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In computing, traceroute is a computer network diagnostic tool for displaying the route (path) and measuring transit delays of packets across an Internet Protocol (IP) network. The history of the route is recorded as the round-trip times of the packets received from each successive host (remote node) in the route (path); the sum of the mean times in each hop indicates the total time spent to establish the connection. Traceroute proceeds unless all (three) sent packets are lost more than twice, then the connection is lost and the route cannot be evaluated. Ping, on the other hand, only computes the final round-trip times from the destination point. The command is available on a number of modern operating systems. On Apple Mac OS, it is available by opening "Network Utilities" and selecting "Traceroute" tab, as well as by typing the "traceroute" command in the terminal. On other Unix systems, such as FreeBSD or Linux, it is available as a command in a terminal. On Microsoft Windows, it is named . Windows NT-based operating systems also provide PathPing, with similar functionality. For Internet Protocol Version 6 (IPv6) the tool sometimes has the name or . == Implementation == Traceroute, by default, sends a sequence of User Datagram Protocol (UDP) packets addressed to a destination host; ICMP Echo Request or TCP SYN packets can also be used.〔(【引用サイトリンク】title=traceroute(8) - Linux man page )〕 The time-to-live (TTL) value, also known as ''hop limit'', is used in determining the intermediate routers being traversed towards the destination. Routers decrement TTL values of packets by one when routing and discard packets whose TTL value has reached zero, returning the ICMP error message ICMP Time Exceeded. Common default values for TTL are 128 (Windows OS) and 64 (Unix-based OS). Traceroute works by sending packets with gradually increasing TTL value, starting with TTL value of one. The first router receives the packet, decrements the TTL value and drops the packet because it then has TTL value zero. The router sends an ICMP Time Exceeded message back to the source. The next set of packets are given a TTL value of two, so the first router forwards the packets, but the second router drops them and replies with ICMP Time Exceeded. Proceeding in this way, traceroute uses the returned ICMP Time Exceeded messages to build a list of routers that packets traverse, until the destination is reached and returns an ICMP Echo Reply message.〔 The timestamp values returned for each router along the path are the delay (latency) values, typically measured in milliseconds for each packet. Hop 192.168.1.2 Depth 1 Probe status: unsuccessful Parent: () Return code: Label-switched at stack-depth 1 Sender timestamp: 2008-04-17 09:35:27 EDT 400.88 msec Receiver timestamp: 2008-04-17 09:35:27 EDT 427.87 msec Response time: 26.92 msec MTU: Unknown Multipath type: IP Address Range 1: 127.0.0.64 ~ 127.0.0.127 Label Stack: Label 1 Value 299792 Protocol RSVP-TE The sender expects a reply within a specified number of seconds. If a packet is not acknowledged within the expected interval, an asterisk is displayed. The Internet Protocol does not require packets to take the same route towards a particular destination, thus hosts listed might be hosts that other packets have traversed. If the host at hop #N does not reply, the hop is skipped in the output. On Unix-like operating systems, the utility uses User Datagram Protocol (UDP) datagrams by default, with destination port numbers ranging from 33434 to 33534. The traceroute utility usually has an option to instead use ICMP Echo Request (type 8) packets, like the Windows utility does, or to use TCP SYN packets.〔〔 If a network has a firewall and operates both Windows and Unix-like systems, more than one protocol must be enabled inbound through the firewall for traceroute to work and receive replies. Some traceroute implementations use TCP packets, such as tcptraceroute or layer four traceroute. PathPing is a utility introduced with Windows NT that combines ping and traceroute functionality. MTR is an enhanced version of ICMP traceroute available for Unix-like and Windows systems. The various implementations of traceroute all rely on ICMP Time Exceeded (type 11) packets being sent to the source. The implementations of shipped with Linux, FreeBSD, NetBSD, OpenBSD, DragonFly BSD, and OS X include an option to use ICMP Echo packets (), or any arbitrary protocol () such as UDP, TCP or ICMP. On Linux, is a utility similar to , with the primary difference of not requiring superuser privileges. Cisco's implementation of traceroute also uses a sequence of UDP datagrams, each with incrementing TTL values, to an invalid port number at the remote host; by default, UDP port 33434 is used. Extended version of this command (known as the ''extended traceroute'' command) can change the destination port number used by the UDP probe messages. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Traceroute」の詳細全文を読む スポンサード リンク
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