Hbr: 3410: Command: INIT_SESSION: error result=Failed gen=-1: Group GID-GID-39ce####-####-####-####-####58d5 not registered
2025-12-29T04:44:42.025Z cpu62:6226347)WARNING: Hbr: 3438: Command INIT_SESSION failed (result=Failed) (isFatal=FALSE) (Id=0) (GroupID=GID-39ce####-####-####-####-####58d5)
2025-12-29T04:44:42.025Z cpu62:6226347)WARNING: Hbr: 5093: Failed to establish connection to [10.xx.xx.xx]:31031 (groupID=GID-GID-39ce####-####-####-####-####58d5): Failure
2025-12-29T04:46:12.035Z cpu52:6226347)Hbr: 3410: Command: INIT_SESSION: error result=Failed gen=-1: Group GID-GID-39ce####-####-####-####-####58d5 not registered
2025-12-29T04:46:12.035Z cpu52:6226347)WARNING: Hbr: 3438: Command INIT_SESSION failed (result=Failed) (isFatal=FALSE) (Id=0) (GroupID=GID-GID-39ce####-####-####-####-####58d5)

 

Environment

VMware ESXi 8.x

Cause

This issue occurs if the port 31031 is not open.

Resolution

The port 31031 should be open from the ESXi host at the protected site to the vSphere Replication appliance or at the vSphere Replication server on the recovery site.

For more information, kindly refer to : Port numbers that must be open for vSphere Replication