Traffic won't pass through VPN when connected to local network

Question

I use the Azure VPN client on my Mac to connect to an Azure virtual network in order to access my employer's DBs. I can establish the VPN connection, but no traffic passes through it when I attempt to connect to the DB server. This only occurs when I'm connected to my local wifi network. Everything works as it should when I leave my local network and use my phone's 4G service via its wifi hotspot function.

When I attempt to connect to the DB server from Azure Data Studio, Azure VPN client shows zero bytes in. Stack trace from Azure Data Studio:

Microsoft.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 35 - An internal exception was caught)
---> System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (00000005, 0xFFFDFFFF): nodename nor servname provided, or not known
at System.Net.Dns.GetHostEntryOrAddressesCore(String hostName, Boolean justAddresses, AddressFamily addressFamily, ValueStopwatch stopwatch)
at System.Net.Dns.GetHostAddresses(String hostNameOrAddress, AddressFamily family)
at Microsoft.Data.SqlClient.SNI.SNITCPHandle.Connect(String serverName, Int32 port, TimeSpan timeout, Boolean isInfiniteTimeout, SqlConnectionIPAddressPreference ipPreference, String cachedFQDN, SQLDNSInfo& pendingDNSInfo)
at Microsoft.Data.SqlClient.SNI.SNITCPHandle..ctor(String serverName, Int32 port, Int64 timerExpire, Boolean parallel, SqlConnectionIPAddressPreference ipPreference, String cachedFQDN, SQLDNSInfo& pendingDNSInfo)
at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
at Microsoft.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, Boolean withFailover, SqlAuthenticationMethod authType)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, Boolean withFailover)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString connectionOptions, SqlCredential credential, TimeoutTimer timeout)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(TimeoutTimer timeout, SqlConnectionString connectionOptions, SqlCredential credential, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, Boolean applyTransientFaultHandling, String accessToken, DbConnectionPool pool)
at Microsoft.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
at Microsoft.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions)
at Microsoft.Data.ProviderBase.DbConnectionFactory.<>c__DisplayClass48_0.<CreateReplaceConnectionContinuation>b__0(Task1 _) at System.Threading.Tasks.ContinuationResultTaskFromResultTask2.InnerInvoke()
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location ---
at Microsoft.SqlTools.ServiceLayer.Connection.ReliableConnection.ReliableSqlConnection.<>c__DisplayClass30_0.<<OpenAsync>b__0>d.MoveNext() in D:\a_work\1\s\src\Microsoft.SqlTools.ManagedBatchParser\ReliableConnection\ReliableSqlConnection.cs:line 312
--- End of stack trace from previous location ---
at Microsoft.SqlTools.ServiceLayer.Connection.ConnectionService.TryOpenConnection(ConnectionInfo connectionInfo, ConnectParams connectionParams) in D:\a_work\1\s\src\Microsoft.SqlTools.ServiceLayer\Connection\ConnectionService.cs:line 637
ClientConnectionId:00000000-0000-0000-0000-000000000000

When I attempt to connect to the DB server using the mssql extension for VS Code I get a similar exception:

Error connecting to server "sqldb.12345abcde.database.windows.net". Details: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 35 - An internal exception was caught)

Any advice would be much appreciated.

Answer 1

I've solved this problem by overriding the Starlink router's DNS settings on my Mac. I've added Cloudflare's servers (1.1.1.1 and 1.0.0.1) at System Preferences > Network > Advanced > DNS.