yeah... already try restart server twice times. Still doesn't work. :( I only use one DNS server. I already delete the secondary DNS server in case that cause issue. but still keep the same issue. 

Thanks for your reply.yeah,I already checked that updates. And I also check that records on my DNS server. it works fine. only one A record for cucm.Still have this issue.Can you please give some advises ? Thanks a lot,Holly

Hi,Did you get any updates for this issue?I also have the same issue here. I upgraded cucm from 10.5 to 11.0, it shows warning: DNS unreachable.but I can ping dns servers from cli and also hostname can be resolved. also the service hasn't been affect...