Moonergfp opened a new issue, #901: URL: https://github.com/apache/mina-sshd/issues/901
### Version 2.15.0 ### Bug description My use case is remote port forwarding . Both the client and server are implemented with Apache MINA SSHD. And multiple custom global requests are sent before sending the tcpip-forward request. I have discovered several abnormal issues: After the SSH connection is established, the client sends 5 consecutive keepalive heartbeats to the server. However, no global keepalive packets are captured in the server's debug logs. Occasionally, the server receives 1 or 2 keepalive packets and then stops receiving any more randomly. This results in the SSH connection dropping repeatedly. Multiple sessions created by the same client almost disconnect one after another within the same minute, and then all drop together again after a few minutes. I implemented logic on the client side to re-establish a new connection once the session object is closed. Strangely, every reconnection succeeds on the first attempt, and none of the custom global requests get lost. The only faulty behavior occurs with the keepalive mechanism on the server side. The server initiates a TCP connection to a random forwarded port every 20 seconds. If no keepalive response is received and the session remains open at this time, the client often fails to receive the incoming TCP connection notification. ### Below is the client-side code <img width="1301" height="144" alt="Image" src="https://github.com/user-attachments/assets/5c0bbe8d-80a7-438a-ae26-b288aaa5932f"; /> while(true){ try (ClientSession session = SshUtils.getClientSession( sameSshClientObj)) { //send global request1 //send global request2 //send global request3 try (ExplicitPortForwardingTracker portForwardingTracker = createPortForwardingTracker(session)) { while(!session.isClosed()){ //sleep x seconds } } } } ### Below is the server-side code that initiates a connection to a random forwarded port every 20 seconds. try (Socket testSocket = new Socket(host, port)) { } Then I frequently observe debug logs showing heartbeat timeouts on the client side, alongside idle timeout logs on the server side. ### Actual behavior Frequent heartbeat timeouts on the client side, while the server fails to receive heartbeat requests. ### Expected behavior The server can receive heartbeats normally and send corresponding responses. ### Relevant log output ```Shell ### Below is the client-side log 2026-06-16T18:04:23.410+0800 DEBUG - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: signalAuthFailure(ClientSessionImpl[classic-tx-sh anghai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) type=SshException, signal led=false, first=false: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.411+0800 WARN - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: exceptionCaught(ClientSessionImpl[classic-tx-shang hai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822])[state=Opened] SshException: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.412+0800 DEBUG - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] o.a.s.c.session.helpers.SessionTimeoutListener []: sessionException(ClientSessionImpl[classic-tx-shang hai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) SshException: Got 5 heartbea t requests without reply 2026-06-16T18:04:23.412+0800 WARN - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] c.s.p.t.d.u.SshClientCreator$DialerClientConnectionService []: sendHeartBeat(ClientSessionImpl[classic- tx-shanghai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) failed (SshException ) to send heartbeat #6 [email protected]: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.419+0800 DEBUG - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: signalAuthFailure(ClientSessionImpl[classic-tx-sh anghai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) type=SshException, signal led=false, first=false: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.419+0800 WARN - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: exceptionCaught(ClientSessionImpl[classic-tx-shang hai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822])[state=Opened] SshException: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.419+0800 DEBUG - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] o.a.s.c.session.helpers.SessionTimeoutListener []: sessionException(ClientSessionImpl[classic-tx-shang hai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) SshException: Got 5 heartbea t requests without reply 2026-06-16T18:04:23.421+0800 WARN - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] c.s.p.t.d.u.SshClientCreator$DialerClientConnectionService []: sendHeartBeat(ClientSessionImpl[classic- tx-shanghai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) failed (SshException ) to send heartbeat #6 [email protected]: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.681+0800 DEBUG - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: signalAuthFailure(ClientSessionImpl[classic-tx-sh anghai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822]) type=SshException, signal led=false, first=false: Got 5 heartbeat requests without reply 2026-06-16T18:04:23.681+0800 WARN - sshd-LoadBalancedSshClient[624b523]-timer-thread-1 [] org.apache.sshd.client.session.ClientSessionImpl []: exceptionCaught(ClientSessionImpl[classic-tx-shang hai-01.fuchuang.deployx:hybrid01.fuchuang-new.deployx.8...@sfn-tx-shanghai-01.saas.deployx/212.129.159.242:8822])[state=Opened] SshException: Got 5 heartbeat requests without reply ### Below is the server-side log 2026-06-16T18:01:57.990+0800 INFO - sshd-SshServer[2a8a3ada](port=8822)-timer-thread-1 [] c.s.p.t.s.sshd.components.StationServerSessionImpl []: Disconnecting(StationServerSessionImpl[classic-tx-shanghai-01.fuchuang.deploy.sensorsdata.cloud:hybrid01.fuchuang-new.deploy.sensorsdata.cloud.8329@/223.76.236.226:55728]): SSH2_DISCONNECT_PROTOCOL_ERROR - Detected IdleTimeout after 40266/40000 ms. 2026-06-16T18:05:07.990+0800 INFO - sshd-SshServer[2a8a3ada](port=8822)-timer-thread-1 [] c.s.p.t.s.sshd.components.StationServerSessionImpl []: Disconnecting(StationServerSessionImpl[classic-tx-shanghai-01.fuchuang.deploy.sensorsdata.cloud:hybrid01.fuchuang-new.deploy.sensorsdata.cloud.8329@/113.57.11.210:47586]): SSH2_DISCONNECT_PROTOCOL_ERROR - Detected IdleTimeout after 40488/40000 ms. 2026-06-16T18:18:07.990+0800 INFO - sshd-SshServer[2a8a3ada](port=8822)-timer-thread-1 [] c.s.p.t.s.sshd.components.StationServerSessionImpl []: Disconnecting(StationServerSessionImpl[classic-tx-shanghai-01.fuchuang.deploy.sensorsdata.cloud:hybrid01.fuchuang-new.deploy.sensorsdata.cloud.8329@/113.57.11.210:39636]): SSH2_DISCONNECT_PROTOCOL_ERROR - Detected IdleTimeout after 40263/40000 ms. 2026-06-16T18:27:27.990+0800 INFO - sshd-SshServer[2a8a3ada](port=8822)-timer-thread-1 [] c.s.p.t.s.sshd.components.StationServerSessionImpl []: Disconnecting(StationServerSessionImpl[classic-tx-shanghai-01.fuchuang.deploy.sensorsdata.cloud:hybrid01.fuchuang-new.deploy.sensorsdata.cloud.8329@/58.48.59.226:46870]): SSH2_DISCONNECT_PROTOCOL_ERROR - Detected IdleTimeout after 40066/40000 ms. 2026-06-16T18:51:08.990+0800 INFO - sshd-SshServer[2a8a3ada](port=8822)-timer-thread-1 [] c.s.p.t.s.sshd.components.StationServerSessionImpl []: Disconnecting(StationServerSessionImpl[classic-tx-shanghai-01.fuchuang.deploy.sensorsdata.cloud:hybrid01.fuchuang-new.deploy.sensorsdata.cloud.8329@/58.48.59.226:55670]): SSH2_DISCONNECT_PROTOCOL_ERROR - Detected IdleTimeout after 40655/40000 ms. ``` ### Other information _No response_ -- This is an automated message from the Apache Git Service. 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