Python Script for Colorizing Traceroute Output (apologies for top-post)

Chris Angelico rosuav at
Sat Nov 17 19:45:57 CET 2012

On Sun, Nov 18, 2012 at 5:38 AM, Roy Smith <roy at> wrote:
> In article <mailman.3774.1353175657.27098.python-list at>,
>  wrw at wrote:
>> Don't forget that most firewalls don't decrement) the time-to-live number,
>> and unless you REALLY know what to look for, are invisible.
> Interesting.  If the firewall doesn't decrement TTL (a particular nasty
> thing to do, and thus completely expected of a firewall) what REALLY
> knowledge would enable you to detect its presence in a traceroute
> printout at all?

If it's a router, then it definitely should be decrementing TTLs,
though if the firewall is simply a part of another hop, you won't
notice it specifically. What's more common, though, is devices that
decrement TTL and drop packets but don't send back Time Exceeded
messages, giving the classic "* * *" line. I'm not sure if that's what
was being referred to, though. (And they aren't necessarily


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