I Have 3 server in my organization and all three are working fine they are doing their task completely but now I have problem with one of my server its ip add is 10.81.x.x . Whenever I tried to connect it through netbios it can't connected but RDP telnet and VNC are getting perfactly now what to do

NetBIOS name resolution is not routable and is very chatty because of forced elections. Are you using a DNS server? Is your network security configured for Workgroups or Active Directory?