WHMAPI1 function "set_up_dns_resolver_workarounds" does not sufficiently detect IPv6 networking issues

Symptoms

When checking cPanel's "Email Deliverability" module, the records are reported as missing inconsistently show valid/invalid or display timeout errors.

This issue can also be related to issues with determining whether a domain has local authority over DNS records as well as AutoSSL checks as it pertains to the libunbound resolver.

This issue has been seen to be related to IPv6 networking issues.

Description

The WHMAPI1 function "set_up_dns_resolver_workarounds" was created to identify and workaround these networking issues. We've found that the function does not sufficiently detect IPv6 networking issues in certain states.

For reference, the case number is CPANEL-43976. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

There are three options for resolving this issue:

1. Contact a network administrator to fix the IPv6 configuration of the server. You can get started here: How to diagnose IPv6 issues

2. Disable IPv6 with the instructions here:
How to disable IPv6

3. In SSH or "WHM / Terminal" as root, run the following command to manually create the following touch file:

touch /var/cpanel/dns_flags/has_broken_ipv6

Please note the touch file is only temporary and will be removed during nightly maintenance. Any issues with IPv6 configuration should still be addressed by a qualified systems or network administrator.

After applying any of these options, restart the cpsrvd service to load the change by running the following in SSH or "WHM / Terminal" as root:

/scripts/restartsrv_cpsrvd

If the issue persists after restarting the cpsrvd service, run the following in SSH or "WHM / Terminal" as root to synchronize the installed cPanel version from our update servers:

/scripts/upcp --sync