VMware VCF and changing DNS server

I was trying to change DNS servers in an VMware Cloud Foundation environment, but I ran into some problems.

The first problem was that the customer already had removed access to the old DNS server, so the SDDC Manager could not talk to the vCenter.

I tried to make the change in the OVF properties and updating the /etc/resolv.conf file, but they changed back after restarting the VM or just restarting the DNS Client services. I solved this by creating DNS records in the /etc/hosts file on the SDCC Manager,

After that I could get the login to the SDDC Manager.

The the second problem was that when trying to change the DNS server i got a validation error in the UI, but not much information. I then tried to do the validation i the Developer Center and using the REST API for the validation. The result came with an error of validating the VC DNS/IP.

If I checked it manual with “nslookup” it came with the expected results, the looking deep into the logs i could see that the last DNS address to be checked was the vCenter, so maybe this was just a wrong message in the output from the validation.

Then i found this KB from VCF 4.x: https://knowledge.broadcom.com/external/article/314621/unable-to-update-dns-servers-using-the-s.html

I could see that there is a requirement for ping to the DNS server and I check this, and I could not ping them.

The Customer add a firewall rule for allowing ICMP Ping from the SDDC Manager to the DNS servers.

After this I could validate the DNS configuration and do the change of the DNS server.

I think that this is a really bad output from the DNS validation check it should show that the problem was with ping to den DNS servers.