Port monitoring

In communication involving TCP/IP, applications in the network are addressed through a combination of the Internet address and a port number, which uniquely identifies the recipient or the sender of a data packet. The Internet address addresses the computer, and the port number addresses the application within the computer.

An additional security feature offered by NFS is port monitoring. This is active by default. When port monitoring is active, the NFS server checks the port numbers to which an NFS client sends its request. For each client access it checks whether the port number from which the client request arrives is privileged, i.e. is less than 1024. If it is not privileged, the client request is rejected by the server.

Port monitoring can be activated and deactivated by means of the PORTMON parameter in the POSIX information file SYSSSI.POSIX-BC.vvv (refer to "Installation of NFS"):

PORTMON=1

Port monitoring is activated; client requests from unprivileged port numbers are rejected; default

PORTMON=0

Port monitoring is deactivated

In a BS2000 system, privileged port number ranges can also be set differently. However, NFS always considers port numbers less than 1024 to be privileged.