Change the default IP addresses for DTLS samples Changes the IP address to bind to for dtls_server.c to be "::" or optionally "0.0.0.0" if the preprocessor symbol FORCE_IPV4 is defined. Also changes the destinaton IP address for dtls_client.c to be "::1" or if FORCE_IPV4 symbol is defined "127.0.0.1". This change allows on compilation dtls_server.c and dtls_client.c to both be compiled to use either IPv4 or IPv6 so out of the box they will work together without problem, and to avoid dtls_server.c binding to IPv6 and dtls_client.c binding to IPv4.

diff --git a/programs/ssl/dtls_client.c b/programs/ssl/dtls_client.c
index f271bad..c29ab34 100644
--- a/programs/ssl/dtls_client.c
+++ b/programs/ssl/dtls_client.c

@@ -60,9 +60,18 @@
 #include "mbedtls/certs.h"
 #include "mbedtls/timing.h"
 
+/* Uncomment out the following line to default to IPv4 and disable IPv6 */
+//#define FORCE_IPV4
+
 #define SERVER_PORT "4433"
 #define SERVER_NAME "localhost"
-#define SERVER_ADDR "127.0.0.1" /* forces IPv4 */
+
+#ifdef FORCE_IPV4
+#define SERVER_ADDR "127.0.0.1"     /* Forces IPv4 */
+#else
+#define SERVER_ADDR "::1"
+#endif
+
 #define MESSAGE     "Echo this"
 
 #define READ_TIMEOUT_MS 1000