[openssl-users] DTLS with multiple clients
var.kulkarni at gmail.com
Thu Apr 5 17:53:47 UTC 2018
I was able to fix the issue with the following changes. The change was to
create new fd (bound to server address) each time DTLSv1_listen() was
called. Previously, I used the same fd for every DTLSv1_listen call. The
new dgram BIO was created with an old fd. On passing newly created fd to
BIO_new_dgram, the problem seems to be resolved. However, this leads to
another question. Why doesn't DTLS_listen queue up the connections similar
to accept call? Does that mean DTLS can support only one handshake at a
time? Is it recommended to create multiple fds bound to server address and
then spawning a thread (per fd) to listen to DTLS requests.
int fd = socket(AF_INET6, SOCK_DGRAM, 0);bind(fd, &server_addr,
BIO *bio = BIO_new_dgram(fd, BIO_NOCLOSE); SSL *ssl = SSL_new(ctx);
SSL_set_bio(ssl, bio, bio); /* Enable cookie exchange */ SSL_set_options(ssl,
SSL_OP_COOKIE_EXCHANGE); /* Wait for incoming connections */ while (!
DTLSv1_listen(ssl, &client_addr)); /* connect to client on different fd and
complete the handshake and process data packets */
On Thu, Apr 5, 2018 at 1:03 AM, Matt Caswell <matt at openssl.org> wrote:
> Are you able to share a simple reproducer of your problem?
> On 05/04/18 02:14, Varun Kulkarni wrote:
> > Hi,
> > I was able to get DTLS work with the latest version of openssl with a
> > single client and server. However, I was unable to get it to work with
> > multiple clients. The first client completes the handshake and works
> > well. But however the function DTLSv1_listen returns 1 immediately even
> > for an application data packet (after the first client completes the
> > handshake), where it should ideally return 0 and wait for the next
> > client hello. Since it hangs on SSL_accept, the next client hello
> > packets won't be answered.
> > The closest reference I have got is from:
> > https://gist.github.com/Jxck/b211a12423622fe304d2370b1f1d30d5. This
> > doesn't seem to work for multiple clients.
> > Any suggestions/references would be helpful in this regard. If this is
> > not the right mailing list, please point me to the right one.
> > --
> > Thanks and Regards,
> > Varun K S
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Varun K S
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