When performing IPv6 connect with nc command, why it fails to try IPv4 as well if IPv6 method fails in RHEL7?

Solution Verified - Updated -

Issue

  • We note that when nc performs IPv6 connect it does not try IPv4 as well:
$ cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
  • This seems to be a buggy behavior. If IPv6 fails, nc should try the IPv4 method.
  • nc performs IPv6 connect but doesn't try IPv4 as well.

Environment

  • Red Hat Enterprise Linux (RHEL) 7.
  • Nmap packages.

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