Net::Traceroute - traceroute(1) functionality in perl


    use Net::Traceroute;
    $tr = Net::Traceroute->new(host=> "");
    if($tr->found) {
        my $hops = $tr->hops;
        if($hops > 1) {
            print "Router was " .
                $tr->hop_query_host($tr->hops - 1, 0) . "\n";


This module implements traceroute(1) functionality for perl5. It allows you to trace the path IP packets take to a destination. It is currently implemented as a parser around the system traceroute command.


A new Net::Traceroute object must be created with the new method. Depending on exactly how the constructor is invoked, it may perform the traceroute immediately, or it may return a "template" object that can be used to set parameters for several subsequent traceroutes.

Methods are available for accessing information about a given traceroute attempt. There are also methods that view/modify the options that are passed to the object's constructor.

To trace a route, UDP packets are sent with a small TTL (time-to-live) field in an attempt to get intervening routers to generate ICMP TIME_EXCEEDED messages.


    $obj = Net::Traceroute->new([base_port      => $base_port,]
                                [debug          => $debuglvl,]
                                [max_ttl        => $max_ttl,]
                                [host           => $host,]
                                [queries        => $queries,]
                                [query_timeout  => $query_timeout,]
                                [timeout        => $timeout,]
                                [source_address => $srcaddr,]
                                [packetlen      => $packetlen,]
                                [trace_program  => $program,]
                                [no_fragment    => $nofrag,]
                                [use_icmp       => $useicmp,]);
    $frob = $obj->clone([options]);

This is the constructor for a new Net::Traceroute object. If given host, it will actually perform the traceroute. You can call the traceroute method later.

Given an existing Net::Traceroute object $obj as a template, you can call $obj->clone() with the usual constructor parameters. The same rules apply about defining host; that is, traceroute will be run if it is defined. You can always pass host => undef to clone.

Possible options are:

host - A host to traceroute to. If you don't set this, you get a Traceroute object with no traceroute data in it. The module always uses IP addresses internally and will attempt to lookup host names via inet_aton.

base_port - Base port number to use for the UDP queries. Traceroute assumes that nothing is listening to port base_port to base_port + (nhops - 1) where nhops is the number of hops required to reach the destination address. Default is what the system traceroute uses (normally 33434). Traceroute's -p option.

debuglvl - A number indicating how verbose debug information should be. Please include debug=>9 output in bug reports.

max_ttl - Maximum number of hops to try before giving up. Default is what the system traceroute uses (normally 30). Traceroute's -m option.

queries - Number of times to send a query for a given hop. Defaults to whatever the system traceroute uses (3 for most traceroutes). Traceroute's -q option.

query_timeout - How many seconds to wait for a response to each query sent. Uses the system traceroute's default value of 5 if unspecified. Traceroute's -w option.

timeout - Maximum time, in seconds, to wait for the traceroute to complete. If not specified, the traceroute will not return until the host has been reached, or traceroute counts to infinity (max_ttl * queries * query_timeout). Note that this option is implemented by Net::Traceroute, not the underlying traceroute command.

source_address - Select the source address that traceroute wil use.

packetlen - Length of packets to use. Traceroute tries to make the IP packet exactly this long.

trace_program - Name of the traceroute program. Defaults to traceroute. You can pass traceroute6 to do IPv6 traceroutes.

no_fragment - Set the IP don't fragment bit. Some traceroute programs will perform path mtu discovery with this option.

use_icmp - Request that traceroute perform probes with ICMP echo packets, rather than UDP.



Run system traceroute, and parse the results. Will fill in the rest of the object for informational queries.

Controlling traceroute invocation

Each of these methods return the current value of the option specified by the corresponding constructor option. They will set the object's instance variable to the given value if one is provided.

Changing an instance variable will only affect newly performed traceroutes. Setting a different value on a traceroute object that has already performed a trace has no effect.

See the constructor documentation for information about methods that aren't documented here.


Obtaining information about a Trace

These methods return information about a traceroute that has already been performed.

Any of the methods in this section that return a count of something or want an Nth type count to identify something employ one based counting.


Returns the status of a given traceroute object. One of TRACEROUTE_OK, TRACEROUTE_TIMEOUT, or TRACEROUTE_UNKNOWN (each defined as an integer). TRACEROUTE_OK will only be returned if the host was actually reachable.


Returns 1 if the host was found, undef otherwise.


If your traceroute supports MTU discovery, this method will return the MTU in some circumstances. You must set no_fragment, and must use a packetlen larger than the path mtu for this to be set.


Returns the number of hops that it took to reach the host.


Returns the number of queries that were sent for a given hop. This should normally be the same for every query.

hop_query_stat(HOP, QUERY)

Return the status of the given HOP's QUERY. The return status can be one of the following (each of these is actually an integer constant function defined in Net::Traceroute's export list):

QUERY can be zero, in which case the first succesful query will be returned.


Reached the host, no problems.


This query timed out.


Your guess is as good as mine. Shouldn't happen too often.


This hop returned an ICMP Network Unreachable.


This hop returned an ICMP Host Unreachable.


This hop returned an ICMP Protocol unreachable.


Indicates that you can't reach this host without fragmenting your packet further. Shouldn't happen in regular use.


A source routed packet was rejected for some reason. Shouldn't happen.


A firewall or similar device has decreed that your traffic is disallowed by administrative action. Suspect sheer, raving paranoia.


The destination machine appears to exhibit the 4.[23]BSD time exceeded bug.

hop_query_host(HOP, QUERY)

Return the dotted quad IP address of the host that responded to HOP's QUERY.

QUERY can be zero, in which case the first succesful query will be returned.

hop_query_time(HOP, QUERY)

Return the round trip time associated with the given HOP's query. If your system's traceroute supports fractional second timing, so will Net::Traceroute.

QUERY can be zero, in which case the first succesful query will be returned.


Net::Traceroute Versions before 1.04 used new to clone objects. This has been deprecated in favor of the clone() method.

If you have code of the form:

 my $template = Net::Traceroute->new();
 my $tr = $template->new(host => "localhost");

You need to change the $template->new to $template->clone.

This behavior was changed because it interfered with subclassing.


Net::Traceroute parses the output of the system traceroute command. As such, it may not work on your system. Support for more traceroute outputs (e.g. Windows, HPUX) could be done, although currently the code assumes there is "One true traceroute".

The actual functionality of traceroute could also be implemented natively in perl or linked in from a C library.

Versions prior to 1.04 had some interface issues for subclassing. These issues have been addressed, but required a public interface change. If you were relying on the behavior of new to clone existing objects, your code needs to be fixed.

There are some suspected issues in how timeout is handled. I haven't had time to address this yet.




Daniel Hagerty <>


Copyright 1998, 1999 Massachusetts Institute of Technology Copyright 2000, 2001 Daniel Hagerty

Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of M.I.T. not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. M.I.T. makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.