print-ip6.c - platform/external/tcpdump - Git at Google

 /*
  * Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994
  *	The Regents of the University of California.  All rights reserved.
  *
  * 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.
  */

 /* \summary: IPv6 printer */

 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif

 #include "netdissect-stdinc.h"

 #include <string.h>

 #include "netdissect.h"
 #include "addrtoname.h"
 #include "extract.h"

 #include "ip6.h"
 #include "ipproto.h"

 /*
  * If routing headers are presend and valid, set dst to the final destination.
  * Otherwise, set it to the IPv6 destination.
  *
  * This is used for UDP and TCP pseudo-header in the checksum
  * calculation.
  */
 static void
 ip6_finddst(netdissect_options *ndo, nd_ipv6 *dst,
             const struct ip6_hdr *ip6)
 {
 	const u_char *cp;
 	u_int advance;
 	u_int nh;
 	const void *dst_addr;
 	const struct ip6_rthdr *dp;
 	const struct ip6_rthdr0 *dp0;
 	const struct ip6_srh *srh;
 	const u_char *p;
 	int i, len;

 	cp = (const u_char *)ip6;
 	advance = sizeof(struct ip6_hdr);
 	nh = GET_U_1(ip6->ip6_nxt);
 	dst_addr = (const void *)ip6->ip6_dst;

 	while (cp < ndo->ndo_snapend) {
 		cp += advance;

 		switch (nh) {

 		case IPPROTO_HOPOPTS:
 		case IPPROTO_DSTOPTS:
 		case IPPROTO_MOBILITY_OLD:
 		case IPPROTO_MOBILITY:
 			/*
 			 * These have a header length byte, following
 			 * the next header byte, giving the length of
 			 * the header, in units of 8 octets, excluding
 			 * the first 8 octets.
 			 */
 			advance = (GET_U_1(cp + 1) + 1) << 3;
 			nh = GET_U_1(cp);
 			break;

 		case IPPROTO_FRAGMENT:
 			/*
 			 * The byte following the next header byte is
 			 * marked as reserved, and the header is always
 			 * the same size.
 			 */
 			advance = sizeof(struct ip6_frag);
 			nh = GET_U_1(cp);
 			break;

 		case IPPROTO_ROUTING:
 			/*
 			 * OK, we found it.
 			 */
 			dp = (const struct ip6_rthdr *)cp;
 			ND_TCHECK_SIZE(dp);
 			len = GET_U_1(dp->ip6r_len);
 			switch (GET_U_1(dp->ip6r_type)) {

 			case IPV6_RTHDR_TYPE_0:
 			case IPV6_RTHDR_TYPE_2:		/* Mobile IPv6 ID-20 */
 				dp0 = (const struct ip6_rthdr0 *)dp;
 				if (len % 2 == 1)
 					goto trunc;
 				len >>= 1;
 				p = (const u_char *) dp0->ip6r0_addr;
 				for (i = 0; i < len; i++) {
 					ND_TCHECK_16(p);
 					dst_addr = (const void *)p;
 					p += 16;
 				}
 				break;
 			case IPV6_RTHDR_TYPE_4:
 				/* IPv6 Segment Routing Header (SRH) */
 				srh = (const struct ip6_srh *)dp;
 				if (len % 2 == 1)
 					goto trunc;
 				p = (const u_char *) srh->srh_segments;
 				/*
 				 * The list of segments are encoded in the reverse order.
 				 * Accordingly, the final DA is encoded in srh_segments[0]
 				 */
 				ND_TCHECK_16(p);
 				dst_addr = (const void *)p;
 				break;

 			default:
 				break;
 			}

 			/*
 			 * Only one routing header to a customer.
 			 */
 			goto done;

 		case IPPROTO_AH:
 		case IPPROTO_ESP:
 		case IPPROTO_IPCOMP:
 		default:
 			/*
 			 * AH and ESP are, in the RFCs that describe them,
 			 * described as being "viewed as an end-to-end
 			 * payload" "in the IPv6 context, so that they
 			 * "should appear after hop-by-hop, routing, and
 			 * fragmentation extension headers".  We assume
 			 * that's the case, and stop as soon as we see
 			 * one.  (We can't handle an ESP header in
 			 * the general case anyway, as its length depends
 			 * on the encryption algorithm.)
 			 *
 			 * IPComp is also "viewed as an end-to-end
 			 * payload" "in the IPv6 context".
 			 *
 			 * All other protocols are assumed to be the final
 			 * protocol.
 			 */
 			goto done;
 		}
 	}

 done:
 trunc:
 	GET_CPY_BYTES(dst, dst_addr, sizeof(nd_ipv6));
 }

 /*
  * Compute a V6-style checksum by building a pseudoheader.
  */
 uint16_t
 nextproto6_cksum(netdissect_options *ndo,
                  const struct ip6_hdr *ip6, const uint8_t *data,
 		 u_int len, u_int covlen, uint8_t next_proto)
 {
         struct {
                 nd_ipv6 ph_src;
                 nd_ipv6 ph_dst;
                 uint32_t       ph_len;
                 uint8_t        ph_zero[3];
                 uint8_t        ph_nxt;
         } ph;
         struct cksum_vec vec[2];
         u_int nh;

         /* pseudo-header */
         memset(&ph, 0, sizeof(ph));
         GET_CPY_BYTES(&ph.ph_src, ip6->ip6_src, sizeof(nd_ipv6));
         nh = GET_U_1(ip6->ip6_nxt);
         switch (nh) {

         case IPPROTO_HOPOPTS:
         case IPPROTO_DSTOPTS:
         case IPPROTO_MOBILITY_OLD:
         case IPPROTO_MOBILITY:
         case IPPROTO_FRAGMENT:
         case IPPROTO_ROUTING:
                 /*
                  * The next header is either a routing header or a header
                  * after which there might be a routing header, so scan
                  * for a routing header.
                  */
                 ip6_finddst(ndo, &ph.ph_dst, ip6);
                 break;

         default:
                 GET_CPY_BYTES(&ph.ph_dst, ip6->ip6_dst, sizeof(nd_ipv6));
                 break;
         }
         ph.ph_len = htonl(len);
         ph.ph_nxt = next_proto;

         vec[0].ptr = (const uint8_t *)(void *)&ph;
         vec[0].len = sizeof(ph);
         vec[1].ptr = data;
         vec[1].len = covlen;

         return in_cksum(vec, 2);
 }

 /*
  * print an IP6 datagram.
  */
 void
 ip6_print(netdissect_options *ndo, const u_char *bp, u_int length)
 {
 	const struct ip6_hdr *ip6;
 	int advance;
 	u_int len;
 	u_int total_advance;
 	const u_char *cp;
 	uint32_t payload_len;
 	uint8_t ph, nh;
 	int fragmented = 0;
 	u_int flow;
 	int found_extension_header;
 	int found_jumbo;
 	int found_hbh;

 	ndo->ndo_protocol = "ip6";
 	ip6 = (const struct ip6_hdr *)bp;

 	ND_TCHECK_SIZE(ip6);
 	if (length < sizeof (struct ip6_hdr)) {
 		ND_PRINT("truncated-ip6 %u", length);
 		return;
 	}

 	if (!ndo->ndo_eflag)
 	    ND_PRINT("IP6 ");

 	if (IP6_VERSION(ip6) != 6) {
 	  ND_PRINT("version error: %u != 6", IP6_VERSION(ip6));
 	  return;
 	}

 	payload_len = GET_BE_U_2(ip6->ip6_plen);
 	/*
 	 * RFC 1883 says:
 	 *
 	 * The Payload Length field in the IPv6 header must be set to zero
 	 * in every packet that carries the Jumbo Payload option.  If a
 	 * packet is received with a valid Jumbo Payload option present and
 	 * a non-zero IPv6 Payload Length field, an ICMP Parameter Problem
 	 * message, Code 0, should be sent to the packet's source, pointing
 	 * to the Option Type field of the Jumbo Payload option.
 	 *
 	 * Later versions of the IPv6 spec don't discuss the Jumbo Payload
 	 * option.
 	 *
 	 * If the payload length is 0, we temporarily just set the total
 	 * length to the remaining data in the packet (which, for Ethernet,
 	 * could include frame padding, but if it's a Jumbo Payload frame,
 	 * it shouldn't even be sendable over Ethernet, so we don't worry
 	 * about that), so we can process the extension headers in order
 	 * to *find* a Jumbo Payload hop-by-hop option and, when we've
 	 * processed all the extension headers, check whether we found
 	 * a Jumbo Payload option, and fail if we haven't.
 	 */
 	if (payload_len != 0) {
 		len = payload_len + sizeof(struct ip6_hdr);
 		if (length < len)
 			ND_PRINT("truncated-ip6 - %u bytes missing!",
 				len - length);
 	} else
 		len = length + sizeof(struct ip6_hdr);

 	ph = 255;
 	nh = GET_U_1(ip6->ip6_nxt);
 	if (ndo->ndo_vflag) {
 	    flow = GET_BE_U_4(ip6->ip6_flow);
 	    ND_PRINT("(");
 	    /* RFC 2460 */
 	    if (flow & 0x0ff00000)
 	        ND_PRINT("class 0x%02x, ", (flow & 0x0ff00000) >> 20);
 	    if (flow & 0x000fffff)
 	        ND_PRINT("flowlabel 0x%05x, ", flow & 0x000fffff);

 	    ND_PRINT("hlim %u, next-header %s (%u) payload length: %u) ",
 	                 GET_U_1(ip6->ip6_hlim),
 	                 tok2str(ipproto_values,"unknown",nh),
 	                 nh,
 	                 payload_len);
 	}

 	/*
 	 * Cut off the snapshot length to the end of the IP payload.
 	 */
 	if (!nd_push_snaplen(ndo, bp, len)) {
 		(*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
 			"%s: can't push snaplen on buffer stack", __func__);
 	}

 	cp = (const u_char *)ip6;
 	advance = sizeof(struct ip6_hdr);
 	total_advance = 0;
 	/* Process extension headers */
 	found_extension_header = 0;
 	found_jumbo = 0;
 	found_hbh = 0;
 	while (cp < ndo->ndo_snapend && advance > 0) {
 		if (len < (u_int)advance)
 			goto trunc;
 		cp += advance;
 		len -= advance;
 		total_advance += advance;

 		if (cp == (const u_char *)(ip6 + 1) &&
 		    nh != IPPROTO_TCP && nh != IPPROTO_UDP &&
 		    nh != IPPROTO_DCCP && nh != IPPROTO_SCTP) {
 			ND_PRINT("%s > %s: ", GET_IP6ADDR_STRING(ip6->ip6_src),
 				     GET_IP6ADDR_STRING(ip6->ip6_dst));
 		}

 		switch (nh) {

 		case IPPROTO_HOPOPTS:
 			/*
 			 * The Hop-by-Hop Options header, when present,
 			 * must immediately follow the IPv6 header (RFC 8200)
 			 */
 			if (found_hbh == 1) {
 				ND_PRINT("[The Hop-by-Hop Options header was already found]");
 				nd_print_invalid(ndo);
 				return;
 			}
 			if (ph != 255) {
 				ND_PRINT("[The Hop-by-Hop Options header don't follow the IPv6 header]");
 				nd_print_invalid(ndo);
 				return;
 			}
 			advance = hbhopt_process(ndo, cp, &found_jumbo, &payload_len);
 			if (payload_len == 0 && found_jumbo == 0) {
 				ND_PRINT("[No valid Jumbo Payload Hop-by-Hop option found]");
 				nd_print_invalid(ndo);
 				return;
 			}
 			if (advance < 0) {
 				nd_pop_packet_info(ndo);
 				return;
 			}
 			found_extension_header = 1;
 			found_hbh = 1;
 			nh = GET_U_1(cp);
 			break;

 		case IPPROTO_DSTOPTS:
 			advance = dstopt_process(ndo, cp);
 			if (advance < 0) {
 				nd_pop_packet_info(ndo);
 				return;
 			}
 			found_extension_header = 1;
 			nh = GET_U_1(cp);
 			break;

 		case IPPROTO_FRAGMENT:
 			advance = frag6_print(ndo, cp, (const u_char *)ip6);
 			if (advance < 0 || ndo->ndo_snapend <= cp + advance) {
 				nd_pop_packet_info(ndo);
 				return;
 			}
 			found_extension_header = 1;
 			nh = GET_U_1(cp);
 			fragmented = 1;
 			break;

 		case IPPROTO_MOBILITY_OLD:
 		case IPPROTO_MOBILITY:
 			/*
 			 * XXX - we don't use "advance"; RFC 3775 says that
 			 * the next header field in a mobility header
 			 * should be IPPROTO_NONE, but speaks of
 			 * the possibility of a future extension in
 			 * which payload can be piggybacked atop a
 			 * mobility header.
 			 */
 			advance = mobility_print(ndo, cp, (const u_char *)ip6);
 			if (advance < 0) {
 				nd_pop_packet_info(ndo);
 				return;
 			}
 			found_extension_header = 1;
 			nh = GET_U_1(cp);
 			nd_pop_packet_info(ndo);
 			return;

 		case IPPROTO_ROUTING:
 			ND_TCHECK_1(cp);
 			advance = rt6_print(ndo, cp, (const u_char *)ip6);
 			if (advance < 0) {
 				nd_pop_packet_info(ndo);
 				return;
 			}
 			found_extension_header = 1;
 			nh = GET_U_1(cp);
 			break;

 		default:
 			/*
 			 * Not an extension header; hand off to the
 			 * IP protocol demuxer.
 			 */
 			if (found_jumbo) {
 				/*
 				 * We saw a Jumbo Payload option.
 				 * Set the length to the payload length
 				 * plus the IPv6 header length, and
 				 * change the snapshot length accordingly.
 				 *
 				 * But make sure it's not shorter than
 				 * the total number of bytes we've
 				 * processed so far.
 				 */
 				len = payload_len + sizeof(struct ip6_hdr);
 				if (len < total_advance)
 					goto trunc;
 				if (length < len)
 					ND_PRINT("truncated-ip6 - %u bytes missing!",
 						len - length);
 				nd_change_snaplen(ndo, bp, len);

 				/*
 				 * Now subtract the length of the IPv6
 				 * header plus extension headers to get
 				 * the payload length.
 				 */
 				len -= total_advance;
 			} else {
 				/*
 				 * We didn't see a Jumbo Payload option;
 				 * was the payload length zero?
 				 */
 				if (payload_len == 0) {
 					/*
 					 * Yes.  If we found an extension
 					 * header, treat that as a truncated
 					 * packet header, as there was
 					 * no payload to contain an
 					 * extension header.
 					 */
 					if (found_extension_header)
 						goto trunc;

 					/*
 					 * OK, we didn't see any extension
 					 * header, but that means we have
 					 * no payload, so set the length
 					 * to the IPv6 header length,
 					 * and change the snapshot length
 					 * accordingly.
 					 */
 					len = sizeof(struct ip6_hdr);
 					nd_change_snaplen(ndo, bp, len);

 					/*
 					 * Now subtract the length of
 					 * the IPv6 header plus extension
 					 * headers (there weren't any, so
 					 * that's just the IPv6 header
 					 * length) to get the payload length.
 					 */
 					len -= total_advance;
 				}
 			}
 			ip_demux_print(ndo, cp, len, 6, fragmented,
 				       GET_U_1(ip6->ip6_hlim), nh, bp);
 			nd_pop_packet_info(ndo);
 			return;
 		}
 		ph = nh;

 		/* ndo_protocol reassignment after xxx_print() calls */
 		ndo->ndo_protocol = "ip6";
 	}

 	nd_pop_packet_info(ndo);
 	return;
 trunc:
 	nd_print_trunc(ndo);
 }
	/*
	* Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994
	* The Regents of the University of California. All rights reserved.
	*
	* 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.
	*/

	/* \summary: IPv6 printer */

	#ifdef HAVE_CONFIG_H
	#include <config.h>
	#endif

	#include "netdissect-stdinc.h"

	#include <string.h>

	#include "netdissect.h"
	#include "addrtoname.h"
	#include "extract.h"

	#include "ip6.h"
	#include "ipproto.h"

	/*
	* If routing headers are presend and valid, set dst to the final destination.
	* Otherwise, set it to the IPv6 destination.
	*
	* This is used for UDP and TCP pseudo-header in the checksum
	* calculation.
	*/
	static void
	ip6_finddst(netdissect_options ndo, nd_ipv6 dst,
	const struct ip6_hdr *ip6)
	{
	const u_char *cp;
	u_int advance;
	u_int nh;
	const void *dst_addr;
	const struct ip6_rthdr *dp;
	const struct ip6_rthdr0 *dp0;
	const struct ip6_srh *srh;
	const u_char *p;
	int i, len;

	cp = (const u_char *)ip6;
	advance = sizeof(struct ip6_hdr);
	nh = GET_U_1(ip6->ip6_nxt);
	dst_addr = (const void *)ip6->ip6_dst;

	while (cp < ndo->ndo_snapend) {
	cp += advance;

	switch (nh) {

	case IPPROTO_HOPOPTS:
	case IPPROTO_DSTOPTS:
	case IPPROTO_MOBILITY_OLD:
	case IPPROTO_MOBILITY:
	/*
	* These have a header length byte, following
	* the next header byte, giving the length of
	* the header, in units of 8 octets, excluding
	* the first 8 octets.
	*/
	advance = (GET_U_1(cp + 1) + 1) << 3;
	nh = GET_U_1(cp);
	break;

	case IPPROTO_FRAGMENT:
	/*
	* The byte following the next header byte is
	* marked as reserved, and the header is always
	* the same size.
	*/
	advance = sizeof(struct ip6_frag);
	nh = GET_U_1(cp);
	break;

	case IPPROTO_ROUTING:
	/*
	* OK, we found it.
	*/
	dp = (const struct ip6_rthdr *)cp;
	ND_TCHECK_SIZE(dp);
	len = GET_U_1(dp->ip6r_len);
	switch (GET_U_1(dp->ip6r_type)) {

	case IPV6_RTHDR_TYPE_0:
	case IPV6_RTHDR_TYPE_2: /* Mobile IPv6 ID-20 */
	dp0 = (const struct ip6_rthdr0 *)dp;
	if (len % 2 == 1)
	goto trunc;
	len >>= 1;
	p = (const u_char *) dp0->ip6r0_addr;
	for (i = 0; i < len; i++) {
	ND_TCHECK_16(p);
	dst_addr = (const void *)p;
	p += 16;
	}
	break;
	case IPV6_RTHDR_TYPE_4:
	/* IPv6 Segment Routing Header (SRH) */
	srh = (const struct ip6_srh *)dp;
	if (len % 2 == 1)
	goto trunc;
	p = (const u_char *) srh->srh_segments;
	/*
	* The list of segments are encoded in the reverse order.
	* Accordingly, the final DA is encoded in srh_segments[0]
	*/
	ND_TCHECK_16(p);
	dst_addr = (const void *)p;
	break;

	default:
	break;
	}

	/*
	* Only one routing header to a customer.
	*/
	goto done;

	case IPPROTO_AH:
	case IPPROTO_ESP:
	case IPPROTO_IPCOMP:
	default:
	/*
	* AH and ESP are, in the RFCs that describe them,
	* described as being "viewed as an end-to-end
	* payload" "in the IPv6 context, so that they
	* "should appear after hop-by-hop, routing, and
	* fragmentation extension headers". We assume
	* that's the case, and stop as soon as we see
	* one. (We can't handle an ESP header in
	* the general case anyway, as its length depends
	* on the encryption algorithm.)
	*
	* IPComp is also "viewed as an end-to-end
	* payload" "in the IPv6 context".
	*
	* All other protocols are assumed to be the final
	* protocol.
	*/
	goto done;
	}
	}

	done:
	trunc:
	GET_CPY_BYTES(dst, dst_addr, sizeof(nd_ipv6));
	}

	/*
	* Compute a V6-style checksum by building a pseudoheader.
	*/
	uint16_t
	nextproto6_cksum(netdissect_options *ndo,
	const struct ip6_hdr ip6, const uint8_t data,
	u_int len, u_int covlen, uint8_t next_proto)
	{
	struct {
	nd_ipv6 ph_src;
	nd_ipv6 ph_dst;
	uint32_t ph_len;
	uint8_t ph_zero[3];
	uint8_t ph_nxt;
	} ph;
	struct cksum_vec vec[2];
	u_int nh;

	/* pseudo-header */
	memset(&ph, 0, sizeof(ph));
	GET_CPY_BYTES(&ph.ph_src, ip6->ip6_src, sizeof(nd_ipv6));
	nh = GET_U_1(ip6->ip6_nxt);
	switch (nh) {

	case IPPROTO_HOPOPTS:
	case IPPROTO_DSTOPTS:
	case IPPROTO_MOBILITY_OLD:
	case IPPROTO_MOBILITY:
	case IPPROTO_FRAGMENT:
	case IPPROTO_ROUTING:
	/*
	* The next header is either a routing header or a header
	* after which there might be a routing header, so scan
	* for a routing header.
	*/
	ip6_finddst(ndo, &ph.ph_dst, ip6);
	break;

	default:
	GET_CPY_BYTES(&ph.ph_dst, ip6->ip6_dst, sizeof(nd_ipv6));
	break;
	}
	ph.ph_len = htonl(len);
	ph.ph_nxt = next_proto;

	vec[0].ptr = (const uint8_t )(void )&ph;
	vec[0].len = sizeof(ph);
	vec[1].ptr = data;
	vec[1].len = covlen;

	return in_cksum(vec, 2);
	}

	/*
	* print an IP6 datagram.
	*/
	void
	ip6_print(netdissect_options ndo, const u_char bp, u_int length)
	{
	const struct ip6_hdr *ip6;
	int advance;
	u_int len;
	u_int total_advance;
	const u_char *cp;
	uint32_t payload_len;
	uint8_t ph, nh;
	int fragmented = 0;
	u_int flow;
	int found_extension_header;
	int found_jumbo;
	int found_hbh;

	ndo->ndo_protocol = "ip6";
	ip6 = (const struct ip6_hdr *)bp;

	ND_TCHECK_SIZE(ip6);
	if (length < sizeof (struct ip6_hdr)) {
	ND_PRINT("truncated-ip6 %u", length);
	return;
	}

	if (!ndo->ndo_eflag)
	ND_PRINT("IP6 ");

	if (IP6_VERSION(ip6) != 6) {
	ND_PRINT("version error: %u != 6", IP6_VERSION(ip6));
	return;
	}

	payload_len = GET_BE_U_2(ip6->ip6_plen);
	/*
	* RFC 1883 says:
	*
	* The Payload Length field in the IPv6 header must be set to zero
	* in every packet that carries the Jumbo Payload option. If a
	* packet is received with a valid Jumbo Payload option present and
	* a non-zero IPv6 Payload Length field, an ICMP Parameter Problem
	* message, Code 0, should be sent to the packet's source, pointing
	* to the Option Type field of the Jumbo Payload option.
	*
	* Later versions of the IPv6 spec don't discuss the Jumbo Payload
	* option.
	*
	* If the payload length is 0, we temporarily just set the total
	* length to the remaining data in the packet (which, for Ethernet,
	* could include frame padding, but if it's a Jumbo Payload frame,
	* it shouldn't even be sendable over Ethernet, so we don't worry
	* about that), so we can process the extension headers in order
	* to find a Jumbo Payload hop-by-hop option and, when we've
	* processed all the extension headers, check whether we found
	* a Jumbo Payload option, and fail if we haven't.
	*/
	if (payload_len != 0) {
	len = payload_len + sizeof(struct ip6_hdr);
	if (length < len)
	ND_PRINT("truncated-ip6 - %u bytes missing!",
	len - length);
	} else
	len = length + sizeof(struct ip6_hdr);

	ph = 255;
	nh = GET_U_1(ip6->ip6_nxt);
	if (ndo->ndo_vflag) {
	flow = GET_BE_U_4(ip6->ip6_flow);
	ND_PRINT("(");
	/* RFC 2460 */
	if (flow & 0x0ff00000)
	ND_PRINT("class 0x%02x, ", (flow & 0x0ff00000) >> 20);
	if (flow & 0x000fffff)
	ND_PRINT("flowlabel 0x%05x, ", flow & 0x000fffff);

	ND_PRINT("hlim %u, next-header %s (%u) payload length: %u) ",
	GET_U_1(ip6->ip6_hlim),
	tok2str(ipproto_values,"unknown",nh),
	nh,
	payload_len);
	}

	/*
	* Cut off the snapshot length to the end of the IP payload.
	*/
	if (!nd_push_snaplen(ndo, bp, len)) {
	(*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
	"%s: can't push snaplen on buffer stack", __func__);
	}

	cp = (const u_char *)ip6;
	advance = sizeof(struct ip6_hdr);
	total_advance = 0;
	/* Process extension headers */
	found_extension_header = 0;
	found_jumbo = 0;
	found_hbh = 0;
	while (cp < ndo->ndo_snapend && advance > 0) {
	if (len < (u_int)advance)
	goto trunc;
	cp += advance;
	len -= advance;
	total_advance += advance;

	if (cp == (const u_char *)(ip6 + 1) &&
	nh != IPPROTO_TCP && nh != IPPROTO_UDP &&
	nh != IPPROTO_DCCP && nh != IPPROTO_SCTP) {
	ND_PRINT("%s > %s: ", GET_IP6ADDR_STRING(ip6->ip6_src),
	GET_IP6ADDR_STRING(ip6->ip6_dst));
	}

	switch (nh) {

	case IPPROTO_HOPOPTS:
	/*
	* The Hop-by-Hop Options header, when present,
	* must immediately follow the IPv6 header (RFC 8200)
	*/
	if (found_hbh == 1) {
	ND_PRINT("[The Hop-by-Hop Options header was already found]");
	nd_print_invalid(ndo);
	return;
	}
	if (ph != 255) {
	ND_PRINT("[The Hop-by-Hop Options header don't follow the IPv6 header]");
	nd_print_invalid(ndo);
	return;
	}
	advance = hbhopt_process(ndo, cp, &found_jumbo, &payload_len);
	if (payload_len == 0 && found_jumbo == 0) {
	ND_PRINT("[No valid Jumbo Payload Hop-by-Hop option found]");
	nd_print_invalid(ndo);
	return;
	}
	if (advance < 0) {
	nd_pop_packet_info(ndo);
	return;
	}
	found_extension_header = 1;
	found_hbh = 1;
	nh = GET_U_1(cp);
	break;

	case IPPROTO_DSTOPTS:
	advance = dstopt_process(ndo, cp);
	if (advance < 0) {
	nd_pop_packet_info(ndo);
	return;
	}
	found_extension_header = 1;
	nh = GET_U_1(cp);
	break;

	case IPPROTO_FRAGMENT:
	advance = frag6_print(ndo, cp, (const u_char *)ip6);
	if (advance < 0 \|\| ndo->ndo_snapend <= cp + advance) {
	nd_pop_packet_info(ndo);
	return;
	}
	found_extension_header = 1;
	nh = GET_U_1(cp);
	fragmented = 1;
	break;

	case IPPROTO_MOBILITY_OLD:
	case IPPROTO_MOBILITY:
	/*
	* XXX - we don't use "advance"; RFC 3775 says that
	* the next header field in a mobility header
	* should be IPPROTO_NONE, but speaks of
	* the possibility of a future extension in
	* which payload can be piggybacked atop a
	* mobility header.
	*/
	advance = mobility_print(ndo, cp, (const u_char *)ip6);
	if (advance < 0) {
	nd_pop_packet_info(ndo);
	return;
	}
	found_extension_header = 1;
	nh = GET_U_1(cp);
	nd_pop_packet_info(ndo);
	return;

	case IPPROTO_ROUTING:
	ND_TCHECK_1(cp);
	advance = rt6_print(ndo, cp, (const u_char *)ip6);
	if (advance < 0) {
	nd_pop_packet_info(ndo);
	return;
	}
	found_extension_header = 1;
	nh = GET_U_1(cp);
	break;

	default:
	/*
	* Not an extension header; hand off to the
	* IP protocol demuxer.
	*/
	if (found_jumbo) {
	/*
	* We saw a Jumbo Payload option.
	* Set the length to the payload length
	* plus the IPv6 header length, and
	* change the snapshot length accordingly.
	*
	* But make sure it's not shorter than
	* the total number of bytes we've
	* processed so far.
	*/
	len = payload_len + sizeof(struct ip6_hdr);
	if (len < total_advance)
	goto trunc;
	if (length < len)
	ND_PRINT("truncated-ip6 - %u bytes missing!",
	len - length);
	nd_change_snaplen(ndo, bp, len);

	/*
	* Now subtract the length of the IPv6
	* header plus extension headers to get
	* the payload length.
	*/
	len -= total_advance;
	} else {
	/*
	* We didn't see a Jumbo Payload option;
	* was the payload length zero?
	*/
	if (payload_len == 0) {
	/*
	* Yes. If we found an extension
	* header, treat that as a truncated
	* packet header, as there was
	* no payload to contain an
	* extension header.
	*/
	if (found_extension_header)
	goto trunc;

	/*
	* OK, we didn't see any extension
	* header, but that means we have
	* no payload, so set the length
	* to the IPv6 header length,
	* and change the snapshot length
	* accordingly.
	*/
	len = sizeof(struct ip6_hdr);
	nd_change_snaplen(ndo, bp, len);

	/*
	* Now subtract the length of
	* the IPv6 header plus extension
	* headers (there weren't any, so
	* that's just the IPv6 header
	* length) to get the payload length.
	*/
	len -= total_advance;
	}
	}
	ip_demux_print(ndo, cp, len, 6, fragmented,
	GET_U_1(ip6->ip6_hlim), nh, bp);
	nd_pop_packet_info(ndo);
	return;
	}
	ph = nh;

	/* ndo_protocol reassignment after xxx_print() calls */
	ndo->ndo_protocol = "ip6";
	}

	nd_pop_packet_info(ndo);
	return;
	trunc:
	nd_print_trunc(ndo);
	}