mount. Nfs: access denied by server while mounting

The company has two intranet resources centos Server pass nfs Realize directory sharing , But in execution mount Always prompt when mount.nfs: access denied by server while mounting, I've tried all the methods on the Internet , Set the permissions 777, If the port range is not within a reasonable range, it will not work . Finally, I implemented

exportfs -r

Re execution mount Problem solving .
How many people didn't execute this sentence like me ？
exportfs -r
exportfs -r
exportfs -r