matlab-discover-opcua-servers

OPC UA Server Discovery

Discover available OPC UA servers on the network using opcuaserverinfo

When to Use

Finding available OPC UA servers on the local network
Getting the discovery URL or endpoint information for a known server
Querying server security policies and supported authentication types
Troubleshooting empty discovery results (LDS issues, certificate trust)
Setting up prerequisites for OPC UA server discovery

When NOT to Use

Creating OPC UA client connections (use opcua() directly)
Reading, writing, or subscribing to OPC UA node values
Configuring OPC UA connection security (message security, certificates)
Working with non-OPC UA protocols (Modbus, MQTT)
Discovering OPC Classic servers (OPC DA, OPC HDA)

Workflow

1. Check prerequisites

Before calling opcuaserverinfo, ensure:

The OPC UA Local Discovery Service (LDS) is installed and running
The target server is registered with the LDS
The server's certificate is trusted by the LDS certificate store at C:\ProgramData\OPC Foundation\UA\pki\trusted\certs\

Warning: A pki\ folder may also exist under UA\Discovery\ — that is a backward-compatibility fallback from older LDS deployments. The primary store is UA\pki\. Always place certificates in UA\pki\trusted\certs\.

See references/lds-setup-and-troubleshooting.md for paths and setup details.

2. Discover servers

Preferred approach — LDS-based discovery (finds all registered servers):

serverInfo = opcuaserverinfo('localhost');

A single call to opcuaserverinfo with a hostname queries that host's LDS on port 4840. The LDS returns information about ALL servers registered with it. Do not scan IP ranges or iterate over hosts — the LDS aggregates this.

Alternative — direct endpoint discovery (when you know the server URL):

serverInfo = opcuaserverinfo('opc.tcp://myserver:53530/OPCUA/SimulationServer');

Use this when connecting to a specific known server that may not be registered with the LDS, or when the LDS is not available.

3. Inspect results

for k = 1:numel(serverInfo)
    fprintf('Server: %s (port %d)\n', serverInfo(k).Hostname, serverInfo(k).Port);
    fprintf('  Best security: %s / %s\n', ...
        serverInfo(k).BestMessageSecurity, serverInfo(k).BestChannelSecurity);
    fprintf('  Endpoints: %d available\n', numel(serverInfo(k).Endpoints));
end

4. Connect to a discovered server

uaClient = opcua(serverInfo(1));
connect(uaClient);

The opcua() function accepts a ServerInfo object directly — no need to extract hostname and port manually.

Key Functions

Function	Syntax	Purpose
`opcuaserverinfo`	`opcuaserverinfo(hostname)`	Query LDS on a host for all registered servers
`opcuaserverinfo`	`opcuaserverinfo(discoveryUrl)`	Query a specific discovery endpoint URL
`opcua`	`opcua(serverInfoObj)`	Create client from ServerInfo object
`findDescription`	`findDescription(serverInfo, text)`	Filter servers by description text
`findAuthentication`	`findAuthentication(serverInfo, type)`	Filter servers by auth type

There is no opcuaserverinfo(hostname, port) syntax. To specify a port, use the discovery URL form: opcuaserverinfo('opc.tcp://hostname:port').

opc.ua.ServerInfo Properties

Property	Type	Description
`Hostname`	char	Host name of the OPC UA server
`Port`	double	TCP port for connections
`Description`	char	Human-readable server description
`UserTokenTypes`	cell array	Supported auth types (e.g., `{'Anonymous', 'Username', 'Certificate'}`)
`BestMessageSecurity`	enum	Highest message security: `SignAndEncrypt`, `Sign`, or `None`
`BestChannelSecurity`	enum	Highest channel security policy
`Endpoints`	array	Array of `opc.ua.EndpointDescription` objects

Note: opc.ua.ServerInfo has Description, not Name. The Name property belongs to opc.ua.Client, not ServerInfo.

opc.ua.EndpointDescription Properties

Property	Type	Description
`EndpointUrl`	char	Full endpoint URL for connection
`MessageSecurityMode`	enum	Security mode for this endpoint
`ChannelSecurityPolicy`	enum	Channel security policy for this endpoint
`UserAuthTypes`	cell array	Auth types supported on this endpoint

Patterns

Discover all servers via LDS

serverInfo = opcuaserverinfo('localhost');
if isempty(serverInfo)
    disp('No servers found. Check LDS prerequisites.');
else
    disp(serverInfo);
end

Discover a specific server by URL

serverInfo = opcuaserverinfo('opc.tcp://myserver:53530/OPCUA/SimulationServer');
disp(serverInfo);

Filter servers by authentication type

serverInfo = opcuaserverinfo('localhost');
anonServers = findAuthentication(serverInfo, 'Anonymous');
certServers = findAuthentication(serverInfo, 'Certificate');

Pass discovery result to opcua() for connection

serverInfo = opcuaserverinfo('localhost');
uaClient = opcua(serverInfo(1));
connect(uaClient);

Common Mistakes

Mistake	Why It's Wrong	Correct Approach
`opcuaserverinfo(host, port)`	Two-argument syntax does not exist	`opcuaserverinfo('opc.tcp://host:port')`
Scanning subnet IPs in a loop	LDS already aggregates all registered servers	`opcuaserverinfo('localhost')` returns all servers
Using `serverInfo.Name`	Property does not exist on `ServerInfo`	Use `serverInfo.Description`
Using `serverInfo.EndpointUrl`	Property belongs to `opc.ua.Client`, not `ServerInfo`	Use `serverInfo.Endpoints(k).EndpointUrl`
Assuming empty result means LDS is down	Empty result can also mean no servers registered or cert not trusted	First run `sc query UALDS` to confirm LDS status, then check registration and trust
Using `UA\Discovery\pki\` as the cert store	`Discovery\pki\` is a backward-compatibility fallback (only has `trusted\`) — not the primary store	The LDS primary cert store is at `C:\ProgramData\OPC Foundation\UA\pki\` (has both `trusted\` and `rejected\`) — check `rejected\certs\` for untrusted certs, copy to `trusted\certs\` to trust them
Not mentioning LDS prerequisites	Discovery returns empty without proper setup	Always check: LDS running, server registered, certificate trusted

Conventions

Always prefer LDS-based discovery (opcuaserverinfo(hostname)) over direct endpoint queries when finding all servers on a network
Always mention the three LDS prerequisites when discussing discovery setup
Use serverInfo.Description for display — not Name (which doesn't exist)
Pass the ServerInfo object directly to opcua() — don't extract hostname/port manually
When discovery returns empty, do NOT assume the LDS is down — first verify with sc query UALDS, then check server registration, then certificate trust (in that order)