README
1Tue Dec 27 06:24:24 PST 1988
2
3Traceroute is a system administrators utility to trace the route
4ip packets from the current system take in getting to some
5destination system. See the comments at the front of the
6program for a description of its use.
7
8This program
9
10 a) can only be run by root (it uses raw ip sockets).
11
12 b) REQUIRES A KERNEL MOD to the raw ip output code to run.
13
14If you want to hack on your kernel, my modified version of the
15routine rip_output (in file /sys/netinet/raw_ip.c) is attached.
16This code may or may not resemble the code in your kernel.
17It may offer you a place to start but I make no promises.
18If you do hack your kernel, remember to test everything that uses
19raw ip sockets (e.g., ping and egpup/gated) & make sure they still
20work. I wish you the best of luck and you're on your own.
21
22If your system has the ttl bug mentioned in the source, you
23might want to fix it while you're in the kernel. (This bug
24appears in all releases of BSD up to but not including 4.3tahoe.
25If your version of netinet/ip_icmp.c is any earlier than 7.3
26(April, '87), it has the bug.) The fix is just to add the line
27 ip->ip_ttl = MAXTTL;
28after the line
29 ip->ip_src = t;
30(or anywhere before the call to icmp_send) in routine icmp_reflect.
31
32If you're running this on a pre-4.3bsd system (e.g., Sun 3.x,
33Ultrix) that strips ip headers from icmp messages, add -DARCHAIC
34to CFLAGS in the Makefile. Also note that rip_output contains
35a conditional for a 4.2/4.3 change in the location of a raw
36socket's protocol number. I've checked this under 4.3 & Sun OS
373.5 but you should double-check your system to make sure the
38appropriate branch of the #if is taken (check the line that
39assigned to ip->ip_p in your system's original rip_output).
40
41A couple of awk programs to massage the traceroute output are
42included. "mean.awk" and "median.awk" compute the mean and median
43time to each hop, respectively. I've found that something like
44
45 traceroute -q 7 foo.somewhere >t
46 awk -f median.awk t | graph
47
48can give you a quick picture of the bad spots on a long
49path (median is usually a better noise filter than mean).
50
51Enjoy.
52
53 - Van Jacobson (van@helios.ee.lbl.gov)
54
55-------------------- rip_output from /sys/netinet/raw_ip.c
56rip_output(m, so)
57 register struct mbuf *m;
58 struct socket *so;
59{
60 register struct ip *ip;
61 int error;
62 struct rawcb *rp = sotorawcb(so);
63 struct sockaddr_in *sin;
64#if BSD>=43
65 short proto = rp->rcb_proto.sp_protocol;
66#else
67 short proto = so->so_proto->pr_protocol;
68#endif
69 /*
70 * if the protocol is IPPROTO_RAW, the user handed us a
71 * complete IP packet. Otherwise, allocate an mbuf for a
72 * header and fill it in as needed.
73 */
74 if (proto != IPPROTO_RAW) {
75 /*
76 * Calculate data length and get an mbuf
77 * for IP header.
78 */
79 int len = 0;
80 struct mbuf *m0;
81
82 for (m0 = m; m; m = m->m_next)
83 len += m->m_len;
84
85 m = m_get(M_DONTWAIT, MT_HEADER);
86 if (m == 0) {
87 m = m0;
88 error = ENOBUFS;
89 goto bad;
90 }
91 m->m_off = MMAXOFF - sizeof(struct ip);
92 m->m_len = sizeof(struct ip);
93 m->m_next = m0;
94
95 ip = mtod(m, struct ip *);
96 ip->ip_tos = 0;
97 ip->ip_off = 0;
98 ip->ip_p = proto;
99 ip->ip_len = sizeof(struct ip) + len;
100 ip->ip_ttl = MAXTTL;
101 } else
102 ip = mtod(m, struct ip *);
103
104 if (rp->rcb_flags & RAW_LADDR) {
105 sin = (struct sockaddr_in *)&rp->rcb_laddr;
106 if (sin->sin_family != AF_INET) {
107 error = EAFNOSUPPORT;
108 goto bad;
109 }
110 ip->ip_src.s_addr = sin->sin_addr.s_addr;
111 } else
112 ip->ip_src.s_addr = 0;
113
114 ip->ip_dst = ((struct sockaddr_in *)&rp->rcb_faddr)->sin_addr;
115
116#if BSD>=43
117 return (ip_output(m, rp->rcb_options, &rp->rcb_route,
118 (so->so_options & SO_DONTROUTE) | IP_ALLOWBROADCAST));
119#else
120 return (ip_output(m, (struct mbuf *)0, &rp->rcb_route,
121 (so->so_options & SO_DONTROUTE) | IP_ALLOWBROADCAST));
122#endif
123bad:
124 m_freem(m);
125 return (error);
126}
127