Tracert not resolving IP

Question

I know this is propably a basic question, i did some research on the net as to the whys and hows and got only more confused. I wanted to ask why tracert returns this :

Tracing route to youtube.com [2a00:1450:4007:806::1000] over a maximum of 30 hops:

  1     3 ms    17 ms    10 ms  2a02:582:ca8:3400:964a:cff:fe97:aa40
  2    21 ms    20 ms    18 ms  2a02:580:310::1440
  3    17 ms    17 ms    19 ms  2a02:580:50da:15f::
  4    20 ms    17 ms    36 ms  2a02:580:50da:55::
  5    20 ms    17 ms    17 ms  2a00:1cb8:2000::65
  6    19 ms    19 ms    19 ms  2a00:1cb8:1::35

instead of resolving those to IP addresses. When i run the -4 option it does as usual :

    11    75 ms    71 ms    73 ms  209.85.245.71
    12    71 ms    72 ms    71 ms  66.249.94.77
    13    71 ms    73 ms    70 ms  par03s13-in-f7.1e100.net [173.194.45.71]

Trace complete.

dr_ · Accepted Answer · 2015-11-18T15:46:46.267

1

Traceroute is working fine. These aren't domains, so there is nothing to resolve. What you see are the IPv6 addresses of the hops (thatis, the routers between you and the target).

When you use the -4 option, traceroute traces the route from your machine to the destination using IPv4 addresses only instead. Note that the IPv4 traceroute path and the IPv6 traceroute path might differ.

edited Nov 18 '15 at 15:46

answered Nov 13 '15 at 09:32

dr_

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Those are not servers, they are routers. And saying it shows "the IPv4 address of each hop instead" gives the impression that there is a 1:1 correspondence between the IPv4 hops and the IPv6 hops. In reality one will show an IPv4 path and the other will show an IPv6 path, and those could take entirely different routes through the network. – kasperd Nov 13 '15 at 10:54

score 0 · Answer 2 · answered Nov 18 '15 at 18:10

Tracert tries to show the way your packets take through the network as well as possible from an end-user point of view.

For each hop, tracert obtains the IP address of that hop (by using a little trick that is irrelevant here). It then tries to convert that IP address to a name (using rDNS). If it succeeds, than it shows the name followed by the IP address between brackets. If it does not succeed in obtaining a name, it just shows the IP address.

In your example, only hop 13 of the IPv4 traceroute seems to have a name in rDNS. It is not very surprising that IPv6 addresses do not have rDNS names, it's a bit complicated to set up, it's not mandatory, and IPv6 is not yet used that much.

If you want to know who the IP belongs to and the rDNS does not give you an answer (or enough of an answer), you can consult the IP WHOIS.

Tracert not resolving IP

2 Answers2