Error 1753 (also shown as 0x6D9, 0x800706D9, or EPT_S_NOT_REGISTERED) means an RPC client could not find the interface it needed through the target computer’s Endpoint Mapper. It does not usually mean that the machine has literally run out of endpoints. The correct repair depends on whether the failure occurred during Active Directory replication, a domain join, WSL, or another RPC-dependent application.
RPC normally works in two stages: the client contacts TCP 135, asks the Endpoint Mapper for the service’s dynamic port, and then connects to that port. A service that has not started, failed to register, stopped, is being reached through the wrong DNS address, or is blocked on its dynamic port can all produce the same message.
Start with the operation that failed
| Where the message appears | First place to investigate |
|---|---|
| Domain join | %SystemRoot%debugNETSETUP.LOG, the selected domain controller, DNS, TCP 135 and dynamic RPC |
| Active Directory replication | Source and destination DC health, AD DS registration, _msdcs DNS and intersite firewalls |
| WSL, Sandbox or another Windows feature | The named Windows service, Group Policy and the feature’s event log |
| Third-party software | The application service, its endpoint registration and host-security logs |
Do not apply a domain-controller repair procedure to a workstation feature or a third-party service. Record the decimal and hexadecimal code, client, target host, timestamp, exact operation and whether other RPC operations succeed.
1. Verify that the client is contacting the intended host
For a domain join, open %SystemRoot%debugNETSETUP.LOG and search for NetpJoinDomain, NetpGetComputerObjectDn and 0x6d9. The log identifies the domain controller selected by the client. Test that controller rather than an arbitrary DC.
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For replication, record the source and destination DC, the source’s fully qualified name, its NTDS Settings object GUID and the corresponding _msdcs record. Check both ordinary host records and AD locator records:
nslookup dc01.example.com
nslookup -type=SRV _ldap._tcp.dc._msdcs.example.com
nslookup -type=CNAME <source-DC-NTDS-GUID>._msdcs.example.comResolve-DnsName dc01.example.com
Resolve-DnsName -Type SRV _ldap._tcp.dc._msdcs.example.com
Resolve-DnsName -Type CNAME <source-DC-NTDS-GUID>._msdcs.example.comLook for stale A or AAAA records, an obsolete GUID CNAME, an incorrect DNS suffix, hosts-file or LMHOSTS overrides, WINS entries, split-DNS answers and VPN routes that return an unreachable address. A name resolving successfully is not enough; it must resolve to the correct server. Do not replace AD DNS with public DNS. Domain members and domain controllers need the organization’s AD-integrated records.
2. Test the complete RPC path
Test the Endpoint Mapper entry point from the affected computer:
Test-NetConnection dc01.example.com -Port 135If TCP 135 fails, investigate routing, VPNs, ACLs, host firewalls, security software and whether the target is listening. If it succeeds, that proves only that the mapper is reachable. The client may still be unable to reach the dynamic service port or the requested interface may not be registered.
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On current Windows domain operations, the normal dynamic RPC range is TCP 49152–65535. Custom or restricted configurations can differ. A network firewall that permits 135 but blocks the assigned high port produces a misleading “endpoint mapper” failure. Compare the 135 test with the actual join or replication operation, and inspect firewall and security-product logs. Microsoft’s PortQry guidance can help query Endpoint Mapper responses and distinguish DNS, RPC and firewall faults: PortQry RPC troubleshooting.
3. Check service registration and startup
On the relevant server, inspect service state and recent failures:
Get-Service RpcSs, RpcEptMapper, NTDS, Dnscache
Get-Service Netlogon, LanmanServer, Kdc- RPC Endpoint Mapper provides endpoint discovery.
- Active Directory Domain Services (NTDS) registers the AD interfaces needed for replication and directory operations.
- Netlogon and related services support domain-controller functions but are not substitutes for the mapper.
A DC that has just rebooted may accept TCP connections before AD DS has completed initialization. A service can also start, register an endpoint and then terminate, making the endpoint disappear. Review Event Viewer → Applications and Services Logs → Directory Service, plus System, DNS Server, DFS Replication where applicable, and security-product logs.
Do not blindly restart RPC services on a production DC. RPC is foundational and restarting it can disrupt dependent services. Confirm state and dependencies, correct the startup failure, and reboot only during an approved maintenance window when the evidence or Microsoft guidance supports it.
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4. Active Directory replication branch
For dcdiag, Active Directory Sites and Services “Replicate Now,” topology checks or repeated 1753 (0x6D9) entries in repadmin, Microsoft describes a particularly important distinction: the destination may have reached the source’s Endpoint Mapper on TCP 135, but the mapper cannot locate the AD replication interface. Prioritize an incompletely started or failed NTDS service, failed endpoint registration, a source DC that stopped unexpectedly, wrong-server DNS, static-port mistakes and cross-site filtering.
dcdiag /v
dcdiag /test:dns /v
dcdiag /test:connectivity /v
repadmin /replsummary
repadmin /showrepl *
net share
nltest /dsgetdc:example.com
nltest /sc_verify:example.comConfirm that the source DC is fully booted, that its AD-related services are healthy and that its NTDS GUID CNAME resolves to that DC. Error 1753 is not, by itself, proof of a password mismatch or Kerberos decryption failure; those are different troubleshooting paths. See Microsoft’s replication guidance and the current replication article.
5. Domain-join branch
Use the DC named in NETSETUP.LOG as the test target. Verify its host and SRV records, test TCP 135, then verify that firewalls permit the applicable dynamic RPC range. Check the DC’s health and service state before retrying the join. If a computer account was partially created, follow your organization’s normal account-cleanup procedure rather than repeatedly creating objects.
Microsoft’s domain-join guidance covers the TCP 135-plus-dynamic-port sequence, DNS, security software, port exhaustion and DC health: domain-join error 0x6D9 guidance.
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6. Firewall, security and network checks
- Check the DC’s Windows Defender Firewall profile and inbound RPC/domain-controller rule groups.
- Check intersite firewalls, VPN or SD-WAN policies, NAT and return traffic.
- Determine whether IPv6 is preferred but unroutable.
- Check endpoint-security and RPC-inspection logs for blocked registration or high-port traffic.
- Permit only the documented traffic required by your topology; do not permanently open every high port or disable the firewall.
7. Restricted ranges and port exhaustion
Inspect the configured ranges before changing them:
netstat -ano
netsh int ipv4 show dynamicport tcp
netsh int ipv6 show dynamicport tcpGet-NetTCPConnection | Group-Object StateEstablish whether the range is unusually narrow, whether firewall rules match it, whether a security product consumes ports, or whether the server is under abnormal load. Static RPC settings require matching service and firewall configuration. Microsoft documents a case where static AD DS configuration interacts incorrectly with Endpoint Mapper responses: static AD DS RPC-port guidance. Registry edits and static-port changes are advanced remediation, not a first step.
8. WSL, Sandbox or local Windows feature branch
If the message appears while starting WSL 2 or another local feature, identify the event provider and named dependency first. Microsoft’s WSL troubleshooting documentation associates this message with disabling Internet Connection Sharing (SharedAccess) or disabling ICS through Group Policy, which prevents HNS network creation: WSL troubleshooting. Restore the documented dependency under your policy; AD replication commands will not repair this local condition.
What not to do
- Do not assume the mapper ran out of ports. The requested interface is usually unregistered, unavailable or reached through the wrong path.
- Do not open only TCP 135. It is the discovery entry point, not necessarily the service connection.
- Do not restart RPC as a universal fix. It cannot correct DNS, a dead service or blocked dynamic traffic.
- Do not flush DNS and reboot blindly. That may hide a startup race without repairing authoritative records or firewall policy.
- Do not disable security controls permanently. Use logs and a narrowly scoped, approved test.
Verify recovery
- Repeat the original join, replication, feature start or application operation.
- For AD, run
repadmin /replsummary,repadmin /showrepl *anddcdiag /test:replications. - Confirm the intended DC was contacted and that the relevant logs show success.
- Check for new Directory Service, System, DNS or security events.
- Remove temporary firewall exceptions and restore any diagnostic settings.
Frequently Asked Questions
Is error 1753 the same as “RPC server unavailable” (1722)?
No. They are related RPC errors, but 1753 commonly means the mapper was reached and could not locate the requested interface, while 1722 indicates that the RPC server could not be reached or contacted successfully.
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Will opening TCP 135 fix the problem?
Only if TCP 135 itself was blocked and the service is otherwise healthy. Domain operations commonly require a subsequent dynamic RPC connection, normally in TCP 49152–65535 on modern Windows.
Should I restart the RPC Endpoint Mapper?
Not as a default remedy. First verify DNS, service startup, AD DS health, firewall rules and dynamic-port access; restarting a foundational RPC service can disrupt production workloads.
Why can a domain join fail when DNS appears to work?
The hostname may resolve to the wrong address, the selected DC may be unhealthy, TCP 135 may be reachable while dynamic RPC is blocked, or security software may interrupt the second stage of the exchange.
When should I escalate?
Escalate when multiple DCs, sites or replication partners are affected, static RPC architecture is involved, a DC cannot complete startup, or firewall and security logs show unexplained RPC filtering. A local WSL dependency or one incorrect firewall rule usually does not require an AD specialist.
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