Hook: Why RPC Errors Hinder Your Windows Workflow

You can hear the office hum: printers click, databases sync, backups tick. One quiet morning, a single RPC failure throws the whole rhythm off. Picture a traffic light stuck on red—replication stops, backups stall, and the printer refuses to talk. That’s the reality many IT teams face when the RPC server is unavailable. We’ve seen it happen in midsize firms, where a mis‑configured firewall or a silent service crash turns productivity into a waiting game.

What is Windows RPC?

Remote Procedure Call lets programs on one machine call functions on another as if they were local. Think of it as a telephone that whispers instructions to a distant colleague. In Windows, RPC underpins WMI, Active Directory replication, SQL Server remote queries, and printer sharing. The core services—RpcSs, RpcEptMapper, VDS—must be humming for any of these features to work.

Why It Matters

When RPC falters, the ripple is felt across the network. A stopped RpcSs service is like a power outage in a data center; nothing that relies on remote calls can proceed. Even a single blocked port 135 or dynamic port 49152‑65535 can choke the entire system. That’s why the “RPC server unavailable” error is a red flag, not a gray area.

Common Causes

Disabled services: RpcSs or RpcEptMapper set to Manual or stopped.
Firewall blocks: TCP 135 or the dynamic port range is closed.
DNS or network hiccups: Hostnames resolve incorrectly or VPNs misroute traffic.
Registry corruption: Missing keys for RPC or VDS.
Third‑party interference: Antivirus or security suites inadvertently block RPC traffic.

Real‑World Incident

Last year, a regional office’s backup jobs failed because a firewall rule was overwritten during a security patch. The backup software logged “RPC server unavailable.” The IT crew spent hours chasing logs until they realized the firewall had closed port 135. Fixing the rule restored backups in under an hour. For deeper understanding, see our comprehensive Windows networking guide: <https://learn.microsoft.com/en-us/windows-server/networking/>.

Fast Fixes to Keep the Flow

Check services: Ensure RpcSs and RpcEptMapper run automatically.
Open ports: Allow inbound TCP 135 and dynamic ports 49152‑65535.
Verify DNS: Test nslookup and ping to confirm resolution.
Run sfc /scannow: Spot and repair corrupted system files.
Inspect third‑party tools: Temporarily disable antivirus to rule out interference.

For official guidance, refer to Microsoft's support article: <https://learn.microsoft.com/en-us/troubleshoot/windows-server/user-profiles-and-logon/not-log-on-error-rpc-server-unavailable>.

By addressing these steps, you can turn a potential bottleneck into a smooth workflow. Ready to dive deeper into each scenario? The next section will walk you through tailored solutions for Veeam, Disk Management, and printer setup.

Quick Checklist

RPC services (RpcSs, RpcEptMapper) are running.
TCP port 135 and dynamic ports 49152‑65535 are open in the firewall.
DNS resolves all relevant hostnames correctly.
System files are intact (sfc /scannow passes).
Antivirus or security software is not blocking RPC traffic.

You’ve probably felt that frustration when a printer stops working or a backup job stalls right in the middle of the night. That silent glitch usually shows up as RPC server unavailable—a sign that Windows’ invisible glue has snapped. Think of RPC as a universal remote that lets one computer command another without writing a line of code. If that remote loses power, the whole show stops.

Understanding Windows RPC: The Backbone of Remote Operations

RPC, short for Remote Procedure Call, is the backbone for cross‑machine communication in Windows. It lets applications call functions on distant servers as if they were local, using a simple request‑reply pattern. The core components are RpcSs (the RPC Service), RpcEptMapper (the endpoint mapper on port 135), and VDS (Virtual Disk Service) for disk‑level tasks. These services run over TCP/IP or named pipes and listen on dynamic ports 49152‑65535.

For more detailed information, refer to the Windows networking guide: https://learn.microsoft.com/en-us/windows-server/networking/

Why RPC Matters

Unified interface: System services expose their capabilities through RPC, so WMI, AD replication, SQL Server, and printer sharing all feel like first‑class citizens.
Fail‑fast detection: When RPC breaks, Windows throws the familiar RPC server unavailable error, halting any remote operation.
Performance: RPC uses lightweight messages, keeping network traffic minimal.

Common Causes of the Error

Cause	Typical Symptom	Fix Overview
Stopped services	Event Viewer logs RPC server unavailable	Restart RpcSs and RpcEptMapper
Firewall blocks	No listening process on port 135	Add inbound rules for TCP 135 and 49152‑65535
DNS or network issues	`ping` or `nslookup` fails	Verify host resolution and network routes
Registry corruption	SFC reports missing RPC keys	Run `sfc /scannow` or repair registry
Third‑party interference	Antivirus blocks VeeamVSSSupport	Exclude RPC ports from security software

For troubleshooting details, see the Microsoft support article on RPC server unavailable: https://learn.microsoft.com/en-us/troubleshoot/windows-client/networking/rpc-errors-troubleshooting.

Scenario‑Specific Troubleshooting

1. Windows Services (WMI, AD, SQL Server)

Run sc query RpcSs and sc query RpcEptMapper. Set to Automatic if stopped.
Verify firewall rules allow inbound TCP 135 and dynamic ports.
Test connectivity with rpcping <server>.
Inspect Event Viewer for RPC server is unavailable entries.
Restart the services: net stop RpcSs && net start RpcSs.

2. Veeam Backup & Replication

Confirm Veeam's firewall exclusions for RPC.
Restart the VeeamVSSSupport service.
Ensure the system permits 49152‑65535.
Run Veeam diagnostics and review logs for RPC errors.

3. Disk Management / VDS

Ensure VDS is running: sc query VDS.
Allow inbound TCP 135 and dynamic ports for VDS.
Test remote disk management; if the error persists, temporarily disable the firewall to isolate the cause.
Re‑enable firewall and create a VDS exception.

4. Printer Installation

Verify RpcSs is active.
Restart the Print Spooler.
Add inbound rules for printer sharing (TCP 445, 139, 137, 138).
Check Event Viewer for RPC‑related messages.

Quick Fix Checklist

RpcSs and RpcEptMapper are Running and set to Automatic.
VDS is running for disk tasks.
Firewall allows TCP 135 and 49152‑65535.
Network connectivity works (ping, nslookup).
Run sfc /scannow for file integrity.
Restart affected services (e.g., Print Spooler, VeeamVSSSupport).
Review Event Viewer for RPC errors.
Ensure third‑party security tools do not block RPC.

By following these steps, a silent RPC server unavailable error turns into a clear, actionable path forward. Ready to dive into the next layer of Windows networking?

FAQ

Q: What does "RPC server unavailable" mean? A: It indicates that the RPC service (RpcSs) is not reachable, often due to a stopped service, firewall block, or DNS issue.

Q: How can I check if RpcSs is running? A: Run sc query RpcSs or use Services.msc to verify the status.

Q: Can a firewall cause the RPC error? A: Yes, blocking TCP port 135 or the dynamic port range 49152‑65535 will prevent RPC communication.

Q: What is the default port for RpcEptMapper? A: The endpoint mapper listens on TCP port 135.

Q: Does Windows automatically repair RPC after a reboot? A: Typically, yes, but if the service is disabled or a firewall rule is missing, the error will persist.

You’ve all felt that jarring pause when a critical task stalls because the RPC server is unavailable. It’s like a traffic light stuck on red, stopping backups, printers, and remote management.

The Remote Procedure Call (RPC) service is a core Windows networking protocol that lets programs on one computer call functions on a server or another computer. It’s essential because many Windows services—including file sharing, printer sharing, and Veeam backups—depend on RPC to communicate and coordinate tasks.

In this section, we break down the most common culprits and give you quick wins.

Stopped or Disabled Services

RpcSs and RpcEptMapper must run automatically.
Symptoms: Event Viewer shows "RPC server unavailable" in System logs.
Quick check: sc query RpcSs → if stopped, net start RpcSs.
Log excerpt: "The RPC server is unavailable. Code: 1722."

Firewall or Security Software

TCP 135 and dynamic ports 49152‑65535 must be open.
Symptoms: netstat -ano | findstr 135 shows no listener.
Quick check: netsh advfirewall firewall show rule name=all | findstr 135.
Log excerpt: "Firewall blocked RPC endpoint mapper."

DNS or Network Connectivity

Incorrect host resolution or VPN misconfig causes timeouts.
Symptoms: ping or nslookup fails, traceroute shows no route.
Quick check: nslookup <server>; if it fails, verify DNS records.
Log excerpt: "Unable to resolve RPC server name."

Registry Corruption

Missing keys for RPC or VDS can silently fail.
Symptoms: sfc /scannow reports errors.
Quick check: regedit → HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RpcSs; ensure Start = 2.
Log excerpt: "Registry key not found for RPC service."

Permission or Authentication Failures

Insufficient rights or SSPI issues break RPC.
Symptoms: Event Viewer shows "Access denied" or "SSPI error."
Quick check: Run gpupdate /force and confirm user is in Administrators.
Log excerpt: "SSPI authentication failed for RPC call."

Third‑Party Interference

Antivirus or backup software may block RPC.
Symptoms: Veeam logs show "RPC error: The RPC server is unavailable. Code: 1722."
Quick check: Temporarily disable the antivirus; if the error disappears, add an exception.
Log excerpt: "VeeamVSSSupport service blocked by security software."

Quick Diagnostic Checklist

Verify RpcSs and RpcEptMapper are running.
Ensure firewall allows TCP 135 and 49152‑65535.
Test DNS resolution with nslookup.
Run sfc /scannow for system integrity.
Restart affected services like Print Spooler or VeeamVSSSupport.
Review Event Viewer for RPC error entries.
Confirm third‑party software isn’t blocking ports.

We’ll dive deeper into each scenario in the next section, showing you step‑by‑step fixes for Windows, Veeam, disk management, and printer installation.

We’ve all stared at a blinking red icon and wondered: why is RPC dead? The answer lies in two silent guardians—RpcSs and RpcEptMapper—watching over every remote call. When they falter, WMI, AD, or SQL throw the same red‑flag error. Let’s bring them back to life.

Verify Core RPC Services

Open an elevated Command Prompt.
Run sc query RpcSs and sc query RpcEptMapper.
If either shows STOPPED, type net start RpcSs and net start RpcEptMapper. If the status is RUNNING, leave it.
Remember: these services must be Automatic. Change with sc config RpcSs start= auto if needed.

Configure the Firewall

In Windows Defender Firewall, create inbound rules for TCP port 135 and the dynamic range 49152‑65535.
Use the wizard: New Rule → Port → TCP → Specific local ports.
Name the rule RPC‑Allowed and set it to Allow the connection for Domain, Private, and Public.
Verify the rule is enabled by checking the State column.

Test Connectivity with rpcping

From the command line, type rpcping <server_name>.
A successful reply looks like RPC ping OK.
If it times out, check that the server name resolves: nslookup <server_name>.

Interpret Event Viewer Logs

Open Event Viewer → Windows Logs → System.
Filter for Event ID 1014 or 1015.
A message such as “RPC server is unavailable” confirms the service issue.
Note the Source column; if it lists RpcSs, the service is the culprit.

Quick Troubleshooting Checklist

✔️	Action
✔️	Confirm RpcSs and RpcEptMapper are running.
✔️	Firewall rules for TCP 135 & 49152‑65535 are enabled.
✔️	`rpcping` returns OK.
✔️	Event Viewer shows no 1014/1015 errors.
✔️	System files are intact (`sfc /scannow`).
✔️	No third‑party antivirus blocking RPC ports.

If a service refuses to start, look for error codes in the Event ID 7026 log. Often it’s a missing dependency like DCOM Server Process Launcher. Restart that service first.

We’re almost ready to dive into how these steps differ for Veeam, Disk Management, and printers. Stay tuned for the next section, where we’ll tailor the same principles to those specific environments.

What is Windows RPC and why it matters

RPC, or Remote Procedure Call, is a core Windows networking service that allows a program on one computer to execute code on another computer. It is used by many system components—including the Windows Update service, file sharing, and backup software—to coordinate tasks across the network. When RPC is unavailable, services that rely on it fail, producing errors such as RPC server unavailable.

Common causes of the RPC server unavailable error

Disabled or stopped RPC services (e.g., Remote Procedure Call (RPC) or RPC Endpoint Mapper)
Firewall rules blocking RPC ports (TCP 135 and the dynamic range 49152‑65535)
DNS resolution problems or incorrect host names
Network connectivity issues, such as intermittent link loss or incorrect routing
Misconfigured dynamic port range on the client or server

Step‑by‑step fixes for each scenario

1. Enabling RPC services

Press Win + R, type services.msc, and press Enter.
Locate Remote Procedure Call (RPC) and Remote Procedure Call (RPC) Locator.
Right‑click each service, choose Properties, set Startup type to Automatic, and click Start if the status is stopped.
Verify both services are running.

2. Configuring firewall rules

Open Windows Defender Firewall with Advanced Security.
Create inbound rules for TCP 135 and the dynamic RPC range 49152‑65535.
Ensure the rules allow traffic from the relevant subnets or host names.
If a third‑party firewall is in place, whitelist these ports or add an exception for the Veeam service.

3. Verifying network connectivity

Test DNS resolution with nslookup <hostname>.
Ping the target host to confirm reachability.
Use tracert <hostname> to ensure the path is correct.
If using VPN or proxy, confirm that the connection does not block RPC ports.

Veeam‑specific troubleshooting

Check Firewall Exclusions

Veeam automatically creates rules for TCP 135 and the dynamic RPC range 49152‑65535. If a third‑party firewall overrides these, the VeeamVSSSupport service can’t talk to the VDS. Open Windows Defender Firewall, locate Veeam Backup & Replication, and ensure Allow inbound for those ports. On a corporate network, ask your security team to whitelist the same.

Restart VeeamVSSSupport

The Veeam VSS support service can lock up during large snapshots. Stop it, wait a few seconds, then start it again:

Open Services.msc.
Find VeeamVSSSupport.
Click Stop, then Start.
Verify the status is Running. If it stays Stopped, check Event Viewer for RPC function call failed entries.

Validate Dynamic Port Range

Sometimes Windows is set to a narrow port range that Veeam can’t use. Run:

1netsh int ipv4 show dynamicport tcp

The output should read Start = 49152, Number = 16384. If the start number is higher than 49152 or the number is less than 16384, adjust it with:

1netsh int ipv4 set dynamicport tcp start=49152 num=16384

Run Veeam Diagnostics

From the Veeam console, go to Help → Collect Logs. This bundles Veeam logs, Event Viewer entries, and system data. Search the logs for RPC error or 1722. A typical line looks like:

1RPC function call failed. Function name: IsSnapshotInProgress. RPC error: The RPC server is unavailable. Code: 1722.

If you see Code: 1722 consistently, the RPC channel is broken.

Check Veeam KB and Community Posts

KB1174 explains the RPC function call failed pattern and recommends restarting VeeamVSSSupport.
Forum post RPC error: The RPC server is unavailable (Veeam R&D) shares a script that parses the log and extracts the failing IP.
A community member noted that disabling Windows Remote Management temporarily resolved the issue on a hyper‑converged node.

Log Parsing Example (Textual)

Instead of a script, we can use PowerShell’s Select‑String:

Get‑Content "C:\ProgramData\Veeam\SupportCenter\Logs*.log" | Select‑String "RPC error"
Review the output lines for the IP and error code.
This quick scan pinpoints the host that refuses RPC.

Actionable Checklist

Confirm VeeamVSSSupport is Running.
Verify firewall rules for TCP 135 and 49152‑65535.
Validate dynamic port range with netsh.
Run Collect Logs and search for RPC error.
Cross‑check Event Viewer for RPC server is unavailable.
Apply the KB1174 fix if the error persists.

We’ve seen teams recover a 3‑hour backup window in under 30 minutes by following these steps. Ready to get your backups back on track? Let’s dive in.

Windows Networking Guide
Microsoft Support – RPC error 1722

Fixing RPC Server Unavailable Errors in Windows Networks