[openssl-users] DTLS and packet loss

[Matt Caswell]

On 01/06/15 12:52, Alfred E. Heggestad wrote:
> Hey Matt,
> 
> 
> openssl version 1.0.2a on both sides (Client and Server)
> 
> 
>> Are you also running OpenSSL on the server side (and if so which version
>> there)?
>>
>> The error message suggests that the NewSessionTicket message that has
>> been received by the client is incorrectly formatted.
>>
>> A packet capture for a problem handshake might help diagnose the problem
>> further.
>>
> 
> please see the attached PCAP file, in this case Packet #4 is dropped
> internally
> in the software (to simulate Packet-loss).
> 
> 
> 
> that test-code has the following option set, to avoid fragmentation:
> 
>     SSL_set_options(tc->ssl, SSL_OP_NO_QUERY_MTU);
>     DTLS_set_link_mtu(tc->ssl, 1480);
> 
> 
> please note that dropping Packet #1, #2 and #3 works as expected.
> but dropping the final packet (packet #4) does not work.

Thanks - I've figured it out. This is a manifestation of a known issue
with retransmits in 1.0.2a. It will be fixed in 1.0.2b. I have attached
a patch for 1.0.2a which should solve your problems for now.

The relevant 1.0.2 commits that fix this are here:
https://github.com/openssl/openssl/commit/a20718fa2c0a45e6acb975cf6c0438c3ebd45b13

and here:
https://github.com/openssl/openssl/commit/4285b851637a3da8bd6e96848f0deffb6be5e626


Matt
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