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diff --git a/print-realtek.c b/print-realtek.c
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+/*
+ * Copyright (c) 2007 - Andrey "nording" Chernyak <andrew@nording.ru>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that: (1) source code distributions
+ * retain the above copyright notice and this paragraph in its entirety, (2)
+ * distributions including binary code include the above copyright notice and
+ * this paragraph in its entirety in the documentation or other materials
+ * provided with the distribution, and (3) all advertising materials mentioning
+ * features or use of this software display the following acknowledgement:
+ * ``This product includes software developed by the University of California,
+ * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
+ * the University nor the names of its contributors may be used to endorse
+ * or promote products derived from this software without specific prior
+ * written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * Format and print Realtek Remote Control Protocol (RRCP), Realtek
+ * Loop Detection Protocol (RLDP), and Realtek Echo Protocol (REP) packets,
+ * as well as tag formats used by some Realtek switch chips to supply
+ * tag information to a host CPU for a switch.
+ */
+
+/* \summary: printer for various Realtek protocols */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include "netdissect-stdinc.h"
+
+#include "netdissect.h"
+#include "addrtoname.h"
+#include "extract.h"
+
+#define RTL_PROTOCOL_OFFSET	0	/* Protocol and possibly other data - 1 byte */
+
+#define RTL_PROTOCOL_RRCP	0x01	/* RRCP */
+#define RTL_PROTOCOL_REP	0x02	/* REP */
+#define RTL_PROTOCOL_RLDP	0x03	/* RLDP */
+#define RTL_PROTOCOL_RLDP2	0x23	/* also RLDP */
+#define RTL_PROTOCOL_XXX_DSA	0x04	/* DSA protocol for some chip(s) */
+
+/*
+ * Values for the upper 4 bits of the protocol field, for
+ * protocols where the lower 4 bits contain protocol data.
+ *
+ * See section 8.10 "CPU Tag Function" of
+ *
+ *    http://realtek.info/pdf/rtl8306sd%28m%29_datasheet_1.1.pdf
+ *
+ * for the RTL8306 DSA protocol tag format.
+ */
+#define RTL_PROTOCOL_8306_DSA		0x90	/* RTL8306 DSA protocol */
+#define RTL_PROTOCOL_8366RB_DSA		0xA0	/* RTL8366RB DSA protocol */
+
+#define RRCP_OPCODE_ISREPLY_OFFSET	1	/* opcode and isreply flag - 1 byte */
+
+#define RRCP_OPCODE_MASK		0x7F	/* 0x00 = hello, 0x01 = get, 0x02 = set */
+#define RRCP_ISREPLY			0x80	/* 0 = request to switch, 0x80 = reply from switch */
+
+#define RRCP_OPCODE_HELLO		0x00
+#define RRCP_OPCODE_GET_CONFIGURATION	0x01
+#define RRCP_OPCODE_SET_CONFIGURATION	0x02
+
+#define RRCP_AUTHKEY_OFFSET		2	/* authorization key - 2 bytes, 0x2379 by default */
+
+/* most packets */
+#define RRCP_REG_ADDR_OFFSET		4	/* register address - 2 bytes */
+#define RRCP_REG_DATA_OFFSET		6	/* register data - 4 bytes */
+#define RRCP_COOKIE1_OFFSET		10	/* 4 bytes */
+#define RRCP_COOKIE2_OFFSET		14	/* 4 bytes */
+
+/* hello reply packets */
+#define RRCP_DOWNLINK_PORT_OFFSET	4	/* 1 byte */
+#define RRCP_UPLINK_PORT_OFFSET		5	/* 1 byte */
+#define RRCP_UPLINK_MAC_OFFSET		6	/* 6 byte MAC address */
+#define RRCP_CHIP_ID_OFFSET		12	/* 2 bytes */
+#define RRCP_VENDOR_ID_OFFSET		14	/* 4 bytes */
+
+static const struct tok opcode_values[] = {
+	{ RRCP_OPCODE_HELLO,             "hello" },
+	{ RRCP_OPCODE_GET_CONFIGURATION, "get" },
+	{ RRCP_OPCODE_SET_CONFIGURATION, "set" },
+	{ 0, NULL }
+};
+
+/*
+ * Print RRCP packets.
+ *
+ * See, for example, section 8.20 "Realtek Remote Control Protocol" of
+ *
+ *    http://realtek.info/pdf/rtl8324.pdf
+ *
+ * and section 7.22 "Realtek Remote Control Protocol" of
+ *
+ *    http://realtek.info/pdf/rtl8326.pdf
+ *
+ * and this page on the OpenRRCP Wiki:
+ *
+ *    http://openrrcp.org.ru/wiki/rrcp_protocol
+ *
+ * for information on RRCP.
+ */
+static void
+rrcp_print(netdissect_options *ndo,
+	  const u_char *cp)
+{
+	uint8_t rrcp_opcode;
+
+	ndo->ndo_protocol = "rrcp";
+	rrcp_opcode = GET_U_1((cp + RRCP_OPCODE_ISREPLY_OFFSET)) & RRCP_OPCODE_MASK;
+	ND_PRINT("RRCP %s: %s",
+		((GET_U_1(cp + RRCP_OPCODE_ISREPLY_OFFSET)) & RRCP_ISREPLY) ? "reply" : "query",
+		tok2str(opcode_values,"unknown opcode (0x%02x)",rrcp_opcode));
+	if (rrcp_opcode==RRCP_OPCODE_GET_CONFIGURATION ||
+	    rrcp_opcode==RRCP_OPCODE_SET_CONFIGURATION){
+    	    ND_PRINT(" addr=0x%04x, data=0x%08x",
+		     GET_LE_U_2(cp + RRCP_REG_ADDR_OFFSET),
+		     GET_LE_U_4(cp + RRCP_REG_DATA_OFFSET));
+	}
+	ND_PRINT(", auth=0x%04x",
+	         GET_BE_U_2(cp + RRCP_AUTHKEY_OFFSET));
+	if (rrcp_opcode==RRCP_OPCODE_HELLO &&
+	     ((GET_U_1(cp + RRCP_OPCODE_ISREPLY_OFFSET)) & RRCP_ISREPLY)){
+	    ND_PRINT(" downlink_port=%u, uplink_port=%u, uplink_mac=%s, vendor_id=%08x ,chip_id=%04x ",
+		     GET_U_1(cp + RRCP_DOWNLINK_PORT_OFFSET),
+		     GET_U_1(cp + RRCP_UPLINK_PORT_OFFSET),
+		     GET_ETHERADDR_STRING(cp + RRCP_UPLINK_MAC_OFFSET),
+		     GET_BE_U_4(cp + RRCP_VENDOR_ID_OFFSET),
+		     GET_BE_U_2(cp + RRCP_CHIP_ID_OFFSET));
+	}else if (rrcp_opcode==RRCP_OPCODE_GET_CONFIGURATION ||
+	          rrcp_opcode==RRCP_OPCODE_SET_CONFIGURATION){
+	    ND_PRINT(", cookie=0x%08x%08x ",
+		    GET_BE_U_4(cp + RRCP_COOKIE2_OFFSET),
+		    GET_BE_U_4(cp + RRCP_COOKIE1_OFFSET));
+	}
+}
+
+/*
+ * Print Realtek packets.
+ *
+ * See, for example, section 8.22 "Realtek Echo Protocol" of
+ *
+ *    http://realtek.info/pdf/rtl8324.pdf
+ *
+ * and section 7.24 "Realtek Echo Protocol" of
+ *
+ *    http://realtek.info/pdf/rtl8326.pdf
+ *
+ * for information on REP.
+ *
+ * See section 8.21 "Network Loop Connection Fault Detection" of
+ *
+ *    http://realtek.info/pdf/rtl8324.pdf
+ *
+ * and section 7.23 "Network Loop Connection Fault Detection" of
+ *
+ *    http://realtek.info/pdf/rtl8326.pdf
+ *
+ * for information on RLDP.
+ *
+ * See also section 7.3.8 "Loop Detection" of
+ *
+ *    http://www.ibselectronics.com/ibsstore/datasheet/RTL8306E-CG.pdf
+ *
+ * (revision 1.1 of the RTL8306E-CG datasheet), which describes a loop
+ * detection protocol for which the payload has a 16-bit (presumably
+ * big-endian) field containing the value 0x0300, followed by what is
+ * presumably a 16-bit big-endian field the upper 12 bits of which are 0
+ * and the lower 4 bits of which are a TTL value, followed by zeroes to
+ * pad the packet out to the minimum Ethernet packet size.
+ *
+ * See also section 7.3.13 "Loop Detection" of
+ *
+ *    http://realtek.info/pdf/rtl8305sb.pdf
+ *
+ * (revision 1.3 of the RTL8305SB datasheet), which describes a similar
+ * loop detection protocol that lacks the TTL field - all the bytes
+ * after 0x0300 are zero.
+ *
+ * See also section 7.3.7 "Loop Detection" of
+ *
+ *    https://datasheet.lcsc.com/lcsc/1810221720_Realtek-Semicon-RTL8305NB-CG_C52146.pdf
+ *
+ * (revision 1.0 of the RTL8305NB-CT datasheet), which describes a loop
+ * detection protocol similar to the one from the RTL8306E-CG datasheet,
+ * except that the first value is 0x2300, not 0x0300.
+ *
+ * And, on top of all that, I've seen packets where the first octet of
+ * the packet is 0x23, and that's followed by 6 unknown octets (a MAC
+ * address of some sort?  It differs from packet to packet in a capture),
+ * followed by the MAC address that appears in the source address in the
+ * Ethernet header (possibly the originator, in case the packet is forwarded,
+ * in which case the forwarded packets won't have the source address from
+ * the Ethernet header there), followed by unknown stuff (0x0d followed by
+ * zeroes for all such packets in one capture, 0x01 followed by zeroes for
+ * all such packets in another capture, 0x07 followed by 0x20's for all
+ * such packets in yet another capture).  The OpenRRCP issue at
+ * https://github.com/illarionov/OpenRRCP/issues/3 shows a capture
+ * similar to the last of those, but with 0x02 instead of 0x07.  Or is that
+ * just crap in the buffer in which the chip constructed the packet, left
+ * over from something else?
+ */
+void
+rtl_print(netdissect_options *ndo,
+	  const u_char *cp,
+	  u_int length _U_,
+	  const struct lladdr_info *src,
+	  const struct lladdr_info *dst)
+{
+	uint8_t rtl_proto;
+
+	ndo->ndo_protocol = "rtl";
+
+	if (src != NULL && dst != NULL) {
+		ND_PRINT("%s > %s, ",
+			(src->addr_string)(ndo, src->addr),
+			(dst->addr_string)(ndo, dst->addr));
+	}
+
+	rtl_proto = GET_U_1(cp + RTL_PROTOCOL_OFFSET);
+
+	if (rtl_proto == RTL_PROTOCOL_RRCP)
+		rrcp_print(ndo, cp);
+	else if (rtl_proto == RTL_PROTOCOL_REP) {
+		/*
+		 * REP packets have no payload.
+		 */
+		ND_PRINT("REP");
+	} else if (rtl_proto == RTL_PROTOCOL_RLDP ||
+	           rtl_proto == RTL_PROTOCOL_RLDP2) {
+		/*
+		 * RLDP packets have no payload.
+		 * (XXX - except when they do?  See above.)
+		 */
+		ND_PRINT("RLDP");
+	} else if (rtl_proto == RTL_PROTOCOL_XXX_DSA)
+		ND_PRINT("Realtek 8-byte DSA tag");
+	else if ((rtl_proto & 0xF0) == RTL_PROTOCOL_8306_DSA)
+		ND_PRINT("Realtek RTL8306 4-byte DSA tag");
+	else if ((rtl_proto & 0xF0) == RTL_PROTOCOL_8366RB_DSA)
+		ND_PRINT("Realtek RTL8366RB 4-byte DSA tag");
+	else
+		ND_PRINT("Realtek unknown type 0x%02x", rtl_proto);
+}