Index: sys/netinet/dccp.h
===================================================================
--- /dev/null
+++ sys/netinet/dccp.h
@@ -0,0 +1,78 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2019 Tom Jones <thj@freebsd.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+#ifndef _NETINET_DCCP_H_
+#define _NETINET_DCCP_H_
+
+__FBSDID("$FreeBSD$");
+
+/* DCCP protocol header as per RFC4340 */
+struct dccphdr {
+	uint16_t	d_sport;
+	uint16_t	d_dport;
+	uint8_t		d_doff;
+#if BYTE_ORDER == LITTLE_ENDIAN
+	uint8_t		d_cscov:4,
+			d_ccval:4;
+#endif
+#if BYTE_ORDER == BIG_ENDIAN
+	uint8_t		d_ccval:4,
+			d_cscov:4;
+#endif
+	uint8_t		d_cksum[2];
+#if BYTE_ORDER == LITTLE_ENDIAN
+	uint8_t		d_res:3,
+			d_type:4,
+			d_x:1;
+#endif
+#if BYTE_ORDER == BIG_ENDIAN
+	uint8_t		d_x:1,
+			d_type:4,
+			d_res:3;
+#endif
+       /*
+        * Provide enough space for both the short (24 bit) sequence number and
+        * the long (48 bit) sequene number and a leading reserved byte in
+        * front of the long sequence number.
+        */
+       union dccp_seqno {
+               uint8_t shortseq[3];
+               struct dccp_long_seqno {
+                       uint8_t res;
+                       uint8_t seq[6];
+               } longseq;
+       } d_seqno;
+};
+
+#define d_seqno_short d_seqno.shortseq;
+#define d_seqno_long d_seqno.longseq.seq;
+
+#define DCCP_SHORTHDR	12
+#define DCCP_LONGHDR	16
+#define DCCP_EXTHDR	0x80
+
+#endif /* _NETINET_DCCP_H */