diff --git a/configs/baremetal.h b/configs/baremetal.h
index 7168976..9541542 100644
--- a/configs/baremetal.h
+++ b/configs/baremetal.h
@@ -115,6 +115,9 @@
 #define MBEDTLS_SSL_CONF_ENFORCE_EXTENDED_MASTER_SECRET \
     MBEDTLS_SSL_EXTENDED_MS_ENFORCE_ENABLED
 
+#define MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+#define MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+
 #define MBEDTLS_USE_TINYCRYPT
 #define MBEDTLS_HAVE_ASM
 #if !( defined(__STRICT_ANSI__) && defined(__CC_ARM) )
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 3587bba..5534ec4 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1910,6 +1910,13 @@
 //#define MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT
 
 /**
+ * \def MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+ *
+ * Enable modifying the maximum I/O buffer size.
+ */
+//#define MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+
+/**
  * \def MBEDTLS_THREADING_ALT
  *
  * Provide your own alternate threading implementation.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index ee231a5..f447cf3 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1370,6 +1370,10 @@
     int in_msgtype;             /*!< record header: message type      */
     size_t in_msglen;           /*!< record header: message length    */
     size_t in_left;             /*!< amount of data read so far       */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len;          /*!< length of input buffer           */
+#endif
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     size_t next_record_offset;  /*!< offset of the next record in datagram
                                      (equal to in_left if none)       */
@@ -1399,6 +1403,9 @@
     int out_msgtype;            /*!< record header: message type      */
     size_t out_msglen;          /*!< record header: message length    */
     size_t out_left;            /*!< amount of data not yet written   */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len;         /*!< length of output buffer          */
+#endif
 
 #if defined(MBEDTLS_ZLIB_SUPPORT)
     unsigned char *compress_buf;        /*!<  zlib data buffer        */
@@ -3597,18 +3604,61 @@
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
 /**
- * \brief          Return the maximum fragment length (payload, in bytes).
- *                 This is the value negotiated with peer if any,
- *                 or the locally configured value.
+ * \brief          Return the maximum fragment length (payload, in bytes) for
+ *                 the output buffer. For the client, this is the configured
+ *                 value. For the server, it is the minimum of two - the
+ *                 configured value and the negotiated one.
  *
  * \sa             mbedtls_ssl_conf_max_frag_len()
  * \sa             mbedtls_ssl_get_max_record_payload()
  *
  * \param ssl      SSL context
  *
- * \return         Current maximum fragment length.
+ * \return         Current maximum fragment length for the output buffer.
  */
-size_t mbedtls_ssl_get_max_frag_len( const mbedtls_ssl_context *ssl );
+size_t mbedtls_ssl_get_output_max_frag_len( const mbedtls_ssl_context *ssl );
+
+/**
+ * \brief          Return the maximum fragment length (payload, in bytes) for
+ *                 the input buffer. This is the negotiated maximum fragment
+ *                 length, or, if there is none, MBEDTLS_SSL_MAX_CONTENT_LEN.
+ *                 If it is not defined either, the value is 2^14. This function
+ *                 works as its predecessor, \c mbedtls_ssl_get_max_frag_len().
+ *
+ * \sa             mbedtls_ssl_conf_max_frag_len()
+ * \sa             mbedtls_ssl_get_max_record_payload()
+ *
+ * \param ssl      SSL context
+ *
+ * \return         Current maximum fragment length for the output buffer.
+ */
+size_t mbedtls_ssl_get_input_max_frag_len( const mbedtls_ssl_context *ssl );
+
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#define MBEDTLS_DEPRECATED    __attribute__((deprecated))
+#else
+#define MBEDTLS_DEPRECATED
+#endif
+
+/**
+ * \brief          This function is a deprecated approach to getting the max
+ *                 fragment length. Its an alias for
+ *                 \c mbedtls_ssl_get_output_max_frag_len(), as the behaviour
+ *                 is the same. See \c mbedtls_ssl_get_output_max_frag_len() for
+ *                 more detail.
+ *
+ * \sa             mbedtls_ssl_get_input_max_frag_len()
+ * \sa             mbedtls_ssl_get_output_max_frag_len()
+ *
+ * \param ssl      SSL context
+ *
+ * \return         Current maximum fragment length for the output buffer.
+ */
+MBEDTLS_DEPRECATED size_t mbedtls_ssl_get_max_frag_len(
+                                        const mbedtls_ssl_context *ssl );
+#endif /* MBEDTLS_DEPRECATED_REMOVED */
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
 /**
@@ -3629,7 +3679,8 @@
  *                 when record compression is enabled.
  *
  * \sa             mbedtls_ssl_set_mtu()
- * \sa             mbedtls_ssl_get_max_frag_len()
+ * \sa             mbedtls_ssl_get_output_max_frag_len()
+ * \sa             mbedtls_ssl_get_input_max_frag_len()
  * \sa             mbedtls_ssl_get_record_expansion()
  *
  * \param ssl      SSL context
@@ -3930,8 +3981,8 @@
  *                 or negotiated with the peer), then:
  *                 - with TLS, less bytes than requested are written.
  *                 - with DTLS, MBEDTLS_ERR_SSL_BAD_INPUT_DATA is returned.
- *                 \c mbedtls_ssl_get_max_frag_len() may be used to query the
- *                 active maximum fragment length.
+ *                 \c mbedtls_ssl_get_output_max_frag_len() may be used to
+ *                 query the active maximum fragment length.
  *
  * \note           Attempting to write 0 bytes will result in an empty TLS
  *                 application record being sent.
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index a1c5d1d..17c5763 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -260,7 +260,7 @@
    implicit sequence number. */
 #define MBEDTLS_SSL_HEADER_LEN 13
 
-#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 #define MBEDTLS_SSL_IN_BUFFER_LEN  \
     ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) )
 #else
@@ -269,7 +269,7 @@
       + ( MBEDTLS_SSL_CID_IN_LEN_MAX ) )
 #endif
 
-#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 #define MBEDTLS_SSL_OUT_BUFFER_LEN  \
     ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) )
 #else
@@ -278,6 +278,32 @@
       + ( MBEDTLS_SSL_CID_OUT_LEN_MAX ) )
 #endif
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+static inline uint32_t mbedtls_ssl_get_output_buflen( const mbedtls_ssl_context *ctx )
+{
+#if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    return (uint32_t) mbedtls_ssl_get_output_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
+               + MBEDTLS_SSL_CID_OUT_LEN_MAX;
+#else
+    return (uint32_t) mbedtls_ssl_get_output_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
+#endif
+}
+
+static inline uint32_t mbedtls_ssl_get_input_buflen( const mbedtls_ssl_context *ctx )
+{
+#if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    return (uint32_t) mbedtls_ssl_get_input_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
+               + MBEDTLS_SSL_CID_IN_LEN_MAX;
+#else
+    return (uint32_t) mbedtls_ssl_get_input_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
+#endif
+}
+#endif
+
 #ifdef MBEDTLS_ZLIB_SUPPORT
 /* Compression buffer holds both IN and OUT buffers, so should be size of the larger */
 #define MBEDTLS_SSL_COMPRESS_BUFFER_LEN (                               \
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 7dfc0af..8a014ce 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -432,11 +432,16 @@
 static size_t ssl_get_maximum_datagram_size( mbedtls_ssl_context const *ssl )
 {
     size_t mtu = ssl_get_current_mtu( ssl );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len = ssl->out_buf_len;
+#else
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
 
-    if( mtu != 0 && mtu < MBEDTLS_SSL_OUT_BUFFER_LEN )
+    if( mtu != 0 && mtu < out_buf_len )
         return( mtu );
 
-    return( MBEDTLS_SSL_OUT_BUFFER_LEN );
+    return( out_buf_len );
 }
 
 static int ssl_get_remaining_space_in_datagram( mbedtls_ssl_context const *ssl )
@@ -462,7 +467,7 @@
     size_t max_len = MBEDTLS_SSL_OUT_CONTENT_LEN;
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-    const size_t mfl = mbedtls_ssl_get_max_frag_len( ssl );
+    const size_t mfl = mbedtls_ssl_get_output_max_frag_len( ssl );
 
     if( max_len > mfl )
         max_len = mfl;
@@ -640,6 +645,29 @@
     return( 0 );
 }
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+static int resize_buffer( unsigned char **buffer, size_t len_new, size_t *len_old )
+{
+    unsigned char* resized_buffer = mbedtls_calloc( 1, len_new );
+    if( resized_buffer == NULL )
+        return -1;
+
+    /* We want to copy len_new bytes when downsizing the buffer, and
+     * len_old bytes when upsizing, so we choose the smaller of two sizes,
+     * to fit one buffer into another. Size checks, ensuring that no data is
+     * lost, are done outside of this function. */
+    memcpy( resized_buffer, *buffer,
+            ( len_new < *len_old ) ? len_new : *len_old );
+    mbedtls_platform_zeroize( *buffer, *len_old );
+    mbedtls_free( *buffer );
+
+    *buffer = resized_buffer;
+    *len_old = len_new;
+
+    return 0;
+}
+#endif /* MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH */
+
 #if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
 int (*mbedtls_ssl_hw_record_init)( mbedtls_ssl_context *ssl,
                      const unsigned char *key_enc, const unsigned char *key_dec,
@@ -3810,6 +3838,11 @@
     ptrdiff_t bytes_written = ssl->out_msg - ssl->out_buf;
     size_t len_pre = ssl->out_msglen;
     unsigned char *msg_pre = ssl->compress_buf;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len = ssl->out_buf_len;
+#else
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> compress buf" ) );
 
@@ -3827,7 +3860,7 @@
     ssl->transform_out->ctx_deflate.next_in = msg_pre;
     ssl->transform_out->ctx_deflate.avail_in = len_pre;
     ssl->transform_out->ctx_deflate.next_out = msg_post;
-    ssl->transform_out->ctx_deflate.avail_out = MBEDTLS_SSL_OUT_BUFFER_LEN - bytes_written;
+    ssl->transform_out->ctx_deflate.avail_out = out_buf_len - bytes_written;
 
     ret = deflate( &ssl->transform_out->ctx_deflate, Z_SYNC_FLUSH );
     if( ret != Z_OK )
@@ -3836,7 +3869,7 @@
         return( MBEDTLS_ERR_SSL_COMPRESSION_FAILED );
     }
 
-    ssl->out_msglen = MBEDTLS_SSL_OUT_BUFFER_LEN -
+    ssl->out_msglen = out_buf_len -
                       ssl->transform_out->ctx_deflate.avail_out - bytes_written;
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "after compression: msglen = %d, ",
@@ -3857,6 +3890,11 @@
     ptrdiff_t header_bytes = ssl->in_msg - ssl->in_buf;
     size_t len_pre = ssl->in_msglen;
     unsigned char *msg_pre = ssl->compress_buf;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> decompress buf" ) );
 
@@ -3874,7 +3912,7 @@
     ssl->transform_in->ctx_inflate.next_in = msg_pre;
     ssl->transform_in->ctx_inflate.avail_in = len_pre;
     ssl->transform_in->ctx_inflate.next_out = msg_post;
-    ssl->transform_in->ctx_inflate.avail_out = MBEDTLS_SSL_IN_BUFFER_LEN -
+    ssl->transform_in->ctx_inflate.avail_out = in_buf_len -
                                                header_bytes;
 
     ret = inflate( &ssl->transform_in->ctx_inflate, Z_SYNC_FLUSH );
@@ -3884,7 +3922,7 @@
         return( MBEDTLS_ERR_SSL_COMPRESSION_FAILED );
     }
 
-    ssl->in_msglen = MBEDTLS_SSL_IN_BUFFER_LEN -
+    ssl->in_msglen = in_buf_len -
                      ssl->transform_in->ctx_inflate.avail_out - header_bytes;
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "after decompression: msglen = %d, ",
@@ -3951,6 +3989,11 @@
 {
     int ret;
     size_t len;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> fetch input" ) );
 
@@ -3962,7 +4005,7 @@
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
     }
 
-    if( nb_want > MBEDTLS_SSL_IN_BUFFER_LEN - (size_t)( ssl->in_hdr - ssl->in_buf ) )
+    if( nb_want > in_buf_len - (size_t)( ssl->in_hdr - ssl->in_buf ) )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "requesting more data than fits" ) );
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
@@ -4049,7 +4092,7 @@
         }
         else
         {
-            len = MBEDTLS_SSL_IN_BUFFER_LEN - ( ssl->in_hdr - ssl->in_buf );
+            len = in_buf_len - ( ssl->in_hdr - ssl->in_buf );
 
             if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
                 timeout = ssl->handshake->retransmit_timeout;
@@ -4821,6 +4864,11 @@
         unsigned i;
         size_t protected_record_size;
         volatile int encrypted_fi = 0;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+        size_t out_buf_len = ssl->out_buf_len;
+#else
+        size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
 
         /* Skip writing the record content type to after the encryption,
          * as it may change when using the CID extension. */
@@ -4837,8 +4885,7 @@
             mbedtls_record rec;
 
             rec.buf         = ssl->out_iv;
-            rec.buf_len     = MBEDTLS_SSL_OUT_BUFFER_LEN -
-                ( ssl->out_iv - ssl->out_buf );
+            rec.buf_len     = out_buf_len - ( ssl->out_iv - ssl->out_buf );
             rec.data_len    = ssl->out_msglen;
             rec.data_offset = ssl->out_msg - rec.buf;
 
@@ -6563,6 +6610,11 @@
     unsigned char * rec;
     size_t rec_len;
     unsigned rec_epoch;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
 
     if( MBEDTLS_SSL_TRANSPORT_IS_TLS( ssl->conf->transport ) )
         return( 0 );
@@ -6593,8 +6645,7 @@
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "Found buffered record from current epoch - load" ) );
 
     /* Double-check that the record is not too large */
-    if( rec_len > MBEDTLS_SSL_IN_BUFFER_LEN -
-        (size_t)( ssl->in_hdr - ssl->in_buf ) )
+    if( rec_len > in_buf_len - (size_t)( ssl->in_hdr - ssl->in_buf ) )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
         return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
@@ -8761,6 +8812,66 @@
         ssl->handshake = mbedtls_calloc( 1, sizeof(mbedtls_ssl_handshake_params) );
     }
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    /* If the buffers are too small - reallocate */
+    {
+        int modified = 0;
+        size_t written_in = 0, len_offset_in = 0;
+        size_t written_out = 0, iv_offset_out = 0, len_offset_out = 0;
+        if( ssl->in_buf != NULL )
+        {
+            written_in = ssl->in_msg - ssl->in_buf;
+            len_offset_in = ssl->in_len - ssl->in_buf;
+            if( ssl->in_buf_len < MBEDTLS_SSL_IN_BUFFER_LEN )
+            {
+                if( resize_buffer( &ssl->in_buf, MBEDTLS_SSL_IN_BUFFER_LEN,
+                                   &ssl->in_buf_len ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "input buffer resizing failed - out of memory" ) );
+                }
+                else
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating in_buf to %d", MBEDTLS_SSL_IN_BUFFER_LEN ) );
+                    modified = 1;
+                }
+            }
+        }
+
+        if( ssl->out_buf != NULL )
+        {
+            written_out = ssl->out_msg - ssl->out_buf;
+            iv_offset_out = ssl->out_iv - ssl->out_buf;
+            len_offset_out = ssl->out_len - ssl->out_buf;
+            if( ssl->out_buf_len < MBEDTLS_SSL_OUT_BUFFER_LEN )
+            {
+                if( resize_buffer( &ssl->out_buf, MBEDTLS_SSL_OUT_BUFFER_LEN,
+                                   &ssl->out_buf_len ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "output buffer resizing failed - out of memory" ) );
+                }
+                else
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating out_buf to %d", MBEDTLS_SSL_OUT_BUFFER_LEN ) );
+                    modified = 1;
+                }
+            }
+        }
+        if( modified )
+        {
+            /* Update pointers here to avoid doing it twice. */
+            ssl_reset_in_out_pointers( ssl );
+            /* Fields below might not be properly updated with record
+             * splitting or with CID, so they are manually updated here. */
+            ssl->out_msg = ssl->out_buf + written_out;
+            ssl->out_len = ssl->out_buf + len_offset_out;
+            ssl->out_iv = ssl->out_buf + iv_offset_out;
+
+            ssl->in_msg = ssl->in_buf + written_in;
+            ssl->in_len = ssl->in_buf + len_offset_in;
+        }
+    }
+#endif
+
     /* All pointers should exist and can be directly freed without issue */
     if( ssl->handshake == NULL ||
         ssl->transform_negotiate == NULL ||
@@ -8966,6 +9077,8 @@
                        const mbedtls_ssl_config *conf )
 {
     int ret;
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
 
     ssl->conf = conf;
 
@@ -8980,18 +9093,25 @@
     /* Set to NULL in case of an error condition */
     ssl->out_buf = NULL;
 
-    ssl->in_buf = mbedtls_calloc( 1, MBEDTLS_SSL_IN_BUFFER_LEN );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    ssl->in_buf_len = in_buf_len;
+#endif
+    ssl->in_buf = mbedtls_calloc( 1, in_buf_len );
     if( ssl->in_buf == NULL )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed", MBEDTLS_SSL_IN_BUFFER_LEN) );
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed", in_buf_len) );
         ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
         goto error;
     }
 
-    ssl->out_buf = mbedtls_calloc( 1, MBEDTLS_SSL_OUT_BUFFER_LEN );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    ssl->out_buf_len = out_buf_len;
+#endif
+
+    ssl->out_buf = mbedtls_calloc( 1, out_buf_len  );
     if( ssl->out_buf == NULL )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed", MBEDTLS_SSL_OUT_BUFFER_LEN) );
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed", out_buf_len) );
         ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
         goto error;
     }
@@ -9011,6 +9131,11 @@
 
     ssl->conf = NULL;
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    ssl->in_buf_len = 0;
+    ssl->out_buf_len = 0;
+#endif
+
     ssl->in_buf = NULL;
     ssl->out_buf = NULL;
 
@@ -9038,6 +9163,13 @@
 static int ssl_session_reset_int( mbedtls_ssl_context *ssl, int partial )
 {
     int ret;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+    size_t out_buf_len = ssl->out_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
 
 #if !defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) ||     \
     !defined(MBEDTLS_SSL_SRV_C)
@@ -9093,14 +9225,14 @@
     ssl->session_in = NULL;
     ssl->session_out = NULL;
 
-    mbedtls_platform_memset( ssl->out_buf, 0, MBEDTLS_SSL_OUT_BUFFER_LEN );
+    mbedtls_platform_memset( ssl->out_buf, 0, out_buf_len );
 
 #if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
     if( partial == 0 )
 #endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
     {
         ssl->in_left = 0;
-        mbedtls_platform_memset( ssl->in_buf, 0, MBEDTLS_SSL_IN_BUFFER_LEN );
+        mbedtls_platform_memset( ssl->in_buf, 0, in_buf_len );
     }
 
 #if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
@@ -10167,7 +10299,42 @@
 }
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-size_t mbedtls_ssl_get_max_frag_len( const mbedtls_ssl_context *ssl )
+size_t mbedtls_ssl_get_input_max_frag_len( const mbedtls_ssl_context *ssl )
+{
+    size_t max_len = MBEDTLS_SSL_MAX_CONTENT_LEN;
+    size_t read_mfl;
+
+    /* Use the configured MFL for the client if we're past SERVER_HELLO_DONE */
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
+        ssl->state >= MBEDTLS_SSL_SERVER_HELLO_DONE )
+    {
+        return ssl_mfl_code_to_length( ssl->conf->mfl_code );
+    }
+
+    /* Check if a smaller max length was negotiated */
+    if( ssl->session_out != NULL )
+    {
+        read_mfl = ssl_mfl_code_to_length( ssl->session_out->mfl_code );
+        if( read_mfl < max_len )
+        {
+            max_len = read_mfl;
+        }
+    }
+
+    // During a handshake, use the value being negotiated
+    if( ssl->session_negotiate != NULL )
+    {
+        read_mfl = ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code );
+        if( read_mfl < max_len )
+        {
+            max_len = read_mfl;
+        }
+    }
+
+    return( max_len );
+}
+
+size_t mbedtls_ssl_get_output_max_frag_len( const mbedtls_ssl_context *ssl )
 {
     size_t max_len;
 
@@ -10192,6 +10359,13 @@
 
     return( max_len );
 }
+
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+size_t mbedtls_ssl_get_max_frag_len( const mbedtls_ssl_context *ssl )
+{
+    return mbedtls_ssl_get_output_max_frag_len( ssl );
+}
+#endif /* !MBEDTLS_DEPRECATED_REMOVED */
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
@@ -10224,7 +10398,7 @@
 #endif
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-    const size_t mfl = mbedtls_ssl_get_max_frag_len( ssl );
+    const size_t mfl = mbedtls_ssl_get_output_max_frag_len( ssl );
 
     if( max_len > mfl )
         max_len = mfl;
@@ -11880,6 +12054,71 @@
 
     mbedtls_platform_zeroize( handshake,
                               sizeof( mbedtls_ssl_handshake_params ) );
+
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    /* If the buffers are too big - reallocate. Because of the way Mbed TLS
+     * processes datagrams and the fact that a datagram is allowed to have
+     * several records in it, it is possible that the I/O buffers are not
+     * empty at this stage */
+    {
+        int modified = 0;
+        uint32_t buf_len = mbedtls_ssl_get_input_buflen( ssl );
+        size_t written_in = 0, len_offset_in = 0;
+        size_t written_out = 0, iv_offset_out = 0, len_offset_out = 0;
+        if( ssl->in_buf != NULL )
+        {
+            written_in = ssl->in_msg - ssl->in_buf;
+            len_offset_in = ssl->in_len - ssl->in_buf;
+            if( ssl->in_buf_len > buf_len && ssl->in_left < buf_len )
+            {
+                if( resize_buffer( &ssl->in_buf, buf_len, &ssl->in_buf_len ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "input buffer resizing failed - out of memory" ) );
+                }
+                else
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating in_buf to %d", buf_len ) );
+                    modified = 1;
+                }
+            }
+        }
+
+
+        buf_len = mbedtls_ssl_get_output_buflen( ssl );
+        if( ssl->out_buf != NULL )
+        {
+            written_out = ssl->out_msg - ssl->out_buf;
+            iv_offset_out = ssl->out_iv - ssl->out_buf;
+            len_offset_out = ssl->out_len - ssl->out_buf;
+            if( ssl->out_buf_len > mbedtls_ssl_get_output_buflen( ssl ) &&
+                ssl->out_left < buf_len )
+            {
+                if( resize_buffer( &ssl->out_buf, buf_len, &ssl->out_buf_len ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "output buffer resizing failed - out of memory" ) );
+                }
+                else
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating out_buf to %d", buf_len ) );
+                    modified = 1;
+                }
+            }
+        }
+        if( modified )
+        {
+            /* Update pointers here to avoid doing it twice. */
+            ssl_reset_in_out_pointers( ssl );
+            /* Fields below might not be properly updated with record
+             * splitting or with CID, so they are manually updated here. */
+            ssl->out_msg = ssl->out_buf + written_out;
+            ssl->out_len = ssl->out_buf + len_offset_out;
+            ssl->out_iv = ssl->out_buf + iv_offset_out;
+
+            ssl->in_msg = ssl->in_buf + written_in;
+            ssl->in_len = ssl->in_buf + len_offset_in;
+        }
+    }
+#endif
 }
 
 void mbedtls_ssl_session_free( mbedtls_ssl_session *session )
@@ -12495,13 +12734,23 @@
 
     if( ssl->out_buf != NULL )
     {
-        mbedtls_platform_zeroize( ssl->out_buf, MBEDTLS_SSL_OUT_BUFFER_LEN );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+        size_t out_buf_len = ssl->out_buf_len;
+#else
+        size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
+        mbedtls_platform_zeroize( ssl->out_buf, out_buf_len );
         mbedtls_free( ssl->out_buf );
     }
 
     if( ssl->in_buf != NULL )
     {
-        mbedtls_platform_zeroize( ssl->in_buf, MBEDTLS_SSL_IN_BUFFER_LEN );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+        size_t in_buf_len = ssl->in_buf_len;
+#else
+        size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
+        mbedtls_platform_zeroize( ssl->in_buf, in_buf_len );
         mbedtls_free( ssl->in_buf );
     }
 
diff --git a/library/version_features.c b/library/version_features.c
index 1a226c8..b0e1637 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -555,6 +555,9 @@
 #if defined(MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT)
     "MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT",
 #endif /* MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    "MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH",
+#endif /* MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH */
 #if defined(MBEDTLS_THREADING_ALT)
     "MBEDTLS_THREADING_ALT",
 #endif /* MBEDTLS_THREADING_ALT */
diff --git a/programs/ssl/query_config.c b/programs/ssl/query_config.c
index ba4b596..21800bb 100644
--- a/programs/ssl/query_config.c
+++ b/programs/ssl/query_config.c
@@ -1522,6 +1522,14 @@
     }
 #endif /* MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT */
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    if( strcmp( "MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH", config ) == 0 )
+    {
+        MACRO_EXPANSION_TO_STR( MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH );
+        return( 0 );
+    }
+#endif /* MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH */
+
 #if defined(MBEDTLS_THREADING_ALT)
     if( strcmp( "MBEDTLS_THREADING_ALT", config ) == 0 )
     {
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 3bf9e62..f6907f2 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -2332,8 +2332,10 @@
         mbedtls_printf( "    [ Record expansion is unknown (compression) ]\n" );
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-    mbedtls_printf( "    [ Maximum fragment length is %u ]\n",
-                    (unsigned int) mbedtls_ssl_get_max_frag_len( ssl ) );
+    mbedtls_printf( "    [ Maximum input fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_input_max_frag_len( ssl ) );
+    mbedtls_printf( "    [ Maximum output fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_output_max_frag_len( ssl ) );
 #endif
 
 #if defined(MBEDTLS_SSL_ALPN)
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index bf10987..52c4742 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -2312,7 +2312,10 @@
 
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
     mbedtls_memory_buffer_alloc_init( alloc_buf, sizeof(alloc_buf) );
-#endif
+#if defined(MBEDTLS_MEMORY_DEBUG)
+    size_t current_heap_memory, peak_heap_memory, heap_blocks;
+#endif  /* MBEDTLS_MEMORY_DEBUG */
+#endif  /* MBEDTLS_MEMORY_BUFFER_ALLOC_C */
 
     ssl         = mbedtls_calloc( 1, sizeof( *ssl ) );
     conf        = mbedtls_calloc( 1, sizeof( *conf ) );
@@ -3420,8 +3423,10 @@
         mbedtls_printf( "    [ Record expansion is unknown (compression) ]\n" );
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-    mbedtls_printf( "    [ Maximum fragment length is %u ]\n",
-                    (unsigned int) mbedtls_ssl_get_max_frag_len( ssl ) );
+    mbedtls_printf( "    [ Maximum input fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_input_max_frag_len( ssl ) );
+    mbedtls_printf( "    [ Maximum output fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_output_max_frag_len( ssl ) );
 #endif
 
 #if defined(MBEDTLS_SSL_ALPN)
@@ -3486,6 +3491,13 @@
     }
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
+#if defined(MBEDTLS_MEMORY_DEBUG)
+    mbedtls_memory_buffer_alloc_cur_get( &current_heap_memory, &heap_blocks );
+    mbedtls_memory_buffer_alloc_max_get( &peak_heap_memory, &heap_blocks );
+    mbedtls_printf( "Heap memory usage after handshake: %lu bytes. Peak memory usage was %lu\n",
+                    (unsigned long) current_heap_memory, (unsigned long) peak_heap_memory );
+#endif  /* MBEDTLS_MEMORY_DEBUG */
+
     if( opt.exchanges == 0 )
         goto close_notify;
 
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 7ae1425..a8747c2 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1276,6 +1276,75 @@
     if_build_succeeded tests/ssl-opt.sh -f "Max fragment length\|Large buffer"
 }
 
+component_test_variable_ssl_in_out_buffer_len () {
+    msg "build: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH enabled (ASan build)"
+    scripts/config.pl set MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+    CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
+    make
+
+    msg "test: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH enabled"
+    make test
+
+    msg "test: ssl-opt.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH enabled"
+    if_build_succeeded tests/ssl-opt.sh
+
+    msg "test: compat.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH enabled"
+    if_build_succeeded tests/compat.sh
+}
+
+component_test_variable_ssl_in_out_buffer_len_CID () {
+    msg "build: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_DTLS_CONNECTION_ID enabled (ASan build)"
+    scripts/config.pl set MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+    scripts/config.pl set MBEDTLS_SSL_DTLS_CONNECTION_ID
+
+    CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
+    make
+
+    msg "test: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_DTLS_CONNECTION_ID"
+    make test
+
+    msg "test: ssl-opt.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_DTLS_CONNECTION_ID enabled"
+    if_build_succeeded tests/ssl-opt.sh
+
+    msg "test: compat.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_DTLS_CONNECTION_ID enabled"
+    if_build_succeeded tests/compat.sh
+}
+
+component_test_variable_ssl_in_out_buffer_len_record_splitting () {
+    msg "build: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_CBC_RECORD_SPLITTING enabled (ASan build)"
+    scripts/config.pl set MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+    scripts/config.pl set MBEDTLS_SSL_CBC_RECORD_SPLITTING
+
+    CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
+    make
+
+    msg "test: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_CBC_RECORD_SPLITTING"
+    make test
+
+    msg "test: ssl-opt.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_CBC_RECORD_SPLITTING enabled"
+    if_build_succeeded tests/ssl-opt.sh
+
+    msg "test: compat.sh, MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH and MBEDTLS_SSL_CBC_RECORD_SPLITTING enabled"
+    if_build_succeeded tests/compat.sh
+}
+
+component_test_ssl_alloc_buffer_and_mfl () {
+    msg "build: default config with memory buffer allocator and MFL extension"
+    scripts/config.pl set MBEDTLS_MEMORY_BUFFER_ALLOC_C
+    scripts/config.pl set MBEDTLS_PLATFORM_MEMORY
+    scripts/config.pl set MBEDTLS_MEMORY_DEBUG
+    scripts/config.pl set MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+    scripts/config.pl set MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+    CC=gcc cmake .
+    make
+
+    msg "test: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH, MBEDTLS_MEMORY_BUFFER_ALLOC_C, MBEDTLS_MEMORY_DEBUG and MBEDTLS_SSL_MAX_FRAGMENT_LENGTH"
+    make test
+
+    msg "test: MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH, MBEDTLS_MEMORY_BUFFER_ALLOC_C, MBEDTLS_MEMORY_DEBUG and MBEDTLS_SSL_MAX_FRAGMENT_LENGTH"
+    if_build_succeeded tests/ssl-opt.sh -f "Handshake memory usage"
+}
+
 component_test_when_no_ciphersuites_have_mac () {
     msg "build: when no ciphersuites have MAC"
     scripts/config.pl unset MBEDTLS_CIPHER_NULL_CIPHER
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index b211310..81ea9e1 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -153,7 +153,7 @@
 }
 
 requires_ciphersuite_enabled() {
-    if [ -z "$($P_CLI --help | grep "$1")" ]; then
+    if [ -z "$($P_CLI --help 2>/dev/null | grep $1)" ]; then
         SKIP_NEXT="YES"
     fi
 }
@@ -510,6 +510,45 @@
     fi
 }
 
+# Get handshake memory usage from server or client output and put it into the variable specified by the first argument
+handshake_memory_get() {
+    OUTPUT_VARIABLE="$1"
+    OUTPUT_FILE="$2"
+
+    # Get memory usage from a pattern like "Heap memory usage after handshake: 23112 bytes. Peak memory usage was 33112"
+    MEM_USAGE=$(sed -n 's/.*Heap memory usage after handshake: //p' < "$OUTPUT_FILE" | grep -o "[0-9]*" | head -1)
+
+    # Check if memory usage was read
+    if [ -z "$MEM_USAGE" ]; then
+        echo "Error: Can not read the value of handshake memory usage"
+        return 1
+    else
+        eval "$OUTPUT_VARIABLE=$MEM_USAGE"
+        return 0
+    fi
+}
+
+# Get handshake memory usage from server or client output and check if this value
+# is not higher than the maximum given by the first argument
+handshake_memory_check() {
+    MAX_MEMORY="$1"
+    OUTPUT_FILE="$2"
+
+    # Get memory usage
+    if ! handshake_memory_get "MEMORY_USAGE" "$OUTPUT_FILE"; then
+        return 1
+    fi
+
+    # Check if memory usage is below max value
+    if [ "$MEMORY_USAGE" -gt "$MAX_MEMORY" ]; then
+        echo "\nFailed: Handshake memory usage was $MEMORY_USAGE bytes," \
+             "but should be below $MAX_MEMORY bytes"
+        return 1
+    else
+        return 0
+    fi
+}
+
 # wait for client to terminate and set CLI_EXIT
 # must be called right after starting the client
 wait_client_done() {
@@ -999,6 +1038,58 @@
     rm -f $SRV_OUT $CLI_OUT $PXY_OUT
 }
 
+# Test that the server's memory usage after a handshake is reduced when a client specifies
+# a maximum fragment length.
+#  first argument ($1) is MFL for SSL client
+#  second argument ($2) is memory usage for SSL client with default MFL (16k)
+run_test_memory_after_hanshake_with_mfl()
+{
+    # The test passes if the difference is around 2*(16k-MFL)
+    local MEMORY_USAGE_LIMIT="$(( $2 - ( 2 * ( 16384 - $1 )) ))"
+
+    # Leave some margin for robustness
+    MEMORY_USAGE_LIMIT="$(( ( MEMORY_USAGE_LIMIT * 110 ) / 100 ))"
+
+    run_test    "Handshake memory usage (MFL $1)" \
+                "$P_SRV debug_level=3 auth_mode=required force_version=tls1_2" \
+                "$P_CLI debug_level=3 force_version=tls1_2 \
+                    crt_file=data_files/server5.crt key_file=data_files/server5.key \
+                    force_ciphersuite=TLS-ECDHE-ECDSA-WITH-AES-128-CCM max_frag_len=$1" \
+                0 \
+                -F "handshake_memory_check $MEMORY_USAGE_LIMIT"
+}
+
+
+# Test that the server's memory usage after a handshake is reduced when a client specifies
+# different values of Maximum Fragment Length: default (16k), 4k, 2k, 1k and 512 bytes
+run_tests_memory_after_hanshake()
+{
+    # all tests in this sequence requires the same configuration (see requires_config_enabled())
+    SKIP_THIS_TESTS="$SKIP_NEXT"
+
+    # first test with default MFU is to get reference memory usage
+    MEMORY_USAGE_MFL_16K=0
+    run_test    "Handshake memory usage initial (MFL 16384 - default)" \
+                "$P_SRV debug_level=3 auth_mode=required force_version=tls1_2" \
+                "$P_CLI debug_level=3 force_version=tls1_2 \
+                    crt_file=data_files/server5.crt key_file=data_files/server5.key \
+                    force_ciphersuite=TLS-ECDHE-ECDSA-WITH-AES-128-CCM" \
+                0 \
+                -F "handshake_memory_get MEMORY_USAGE_MFL_16K"
+
+    SKIP_NEXT="$SKIP_THIS_TESTS"
+    run_test_memory_after_hanshake_with_mfl 4096 "$MEMORY_USAGE_MFL_16K"
+
+    SKIP_NEXT="$SKIP_THIS_TESTS"
+    run_test_memory_after_hanshake_with_mfl 2048 "$MEMORY_USAGE_MFL_16K"
+
+    SKIP_NEXT="$SKIP_THIS_TESTS"
+    run_test_memory_after_hanshake_with_mfl 1024 "$MEMORY_USAGE_MFL_16K"
+
+    SKIP_NEXT="$SKIP_THIS_TESTS"
+    run_test_memory_after_hanshake_with_mfl 512 "$MEMORY_USAGE_MFL_16K"
+}
+
 cleanup() {
     rm -f $CLI_OUT $SRV_OUT $PXY_OUT $SESSION
     test -n "${SRV_PID:-}" && kill $SRV_PID >/dev/null 2>&1
@@ -2176,6 +2267,32 @@
             -c "ignoring unexpected CID" \
             -s "ignoring unexpected CID"
 
+requires_config_enabled MBEDTLS_SSL_DTLS_CONNECTION_ID
+requires_config_enabled MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+run_test    "Connection ID: Cli+Srv enabled, variable buffer lengths, MFL=512" \
+            "$P_SRV dtls=1 cid=1 cid_val=dead debug_level=2" \
+            "$P_CLI force_ciphersuite="TLS-ECDHE-ECDSA-WITH-AES-128-CCM-8" max_frag_len=512 dtls=1 cid=1 cid_val=beef" \
+            0 \
+            -c "(initial handshake) Peer CID (length 2 Bytes): de ad" \
+            -s "(initial handshake) Peer CID (length 2 Bytes): be ef" \
+            -s "(initial handshake) Use of Connection ID has been negotiated" \
+            -c "(initial handshake) Use of Connection ID has been negotiated" \
+            -s "Reallocating in_buf" \
+            -s "Reallocating out_buf"
+
+requires_config_enabled MBEDTLS_SSL_DTLS_CONNECTION_ID
+requires_config_enabled MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
+run_test    "Connection ID: Cli+Srv enabled, variable buffer lengths, MFL=1024" \
+            "$P_SRV dtls=1 cid=1 cid_val=dead debug_level=2" \
+            "$P_CLI force_ciphersuite="TLS-ECDHE-ECDSA-WITH-AES-128-CCM-8" max_frag_len=1024 dtls=1 cid=1 cid_val=beef" \
+            0 \
+            -c "(initial handshake) Peer CID (length 2 Bytes): de ad" \
+            -s "(initial handshake) Peer CID (length 2 Bytes): be ef" \
+            -s "(initial handshake) Use of Connection ID has been negotiated" \
+            -c "(initial handshake) Use of Connection ID has been negotiated" \
+            -s "Reallocating in_buf" \
+            -s "Reallocating out_buf"
+
 # Tests for Encrypt-then-MAC extension
 
 run_test    "Encrypt then MAC: default" \
@@ -3047,14 +3164,15 @@
 if [ $MAX_CONTENT_LEN -ne 16384 ]; then
     printf "Using non-default maximum content length $MAX_CONTENT_LEN\n"
 fi
-
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
 run_test    "Max fragment length: enabled, default" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3" \
             0 \
-            -c "Maximum fragment length is $MAX_CONTENT_LEN" \
-            -s "Maximum fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum output fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum output fragment length is $MAX_CONTENT_LEN" \
             -C "client hello, adding max_fragment_length extension" \
             -S "found max fragment length extension" \
             -S "server hello, max_fragment_length extension" \
@@ -3065,8 +3183,10 @@
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 request_size=$(( $MAX_CONTENT_LEN + 1))" \
             0 \
-            -c "Maximum fragment length is $MAX_CONTENT_LEN" \
-            -s "Maximum fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum output fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum output fragment length is $MAX_CONTENT_LEN" \
             -C "client hello, adding max_fragment_length extension" \
             -S "found max fragment length extension" \
             -S "server hello, max_fragment_length extension" \
@@ -3076,13 +3196,14 @@
             -s "1 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 run_test    "Max fragment length, DTLS: enabled, default, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 request_size=$(( $MAX_CONTENT_LEN + 1))" \
             1 \
-            -c "Maximum fragment length is $MAX_CONTENT_LEN" \
-            -s "Maximum fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum output fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum output fragment length is $MAX_CONTENT_LEN" \
             -C "client hello, adding max_fragment_length extension" \
             -S "found max fragment length extension" \
             -S "server hello, max_fragment_length extension" \
@@ -3094,72 +3215,245 @@
 # content length configuration.)
 
 requires_config_disabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 16384
 run_test    "Max fragment length: disabled, larger message" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 request_size=$(( $MAX_CONTENT_LEN + 1))" \
             0 \
-            -C "Maximum fragment length is 16384" \
-            -S "Maximum fragment length is 16384" \
+            -C "Maximum input fragment length is 16384" \
+            -C "Maximum output fragment length is 16384" \
+            -S "Maximum input fragment length is 16384" \
+            -S "Maximum output fragment length is 16384" \
             -c "$(( $MAX_CONTENT_LEN + 1)) bytes written in 2 fragments" \
             -s "$MAX_CONTENT_LEN bytes read" \
             -s "1 bytes read"
 
 requires_config_disabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 16384
 run_test    "Max fragment length DTLS: disabled, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 request_size=$(( $MAX_CONTENT_LEN + 1))" \
             1 \
-            -C "Maximum fragment length is 16384" \
-            -S "Maximum fragment length is 16384" \
+            -C "Maximum input fragment length is 16384" \
+            -C "Maximum output fragment length is 16384" \
+            -S "Maximum input fragment length is 16384" \
+            -S "Maximum output fragment length is 16384" \
             -c "fragment larger than.*maximum "
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 run_test    "Max fragment length: used by client" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=4096" \
             0 \
-            -c "Maximum fragment length is 4096" \
-            -s "Maximum fragment length is 4096" \
+            -c "Maximum input fragment length is 4096" \
+            -c "Maximum output fragment length is 4096" \
+            -s "Maximum input fragment length is 4096" \
+            -s "Maximum output fragment length is 4096" \
             -c "client hello, adding max_fragment_length extension" \
             -s "found max fragment length extension" \
             -s "server hello, max_fragment_length extension" \
             -c "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
+run_test    "Max fragment length: client 512, server 1024" \
+            "$P_SRV debug_level=3 max_frag_len=1024" \
+            "$P_CLI debug_level=3 max_frag_len=512" \
+            0 \
+            -c "Maximum input fragment length is 512" \
+            -c "Maximum output fragment length is 512" \
+            -s "Maximum input fragment length is 512" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 512, server 2048" \
+            "$P_SRV debug_level=3 max_frag_len=2048" \
+            "$P_CLI debug_level=3 max_frag_len=512" \
+            0 \
+            -c "Maximum input fragment length is 512" \
+            -c "Maximum output fragment length is 512" \
+            -s "Maximum input fragment length is 512" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 512, server 4096" \
+            "$P_SRV debug_level=3 max_frag_len=4096" \
+            "$P_CLI debug_level=3 max_frag_len=512" \
+            0 \
+            -c "Maximum input fragment length is 512" \
+            -c "Maximum output fragment length is 512" \
+            -s "Maximum input fragment length is 512" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 1024, server 512" \
+            "$P_SRV debug_level=3 max_frag_len=512" \
+            "$P_CLI debug_level=3 max_frag_len=1024" \
+            0 \
+            -c "Maximum input fragment length is 1024" \
+            -c "Maximum output fragment length is 1024" \
+            -s "Maximum input fragment length is 1024" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 1024, server 2048" \
+            "$P_SRV debug_level=3 max_frag_len=2048" \
+            "$P_CLI debug_level=3 max_frag_len=1024" \
+            0 \
+            -c "Maximum input fragment length is 1024" \
+            -c "Maximum output fragment length is 1024" \
+            -s "Maximum input fragment length is 1024" \
+            -s "Maximum output fragment length is 1024" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 1024, server 4096" \
+            "$P_SRV debug_level=3 max_frag_len=4096" \
+            "$P_CLI debug_level=3 max_frag_len=1024" \
+            0 \
+            -c "Maximum input fragment length is 1024" \
+            -c "Maximum output fragment length is 1024" \
+            -s "Maximum input fragment length is 1024" \
+            -s "Maximum output fragment length is 1024" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 2048, server 512" \
+            "$P_SRV debug_level=3 max_frag_len=512" \
+            "$P_CLI debug_level=3 max_frag_len=2048" \
+            0 \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 2048, server 1024" \
+            "$P_SRV debug_level=3 max_frag_len=1024" \
+            "$P_CLI debug_level=3 max_frag_len=2048" \
+            0 \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 1024" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 2048, server 4096" \
+            "$P_SRV debug_level=3 max_frag_len=4096" \
+            "$P_CLI debug_level=3 max_frag_len=2048" \
+            0 \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 2048" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 4096, server 512" \
+            "$P_SRV debug_level=3 max_frag_len=512" \
+            "$P_CLI debug_level=3 max_frag_len=4096" \
+            0 \
+            -c "Maximum input fragment length is 4096" \
+            -c "Maximum output fragment length is 4096" \
+            -s "Maximum input fragment length is 4096" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 4096, server 1024" \
+            "$P_SRV debug_level=3 max_frag_len=1024" \
+            "$P_CLI debug_level=3 max_frag_len=4096" \
+            0 \
+            -c "Maximum input fragment length is 4096" \
+            -c "Maximum output fragment length is 4096" \
+            -s "Maximum input fragment length is 4096" \
+            -s "Maximum output fragment length is 1024" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Max fragment length: client 4096, server 2048" \
+            "$P_SRV debug_level=3 max_frag_len=2048" \
+            "$P_CLI debug_level=3 max_frag_len=4096" \
+            0 \
+            -c "Maximum input fragment length is 4096" \
+            -c "Maximum output fragment length is 4096" \
+            -s "Maximum input fragment length is 4096" \
+            -s "Maximum output fragment length is 2048" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension"
+
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
 run_test    "Max fragment length: used by server" \
             "$P_SRV debug_level=3 max_frag_len=4096" \
             "$P_CLI debug_level=3" \
             0 \
-            -c "Maximum fragment length is $MAX_CONTENT_LEN" \
-            -s "Maximum fragment length is 4096" \
+            -c "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -c "Maximum output fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum input fragment length is $MAX_CONTENT_LEN" \
+            -s "Maximum output fragment length is 4096" \
             -C "client hello, adding max_fragment_length extension" \
             -S "found max fragment length extension" \
             -S "server hello, max_fragment_length extension" \
             -C "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 requires_gnutls
 run_test    "Max fragment length: gnutls server" \
             "$G_SRV" \
-            "$P_CLI debug_level=3 max_frag_len=4096 ca_file=data_files/test-ca2.crt" \
+            "$P_CLI debug_level=3 max_frag_len=4096" \
             0 \
-            -c "Maximum fragment length is 4096" \
+            -c "Maximum input fragment length is 4096" \
+            -c "Maximum output fragment length is 4096" \
             -c "client hello, adding max_fragment_length extension" \
             -c "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: client, message just fits" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=2048 request_size=2048" \
             0 \
-            -c "Maximum fragment length is 2048" \
-            -s "Maximum fragment length is 2048" \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 2048" \
             -c "client hello, adding max_fragment_length extension" \
             -s "found max fragment length extension" \
             -s "server hello, max_fragment_length extension" \
@@ -3168,13 +3462,14 @@
             -s "2048 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: client, larger message" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=2048 request_size=2345" \
             0 \
-            -c "Maximum fragment length is 2048" \
-            -s "Maximum fragment length is 2048" \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 2048" \
             -c "client hello, adding max_fragment_length extension" \
             -s "found max fragment length extension" \
             -s "server hello, max_fragment_length extension" \
@@ -3184,13 +3479,14 @@
             -s "297 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
-requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: DTLS client, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 max_frag_len=2048 request_size=2345" \
             1 \
-            -c "Maximum fragment length is 2048" \
-            -s "Maximum fragment length is 2048" \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 2048" \
             -c "client hello, adding max_fragment_length extension" \
             -s "found max fragment length extension" \
             -s "server hello, max_fragment_length extension" \
@@ -3292,6 +3588,29 @@
             -s "write hello request"
 
 requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_test    "Renegotiation with max fragment length: client 2048, server 512" \
+            "$P_SRV debug_level=3 exchanges=2 renegotiation=1 auth_mode=optional renegotiate=1 max_frag_len=512" \
+            "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 max_frag_len=2048 force_ciphersuite=TLS-ECDHE-ECDSA-WITH-AES-128-CCM-8" \
+            0 \
+            -c "Maximum input fragment length is 2048" \
+            -c "Maximum output fragment length is 2048" \
+            -s "Maximum input fragment length is 2048" \
+            -s "Maximum output fragment length is 512" \
+            -c "client hello, adding max_fragment_length extension" \
+            -s "found max fragment length extension" \
+            -s "server hello, max_fragment_length extension" \
+            -c "found max_fragment_length extension" \
+            -c "client hello, adding renegotiation extension" \
+            -s "received TLS_EMPTY_RENEGOTIATION_INFO" \
+            -s "found renegotiation extension" \
+            -s "server hello, secure renegotiation extension" \
+            -c "found renegotiation extension" \
+            -c "=> renegotiate" \
+            -s "=> renegotiate" \
+            -s "write hello request"
+
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: client-initiated, server-rejected" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=0 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -8774,6 +9093,12 @@
             -s "Extra-header:" \
             -c "Extra-header:"
 
+# Test heap memory usage after handshake
+requires_config_enabled MBEDTLS_MEMORY_DEBUG
+requires_config_enabled MBEDTLS_MEMORY_BUFFER_ALLOC_C
+requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+run_tests_memory_after_hanshake
+
 # Final report
 
 echo "------------------------------------------------------------------------"