networking/traceroute.c

/* vi: set sw=4 ts=4: */
/*
 * Copyright (c) 1988, 1989, 1991, 1994, 1995, 1996, 1997, 1998, 1999, 2000
 *      The Regents of the University of California.  All rights reserved.
 *
 * Busybox port by Vladimir Oleynik (C) 2005 <dzo@simtreas.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.
 */

/*
 *	traceroute6
 *
 *      Modified for NRL 4.4BSD IPv6 release.
 *      07/31/96 bgp
 *
 *	Modified for Linux IPv6 by Pedro Roque <roque@di.fc.ul.pt>
 *	31/07/1996
 *
 *	As ICMP error messages for IPv6 now include more than 8 bytes
 *	UDP datagrams are now sent via an UDP socket instead of magic
 *	RAW socket tricks.
 *
 *	Converted to busybox applet by Leonid Lisovskiy <lly@sf.net>
 *	2009-11-16
 */

/*
 * traceroute host  - trace the route ip packets follow going to "host".
 *
 * Attempt to trace the route an ip packet would follow to some
 * internet host.  We find out intermediate hops by launching probe
 * packets with a small ttl (time to live) then listening for an
 * icmp "time exceeded" reply from a gateway.  We start our probes
 * with a ttl of one and increase by one until we get an icmp "port
 * unreachable" (which means we got to "host") or hit a max (which
 * defaults to 30 hops & can be changed with the -m flag).  Three
 * probes (change with -q flag) are sent at each ttl setting and a
 * line is printed showing the ttl, address of the gateway and
 * round trip time of each probe.  If the probe answers come from
 * different gateways, the address of each responding system will
 * be printed.  If there is no response within a 5 sec. timeout
 * interval (changed with the -w flag), a "*" is printed for that
 * probe.
 *
 * Probe packets are UDP format.  We don't want the destination
 * host to process them so the destination port is set to an
 * unlikely value (if some clod on the destination is using that
 * value, it can be changed with the -p flag).
 *
 * A sample use might be:
 *
 *     [yak 71]% traceroute nis.nsf.net.
 *     traceroute to nis.nsf.net (35.1.1.48), 30 hops max, 56 byte packet
 *      1  helios.ee.lbl.gov (128.3.112.1)  19 ms  19 ms  0 ms
 *      2  lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  39 ms  19 ms
 *      3  lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  39 ms  19 ms
 *      4  ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  39 ms  40 ms  39 ms
 *      5  ccn-nerif22.Berkeley.EDU (128.32.168.22)  39 ms  39 ms  39 ms
 *      6  128.32.197.4 (128.32.197.4)  40 ms  59 ms  59 ms
 *      7  131.119.2.5 (131.119.2.5)  59 ms  59 ms  59 ms
 *      8  129.140.70.13 (129.140.70.13)  99 ms  99 ms  80 ms
 *      9  129.140.71.6 (129.140.71.6)  139 ms  239 ms  319 ms
 *     10  129.140.81.7 (129.140.81.7)  220 ms  199 ms  199 ms
 *     11  nic.merit.edu (35.1.1.48)  239 ms  239 ms  239 ms
 *
 * Note that lines 2 & 3 are the same.  This is due to a buggy
 * kernel on the 2nd hop system -- lbl-csam.arpa -- that forwards
 * packets with a zero ttl.
 *
 * A more interesting example is:
 *
 *     [yak 72]% traceroute allspice.lcs.mit.edu.
 *     traceroute to allspice.lcs.mit.edu (18.26.0.115), 30 hops max
 *      1  helios.ee.lbl.gov (128.3.112.1)  0 ms  0 ms  0 ms
 *      2  lilac-dmc.Berkeley.EDU (128.32.216.1)  19 ms  19 ms  19 ms
 *      3  lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  19 ms  19 ms
 *      4  ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  19 ms  39 ms  39 ms
 *      5  ccn-nerif22.Berkeley.EDU (128.32.168.22)  20 ms  39 ms  39 ms
 *      6  128.32.197.4 (128.32.197.4)  59 ms  119 ms  39 ms
 *      7  131.119.2.5 (131.119.2.5)  59 ms  59 ms  39 ms
 *      8  129.140.70.13 (129.140.70.13)  80 ms  79 ms  99 ms
 *      9  129.140.71.6 (129.140.71.6)  139 ms  139 ms  159 ms
 *     10  129.140.81.7 (129.140.81.7)  199 ms  180 ms  300 ms
 *     11  129.140.72.17 (129.140.72.17)  300 ms  239 ms  239 ms
 *     12  * * *
 *     13  128.121.54.72 (128.121.54.72)  259 ms  499 ms  279 ms
 *     14  * * *
 *     15  * * *
 *     16  * * *
 *     17  * * *
 *     18  ALLSPICE.LCS.MIT.EDU (18.26.0.115)  339 ms  279 ms  279 ms
 *
 * (I start to see why I'm having so much trouble with mail to
 * MIT.)  Note that the gateways 12, 14, 15, 16 & 17 hops away
 * either don't send ICMP "time exceeded" messages or send them
 * with a ttl too small to reach us.  14 - 17 are running the
 * MIT C Gateway code that doesn't send "time exceeded"s.  God
 * only knows what's going on with 12.
 *
 * The silent gateway 12 in the above may be the result of a bug in
 * the 4.[23]BSD network code (and its derivatives):  4.x (x <= 3)
 * sends an unreachable message using whatever ttl remains in the
 * original datagram.  Since, for gateways, the remaining ttl is
 * zero, the icmp "time exceeded" is guaranteed to not make it back
 * to us.  The behavior of this bug is slightly more interesting
 * when it appears on the destination system:
 *
 *      1  helios.ee.lbl.gov (128.3.112.1)  0 ms  0 ms  0 ms
 *      2  lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  19 ms  39 ms
 *      3  lilac-dmc.Berkeley.EDU (128.32.216.1)  19 ms  39 ms  19 ms
 *      4  ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  39 ms  40 ms  19 ms
 *      5  ccn-nerif35.Berkeley.EDU (128.32.168.35)  39 ms  39 ms  39 ms
 *      6  csgw.Berkeley.EDU (128.32.133.254)  39 ms  59 ms  39 ms
 *      7  * * *
 *      8  * * *
 *      9  * * *
 *     10  * * *
 *     11  * * *
 *     12  * * *
 *     13  rip.Berkeley.EDU (128.32.131.22)  59 ms !  39 ms !  39 ms !
 *
 * Notice that there are 12 "gateways" (13 is the final
 * destination) and exactly the last half of them are "missing".
 * What's really happening is that rip (a Sun-3 running Sun OS3.5)
 * is using the ttl from our arriving datagram as the ttl in its
 * icmp reply.  So, the reply will time out on the return path
 * (with no notice sent to anyone since icmp's aren't sent for
 * icmp's) until we probe with a ttl that's at least twice the path
 * length.  I.e., rip is really only 7 hops away.  A reply that
 * returns with a ttl of 1 is a clue this problem exists.
 * Traceroute prints a "!" after the time if the ttl is <= 1.
 * Since vendors ship a lot of obsolete (DEC's Ultrix, Sun 3.x) or
 * non-standard (HPUX) software, expect to see this problem
 * frequently and/or take care picking the target host of your
 * probes.
 *
 * Other possible annotations after the time are !H, !N, !P (got a host,
 * network or protocol unreachable, respectively), !S or !F (source
 * route failed or fragmentation needed -- neither of these should
 * ever occur and the associated gateway is busted if you see one).  If
 * almost all the probes result in some kind of unreachable, traceroute
 * will give up and exit.
 *
 * Notes
 * -----
 * This program must be run by root or be setuid.  (I suggest that
 * you *don't* make it setuid -- casual use could result in a lot
 * of unnecessary traffic on our poor, congested nets.)
 *
 * This program requires a kernel mod that does not appear in any
 * system available from Berkeley:  A raw ip socket using proto
 * IPPROTO_RAW must interpret the data sent as an ip datagram (as
 * opposed to data to be wrapped in a ip datagram).  See the README
 * file that came with the source to this program for a description
 * of the mods I made to /sys/netinet/raw_ip.c.  Your mileage may
 * vary.  But, again, ANY 4.x (x < 4) BSD KERNEL WILL HAVE TO BE
 * MODIFIED TO RUN THIS PROGRAM.
 *
 * The udp port usage may appear bizarre (well, ok, it is bizarre).
 * The problem is that an icmp message only contains 8 bytes of
 * data from the original datagram.  8 bytes is the size of a udp
 * header so, if we want to associate replies with the original
 * datagram, the necessary information must be encoded into the
 * udp header (the ip id could be used but there's no way to
 * interlock with the kernel's assignment of ip id's and, anyway,
 * it would have taken a lot more kernel hacking to allow this
 * code to set the ip id).  So, to allow two or more users to
 * use traceroute simultaneously, we use this task's pid as the
 * source port (the high bit is set to move the port number out
 * of the "likely" range).  To keep track of which probe is being
 * replied to (so times and/or hop counts don't get confused by a
 * reply that was delayed in transit), we increment the destination
 * port number before each probe.
 *
 * Don't use this as a coding example.  I was trying to find a
 * routing problem and this code sort-of popped out after 48 hours
 * without sleep.  I was amazed it ever compiled, much less ran.
 *
 * I stole the idea for this program from Steve Deering.  Since
 * the first release, I've learned that had I attended the right
 * IETF working group meetings, I also could have stolen it from Guy
 * Almes or Matt Mathis.  I don't know (or care) who came up with
 * the idea first.  I envy the originators' perspicacity and I'm
 * glad they didn't keep the idea a secret.
 *
 * Tim Seaver, Ken Adelman and C. Philip Wood provided bug fixes and/or
 * enhancements to the original distribution.
 *
 * I've hacked up a round-trip-route version of this that works by
 * sending a loose-source-routed udp datagram through the destination
 * back to yourself.  Unfortunately, SO many gateways botch source
 * routing, the thing is almost worthless.  Maybe one day...
 *
 *  -- Van Jacobson (van@ee.lbl.gov)
 *     Tue Dec 20 03:50:13 PST 1988
 */

#define TRACEROUTE_SO_DEBUG 0

/* TODO: undefs were uncommented - ??! we have config system for that! */
/* probably ok to remove altogether */
//#undef CONFIG_FEATURE_TRACEROUTE_VERBOSE
//#define CONFIG_FEATURE_TRACEROUTE_VERBOSE
//#undef CONFIG_FEATURE_TRACEROUTE_SOURCE_ROUTE
//#define CONFIG_FEATURE_TRACEROUTE_SOURCE_ROUTE
//#undef CONFIG_FEATURE_TRACEROUTE_USE_ICMP
//#define CONFIG_FEATURE_TRACEROUTE_USE_ICMP


#include <net/if.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/udp.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#if ENABLE_FEATURE_IPV6
# include <netinet/ip6.h>
# include <netinet/icmp6.h>
# ifndef SOL_IPV6
#  define SOL_IPV6 IPPROTO_IPV6
# endif
#endif

#include "libbb.h"
#include "inet_common.h"

#ifndef IPPROTO_ICMP
# define IPPROTO_ICMP 1
#endif
#ifndef IPPROTO_IP
# define IPPROTO_IP 0
#endif


#define OPT_STRING "FIlnrdvxt:i:m:p:q:s:w:z:f:" \
		    IF_FEATURE_TRACEROUTE_SOURCE_ROUTE("g:") \
		    "4" IF_TRACEROUTE6("6")
enum {
	OPT_DONT_FRAGMNT = (1 << 0),    /* F */
	OPT_USE_ICMP     = (1 << 1) * ENABLE_FEATURE_TRACEROUTE_USE_ICMP, /* I */
	OPT_TTL_FLAG     = (1 << 2),    /* l */
	OPT_ADDR_NUM     = (1 << 3),    /* n */
	OPT_BYPASS_ROUTE = (1 << 4),    /* r */
	OPT_DEBUG        = (1 << 5),    /* d */
	OPT_VERBOSE      = (1 << 6) * ENABLE_FEATURE_TRACEROUTE_VERBOSE, /* v */
	OPT_IP_CHKSUM    = (1 << 7),    /* x */
	OPT_TOS          = (1 << 8),    /* t */
	OPT_DEVICE       = (1 << 9),    /* i */
	OPT_MAX_TTL      = (1 << 10),   /* m */
	OPT_PORT         = (1 << 11),   /* p */
	OPT_NPROBES      = (1 << 12),   /* q */
	OPT_SOURCE       = (1 << 13),   /* s */
	OPT_WAITTIME     = (1 << 14),   /* w */
	OPT_PAUSE_MS     = (1 << 15),   /* z */
	OPT_FIRST_TTL    = (1 << 16),   /* f */
	OPT_SOURCE_ROUTE = (1 << 17) * ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE, /* g */
	OPT_IPV4         = (1 << (17+ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE)),   /* 4 */
	OPT_IPV6         = (1 << (18+ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE)) * ENABLE_TRACEROUTE6, /* 6 */
};
#define verbose (option_mask32 & OPT_VERBOSE)

enum {
	SIZEOF_ICMP_HDR = 8,
	rcvsock = 3, /* receive (icmp) socket file descriptor */
	sndsock = 4, /* send (udp/icmp) socket file descriptor */
};

/* Data section of the probe packet */
struct outdata_t {
	unsigned char seq;             /* sequence number of this packet */
	unsigned char ttl;             /* ttl packet left with */
// UNUSED. Retaining to have the same packet size.
	struct timeval tv_UNUSED PACKED; /* time packet left */
};

#if ENABLE_TRACEROUTE6
struct outdata6_t {
	uint32_t ident6;
	uint32_t seq6;
	struct timeval tv_UNUSED PACKED; /* time packet left */
};
#endif

struct globals {
	struct ip *outip;
	struct outdata_t *outdata;
	len_and_sockaddr *dest_lsa;
	int packlen;                    /* total length of packet */
	int pmtu;                       /* Path MTU Discovery (RFC1191) */
	uint32_t ident;
	uint16_t port; // 32768 + 666;  /* start udp dest port # for probe packets */
	int waittime; // 5;             /* time to wait for response (in seconds) */
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
	int optlen;                     /* length of ip options */
#else
#define optlen 0
#endif
	unsigned char recv_pkt[512];    /* last inbound (icmp) packet */
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
	/* Maximum number of gateways (include room for one noop) */
#define NGATEWAYS ((int)((MAX_IPOPTLEN - IPOPT_MINOFF - 1) / sizeof(uint32_t)))
	/* loose source route gateway list (including room for final destination) */
	uint32_t gwlist[NGATEWAYS + 1];
#endif
};

#define G (*ptr_to_globals)
#define outip     (G.outip    )
#define outdata   (G.outdata  )
#define dest_lsa  (G.dest_lsa )
#define packlen   (G.packlen  )
#define pmtu      (G.pmtu     )
#define ident     (G.ident    )
#define port      (G.port     )
#define waittime  (G.waittime )
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
# define optlen   (G.optlen   )
#endif
#define recv_pkt  (G.recv_pkt )
#define gwlist    (G.gwlist   )
#define INIT_G() do { \
	SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
	port = 32768 + 666; \
	waittime = 5; \
} while (0)

#define outicmp ((struct icmp *)(outip + 1))
#define outudp  ((struct udphdr *)(outip + 1))


/* libbb candidate? tftp uses this idiom too */
static len_and_sockaddr* dup_sockaddr(const len_and_sockaddr *lsa)
{
	len_and_sockaddr *new_lsa = xzalloc(LSA_LEN_SIZE + lsa->len);
	memcpy(new_lsa, lsa, LSA_LEN_SIZE + lsa->len);
	return new_lsa;
}


static int
wait_for_reply(len_and_sockaddr *from_lsa, struct sockaddr *to)
{
	struct pollfd pfd[1];
	int read_len = 0;

	pfd[0].fd = rcvsock;
	pfd[0].events = POLLIN;
	if (safe_poll(pfd, 1, waittime * 1000) > 0) {
		read_len = recv_from_to(rcvsock,
				recv_pkt, sizeof(recv_pkt),
				/*flags:*/ 0,
				&from_lsa->u.sa, to, from_lsa->len);
	}

	return read_len;
}

/*
 * Checksum routine for Internet Protocol family headers (C Version)
 */
static uint16_t
in_cksum(uint16_t *addr, int len)
{
	int nleft = len;
	uint16_t *w = addr;
	uint16_t answer;
	int sum = 0;

	/*
	 * Our algorithm is simple, using a 32 bit accumulator (sum),
	 * we add sequential 16 bit words to it, and at the end, fold
	 * back all the carry bits from the top 16 bits into the lower
	 * 16 bits.
	 */
	while (nleft > 1) {
		sum += *w++;
		nleft -= 2;
	}

	/* mop up an odd byte, if necessary */
	if (nleft == 1)
		sum += *(unsigned char *)w;

	/* add back carry outs from top 16 bits to low 16 bits */
	sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
	sum += (sum >> 16);                     /* add carry */
	answer = ~sum;                          /* truncate to 16 bits */
	return answer;
}

static void
send_probe(int seq, int ttl)
{
	int len, res;
	void *out;

	/* Payload */
#if ENABLE_TRACEROUTE6
	if (dest_lsa->u.sa.sa_family == AF_INET6) {
		struct outdata6_t *pkt = (struct outdata6_t *) outip;
		pkt->ident6 = htonl(ident);
		pkt->seq6   = htonl(seq);
		/*gettimeofday(&pkt->tv, &tz);*/
	} else
#endif
	{
		outdata->seq = seq;
		outdata->ttl = ttl;
// UNUSED: was storing gettimeofday's result there, but never ever checked it
		/*memcpy(&outdata->tv, tp, sizeof(outdata->tv));*/

		if (option_mask32 & OPT_USE_ICMP) {
			outicmp->icmp_seq = htons(seq);

			/* Always calculate checksum for icmp packets */
			outicmp->icmp_cksum = 0;
			outicmp->icmp_cksum = in_cksum((uint16_t *)outicmp,
						packlen - (sizeof(*outip) + optlen));
			if (outicmp->icmp_cksum == 0)
				outicmp->icmp_cksum = 0xffff;
		}
	}

//BUG! verbose is (x & OPT_VERBOSE), not a counter!
#if 0 //ENABLE_FEATURE_TRACEROUTE_VERBOSE
	/* XXX undocumented debugging hack */
	if (verbose > 1) {
		const uint16_t *sp;
		int nshorts, i;

		sp = (uint16_t *)outip;
		nshorts = (unsigned)packlen / sizeof(uint16_t);
		i = 0;
		printf("[ %d bytes", packlen);
		while (--nshorts >= 0) {
			if ((i++ % 8) == 0)
				printf("\n\t");
			printf(" %04x", ntohs(*sp));
			sp++;
		}
		if (packlen & 1) {
			if ((i % 8) == 0)
				printf("\n\t");
			printf(" %02x", *(unsigned char *)sp);
		}
		printf("]\n");
	}
#endif

#if ENABLE_TRACEROUTE6
	if (dest_lsa->u.sa.sa_family == AF_INET6) {
		res = setsockopt(sndsock, SOL_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
		if (res < 0)
			bb_perror_msg_and_die("setsockopt UNICAST_HOPS %d", ttl);
		out = outip;
		len = packlen;
	} else
#endif
	{
#if defined IP_TTL
		res = setsockopt(sndsock, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
		if (res < 0)
			bb_perror_msg_and_die("setsockopt ttl %d", ttl);
#endif
		out = outicmp;
		len = packlen - sizeof(*outip);
		if (!(option_mask32 & OPT_USE_ICMP)) {
			out = outdata;
			len -= sizeof(*outudp);
			set_nport(dest_lsa, htons(port + seq));
		}
	}

	res = xsendto(sndsock, out, len, &dest_lsa->u.sa, dest_lsa->len);
	if (res != len)
		bb_info_msg("sent %d octets, ret=%d", len, res);
}

#if ENABLE_FEATURE_TRACEROUTE_VERBOSE
/*
 * Convert an ICMP "type" field to a printable string.
 */
static const char *
pr_type(unsigned char t)
{
	static const char *const ttab[] = {
	"Echo Reply",   "ICMP 1",       "ICMP 2",       "Dest Unreachable",
	"Source Quench", "Redirect",    "ICMP 6",       "ICMP 7",
	"Echo",         "Router Advert", "Router Solicit", "Time Exceeded",
	"Param Problem", "Timestamp",   "Timestamp Reply", "Info Request",
	"Info Reply",   "Mask Request", "Mask Reply"
	};
# if ENABLE_TRACEROUTE6
	static const char *const ttab6[] = {
[0]	"Error", "Dest Unreachable", "Packet Too Big", "Time Exceeded",
[4]	"Param Problem",
[8]	"Echo Request", "Echo Reply", "Membership Query", "Membership Report",
[12]	"Membership Reduction", "Router Solicit", "Router Advert", "Neighbor Solicit",
[16]	"Neighbor Advert", "Redirect",
	};

	if (dest_lsa->u.sa.sa_family == AF_INET6) {
		if (t < 5)
			return ttab6[t];
		if (t < 128 || t > ND_REDIRECT)
			return "OUT-OF-RANGE";
		return ttab6[(t & 63) + 8];
	}
# endif
	if (t >= ARRAY_SIZE(ttab))
		return "OUT-OF-RANGE";

	return ttab[t];
}
#endif

#if !ENABLE_FEATURE_TRACEROUTE_VERBOSE
#define packet4_ok(read_len, from, seq) \
	packet4_ok(read_len, seq)
#endif
static int
packet4_ok(int read_len, const struct sockaddr_in *from, int seq)
{
	const struct icmp *icp;
	unsigned char type, code;
	int hlen;
	const struct ip *ip;

	ip = (struct ip *) recv_pkt;
	hlen = ip->ip_hl << 2;
	if (read_len < hlen + ICMP_MINLEN) {
#if ENABLE_FEATURE_TRACEROUTE_VERBOSE
		if (verbose)
			printf("packet too short (%d bytes) from %s\n", read_len,
				inet_ntoa(from->sin_addr));
#endif
		return 0;
	}
	read_len -= hlen;
	icp = (struct icmp *)(recv_pkt + hlen);
	type = icp->icmp_type;
	code = icp->icmp_code;
	/* Path MTU Discovery (RFC1191) */
	pmtu = 0;
	if (code == ICMP_UNREACH_NEEDFRAG)
		pmtu = ntohs(icp->icmp_nextmtu);

	if ((type == ICMP_TIMXCEED && code == ICMP_TIMXCEED_INTRANS)
	 || type == ICMP_UNREACH
	 || type == ICMP_ECHOREPLY
	) {
		const struct ip *hip;
		const struct udphdr *up;

		hip = &icp->icmp_ip;
		hlen = hip->ip_hl << 2;
		if (option_mask32 & OPT_USE_ICMP) {
			struct icmp *hicmp;

			/* XXX */
			if (type == ICMP_ECHOREPLY
			 && icp->icmp_id == htons(ident)
			 && icp->icmp_seq == htons(seq)
			) {
				return ICMP_UNREACH_PORT+1;
			}

			hicmp = (struct icmp *)((unsigned char *)hip + hlen);
			if (hlen + SIZEOF_ICMP_HDR <= read_len
			 && hip->ip_p == IPPROTO_ICMP
			 && hicmp->icmp_id == htons(ident)
			 && hicmp->icmp_seq == htons(seq)
			) {
				return (type == ICMP_TIMXCEED ? -1 : code + 1);
			}
		} else {
			up = (struct udphdr *)((char *)hip + hlen);
			if (hlen + 12 <= read_len
			 && hip->ip_p == IPPROTO_UDP
// Off: since we do not form the entire IP packet,
// but defer it to kernel, we can't set source port,
// and thus can't check it here in the reply
			/* && up->source == htons(ident) */
			 && up->dest == htons(port + seq)
			) {
				return (type == ICMP_TIMXCEED ? -1 : code + 1);
			}
		}
	}
#if ENABLE_FEATURE_TRACEROUTE_VERBOSE
	if (verbose) {
		int i;
		uint32_t *lp = (uint32_t *)&icp->icmp_ip;

		printf("\n%d bytes from %s to "
		       "%s: icmp type %d (%s) code %d\n",
			read_len, inet_ntoa(from->sin_addr),
			inet_ntoa(ip->ip_dst),
			type, pr_type(type), icp->icmp_code);
		for (i = 4; i < read_len; i += sizeof(*lp))
			printf("%2d: x%8.8x\n", i, *lp++);
	}
#endif
	return 0;
}

#if ENABLE_TRACEROUTE6
# if !ENABLE_FEATURE_TRACEROUTE_VERBOSE
#define packet_ok(read_len, from_lsa, to, seq) \
	packet_ok(read_len, from_lsa, seq)
# endif
static int
packet_ok(int read_len, len_and_sockaddr *from_lsa,
			struct sockaddr *to,
			int seq)
{
	const struct icmp6_hdr *icp;
	unsigned char type, code;

	if (from_lsa->u.sa.sa_family == AF_INET)
		return packet4_ok(read_len, &from_lsa->u.sin, seq);

	icp = (struct icmp6_hdr *) recv_pkt;

	type = icp->icmp6_type;
	code = icp->icmp6_code;

	if ((type == ICMP6_TIME_EXCEEDED && code == ICMP6_TIME_EXCEED_TRANSIT)
	 || type == ICMP6_DST_UNREACH
	) {
		struct ip6_hdr *hip;
		struct udphdr *up;
		int nexthdr;

		hip = (struct ip6_hdr *)(icp + 1);
		up  = (struct udphdr *) (hip + 1);
		nexthdr = hip->ip6_nxt;

		if (nexthdr == IPPROTO_FRAGMENT) {
			nexthdr = *(unsigned char*)up;
			up++;
		}
		if (nexthdr == IPPROTO_UDP) {
			struct outdata6_t *pkt;

			pkt = (struct outdata6_t *) (up + 1);

			if (ntohl(pkt->ident6) == ident
			 && ntohl(pkt->seq6) == seq
			) {
				return (type == ICMP6_TIME_EXCEEDED ? -1 : (code<<8)+1);
			}
		}
	}

# if ENABLE_FEATURE_TRACEROUTE_VERBOSE
	if (verbose) {
		unsigned char *p;
		char pa1[MAXHOSTNAMELEN];
		char pa2[MAXHOSTNAMELEN];
		int i;

		p = (unsigned char *) (icp + 1);

		printf("\n%d bytes from %s to "
		       "%s: icmp type %d (%s) code %d\n",
			read_len,
			inet_ntop(AF_INET6, &from_lsa->u.sin6.sin6_addr, pa1, sizeof(pa1)),
			inet_ntop(AF_INET6, &((struct sockaddr_in6*)to)->sin6_addr, pa2, sizeof(pa2)),
			type, pr_type(type), icp->icmp6_code);

		read_len -= sizeof(struct icmp6_hdr);
		for (i = 0; i < read_len ; i++) {
			if (i % 16 == 0)
				printf("%04x:", i);
			if (i % 4 == 0)
				bb_putchar(' ');
			printf("%02x", p[i]);
			if ((i % 16 == 15) && (i + 1 < read_len))
				bb_putchar('\n');
		}
		bb_putchar('\n');
	}
# endif

	return 0;
}
#else /* !ENABLE_TRACEROUTE6 */
static ALWAYS_INLINE int
packet_ok(int read_len,
		len_and_sockaddr *from_lsa IF_NOT_FEATURE_TRACEROUTE_VERBOSE(UNUSED_PARAM),
		struct sockaddr *to UNUSED_PARAM,
		int seq)
{
	return packet4_ok(read_len, &from_lsa->u.sin, seq);
}
#endif

/*
 * Construct an Internet address representation.
 * If the -n flag has been supplied, give
 * numeric value, otherwise try for symbolic name.
 */
static void
print_inetname(const struct sockaddr *from)
{
	char *ina = xmalloc_sockaddr2dotted_noport(from);

	if (option_mask32 & OPT_ADDR_NUM) {
		printf("  %s", ina);
	} else {
		char *n = NULL;

		if (from->sa_family != AF_INET
		 || ((struct sockaddr_in*)from)->sin_addr.s_addr != INADDR_ANY
		) {
			/* Try to reverse resolve if it is not 0.0.0.0 */
			n = xmalloc_sockaddr2host_noport((struct sockaddr*)from);
		}
		printf("  %s (%s)", (n ? n : ina), ina);
		free(n);
	}
	free(ina);
}

static void
print(int read_len, const struct sockaddr *from, const struct sockaddr *to)
{
	print_inetname(from);

	if (verbose) {
		char *ina = xmalloc_sockaddr2dotted_noport(to);
#if ENABLE_TRACEROUTE6
		if (to->sa_family == AF_INET6) {
			read_len -= sizeof(struct ip6_hdr);
		} else
#endif
		{
			read_len -= ((struct ip*)recv_pkt)->ip_hl << 2;
		}
		printf(" %d bytes to %s", read_len, ina);
		free(ina);
	}
}

static void
print_delta_ms(unsigned t1p, unsigned t2p)
{
	unsigned tt = t2p - t1p;
	printf("  %u.%03u ms", tt / 1000, tt % 1000);
}

/*
 * Usage: [-dFIlnrvx] [-g gateway] [-i iface] [-f first_ttl]
 * [-m max_ttl] [ -p port] [-q nqueries] [-s src_addr] [-t tos]
 * [-w waittime] [-z pausemsecs] host [packetlen]"
 */
static int
common_traceroute_main(int op, char **argv)
{
	int i;
	int minpacket;
	int tos = 0;
	int max_ttl = 30;
	int nprobes = 3;
	int first_ttl = 1;
	unsigned pausemsecs = 0;
	char *source;
	char *device;
	char *tos_str;
	char *max_ttl_str;
	char *port_str;
	char *nprobes_str;
	char *waittime_str;
	char *pausemsecs_str;
	char *first_ttl_str;
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
	llist_t *source_route_list = NULL;
	int lsrr = 0;
#endif
#if ENABLE_TRACEROUTE6
	sa_family_t af;
#else
	enum { af = AF_INET };
#endif
	int ttl;
	int seq;
	len_and_sockaddr *from_lsa;
	struct sockaddr *lastaddr;
	struct sockaddr *to;

	INIT_G();

	/* minimum 1 arg */
	opt_complementary = "-1:x-x" IF_FEATURE_TRACEROUTE_SOURCE_ROUTE(":g::");
	op |= getopt32(argv, OPT_STRING
		, &tos_str, &device, &max_ttl_str, &port_str, &nprobes_str
		, &source, &waittime_str, &pausemsecs_str, &first_ttl_str
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
		, &source_route_list
#endif
	);
	argv += optind;

#if 0 /* IGNORED */
	if (op & OPT_IP_CHKSUM)
		bb_error_msg("warning: ip checksums disabled");
#endif
	if (op & OPT_TOS)
		tos = xatou_range(tos_str, 0, 255);
	if (op & OPT_MAX_TTL)
		max_ttl = xatou_range(max_ttl_str, 1, 255);
	if (op & OPT_PORT)
		port = xatou16(port_str);
	if (op & OPT_NPROBES)
		nprobes = xatou_range(nprobes_str, 1, INT_MAX);
	if (op & OPT_SOURCE) {
		/*
		 * set the ip source address of the outbound
		 * probe (e.g., on a multi-homed host).
		 */
		if (getuid() != 0)
			bb_error_msg_and_die(bb_msg_you_must_be_root);
	}
	if (op & OPT_WAITTIME)
		waittime = xatou_range(waittime_str, 1, 24 * 60 * 60);
	if (op & OPT_PAUSE_MS)
		pausemsecs = xatou_range(pausemsecs_str, 0, 60 * 60 * 1000);
	if (op & OPT_FIRST_TTL)
		first_ttl = xatou_range(first_ttl_str, 1, max_ttl);

#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE
	if (source_route_list) {
		while (source_route_list) {
			len_and_sockaddr *lsa;

			if (lsrr >= NGATEWAYS)
				bb_error_msg_and_die("no more than %d gateways", NGATEWAYS);
			lsa = xhost_and_af2sockaddr(llist_pop(&source_route_list), 0, AF_INET);
			gwlist[lsrr] = lsa->u.sin.sin_addr.s_addr;
			free(lsa);
			++lsrr;
		}
		optlen = (lsrr + 1) * sizeof(gwlist[0]);
	}
#endif

	/* Process destination and optional packet size */
	minpacket = sizeof(*outip) + SIZEOF_ICMP_HDR + sizeof(*outdata) + optlen;
	if (!(op & OPT_USE_ICMP))
		minpacket += sizeof(*outudp) - SIZEOF_ICMP_HDR;
#if ENABLE_TRACEROUTE6
	af = AF_UNSPEC;
	if (op & OPT_IPV4)
		af = AF_INET;
	if (op & OPT_IPV6)
		af = AF_INET6;
	dest_lsa = xhost_and_af2sockaddr(argv[0], port, af);
	af = dest_lsa->u.sa.sa_family;
	if (af == AF_INET6)
		minpacket = sizeof(struct outdata6_t);
#else
	dest_lsa = xhost2sockaddr(argv[0], port);
#endif
	packlen = minpacket;
	if (argv[1])
		packlen = xatoul_range(argv[1], minpacket, 32 * 1024);

	/* Ensure the socket fds won't be 0, 1 or 2 */
	bb_sanitize_stdio();

#if ENABLE_TRACEROUTE6
	if (af == AF_INET6) {
		xmove_fd(xsocket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6), rcvsock);
# ifdef IPV6_RECVPKTINFO
		setsockopt(rcvsock, SOL_IPV6, IPV6_RECVPKTINFO,
				&const_int_1, sizeof(const_int_1));
		setsockopt(rcvsock, SOL_IPV6, IPV6_2292PKTINFO,
				&const_int_1, sizeof(const_int_1));
# else
		setsockopt(rcvsock, SOL_IPV6, IPV6_PKTINFO,
				&const_int_1, sizeof(const_int_1));
# endif
	} else
#endif
	{
		xmove_fd(xsocket(AF_INET, SOCK_RAW, IPPROTO_ICMP), rcvsock);
	}

#if TRACEROUTE_SO_DEBUG
	if (op & OPT_DEBUG)
		setsockopt(rcvsock, SOL_SOCKET, SO_DEBUG,
				&const_int_1, sizeof(const_int_1));
#endif
	if (op & OPT_BYPASS_ROUTE)
		setsockopt(rcvsock, SOL_SOCKET, SO_DONTROUTE,
				&const_int_1, sizeof(const_int_1));

#if ENABLE_TRACEROUTE6
	if (af == AF_INET6) {
		static const int two = 2;
		if (setsockopt(rcvsock, SOL_RAW, IPV6_CHECKSUM, &two, sizeof(two)) < 0)
			bb_perror_msg_and_die("setsockopt RAW_CHECKSUM");
		xmove_fd(xsocket(af, SOCK_DGRAM, 0), sndsock);
	} else
#endif
	{
		if (op & OPT_USE_ICMP)
			xmove_fd(xsocket(AF_INET, SOCK_RAW, IPPROTO_ICMP), sndsock);
		else
			xmove_fd(xsocket(AF_INET, SOCK_DGRAM, 0), sndsock);
#if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE && defined IP_OPTIONS
		if (lsrr > 0) {
			unsigned char optlist[MAX_IPOPTLEN];

			/* final hop */
			gwlist[lsrr] = dest_lsa->u.sin.sin_addr.s_addr;
			++lsrr;

			/* force 4 byte alignment */
			optlist[0] = IPOPT_NOP;
			/* loose source route option */
			optlist[1] = IPOPT_LSRR;
			i = lsrr * sizeof(gwlist[0]);
			optlist[2] = i + 3;
			/* pointer to LSRR addresses */
			optlist[3] = IPOPT_MINOFF;
			memcpy(optlist + 4, gwlist, i);

			if (setsockopt(sndsock, IPPROTO_IP, IP_OPTIONS,
					(char *)optlist, i + sizeof(gwlist[0])) < 0) {
				bb_perror_msg_and_die("IP_OPTIONS");
			}
		}
#endif
	}

#ifdef SO_SNDBUF
	if (setsockopt(sndsock, SOL_SOCKET, SO_SNDBUF, &packlen, sizeof(packlen)) < 0) {
		bb_perror_msg_and_die("SO_SNDBUF");
	}
#endif
#ifdef IP_TOS
	if ((op & OPT_TOS) && setsockopt(sndsock, IPPROTO_IP, IP_TOS, &tos, sizeof(tos)) < 0) {
		bb_perror_msg_and_die("setsockopt tos %d", tos);
	}
#endif
#ifdef IP_DONTFRAG
	if (op & OPT_DONT_FRAGMNT)
		setsockopt(sndsock, IPPROTO_IP, IP_DONTFRAG,
				&const_int_1, sizeof(const_int_1));
#endif
#if TRACEROUTE_SO_DEBUG
	if (op & OPT_DEBUG)
		setsockopt(sndsock, SOL_SOCKET, SO_DEBUG,
				&const_int_1, sizeof(const_int_1));
#endif
	if (op & OPT_BYPASS_ROUTE)
		setsockopt(sndsock, SOL_SOCKET, SO_DONTROUTE,
				&const_int_1, sizeof(const_int_1));

	outip = xzalloc(packlen);

	ident = getpid();

	if (af == AF_INET) {
		if (op & OPT_USE_ICMP) {
			ident |= 0x8000;
			outicmp->icmp_type = ICMP_ECHO;
			outicmp->icmp_id = htons(ident);
			outdata = (struct outdata_t *)((char *)outicmp + SIZEOF_ICMP_HDR);
		} else {
			outdata = (struct outdata_t *)(outudp + 1);
		}
	}

	if (op & OPT_DEVICE) /* hmm, do we need error check? */
		setsockopt_bindtodevice(sndsock, device);

	if (op & OPT_SOURCE) {
#if ENABLE_TRACEROUTE6
// TODO: need xdotted_and_af2sockaddr?
		len_and_sockaddr *source_lsa = xhost_and_af2sockaddr(source, 0, af);
#else
		len_and_sockaddr *source_lsa = xdotted2sockaddr(source, 0);
#endif
		/* Ping4 does this (why?) */
		if (af == AF_INET)
			if (setsockopt(sndsock, IPPROTO_IP, IP_MULTICAST_IF,
					&source_lsa->u.sa, source_lsa->len))
				bb_error_msg_and_die("can't set multicast source interface");
//TODO: we can query source port we bound to,
// and check it in replies... if we care enough
		xbind(sndsock, &source_lsa->u.sa, source_lsa->len);
		free(source_lsa);
	}
#if ENABLE_TRACEROUTE6
	else if (af == AF_INET6) {
//TODO: why we don't do it for IPv4?
		len_and_sockaddr *source_lsa;

		int probe_fd = xsocket(af, SOCK_DGRAM, 0);
		if (op & OPT_DEVICE)
			setsockopt_bindtodevice(probe_fd, device);
		set_nport(dest_lsa, htons(1025));
		/* dummy connect. makes kernel pick source IP (and port) */
		xconnect(probe_fd, &dest_lsa->u.sa, dest_lsa->len);
		set_nport(dest_lsa, htons(port));

		/* read IP and port */
		source_lsa = get_sock_lsa(probe_fd);
		if (source_lsa == NULL)
			bb_error_msg_and_die("can't get probe addr");

		close(probe_fd);

		/* bind our sockets to this IP (but not port) */
		set_nport(source_lsa, 0);
		xbind(sndsock, &source_lsa->u.sa, source_lsa->len);
		xbind(rcvsock, &source_lsa->u.sa, source_lsa->len);

		free(source_lsa);
	}
#endif

	/* Revert to non-privileged user after opening sockets */
	xsetgid(getgid());
	xsetuid(getuid());

	printf("traceroute to %s (%s)", argv[0],
			xmalloc_sockaddr2dotted_noport(&dest_lsa->u.sa));
	if (op & OPT_SOURCE)
		printf(" from %s", source);
	printf(", %d hops max, %d byte packets\n", max_ttl, packlen);

	from_lsa = dup_sockaddr(dest_lsa);
	lastaddr = xzalloc(dest_lsa->len);
	to = xzalloc(dest_lsa->len);
	seq = 0;
	for (ttl = first_ttl; ttl <= max_ttl; ++ttl) {
		int probe;
		int unreachable = 0; /* counter */
		int gotlastaddr = 0; /* flags */
		int got_there = 0;
		int first = 1;

		printf("%2d", ttl);
		for (probe = 0; probe < nprobes; ++probe) {
			int read_len;
			unsigned t1;
			unsigned t2;
			struct ip *ip;

			if (!first && pausemsecs > 0)
				usleep(pausemsecs * 1000);
			fflush_all();

			t1 = monotonic_us();
			send_probe(++seq, ttl);

			first = 0;
			while ((read_len = wait_for_reply(from_lsa, to)) != 0) {
				t2 = monotonic_us();
				i = packet_ok(read_len, from_lsa, to, seq);
				/* Skip short packet */
				if (i == 0)
					continue;

				if (!gotlastaddr
				 || (memcmp(lastaddr, &from_lsa->u.sa, from_lsa->len) != 0)
				) {
					print(read_len, &from_lsa->u.sa, to);
					memcpy(lastaddr, &from_lsa->u.sa, from_lsa->len);
					gotlastaddr = 1;
				}

				print_delta_ms(t1, t2);
				ip = (struct ip *)recv_pkt;

				if (from_lsa->u.sa.sa_family == AF_INET)
					if (op & OPT_TTL_FLAG)
						printf(" (%d)", ip->ip_ttl);

				/* time exceeded in transit */
				if (i == -1)
					break;
				i--;
				switch (i) {
#if ENABLE_TRACEROUTE6
				case ICMP6_DST_UNREACH_NOPORT << 8:
					got_there = 1;
					break;
#endif
				case ICMP_UNREACH_PORT:
					if (ip->ip_ttl <= 1)
						printf(" !");
					got_there = 1;
					break;

				case ICMP_UNREACH_NET:
#if ENABLE_TRACEROUTE6 && (ICMP6_DST_UNREACH_NOROUTE != ICMP_UNREACH_NET)
				case ICMP6_DST_UNREACH_NOROUTE << 8:
#endif
					printf(" !N");
					++unreachable;
					break;
				case ICMP_UNREACH_HOST:
#if ENABLE_TRACEROUTE6
				case ICMP6_DST_UNREACH_ADDR << 8:
#endif
					printf(" !H");
					++unreachable;
					break;
				case ICMP_UNREACH_PROTOCOL:
					printf(" !P");
					got_there = 1;
					break;
				case ICMP_UNREACH_NEEDFRAG:
					printf(" !F-%d", pmtu);
					++unreachable;
					break;
				case ICMP_UNREACH_SRCFAIL:
#if ENABLE_TRACEROUTE6
				case ICMP6_DST_UNREACH_ADMIN << 8:
#endif
					printf(" !S");
					++unreachable;
					break;
				case ICMP_UNREACH_FILTER_PROHIB:
				case ICMP_UNREACH_NET_PROHIB:   /* misuse */
					printf(" !A");
					++unreachable;
					break;
				case ICMP_UNREACH_HOST_PROHIB:
					printf(" !C");
					++unreachable;
					break;
				case ICMP_UNREACH_HOST_PRECEDENCE:
					printf(" !V");
					++unreachable;
					break;
				case ICMP_UNREACH_PRECEDENCE_CUTOFF:
					printf(" !C");
					++unreachable;
					break;
				case ICMP_UNREACH_NET_UNKNOWN:
				case ICMP_UNREACH_HOST_UNKNOWN:
					printf(" !U");
					++unreachable;
					break;
				case ICMP_UNREACH_ISOLATED:
					printf(" !I");
					++unreachable;
					break;
				case ICMP_UNREACH_TOSNET:
				case ICMP_UNREACH_TOSHOST:
					printf(" !T");
					++unreachable;
					break;
				default:
					printf(" !<%d>", i);
					++unreachable;
					break;
				}
				break;
			}
			/* there was no packet at all? */
			if (read_len == 0)
				printf("  *");
		}
		bb_putchar('\n');
		if (got_there
		 || (unreachable > 0 && unreachable >= nprobes - 1)
		) {
			break;
		}
	}

	return 0;
}

int traceroute_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int traceroute_main(int argc UNUSED_PARAM, char **argv)
{
	return common_traceroute_main(0, argv);
}

#if ENABLE_TRACEROUTE6
int traceroute6_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int traceroute6_main(int argc UNUSED_PARAM, char **argv)
{
	return common_traceroute_main(OPT_IPV6, argv);
}
#endif