When performing a traceroute, what function on the ISP gateway is advertising the hostname?

When we traceroute to Google.com for instance;

Tracing route to google.com [] over a maximum of 30 hops:

1    40 ms     2 ms     1 ms
  2    29 ms    11 ms    10 ms
  3    11 ms    11 ms    11 ms
  4    12 ms    11 ms    11 ms  core2-hu0-8-0-1.southbank.ukcore.bt.net []
  5    20 ms    11 ms    13 ms  peer7-et-0-1-7.telehouse.ukcore.bt.net []
  6    12 ms    11 ms    11 ms
  7    12 ms    11 ms    11 ms
  8    13 ms    13 ms    13 ms
  9    12 ms    12 ms    13 ms  ber01s14-in-f14.1e100.net []

For instance we're able to see that this traceroute to Google transits through core2-hu0-8-0-1.southbank.ukcore.bt.net before hopping over to Telehouse peer7-et-0-1-7.telehouse.ukcore.bt.net This appears to me to be the hostname of the ISPs gateway, are these IPs of these routers registered as DNS A records or is it actually the gateway advertising it's hostname to traceroute?

  • For reference, here's code I wrote that carries out a traceroute and does a reverse DNS lookup as part of it. Commented Nov 11, 2020 at 14:02
  • Traceroute has no facility to send host names in either direction. It simply relies on ICMP error messages, and can use DNS to look up the name of the error message source.
    – Ron Maupin
    Commented Nov 11, 2020 at 15:23
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Commented Dec 31, 2020 at 3:53

1 Answer 1


Traceroute does use Reverse DNS lookup or reverse DNS resolution (rDNS). Querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address. The process of reverse resolving of an IP address uses PTR records.

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