+#define L2TP_FLAG_TYPE 0x8000 /* Type (0=Data, 1=Control) */
+#define L2TP_FLAG_LENGTH 0x4000 /* Length */
+#define L2TP_FLAG_SEQUENCE 0x0800 /* Sequence */
+#define L2TP_FLAG_OFFSET 0x0200 /* Offset */
+#define L2TP_FLAG_PRIORITY 0x0100 /* Priority */
+
+#define L2TP_VERSION_MASK 0x000f /* Version Mask */
+#define L2TP_VERSION_L2F 0x0001 /* L2F */
+#define L2TP_VERSION_L2TP 0x0002 /* L2TP */
+
+#define L2TP_AVP_HDR_FLAG_MANDATORY 0x8000 /* Mandatory Flag */
+#define L2TP_AVP_HDR_FLAG_HIDDEN 0x4000 /* Hidden Flag */
+#define L2TP_AVP_HDR_LEN_MASK 0x03ff /* Length Mask */
+
+#define L2TP_FRAMING_CAP_SYNC_MASK 0x00000001 /* Synchronous */
+#define L2TP_FRAMING_CAP_ASYNC_MASK 0x00000002 /* Asynchronous */
+
+#define L2TP_FRAMING_TYPE_SYNC_MASK 0x00000001 /* Synchronous */
+#define L2TP_FRAMING_TYPE_ASYNC_MASK 0x00000002 /* Asynchronous */
+
+#define L2TP_BEARER_CAP_DIGITAL_MASK 0x00000001 /* Digital */
+#define L2TP_BEARER_CAP_ANALOG_MASK 0x00000002 /* Analog */
+
+#define L2TP_BEARER_TYPE_DIGITAL_MASK 0x00000001 /* Digital */
+#define L2TP_BEARER_TYPE_ANALOG_MASK 0x00000002 /* Analog */
+
+/* Authen Type */
+#define L2TP_AUTHEN_TYPE_RESERVED 0x0000 /* Reserved */
+#define L2TP_AUTHEN_TYPE_TEXTUAL 0x0001 /* Textual username/password exchange */
+#define L2TP_AUTHEN_TYPE_CHAP 0x0002 /* PPP CHAP */
+#define L2TP_AUTHEN_TYPE_PAP 0x0003 /* PPP PAP */
+#define L2TP_AUTHEN_TYPE_NO_AUTH 0x0004 /* No Authentication */
+#define L2TP_AUTHEN_TYPE_MSCHAPv1 0x0005 /* MSCHAPv1 */
+
+#define L2TP_PROXY_AUTH_ID_MASK 0x00ff
+