Feature #8504

traceroute should warn when name services are slow

Added by Robert Mustacchi over 3 years ago. Updated over 3 years ago.

cmd - userland programs
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As we've seen in cases like 6211 and 8503, when name services are not working, understanding what's going on in the system can be very confusing. In the case of traceroute, it may appear to the end user that they can't actually reach the end point, when it's actually the opposite – that they reached it just fine. In this case, what we'd like to do is warn once so the user has a hope of understanding what's going on. If this isn't functioning because something else is going on, then we wouldn't end up having any warnings.


Updated by Robert Mustacchi over 3 years ago

To test this we blocked name services from working and ran traceroute:

[root@haswell ~]# traceroute
traceroute to (, 30 hops max, 40 byte packets
 1 traceroute: warning: responses received, but name service lookups are taking a while. Use traceroute -n to disable name service lookups. (  0.214 ms  0.260 ms  0.178 ms
 2 (  0.537 ms  0.628 ms  0.401 ms
 3 (  0.838 ms  0.911 ms  0.748 ms
 4 (  2.811 ms  2.735 ms  1.956 ms
 5 (  2.024 ms  2.306 ms  2.127 ms
 6 (  2.015 ms  2.180 ms  2.039 ms
 7 (  2.658 ms (  2.686 ms  2.753 ms
 8 (  2.827 ms (  3.199 ms (  3.097 ms
 9 ^C

I also ran traceroute without DNS services blocked and everything operated fine. While blocked I also used the -n flag and verified that traceroute worked as expected.


Updated by Electric Monk over 3 years ago

  • Status changed from New to Closed

git commit afee3dc66d7b1fb4aaedced0814360f4334bc2c0

commit  afee3dc66d7b1fb4aaedced0814360f4334bc2c0
Author: Robert Mustacchi <>
Date:   2017-08-08T19:21:49.000Z

    8503 snoop seems to delay packets doing DNS resolution
    8504 traceroute should warn when name services are slow
    8505 netstat should warn when name services are slow
    8506 ping name service warnings should only happen once
    Reviewed by: Jerry Jelinek <>
    Reviewed by: Dan McDonald <>
    Reviewed by: Yuri Pankov <>
    Approved by: Gordon Ross <>

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