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Second IP location of tracerouter is always hidden


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The way traceroute works is that it sends out a packet with a slowly increasing TTL (Time To Live) field. When a machine receives this packet and decides it's not the one to handle it (i.e. any machine in the path towards the actual destination machine) it decrements that field and sends it on except when the value becomes 0. In that case an ICMP Time Exceeded packet is sent back to the sending machine to indicate the packet needed more hops to reach its destination than what was allowed.

When you get all stars in the response it only means that the machine that was supposed to send back an ICMP packet simply didn't.

This often happens when stupid network admins feel that ALL ICMP packets tell the outside world too much about the device, possibly not realising that these packets have an important function in the day-to-day operation of the network. What they often want to do is block PING responses (yes, PING is an ICMP packet) because they prove that a machine is there... Yawn. If a hacker wanted to discover a machine (s)he'd use NMAP and discover it more reliably and silently than via PING. By blocking all ICMP packets when you want to connect to a machine that doesn't exist you don't get the ICMP packet that says the destination host is down, you just get nothing and have to wait for a timeout on the socket due to inactivity. Guess which of the two works faster?

In your case it would appear that your router is the 'culprit' that's not sending back ICMP packets. It's stupid but for the most part harmless on smaller (home) networks.

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