Why NFSv3 share doesn't get mounted with sec=sys, in RHEL 6?

Issue

• NFSv3 share doesn't get mounted on RHEL 6 even with sec=sys forced, but works perfectly on RHEL 7.

mount.nfs: trying text-based options 'sec=sys,nfsvers=3,addr=XXX.XX.X.XXX'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying XXX.XX.X.XXX prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying XXX.XX.X.XXX prog 100005 vers 3 prot UDP port 635
mount.nfs: mount(2): Permission denied                                                                       
mount.nfs: access denied by server while mounting XXX.XX.X.XXX:/share