DTLS session resumption about anjay HOT 4 CLOSED

Hi @kFYatek,

Thank you for your explanation. You have a great software 👍
It seems to be OK (see screenshot). I am performing additional tests on my side and after that I will close this issue.
Thank you for your help.

best regards
Tomasz

from anjay.

Hi Tomasz,

In general, your scenario should "just work", no special configuration should be necessary.

Can you send the actual PCAP file instead of just the screenshot? The lack of proper DTLS session resumption may be a problem on either the client or the server side. My initial suspicion is that the server may not recognize the session ID that is supposedly sent as part of the Client Hello during the reconnection - however I cannot verify this hypothesis based on your screenshot alone.

from anjay.

Hi @kFYatek,

Thank you for your answer. Below I am attaching pcap file and log from my console.
For your information, I also tested DTLS session resumption with LeshanDemoClient and the same LeshanDemoServer and it seems to be OK.

Anjay2LeshanDemoServer.zip

Best regards
Tomasz

from anjay.

Hi @tomekmalek,

We have looked at your PCAP and indeed the client is not sending the session ID, so the problem is on the client side.

I have examined our code once again, and it seems that my previous answer was wrong. In your case (communication with the server is blocked on the router), I think Anjay is attempting to send a Register message (which also causes a DTLS handshake attempt) and fails. When the library determines this failure, the DTLS session cache is cleared, so the resumption will not be attempted.

You can test the DTLS session resumption by, instead of blocking the communication on the router, putting the Anjay library into offline mode and back (see anjay_transport_enter_offline() / anjay_transport_exit_offline() - in the command-line demo client, you can use enter-offline and exit-offline commands). The intended flow is that the Anjay library is expected to be notified when e.g. network link is lost, through these function calls. In case of actual communication errors, though, the DTLS session will get invalidated to effectively reset the state and maximize the chance of a successful connection.

I hope that this explanation makes sense to you.

from anjay.