The Internet is a large and complex aggregation of network hardware, connected by gateways. Tracking the route a packet follows can be difficult. The utility traceroute traces the route that an IP packet follows to another internet host.

The traceroute utility utilizes the both the IPv4 and IPv6 protocols. Use the -A option to override the default behavior. traceroute uses the IPv4 protocol ttl (time to live) field or the IPv6 field hop limit. It attempts to elicit an ICMP or ICMP6 TIME_EXCEEDED response from each gateway along the path, and a PORT_UNREACHABLE(or ECHO_REPLY if -I is used) response from the destination host. It starts by sending probes with a ttl or hop limit of 1 and increases by 1 until it either gets to the host, or it hits the maximum max_hop. The default maximum max_hop is 30 hops, but this can be set by the -m option.

Three probes are sent at each ttl (hop limit) setting, and a line is printed showing the ttl (hop limit), the hostname and the address of the gateway, and the rtt (round trip time) of each probe. The number of probes may be specifically set using the -q option. If the probe answers come from different gateways, the hostname and the address of each responding system will be printed. If there is no response within a 5 second timeout interval, a "*" is printed for that probe. The -w option may be used to set the timeout interval. Other possible annotations that may appear after the time are:

!

the ttl (hop limit) value in the received packet is <= 1.

!H

host unreachable.

!X

communication administratively prohibited.

<!N>

ICMP (ICMP6) unreachable code N.

The following annotations appear only for IPv4:

!F

fragmentation needed. This should never occur. If this is seen, the associated gateway is broken.

!N

network unreachable.

!P

protocol unreachable.

!S

source route failed. This should never occur. If this is seen, the associated gateway is broken.

!T

unreachable for the specified tos (type-of-service).

!U

source host isolated or precedence problem.

The following annotations appear only for IPv6:

!A

host unreachable for a reason other than lack of an entry in the routing table.

!B

packet too big.

!E

destination is not a neighbor.

!R

unrecognized next header.

The destination host is not supposed to process the UDP probe packets, so the destination port default is set to an unlikely value. However, if some application on the destination is using that value, the value of port can be changed with the -p option.

The only mandatory parameter is the destination host name or IP number. The default probe datagram length is 40 bytes (60 bytes for IPv6), but this may be increased by specifying a packet length (in bytes) after the destination host name.

All integer arguments to traceroute can be specified in either decimal or hexadecimal notation. For example, packetlen can be specified either as 256 or 0x100.

-A addr_family

Specify the address family of the target host. addr_family can be either inet or inet6. Address family determines which protocol to use. For an argument of inet, IPv4 is used. For inet6, IPv6 is used.

By default, if the name of a host is provided, not the literal IP address, and a valid IPv6 address exists in the name service database, traceroute will use this address. Otherwise, if the name service database contains an IPv4 address, it will try the IPv4 address.

Specify the address family inet or inet6 to override the default behavior. If the argument specified is inet, traceroute will use the IPv4 address associated with the hostname. If none exists, traceroute will state that the host is unknown and exit. It will not try to determine if an IPv6 address exists in the name service database.

If the specified argument is inet6, traceroute will use the IPv6 address that is associated with the hostname. If none exists, traceroute will state that the host is unknown and exit.

-a

Probe all of the addresses of a multi-homed destination. The output looks like traceroute has been run once for each IP address of the destination. If this option is used together with -A, traceroute probes only the addresses that are of the specified address family. While probing one of the addresses of the destination, user can skip to the next address by sending a SIGINT, or exit traceroute by sending a SIGQUIT signal. See signal(3C)

-c traffic_class

Specify the traffic class of probe packets. The value must be an integer in the range from 0 to 255. Gateways along the path may route the probe packet differently depending upon the value of traffic_class set in the probe packet. This option is valid only on IPv6.

-d

Set the SO_DEBUG socket option.

-F

Set the "don't fragment" bit. This option is valid only on IPv4.

-f first_hop

Set the starting ttl ( hop limit) value to first_hop, to override the default value 1. traceroute skips processing for those intermediate gateways which are less than first_hop hops away.

-g gateway

Specify a loose source route gateway. The user can specify more than one gateway by using -g for each gateway. The maximum number of gateways is 8 for IPv4 and 127 for IPv6. Note that some factors such as the link MTU can further limit the number of gateways for IPv6. This option cannot be used with the -r option.

-I

Use ICMP (ICMP6) ECHO instead of UDP datagrams.

-i iface

For IPv4, this option specifies a network interface to obtain the source IP address. This is normally only useful on a multi-homed host. The -s option is also another way to do this. For IPv6, it specifies the network interface on which probe packets are transmitted. The argument can be either an interface index, for example, 1, 2, or an interface name, for example, le0, hme0.

-L flow_label

Specify the flow label of probe packets. The value must be an integer in the range from 0 to 1048575. This option is valid only on IPv6.

-l

Print the value of the ttl (hop limit) field in each packet received.

-m max_hop

Set the maximum ttl (hop limit) used in outgoing probe packets. The default is 30 hops, which is the same default used for TCP connections.

-n

Print hop addresses numerically rather than symbolically and numerically. This saves a nameserver address-to-name lookup for each gateway found on the path.

-P pause_sec

Specify a delay, in seconds, to pause between probe packets. This may be necessary if the final destination does not accept undeliverable packets in bursts. By default, traceroute sends the next probe as soon as it has received a reply. Note that pause_sec is a real number.

-p port

Set the base UDP port number used in probes.The default is 33434. traceroute hopes that nothing is listening on UDP ports (base+(nhops-1)*nqueries) to (base+(nhops*nqueries)-1)at the destination host, so that an ICMP (ICMP6) PORT_UNREACHABLE message will be returned to terminate the route tracing. If something is listening on a port in the default range, this option can be used to select an unused port range. nhops is defined as the number of hops between the source and the destination.

-Q max_timeout

Stop probing this hop after max_timeout consecutive timeouts are detected. The default value is 5. Useful in combination with the -q option if you have specified a large nqueries probe count.

-q nqueries

Set the desired number of probe queries. The default is 3.

-r

Bypass the normal routing tables and send directly to a host on an attached network. If the host is not on a directly-attached network, an error is returned. This option can be used to send probes to a local host through an interface that has been dropped by the router deamon. See in.routed(1M). You cannot use this option if the -g option is used.

-s src_addr

Use the following address, which usually is given as a literal IP address, not a hostname, as the source address in outgoing probe packets. On multi-homed hosts, those with more than one IP address, this option can be used to force the source address to be something other than the IP address traceroute picks by default. If the IP address is not one of this machine's interface addresses, an error is returned and nothing is sent. For IPv4, when used together with the -i option, the given IP address should be configured on the specified interface. Otherwise, an error will be returned. In the case of IPv6, the interface name and the source address do not have to match.

-t tos

Set the tos(type-of-service) in probe packets to the specified value. The default is zero. The value must be an integer in the range from 0 to 255. Gateways along the path may route the probe packet differently depending upon the tos value set in the probe packet. This option is valid only on IPv4.

-v

Verbose output. For each hop, the size and the destination of the response packets is displayed. Also ICMP (ICMP6) packets received other than TIME_EXCEEDED and UNREACHABLE are listed as well.

-w waittime

Set the time, in seconds, to wait for a response to a probe. The default is 5 seconds.

-x

Prevent traceroute from calculating checksums. Note that checksums are usually required for the last hop when using ICMP ECHO probes. This option is valid only on IPv4. See the -I option.

The following operands are supported:

host

The network host.

The following exit values are returned:

0

Successful operation.

>0

An error occurred.

See attributes(5) for descriptions of the following attributes:

netstat(1M), signal(3C), ping(1M), attributes(5)

This utility 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(1m) during normal operations or from automated scripts.