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Ideas on why a TCP hostname resolves to both an IPv4 and the local IPv6 loopback?

edited Feb 9, 2020 4:00AM in Database Networking (MOSC) 4 commentsAnswered

I had an interesting issue recently which happened twice and apparently after Windows Updates occurred.

Both situations, this was Oracle 12.1 running on Microsoft Windows x64 2012R2 (single instance non-RAC).
Never seen this on Linux or UNIX flavors.

What I found was that when Oracle sent a "snlinGetAddrInfo" function call to get the host name to IP address resolution from the Windows operating system, the resolution came back with the expected IPv4 IP address, but ALSO the local loopback for IPv6.
That is the ::1 address.

Local HOSTS file "looked" clean as well so this has to have come from DNS.
However, what was stranger is that running nslookup against the hostname was not returning any IPv6 ::1 information.

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