I'll definitely be checking this out. A couple style nits:

Strategy in comments. Tactics in code.
Don't mention any actual numbers, operators or data types in a comment, and you're less likely to get out of sync.

use constant TIMEOUT => 5; # seconds, for traceroutes
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Think higher.
If you think about the problem in strategy terms, you won't micromanage your tactics.

open(HOST, $file ) or die "Can't open `$file': $!\n";
my @hosts = <HOST>;
close(HOST);
chomp @hosts;
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