Windows Server 2019 — DHCP failover enters Communication Interrupted state — Fix & Prevention

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution — Primary Fix
7. Solution — Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

DHCP partner relationship degrades and lease synchronization is delayed, increasing outage risk during node failure.

Environment & Reproduction

Two-node DHCP failover pair on Windows Server 2019 across filtered network paths.

Get-DhcpServerv4Failover
Get-DhcpServerv4FailoverStatistics

Root Cause Analysis

TCP 647 is blocked or partner state diverges after unplanned reboot.

Quick Triage

Validate port reachability and service state on both partners.

Test-NetConnection dhcp02.contoso.local -Port 647
Get-Service DHCPServer

Step-by-Step Diagnosis

Review failover events and check lease ownership balance.

Get-WinEvent -LogName 'Microsoft-Windows-DHCP Server Events/Operational' -MaxEvents 100
Get-DhcpServerv4FailoverStatistics

Solution — Primary Fix

Restore TCP 647 communication and force failover replication.

New-NetFirewallRule -DisplayName 'Allow DHCP Failover 647' -Direction Inbound -Protocol TCP -LocalPort 647 -Action Allow
Invoke-DhcpServerv4FailoverReplication -Name 'FO-VLAN20'
Restart-Service DHCPServer

Solution — Alternative Approaches

Recreate the failover partnership during a controlled maintenance window.

Remove-DhcpServerv4Failover -Name 'FO-VLAN20' -Force
Add-DhcpServerv4Failover -Name 'FO-VLAN20' -PartnerServer dhcp02.contoso.local -ScopeId 10.10.20.0 -LoadBalancePercent 50

Verification & Acceptance Criteria

Failover state returns to Normal and replication timestamp advances.

Get-DhcpServerv4Failover | Select Name,State,PartnerServer

Rollback Plan

Temporarily run active scope on primary only if replication cannot be stabilized quickly.

Remove-DhcpServerv4Failover -Name 'FO-VLAN20' -Force

Prevention & Hardening

Monitor partner state continuously and enforce synchronized time sources.

w32tm /monitor
Get-DhcpServerv4Failover | Where-Object State -ne 'Normal'

Related Errors & Cross-Refs

Related to firewall baseline changes and packet inspection timeouts.

Related tutorial: View the step-by-step tutorial for Windows Server 2019.

View all Windows Server 2019 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Microsoft Learn: DHCP failover deployment and troubleshooting.