Linoxide published a tutorial about disabling IPv6 on RHEL or CentOS 8.
How to Disable IPv6 on RHEL/CentOS 8
Here learn 2 ways to disable IPv6 on RHEL/CentOS 8. While IPv6 is intended to replace IPv4, a majority of the systems are still using IPV4.
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How to Disable IPv6 on RHEL/CentOS 8