Summery
あるホストから別のホストの間のネットワーク経路を調査する。
経路により、通信できない場合の確認で行う。
pingで疎通しなかった場合に、この経路調査で、問題点が見える。
Construction
$ traceroute [option] [domain]
Option
-d : デバッグモード
-n : IPアドレスのみの制御する（DNS逆引きをしない）
-g : ゲートウェイを８個まで指定できる
-i : インターフェイスを指定できる
-f : TTLの初期値を指定
-m : TTLの最大値を指定
-p : UDPのポート番号を指定
-q : １つのゲートウェイに対する問い合わせ回数（デフォルト３）
-s : 開始IPアドレスの指定
-w : タイムアウトの時間指定（デフォルト５秒）
Sample
# googleまでの経路を取得
$ traceroute google.com
traceroute: Warning: google.com has multiple addresses; using 173.194.38.193
traceroute to google.com (173.194.38.193), 64 hops max, 52 byte packets
1 192.168.1.250 (192.168.1.250) 2.366 ms 2.067 ms 1.989 ms
2 kanagawa17.ntt-poi.freebit.net (220.150.74.32) 8.104 ms 8.356 ms 6.844 ms
3 37.74.150.220.ap.yournet.ne.jp (220.150.74.37) 6.432 ms 6.519 ms 6.902 ms
4 *.*.*.*.ap.yournet.ne.jp (*.*.*.*) 7.189 ms 7.448 ms 7.341 ms
5 85.75.150.220.ap.yournet.ne.jp (220.150.75.85) 12.005 ms 7.785 ms 6.958 ms
6 210.173.176.243 (210.173.176.243) 10.042 ms 9.422 ms 9.204 ms
7 72.14.235.148 (72.14.235.148) 11.310 ms 11.311 ms 11.527 ms
8 72.14.255.145 (72.14.255.145) 9.621 ms 10.090 ms 9.671 ms
9 nrt13s01-in-f1.1e100.net (173.194.38.193) 10.448 ms 10.006 ms 9.812 ms</code>
<h2>Discription</h2>
<code>
The Internet is a large and complex aggregation of network hardware, connected together
by gateways. Tracking the route one's packets follow (or finding the miscreant gateway
that's discarding your packets) can be difficult. traceroute utilizes the IP protocol
`time to live' field and attempts to elicit an ICMP TIME_EXCEEDED response from each
gateway along the path to some host.
The only mandatory parameter is the destination host name or IP number. The default
probe datagram length is 40 bytes, but this may be increased by specifying a packet size
(in bytes) after the destination host name.
Other options are:
-a Turn on AS# lookups for each hop encountered.
-A as_server
Turn on AS# lookups and use the given server instead of the default.
-d Enable socket level debugging.
-D When an ICMP response to our probe datagram is received, print the differences
between the transmitted packet and the packet quoted by the ICMP response. A
key showing the location of fields within the transmitted packet is printed,
followed by the original packet in hex, followed by the quoted packet in hex.
Bytes that are unchanged in the quoted packet are shown as underscores. Note,
the IP checksum and the TTL of the quoted packet are not expected to match. By
default, only one probe per hop is sent with this option.
-e Firewall evasion mode. Use fixed destination ports for UDP and TCP probes. The
destination port does NOT increment with each packet sent.
-f first_ttl
Set the initial time-to-live used in the first outgoing probe packet.
-F Set the "don't fragment" bit.
-g gateway
Specify a loose source route gateway (8 maximum).
-i iface
Specify a network interface to obtain the source IP address for outgoing probe
packets. This is normally only useful on a multi-homed host. (See the -s flag
for another way to do this.)
-I Use ICMP ECHO instead of UDP datagrams. (A synonym for "-P icmp").
-M first_ttl
Set the initial time-to-live value used in outgoing probe packets. The default
is 1, i.e., start with the first hop.
-m max_ttl
Set the max time-to-live (max number of hops) used in outgoing probe packets.
The default is net.inet.ip.ttl hops (the same default used for TCP connections).
-n Print hop addresses numerically rather than symbolically and numerically (saves
a nameserver address-to-name lookup for each gateway found on the path).
-P proto
Send packets of specified IP protocol. The currently supported protocols are:
UDP , TCP , GRE and ICMP Other protocols may also be specified (either by name
or by number), though traceroute does not implement any special knowledge of
their packet formats. This option is useful for determining which router along a
path may be blocking packets based on IP protocol number. But see BUGS below.
-p port
Protocol specific. For UDP and TCP, sets the base port number used in probes
(default is 33434). traceroute hopes that nothing is listening on UDP ports
base to base+nhops-1 at the destination host (so an ICMP PORT_UNREACHABLE mes-
sage will be returned to terminate the route tracing). If something is listen-
ing on a port in the default range, this option can be used to pick an unused
port range.
-q nqueries
Set the number of probes per ``ttl'' to nqueries (default is three probes).
-r Bypass the normal routing tables and send directly to a host on an attached net-
work. If the host is not on a directly-attached network, an error is returned.
This option can be used to ping a local host through an interface that has no
route through it (e.g., after the interface was dropped by routed(8)).
-s src_addr
Use the following IP address (which must be given as an IP number, not a host-
name) as the source address in outgoing probe packets. On hosts with more than
one IP address, this option can be used to force the source address to be some-
thing other than the IP address of the interface the probe packet is sent on.
If the IP address is not one of this machine's interface addresses, an error is
returned and nothing is sent. (See the -i flag for another way to do this.)
-S Print a summary of how many probes were not answered for each hop.
-t tos Set the type-of-service in probe packets to the following value (default zero).
The value must be a decimal integer in the range 0 to 255. This option can be
used to see if different types-of-service result in different paths. (If you
are not running a 4.4BSD or later system, this may be academic since the normal
network services like telnet and ftp don't let you control the TOS). Not all
values of TOS are legal or meaningful - see the IP spec for definitions. Useful
values are probably `-t 16' (low delay) and `-t 8' (high throughput).
-v Verbose output. Received ICMP packets other than TIME_EXCEEDED and UNREACHABLEs
are listed.
-w Set the time (in seconds) to wait for a response to a probe (default 5 sec.).
-x Toggle IP checksums. Normally, this prevents traceroute from calculating IP
checksums. In some cases, the operating system can overwrite parts of the outgo-
ing packet but not recalculate the checksum (so in some cases the default is to
not calculate checksums and using -x causes them to be calculated). Note that
checksums are usually required for the last hop when using ICMP ECHO probes ( -I
). So they are always calculated when using ICMP.
-z pausemsecs
Set the time (in milliseconds) to pause between probes (default 0). Some sys-
tems such as Solaris and routers such as Ciscos rate limit ICMP messages. A good
value to use with this this is 500 (e.g. 1/2 second).
This program attempts to trace the route an IP packet would follow to some internet host
by launching UDP 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 net.inet.ip.ttl hops & can be changed with the -m flag).
Three probes (changed 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.
We don't want the destination host to process the UDP probe packets 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 and output might be:
[yak 71]% traceroute nis.nsf.net.
traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 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 bug in the distributed ver-
sion of 4.3 BSD). Note that you have to guess what path the packets are taking cross-
country since the NSFNet (129.140) doesn't supply address-to-name translations for its
NSSes.
A more interesting example is:
[yak 72]% traceroute allspice.lcs.mit.edu.
traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 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
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, or !P (host, network or protocol
unreachable), !S (source route failed), (fragmentation needed - the RFC1191 Path MTU
Discovery value is displayed), !U or !W (destination network/host unknown), !I (source
host is isolated), !A (communication with destination network administratively prohib-
ited), !Z (communication with destination host administratively prohibited), !Q (for
this ToS the destination network is unreachable), !T (for this ToS the destination host
is unreachable), !X (communication administratively prohibited), !V (host precedence
violation), !C (precedence cutoff in effect), or !<num> (ICMP unreachable code <num>).
These are defined by RFC1812 (which supersedes RFC1716). If almost all the probes
result in some kind of unreachable, traceroute will give up and exit.
This program is intended for use in network testing, measurement and management. It
should be used primarily for manual fault isolation. Because of the load it could
impose on the network, it is unwise to use traceroute during normal operations or from
automated scripts.
