SQL Server Error 1418

Error number

1418

Severity

16 (user-correctable error)

State

Not documented by Microsoft (not reproduced here)

Product

Microsoft SQL Server Database Engine

Versions

SQL Server 2016 to 2025 (database mirroring endpoints), Azure SQL Managed Instance

Category

High Availability

Last reviewed

23 October 2026

What it means

Error 1418 means SQL Server could not reach the database mirroring endpoint at the TCP address you gave, so the mirroring partnership was not set up.

Database mirroring partners (and availability group replicas) talk to each other through a dedicated endpoint, by default on TCP port 5022, using addresses of the form TCP://host:port. Error 1418 is typically raised by ALTER DATABASE ... SET PARTNER when the server instance cannot establish that connection. The address in quotes is exactly what was tried: check the host name, the port and that something is listening there.

Microsoft points out that the message is broad. The endpoint may be unreachable because of the network or a firewall, but a security problem (for example the partner's service account having no CONNECT permission on the endpoint) can make the other side drop the connection silently, and that looks the same. Corrective action may be needed on both partners, even if you only ran the command on one.

Common causes

• A firewall blocks the endpoint port on the mirror or on the principal (Microsoft notes that Windows blocks ports by default).
• The host name or port in the TCP:// address is wrong, or the name does not resolve to the right server.
• The database mirroring endpoint on one partner is not started, does not exist, or listens on a different port.
• Another process or instance already holds the endpoint port (the error log then shows error 26023).
• The service account of one partner has no login or no CONNECT permission on the other partner's endpoint, or certificate authentication does not match.
• The mirror database is not ready: it was not restored WITH NORECOVERY from a recent full and log backup of the principal.

Diagnose it

Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.

SELECT e.name, e.state_desc, e.role_desc, t.port, t.ip_address,
       e.connection_auth_desc, e.encryption_algorithm_desc
FROM sys.database_mirroring_endpoints AS e
JOIN sys.tcp_endpoints AS t ON t.endpoint_id = e.endpoint_id;

SELECT ep.name AS endpoint_name, pr.name AS grantee, pe.permission_name, pe.state_desc
FROM sys.server_permissions AS pe
JOIN sys.endpoints AS ep ON ep.endpoint_id = pe.major_id
JOIN sys.server_principals AS pr ON pr.principal_id = pe.grantee_principal_id
WHERE pe.class_desc = N'ENDPOINT' AND ep.type = 4;

SELECT servicename, service_account
FROM sys.dm_server_services
WHERE servicename LIKE N'SQL Server (%';

SELECT DB_NAME(database_id) AS database_name, mirroring_state_desc, mirroring_role_desc,
       mirroring_partner_name, mirroring_partner_instance
FROM sys.database_mirroring
WHERE mirroring_guid IS NOT NULL;

EXEC sp_readerrorlog 0, 1, N'26023';
EXEC sp_readerrorlog 0, 1, N'endpoint';

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

# PowerShell on each partner
Resolve-DnsName -Name SQL02.contoso.com
Test-NetConnection -ComputerName SQL02.contoso.com -Port 5022
Get-NetTCPConnection -LocalPort 5022 -State Listen

ALTER ENDPOINT Mirroring STATE = STARTED;

GRANT CONNECT ON ENDPOINT::Mirroring TO [CONTOSO\svc_sql01];

Examples

Setting the partner when the mirror endpoint cannot be reached

Shown as documented by Microsoft (MSSQLSERVER_1418); not reproduced here because it needs two mirroring partners. The state is the commonly reported one. The statement runs on the principal after the mirror database was restored WITH NORECOVERY and SET PARTNER was run on the mirror.

-- On the principal SQL01
ALTER DATABASE SalesDb SET PARTNER = N'TCP://SQL02.contoso.com:5022';

The server network address "TCP://SQL02.contoso.com:5022" can not be reached or does not exist. Check the network address name and that the ports for the local and remote endpoints are operational.

How to prevent it

Script the endpoints, logins, CONNECT grants and firewall rules for every partner, use fully qualified names in partner addresses, and test the port in both directions before setting up the partnership. Keep the endpoint port reserved for SQL Server so no other process takes it.

Database mirroring is deprecated; for new designs, plan Always On availability groups instead, which use the same kind of endpoint and need the same network preparation.

Common questions

Learn more on CodeWithSQL

• SQL Server security: logins, users and permissions

Official documentation

• MSSQLSERVER_1418 (Microsoft Learn)
• Troubleshoot database mirroring configuration
• The database mirroring endpoint

Last technically reviewed 23 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.