#!/usr/bin/perl -w

#

# routewatch.pl by Pegasus Epsilon <pegasus@pimpninjas.org>

# Distribute Unmodified -- http://pegasus.pimpninjas.org/license

#

# Memorizes and monitors a portion of a route for changes over time.

# This includes nodes dropping AND traffic getting rerouted.

use strict;

use Socket;

select((select(STDOUT), $| = 1)[0]);

sub usage {

print "Usage: $0 <remote IP> [first TTL] [last TTL]\n";

exit 0;

}

my %dnscache;

sub ptr {

my $ip = shift;

defined $dnscache{$ip}

&& return $dnscache{$ip};

my $tmp = inet_aton($ip)

|| return $dnscache{$ip} = "NO_RESPONSE";

$tmp = gethostbyaddr($tmp, AF_INET)

|| return $dnscache{$ip} = "PTR_RECORD_NOT_FOUND";

return $dnscache{$ip} = $tmp;

}

sub routeping {

my ($f, $m, $ip) = @_;

my $N = $m - $f + 1;

my @route = map { s/^ *//; s/ +/ /; $_ } split /\n/,

`traceroute -n -f $f -m $m -w 1 -q 1 -N $N $ip`;

shift @route;

return @route;

}

my $ip = shift;

usage unless $ip;

my $first_ttl = shift || 1;

my $last_ttl = shift || 30;

print "memorizing hops $first_ttl to $last_ttl between here and $ip...\n";

my %route;

for my $i (routeping($first_ttl, $last_ttl, $ip)) {

my ($hop, $ip, $rtt) = split / /, $i;

print "$hop $ip ", ptr($route{$last_ttl = $hop} = $ip), "\n";

}

print "memorization complete, monitoring for changes...\n";

for (;;) {

print "sleeping...\r";

sleep 1;

print "polling... \r";

for my $i (routeping($first_ttl, $last_ttl, $ip)) {

my ($hop, $ip, $rtt) = split / /, $i;

if (not $route{$hop} or $route{$hop} ne $ip) {

print scalar localtime, ": route changed: $hop $route{$hop} ",

ptr($route{$hop}), " -> $ip ",

ptr($route{$hop} = $ip), "\n";

}

}

}