DTLS Full Handshake failure

I’m testing client/server DTLS communication with leshan-server-demo and leshan-client-demo v1.3.0 (californium 2.6.0). Leshan client fails to keep connecting with Leshan server after a period of time due to an error of DTLS Full Handshake initiated by client : FAILED (Received ‘fatal alert/HANDSHAKE_FAILURE’). Leshan server restart is required to allow the client to connect again. Please advise on how to solve this issue.

client log

2021-01-27 07:30:21.143 [RegistrationEngine#0] INFO  o.e.l.c.e.DefaultRegistrationEngine - Trying to update registration to coaps://219.x.x.x:5684 (response timeout 120000ms)...
2021-01-27 07:30:21.143 [RegistrationEngine#0] INFO  o.e.l.c.c.CaliforniumEndpointsManager - Clear DTLS session for server coaps://219.x.x.x:5684
2021-01-27 07:30:21.144 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.l.client.demo.LeshanClientDemo - DTLS Full Handshake initiated by client : STARTED ...
2021-01-27 07:30:21.144 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 1, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:21.144 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:21.147 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 3, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:21.148 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:21.154 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.l.client.demo.LeshanClientDemo - DTLS Full Handshake initiated by client : FAILED (Received 'fatal alert/HANDSHAKE_FAILURE')
2021-01-27 07:30:21.155 [RegistrationEngine#0] INFO  o.e.l.c.e.DefaultRegistrationEngine - Unable to send update request : Received 'fatal alert/HANDSHAKE_FAILURE'
2021-01-27 07:30:21.155 [RegistrationEngine#0] INFO  o.e.l.c.e.DefaultRegistrationEngine - Trying to register to coaps://219.x.x.x:5684 ...
2021-01-27 07:30:21.156 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.l.client.demo.LeshanClientDemo - DTLS Full Handshake initiated by client : STARTED ...
2021-01-27 07:30:21.156 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 1, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:21.156 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:21.160 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 3, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:21.160 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:21.165 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.l.client.demo.LeshanClientDemo - DTLS Full Handshake initiated by client : FAILED (Received 'fatal alert/HANDSHAKE_FAILURE')
2021-01-27 07:30:21.165 [RegistrationEngine#0] INFO  o.e.l.c.e.DefaultRegistrationEngine - Unable to send register request : Received 'fatal alert/HANDSHAKE_FAILURE'
2021-01-27 07:30:21.165 [RegistrationEngine#0] INFO  o.e.l.c.e.DefaultRegistrationEngine - Try to register to coaps://219.x.x.x:5684 again in 600s...
2021-01-27 07:30:31.125 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] INFO  o.e.l.client.demo.LeshanClientDemo - DTLS Full Handshake initiated by server : STARTED ...
2021-01-27 07:30:31.133 [DTLS-Timer-0.0.0.0/0.0.0.0:58070#1] WARN  o.e.c.scandium.dtls.ServerHandshaker - Cannot process handshake message from peer [/219.x.x.x:5684] due to [null]
java.lang.NullPointerException: null
	at org.eclipse.californium.scandium.dtls.CertificateRequest.addCerticiateAuthorities(CertificateRequest.java:421)
	at org.eclipse.californium.scandium.dtls.ServerHandshaker.createCertificateRequest(ServerHandshaker.java:576)
	at org.eclipse.californium.scandium.dtls.ServerHandshaker.receivedClientHello(ServerHandshaker.java:449)
	at org.eclipse.californium.scandium.dtls.ServerHandshaker.doProcessMessage(ServerHandshaker.java:225)
	at org.eclipse.californium.scandium.dtls.Handshaker.processNextHandshakeMessages(Handshaker.java:854)
	at org.eclipse.californium.scandium.dtls.Handshaker.processNextMessages(Handshaker.java:702)
	at org.eclipse.californium.scandium.dtls.Handshaker.processMessage(Handshaker.java:660)
	at org.eclipse.californium.scandium.DTLSConnector.startNewHandshake(DTLSConnector.java:2098)
	at org.eclipse.californium.scandium.DTLSConnector.processClientHello(DTLSConnector.java:1989)
	at org.eclipse.californium.scandium.DTLSConnector.access$1200(DTLSConnector.java:231)
	at org.eclipse.californium.scandium.DTLSConnector$14.run(DTLSConnector.java:1929)
	at org.eclipse.californium.elements.util.SerialExecutor$1.run(SerialExecutor.java:289)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.base/java.lang.Thread.run(Unknown Source)

server log

2021-01-27 07:29:28.137 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#20] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:29:28.141 [CoapServer(main)#4] INFO  o.e.l.server.demo.LeshanServerDemo - Accepted registration from endpoint payphonekioskPg001 at /218.x.x.x:58070
2021-01-27 07:30:31.116 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#21] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 1, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:31.116 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#21] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:31.122 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#16] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 3, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:30:31.122 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#16] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:30:31.138 [qtp1003693033-32] WARN  o.e.l.s.demo.servlet.ClientServlet - Unexpected exception
org.eclipse.leshan.core.request.exception.SendFailedException: Request CON-GET    MID=17697, Token=8C5BA5578EC0D4A7, OptionSet={"Uri-Path":["26241","0"]}, Received 'fatal alert/INTERNAL_ERROR' no payload cannot be sent
        at org.eclipse.leshan.core.californium.CoapSyncRequestObserver.onSendError(CoapSyncRequestObserver.java:106)
        at org.eclipse.californium.core.coap.Message.setSendError(Message.java:1063)
        at org.eclipse.californium.core.coap.Request.setSendError(Request.java:1132)
        at org.eclipse.californium.core.network.CoapEndpoint$SendingCallback.onError(CoapEndpoint.java:1531)
        at org.eclipse.californium.elements.RawData.onError(RawData.java:303)
        at org.eclipse.californium.scandium.DTLSConnector$2.handshakeFailed(DTLSConnector.java:521)
        at org.eclipse.californium.scandium.dtls.Handshaker.handshakeFailed(Handshaker.java:1882)
        at org.eclipse.californium.scandium.DTLSConnector.processAlertRecord(DTLSConnector.java:1732)
        at org.eclipse.californium.scandium.DTLSConnector.processRecord(DTLSConnector.java:1503)
        at org.eclipse.californium.scandium.DTLSConnector$12.run(DTLSConnector.java:1365)
        at org.eclipse.californium.elements.util.SerialExecutor$1.run(SerialExecutor.java:289)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.eclipse.californium.scandium.dtls.HandshakeException: Received 'fatal alert/INTERNAL_ERROR'
        at org.eclipse.californium.scandium.DTLSConnector.processAlertRecord(DTLSConnector.java:1722)
        ... 6 common frames omitted
2021-01-27 07:31:31.111 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#23] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 1, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:31:31.111 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#23] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436
2021-01-27 07:31:31.114 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#14] INFO  o.e.c.scandium.dtls.DTLSFlight - Prepare flight 3, using max. datagram size 1436, max. fragment size 16384 [mhm=false, mr=true]
2021-01-27 07:31:31.114 [DTLS-Worker-0.0.0.0/0.0.0.0:5684#14] INFO  o.e.c.scandium.dtls.DTLSFlight - Effective max. datagram size 1436

[sbernard31]

@francopo : release 1.3.1 is out.

[boaks]

No, I wasn’t faced by such issues. It depends heavily on the exact dtls-configuration, so I’m not sure, what caused it. For the future, I add a detailed logging for the client and server hello in that case (for Californium 3.0).