diff --git a/cyassl/internal.h b/cyassl/internal.h
index 1d81f043a..5c69e622a 100644
--- a/cyassl/internal.h
+++ b/cyassl/internal.h
@@ -1363,6 +1363,30 @@ enum ClientCertificateType {
 enum CipherType { stream, block, aead };
 
 
+#ifdef CYASSL_DTLS
+
+    #ifdef WORD64_AVAILABLE
+        typedef word64 DtlsSeq;
+    #else
+        typedef word32 DtlsSeq;
+    #endif
+    #define DTLS_SEQ_BITS (sizeof(DtlsSeq) * CHAR_BIT)
+
+    typedef struct DtlsState {
+        DtlsSeq window;     /* Sliding window for current epoch    */
+        word16 nextEpoch;   /* Expected epoch in next record       */
+        word32 nextSeq;     /* Expected sequence in next record    */
+
+        word16 curEpoch;    /* Received epoch in current record    */
+        word32 curSeq;      /* Received sequence in current record */
+
+        DtlsSeq prevWindow; /* Sliding window for old epoch        */
+        word32 prevSeq;     /* Next sequence in allowed old epoch  */
+    } DtlsState;
+
+#endif /* CYASSL_DTLS */
+
+
 /* keys and secrets */
 typedef struct Keys {
     byte client_write_MAC_secret[MAX_DIGEST_SIZE];   /* max sizes */
@@ -1381,15 +1405,13 @@ typedef struct Keys {
     word32 sequence_number;
     
 #ifdef CYASSL_DTLS
-    word32 dtls_sequence_number;
-    word32 dtls_peer_sequence_number;
-    word32 dtls_expected_peer_sequence_number;
-    word16 dtls_handshake_number;
+    DtlsState dtls_state;                       /* Peer's state */
     word16 dtls_peer_handshake_number;
     word16 dtls_expected_peer_handshake_number;
-    word16 dtls_epoch;
-    word16 dtls_peer_epoch;
-    word16 dtls_expected_peer_epoch;
+
+    word16 dtls_epoch;                          /* Current tx epoch    */
+    word32 dtls_sequence_number;                /* Current tx sequence */
+    word16 dtls_handshake_number;               /* Current tx handshake seq */
 #endif
 
     word32 encryptSz;             /* last size of encrypted data   */
diff --git a/src/internal.c b/src/internal.c
index 85e64f962..dfb4a79b8 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -87,6 +87,13 @@ CYASSL_CALLBACKS needs LARGE_STATIC_BUFFERS, please add LARGE_STATIC_BUFFERS
     #endif
 #endif
 
+
+#ifdef CYASSL_DTLS
+    static int DtlsCheckWindow(DtlsState* state);
+    static int DtlsUpdateWindow(DtlsState* state);
+#endif
+
+
 typedef enum {
     doProcessInit = 0,
 #ifndef NO_CYASSL_SERVER
@@ -1421,6 +1428,9 @@ int InitSSL(CYASSL* ssl, CYASSL_CTX* ctx)
 #ifdef CYASSL_DTLS
     ssl->IOCB_CookieCtx = NULL;      /* we don't use for default cb */
     ssl->dtls_expected_rx = MAX_MTU;
+    ssl->keys.dtls_state.window = 0;
+    ssl->keys.dtls_state.nextEpoch = 0;
+    ssl->keys.dtls_state.nextSeq = 0;
 #endif
 
 #ifndef NO_OLD_TLS
@@ -1478,13 +1488,13 @@ int InitSSL(CYASSL* ssl, CYASSL_CTX* ctx)
 
 #ifdef CYASSL_DTLS
     ssl->keys.dtls_sequence_number      = 0;
-    ssl->keys.dtls_peer_sequence_number = 0;
-    ssl->keys.dtls_expected_peer_sequence_number = 0;
+    ssl->keys.dtls_state.curSeq         = 0;
+    ssl->keys.dtls_state.nextSeq        = 0;
     ssl->keys.dtls_handshake_number     = 0;
     ssl->keys.dtls_expected_peer_handshake_number = 0;
     ssl->keys.dtls_epoch                = 0;
-    ssl->keys.dtls_peer_epoch           = 0;
-    ssl->keys.dtls_expected_peer_epoch  = 0;
+    ssl->keys.dtls_state.curEpoch       = 0;
+    ssl->keys.dtls_state.nextEpoch      = 0;
     ssl->dtls_timeout_init              = DTLS_TIMEOUT_INIT;
     ssl->dtls_timeout_max               = DTLS_TIMEOUT_MAX;
     ssl->dtls_timeout                   = ssl->dtls_timeout_init;
@@ -2762,9 +2772,9 @@ static int GetRecordHeader(CYASSL* ssl, const byte* input, word32* inOutIdx,
         /* type and version in same sport */
         XMEMCPY(rh, input + *inOutIdx, ENUM_LEN + VERSION_SZ);
         *inOutIdx += ENUM_LEN + VERSION_SZ;
-        ato16(input + *inOutIdx, &ssl->keys.dtls_peer_epoch);
+        ato16(input + *inOutIdx, &ssl->keys.dtls_state.curEpoch);
         *inOutIdx += 4; /* advance past epoch, skip first 2 seq bytes for now */
-        ato32(input + *inOutIdx, &ssl->keys.dtls_peer_sequence_number);
+        ato32(input + *inOutIdx, &ssl->keys.dtls_state.curSeq);
         *inOutIdx += 4;  /* advance past rest of seq */
         ato16(input + *inOutIdx, size);
         *inOutIdx += LENGTH_SZ;
@@ -2785,27 +2795,14 @@ static int GetRecordHeader(CYASSL* ssl, const byte* input, word32* inOutIdx,
             return VERSION_ERROR;              /* only use requested version */
         }
     }
-#if 0
-    /* Instead of this, check the datagram against the sliding window of
-     * received datagram goodness. */
+
 #ifdef CYASSL_DTLS
-    /* If DTLS, check the sequence number against expected. If out of
-     * order, drop the record. Allows newer records in and resets the
-     * expected to the next record. */
     if (ssl->options.dtls) {
-        if ((ssl->keys.dtls_expected_peer_epoch ==
-                                        ssl->keys.dtls_peer_epoch) &&
-                (ssl->keys.dtls_peer_sequence_number >=
-                                ssl->keys.dtls_expected_peer_sequence_number)) {
-            ssl->keys.dtls_expected_peer_sequence_number =
-                            ssl->keys.dtls_peer_sequence_number + 1;
-        }
-        else {
+        if (DtlsCheckWindow(&ssl->keys.dtls_state) != 1)
             return SEQUENCE_ERROR;
-        }
     }
 #endif
-#endif
+
     /* record layer length check */
 #ifdef HAVE_MAX_FRAGMENT
     if (*size > (ssl->max_fragment + MAX_COMP_EXTRA + MAX_MSG_EXTRA))
@@ -3868,6 +3865,68 @@ static int DoHandShakeMsg(CYASSL* ssl, byte* input, word32* inOutIdx,
 
 
 #ifdef CYASSL_DTLS
+
+static INLINE int DtlsCheckWindow(DtlsState* state)
+{
+    word32 cur;
+    word32 next;
+    DtlsSeq window;
+
+    if (state->curEpoch == state->nextEpoch) {
+        next = state->nextSeq;
+        window = state->window;
+    }
+    else if (state->curEpoch < state->nextEpoch) {
+        next = state->prevSeq;
+        window = state->prevWindow;
+    }
+    else {
+        return 0;
+    }
+
+    cur = state->curSeq;
+
+    if ((next > DTLS_SEQ_BITS) && (cur < next - DTLS_SEQ_BITS)) {
+        return 0;
+    }
+    else if ((cur < next) && (window & (1 << (next - cur - 1)))) {
+        return 0;
+    }
+
+    return 1;
+}
+
+
+static INLINE int DtlsUpdateWindow(DtlsState* state)
+{
+    word32 cur;
+    word32* next;
+    DtlsSeq* window;
+
+    if (state->curEpoch == state->nextEpoch) {
+        next = &state->nextSeq;
+        window = &state->window;
+    }
+    else {
+        next = &state->prevSeq;
+        window = &state->prevWindow;
+    }
+
+    cur = state->curSeq;
+
+    if (cur < *next) {
+        *window |= (1 << (*next - cur - 1));
+    }
+    else {
+        *window <<= (1 + cur - *next);
+        *window |= 1;
+        *next = cur + 1;
+    }
+
+    return 1;
+}
+
+
 static int DtlsMsgDrain(CYASSL* ssl)
 {
     DtlsMsg* item = ssl->dtls_msg_list;
@@ -4888,8 +4947,6 @@ int ProcessReply(CYASSL* ssl)
                                        &ssl->curRL, &ssl->curSize);
 #ifdef CYASSL_DTLS
             if (ssl->options.dtls && ret == SEQUENCE_ERROR) {
-                /* This message is out of order. If we are handshaking, save
-                 *it for later. Otherwise go ahead and process it. */
                 ssl->options.processReply = doProcessInit;
                 ssl->buffers.inputBuffer.length = 0;
                 ssl->buffers.inputBuffer.idx = 0;
@@ -4925,7 +4982,14 @@ int ProcessReply(CYASSL* ssl)
         /* the record layer is here */
         case runProcessingOneMessage:
 
-            if (ssl->keys.encryptionOn && ssl->keys.decryptedCur == 0) {
+            #ifdef CYASSL_DTLS
+            if (ssl->options.dtls &&
+                ssl->keys.dtls_state.curEpoch < ssl->keys.dtls_state.nextEpoch)
+                ssl->keys.decryptedCur = 1;
+            #endif
+
+            if (ssl->keys.encryptionOn && ssl->keys.decryptedCur == 0)
+            {
                 ret = SanityCheckCipherText(ssl, ssl->curSize);
                 if (ret < 0)
                     return ret;
@@ -4975,6 +5039,12 @@ int ProcessReply(CYASSL* ssl)
                 ssl->keys.decryptedCur = 1;
             }
 
+            if (ssl->options.dtls) {
+            #ifdef CYASSL_DTLS
+                DtlsUpdateWindow(&ssl->keys.dtls_state);
+            #endif /* CYASSL_DTLS */
+            }
+
             CYASSL_MSG("received record layer msg");
 
             switch (ssl->curRL.type) {
@@ -5034,8 +5104,8 @@ int ProcessReply(CYASSL* ssl)
                     #ifdef CYASSL_DTLS
                         if (ssl->options.dtls) {
                             DtlsPoolReset(ssl);
-                            ssl->keys.dtls_expected_peer_epoch++;
-                            ssl->keys.dtls_expected_peer_sequence_number = 0;
+                            ssl->keys.dtls_state.nextEpoch++;
+                            ssl->keys.dtls_state.nextSeq = 0;
                         }
                     #endif
 
diff --git a/src/tls.c b/src/tls.c
index 3d9a83a20..b8f6b1d8a 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -401,7 +401,7 @@ static INLINE word32 GetSEQIncrement(CYASSL* ssl, int verify)
 #ifdef CYASSL_DTLS
     if (ssl->options.dtls) {
         if (verify)
-            return ssl->keys.dtls_peer_sequence_number; /* explicit from peer */
+            return ssl->keys.dtls_state.curSeq; /* explicit from peer */
         else
             return ssl->keys.dtls_sequence_number - 1; /* already incremented */
     }
@@ -418,9 +418,9 @@ static INLINE word32 GetSEQIncrement(CYASSL* ssl, int verify)
 static INLINE word32 GetEpoch(CYASSL* ssl, int verify)
 {
     if (verify)
-        return ssl->keys.dtls_peer_epoch; 
+        return ssl->keys.dtls_state.curEpoch;
     else
-        return ssl->keys.dtls_epoch; 
+        return ssl->keys.dtls_epoch;
 }
 
 #endif /* CYASSL_DTLS */