How to fix Error 8576 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 8576 – RPC Endpoint Mapper Unreachable

Why This Error Happens

This error occurs when SQL Server 2025 attempts to register or communicate with the RPC Endpoint Mapper service on a remote host, but the connection fails due to network-level blocking or service unavailability. Common root causes include the Windows Firewall blocking port 135 (the standard RPC Endpoint Mapper port), the RPC Endpoint Mapper (RpcEptMapper) or DCOM Server Process Launcher services being stopped on the target host, or DNS/name resolution issues preventing the source server from locating the target host correctly. In clustered or Always On Availability Group configurations, this can also stem from stale cluster network name registrations.

Step-by-Step Resolution Guide

Step 1: Verify RPC-Related Services Are Running

  • On the target host (‘%ls’), open services.msc and confirm that Remote Procedure Call (RPC) and RPC Endpoint Mapper are set to “Automatic” and currently “Running.”
  • Also check DCOM Server Process Launcher, as RPC Endpoint Mapper depends on it.
  • Restart the services if needed using PowerShell:
  Restart-Service RpcEptMapper -Force

Step 2: Check Windows Firewall Rules for Port 135

  • Confirm that inbound rule “RPC Endpoint Mapper” is enabled under Windows Defender Firewall with Advanced Security > Inbound Rules.
  • Validate the port is listening using:
  netstat -ano | findstr ":135"
  • If using a custom firewall or third-party security software, ensure TCP 135 is explicitly allowed between the source SQL Server host and the target host ‘%ls’.

Step 3: Validate Network Connectivity and Name Resolution

  • Run ping %ls and nslookup %ls from the source SQL Server to confirm the target host resolves to the correct IP address.
  • Use tnc %ls -Port 135 (PowerShell Test-NetConnection) to confirm TCP connectivity to the Endpoint Mapper port specifically.
  • Check for stale entries in DNS or the local hosts file that may be routing traffic incorrectly.

Step 4: Review Cluster/Always On Configuration (If Applicable)

  • If ‘%ls’ is a node in a Windows Server Failover Cluster, run Get-ClusterNetworkInterface in PowerShell to confirm the node’s network interface is healthy and “Up.”
  • Validate that the Cluster Name Object (CNO) and Virtual Network Name (VNN) are correctly registered in Active Directory and DNS.
  • Restart the Cluster Service if stale registrations are found:
  Restart-Service ClusSvc -Force

Alternative or Verification Steps

  • After applying fixes, re-run the failing SQL Server operation (e.g., linked server query, Always On failover, or distributed transaction) and confirm Error 8576 no longer appears in the SQL Server error log.
  • As an alternative, use rpcping -t ncacn_ip_tcp -s %ls -e 135 from an elevated command prompt to manually test RPC Endpoint Mapper reachability before retrying the SQL Server operation.