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Example:

  • a home LAN
  • a simple SOHO router (both DHCP and DNS server at 192.168.1.1)
  • 2 client machines (192.168.1.2 and 192.168.1.3)

Is it possible for the Google public DNS server located at 8.8.8.8 (or any other public DNS server) to know the hostname of those machines on that LAN? If yes how is it possible if they are not mentioned in the zone.conf file on Google's DNS server?

closed as off-topic by JFL, Ron Maupin Sep 21 '18 at 13:19

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "NE is a site for to ask and provide answers about professionally managed networks in a business environment. Your question falls outside the areas our community decided are on topic. Please visit the help center for more details. If you disagree with this closure, please ask on Network Engineering Meta." – JFL, Ron Maupin
If this question can be reworded to fit the rules in the help center, please edit the question.

  • Unfortunately, questions about host/server configurations, protocols above OSI layer-4, and questions about home networking are off-topic here. You could try to ask this question on Super User. – Ron Maupin Sep 21 '18 at 13:19
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You're quite right, no other organisation can magically see into your network and find, for example, host names unless you have some way to publish them.

But specifically regarding 192.168.0.0/16 type addresses: as private IP addresses are not uniquely assigned, any organisation can use them and assign its own names to them.

The machinery of some organisation's public DNS server might give you an answer, but it would be its answer not yours.

However, the policy about private addresses says that such addresses should not be leak out from their organisations.

RFC 1918 "Address allocation for private internets" p 5:

Because private addresses have no global meaning, routing information about private networks shall not be propagated on inter-enterprise links, and packets with private source or destination addresses should not be forwarded across such links. Routers in networks not using private address space, especially those of Internet service providers, are expected to be configured to reject (filter out) routing information about private networks. If such a router receives such information the rejection shall not be treated as a routing protocol error.

Indirect references to such addresses should be contained within the enterprise. Prominent examples of such references are DNS Resource Records and other information referring to internal private addresses. In particular, Internet service providers should take measures to prevent such leakage.

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Technically, there's no difference between a private and a public IP address. It's quite possible that your DNS provider won't accept private IP DNS entries though.

If you run your own authoritative DNS server (pointed to from outside) it's quite possible to have some A record resolve to a private IP address. If you don't like that you need to either be careful, split the DNS scope or use a filter between inside and outside queries.

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