mtr does not resolve the reverse DNS hostnames for any hosts of the trace,
when only DNS servers with IPv6 addresses are listed in resolv.conf. This
applies to console (including mtr-tiny) and X11 interfaces. It also applies
to both IPv4 and IPv6 traces.

If at least one DNS server with IPv4 address is listed, reverse name
resolution starts working again.

Kind regards,
Martin List-Petersen

This is bad software engineering.

I've been thinking about a next generation mtr.

It will use multiple processes to handle different parts of the
mtr system.

So one process will do name resolving. Maybe we'll allow for the "old"
implementation to perform this function (with the current bug
included!), but certainly we'll have an implementation that simply
calls the getnameinfo function. This will be slower than the current
implementation, as queries to different nameservers will not be issued
in parallel. So another implementation will for off as many processes
as neccesary to do all the name queries in parallel. This will cost
you a peak of say 10 processes all stuck in the getnameinfo function
for a few seconds...

	Roger.

Hello,

There are now patches fixing this in https://bugs.launchpad.net/bugs/752583

Hi,

mtr simply exits when /etc/resolv.conf contains only ipv6
nameservers.

$ mtr www.google.com
No nameservers defined.
$ cat /etc/resolv.conf
nameserver 2001:558:feed::1
nameserver 2001:558:feed::2

(These two servers seem to be comcast-only, but
ordns.he.net/2001:470:20::2 appears to work from anywhere
with ipv6 connection.)

When I add an ipv4 server to /etc/resolv.conf, mtr works again.

Cheers,

Yixuan

Dear Maintainer,

In Ubuntu, the attached patch was applied to achieve the following:

My attempt at getting a patch I submitted upstream applied to the mtr
package.

It basically fixes LP: #752583 where IPv6 nameservers specified in
/etc/resolv.conf aren't counted and therefore mtr aborts when there
are *only* IPv6 nameservers specified.

Example /etc/resolv.conf:

| nameserver ::1
| domain local
| options timeout:3 no-check-names

Output from mtr without the fix:

| Start: Fri Aug 15 14:01:25 2014
| No nameservers defined.

A pull request has been submitted on GitHub to have this change
merged upstream[1].

[1]https://github.com/traviscross/mtr/pull/56

  * Non-maintainer upload.
  * Added patch to include count of IPv6 nameservers fixing
    LP:#752583.


Thanks for considering the patch.

Hi Aurelien,

It seems that the change in submitted-resolv-ipv6-nameservers.diff[1]
is causing a regression with the mtr package (and probably other
packages).

The change in question is for statp->nscount to now only count IPv4
nameservers. This now causes mtr to fail on systems where only IPv6
nameservers are specified.

Debian users hvae reported this issue in #528992 [2] as well as Ubuntu
users in LP:#752583 [3].

Is there any chance you could look into this and reconsider?


Thanks,

Haw


[1] https://lists.debian.org/debian-glibc/2014/06/msg00138.html
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=528992
[3] https://bugs.launchpad.net/ubuntu/+source/mtr/+bug/752583

Looks like upstream have resolved this issue:
https://github.com/traviscross/mtr/issues/78

Kind regards,
Martin List-Petersen

Thanks to Marc Haber who reported this upstream in
https://github.com/traviscross/mtr/issues/105 this issue has been fixed.
I can confirm it works fine with only an IPv6-resolver.

You can probably close this bug.

a2824ck@ping:~$ mtr --report www.debian.org
Start: Mon Nov 13 21:16:43 2017
HOST: ping                        Loss%   Snt   Last   Avg  Best  Wrst StDev
  1.|-- vl-60.cvr1-1wr.lrz.de      0.0%    10    0.8   0.9   0.8   1.0   0.0
  2.|-- vl-3077.cvr1-2wr.lrz.de    0.0%    10    0.9   0.9   0.8   1.0   0.0
  3.|-- vl-3075.csr1-2wr.lrz.de    0.0%    10    0.8   0.9   0.8   1.0   0.0
  4.|-- cr-gar1-be2-108.x-win.dfn 40.0%    10    0.9   0.8   0.6   1.0   0.0
  5.|-- ???                       100.0    10    0.0   0.0   0.0   0.0   0.0
  6.|-- ffm-b12-link.telia.net     0.0%    10    9.0   9.8   9.0  16.9   2.4
  7.|-- ffm-bb3-v6.telia.net       0.0%    10    9.7   9.7   9.5  10.0   0.0
  8.|-- ffm-b1-v6.telia.net        0.0%    10    9.8  10.8   9.7  12.8   0.9
  9.|-- ae6.cr1-fra6.ip6.gtt.net   0.0%    10    9.6   9.4   9.4   9.6   0.0
 10.|-- xe-5-1-0.cr1-man1.ip6.gtt  0.0%    10   68.9  33.0  27.7  68.9  13.1
 11.|-- te0-0-1-3-201.cr4.man.byt 20.0%    10   28.4  29.0  28.3  30.8   0.5
 12.|-- te0-0-2-0.cr2.lds.bytemar  0.0%    10   35.8  35.5  35.3  35.8   0.0
 13.|-- te0-0-0-2.cr3.yrk.bytemar  0.0%    10   35.2  35.4  35.2  36.1   0.0
 14.|-- po1.ar1.dc1.yo26.yrk.byte  0.0%    10   35.3  36.5  35.0  47.9   4.0
 15.|-- bm-bl1.debian.org          0.0%    10   34.8  34.8  34.7  34.8   0.0
 16.|-- senfter.debian.org         0.0%    10   35.0  35.0  34.9  35.2   0.0
a2824ck@ping:~$ cat /etc/resolv.conf
nameserver 2001:4ca0::53:1
search srv.lrz.de
a2824ck@ping:~$ mtr --version
mtr 0.87