1

When issue the traceroute command, I get the feeback

me@alpha:~$ traceroute www.youtube.com
traceroute to www.youtube.com (203.98.7.65), 64 hops max
  .........
  4   61.148.6.201  2.463ms  2.298ms  2.119ms 
  5   202.96.12.121  2.714ms  2.520ms  2.444ms 
  6   219.158.5.154  7.203ms  8.785ms  6.966ms 
  7   219.158.16.66  5.199ms  9.587ms  6.808ms 
  8   219.158.103.6  342.937ms  307.527ms  308.729ms 
  9   195.2.22.53  317.321ms  243.056ms  359.128ms 
 10   195.2.8.137  271.794ms  342.338ms  306.371ms 
 11   *  *  * 
 12   *  *  * 
 13   *  *  * 
 14   *  *  * 
 15   *  *  * 
 16   *  *  * 

What does the stars mean?

0
3

Traceroute works by sending ICMP (echo request) packets to the destination, with increasing TTL - field values, starting at 1. Each router decreases the TTL - field by 1. This makes the router answer the request with ('TTL exceeded') packets, at which the TTL fields reaches 0.

The '*' simply mean that the hop (router) does not send ICMP (firewall? config?), and therefore your outgoing ICMP - packet does not get answered.

After a certain timeout, "traceroute" increases the TTL on the outgoing packet which makes the next hop in the route answer. This continues until the destination is reached, or the last router in the route replies with 'host unreachable'.

1
  • A router normally sends ICMP unreachable messages. If the UDP packets to generate the answer are blocked that's a different story though – Rui F Ribeiro Jan 21 '19 at 9:52

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