NFS permission denied error in client

I was trying to configure NFS, faced night mare of issues related to permission.

After some time figured out, adding netmask(24) fixed the error:
# cat /etc/exports
/opt/test2/ 192.168.122.151/24(rw,sync,root_squash)

[ error faced:
mount.nfs: access denied by server while mounting ]


Also, whenever we change exports file , reload it by using exportfs -r

you can see what is exported via
#exportfs -s



PS:
Issue like this should not be present in docker kind of environment, I think.

You get ready made NFS configured server, you only start changing the options as per your requirement. :)