"The source machine hostname '192.168.0.1' resolves to IPv6 address(es) '::ffff:192.168.0.1', but IPv6 networking will not be preserved after the upgrade" while upgrading VCSA 6.5/6.7 fails at precheck

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• vCenter Appliance 6.5 to 6.7 Upgrade is stuck at Stage 2 at Pre-Checks 
• vCenter is deployed using IP as PNID
• IPv6 is disabled on vCenter 
• Error stack seen in PreChecks stage on Phase 2 where IP of vCenter is 192.168.0.1:

"Error: 
The source machine hostname '192.168.0.1' resolves to IPv6 address(es) '::ffff:192.168.0.1', but IPv6 networking will not be preserved after the upgrade. This will prevent certain services preferring IPv6 from establishing network communication.
Resolution
Either remove the DNS IPv6 entry for hostname '192.168.0.1' or change the network configuration of the source machine to pure IPv6 or in case dual networking stack is needed, set a static IPv6 address."

• Command below return values with both ipv4 and ipv6 format (::ffff:IP)  

[email protected] +short VC_IP A VC_IP AAAA
for example below command returns DNS information from localhost:
dig @127.0.0.1 +short 192.168.0.1 A 192.168.0.1 AAAA
for example below command returns DNS information where DNS is 192.168.0.100:
dig @192.168.0.100 +short 192.168.0.1 A 192.168.0.1 AAAA
192.168.0.1
::ffff:192.168.0.1

Environment

VMware vCenter Server Appliance 6.7.x
VMware vCenter Server Appliance 6.5.x

Cause

Upgrade scripts checks for IPv6 resolution and if seen it will check for configuration of IPv6 on vCenter side. If it's not enabled, it will fail with above error.

Resolution

As stated, resolution is from the error stack:

• Either remove the DNS IPv6 entry for hostname '192.168.0.1' or change the network configuration of the source machine to pure IPv6 or in case dual networking stack is needed, set a static IPv6 address.

As per above the options are:

• Configure DNS without IPv6 information or 
• Configure the vCenter to have also IPv6 information

Workaround:
Steps to workaround the pre-check:

1. Add required static IP addresses into /etc/hosts file (all VC and PSC's needed)
2. Comment (hash) DNS servers in /etc/resolv.conf
3. Restart dnsmasq service by using systemctl restart dnsmasq.service
4. Retry the prechecks page which should now allow you to go to next page 
5. Add/enable DNS servers back in /etc/resolv.conf by removing the hash sign