SQL Server Error 19456

Error number

19456

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 with Always On availability groups on a Windows Server Failover Cluster

Category

High Availability

Last reviewed

24 October 2026

What it means

Error 19456 means the availability group has a listener, but the server named in the message has no public cluster network in the subnet of any listener IP address, so the listener could not move to that server.

A listener is a cluster network name with one IP address per subnet it serves. Whichever server hosts the primary replica must be able to bring one of those IP addresses online, and the cluster only places an IP address on a network that covers its subnet and allows client access (a public cluster network). When SQL Server checks a server that might own the listener (typically while you add or join a replica, add a listener, or fail over) and none of the listener IP addresses fits any public network on it, it stops with 19456 instead of leaving the listener unreachable.

The name in quotes is the server that failed the check, not the server you are connected to. Compare the subnets of the listener IP addresses with the networks that server has in the cluster: in almost every case it sits in a subnet the listener does not cover yet (a new data centre, an Azure region, a DR site), or its network in that subnet is set for cluster traffic only.

Common causes

• A multi-subnet availability group: a replica in a new subnet was added or joined, but the listener has IP addresses only for the other subnets.
• The cluster network in that server's subnet is not public: in Failover Cluster Manager it does not allow clients to connect through it (cluster communication only), or cluster use is disabled.
• The listener IP address was entered with the wrong subnet mask, so it does not fall inside any network the server has.
• The server has a new or reconfigured network adapter whose subnet the cluster has not mapped to a cluster network yet.

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 ag.name AS ag_name, l.dns_name, l.port, ip.ip_address, ip.ip_subnet_mask,
       ip.network_subnet_ip, ip.network_subnet_prefix_length, ip.is_dhcp, ip.state_desc
FROM sys.availability_group_listeners AS l
JOIN sys.availability_groups AS ag ON ag.group_id = l.group_id
JOIN sys.availability_group_listener_ip_addresses AS ip ON ip.listener_id = l.listener_id;

SELECT member_name, network_subnet_ip, network_subnet_ipv4_mask,
       network_subnet_prefix_length, is_public, is_ipv4
FROM sys.dm_hadr_cluster_networks
ORDER BY member_name, network_subnet_ip;

SELECT ag.name AS ag_name, ar.replica_server_name, ar.endpoint_url,
       ar.availability_mode_desc, ar.failover_mode_desc
FROM sys.availability_replicas AS ar
JOIN sys.availability_groups AS ag ON ag.group_id = ar.group_id
ORDER BY ag.name, ar.replica_server_name;

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.

ALTER AVAILABILITY GROUP SalesAg
MODIFY LISTENER N'SalesAgListener' (ADD IP ((N'10.20.0.50', N'255.255.255.0')));

# PowerShell on a cluster node (Role 3 = cluster and client)
(Get-ClusterNetwork -Name 'Cluster Network 2').Role = 3

Examples

Joining a replica in a subnet the listener does not cover

Shown as documented by Microsoft (message text); not reproduced here because it needs a failover cluster and an availability group. Microsoft documents no state for 19456 and the query window form was not observed, so no header is shown. The server and group names are examples.

-- On SQL03, a new secondary replica in subnet 10.20.0.0/24;
-- the listener SalesAgListener only has 10.10.0.50 (subnet 10.10.0.0/24)
ALTER AVAILABILITY GROUP SalesAg JOIN;

None of the IP addresses configured for the availability group listener can be hosted by the server 'SQL03'. Either configure a public cluster network on which one of the specified IP addresses can be hosted, or add another listener IP address which can be hosted on a public cluster network for this server.

How to prevent it

Treat a new subnet as part of the availability group design: before adding a replica in another subnet or site, reserve a listener IP address there, confirm the cluster network for it allows client access, and add the address to the listener first. Keep the listener IP list and the replica list in the same build script so they stay in step.

Common questions

Learn more on CodeWithSQL

• RDS Multi-AZ and read replicas

Official documentation

• Configure a listener for an Always On availability group
• sys.availability_group_listener_ip_addresses (Transact-SQL)
• sys.dm_hadr_cluster_networks (Transact-SQL)
• Database engine events and errors (19000 to 20999)

Last technically reviewed 24 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.