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Thread: PortMapper

  1. #1
    Junior Member
    Join Date
    Aug 2004

    Question PortMapper

    do anybody explain me portmapper ?

  2. #2
    (networking) portmapper - A server that converts TCP/IP protocol port numbers into RPC program numbers. It must be running in order to make RPC calls.

    When an RPC server starts, it tells portmap the port number it is listening on and what RPC program numbers it serves. Before a client can call a given RPC program number, it must contacts portmap on the server machine to determine the port number to which RPC packets should be sent.


  3. #3
    Junior Member
    Join Date
    Aug 2004
    Portmapper maps RPC (Remote Procedure Call) program numbers to IP port numbers. For instance, when a server is running NFS it registers a port with the local portmap process. When a client wants to, for instance, use NFS to mount a filesystem, the client starts by asking the portmap on the server for the port number of nfsd. The port number returned is then used by the client to contact the nfsd directly. Portmap usually defaults to listen on TCP/UDP port 111.

    So if a client wants to contact nfsd on a server, it would send a request to the portmap service on that server (to port 111), requesting the port number of "program 100003". That "program number" is mapped by the portmapper to the nfsd (rpc.nfsd) process that has registered with it for TCP/UDP port number 2049 (again, thats usually the default I think). Now the client can send requests directly to TCP/UDP port 2049.

    The basic thing to understand is that portmap is used to map from RPC "program numbers" to TCP/IP ports. So instead of "well known" port numbers, RPC uses well known program numbers.

    Thats my basic, simplified, reasonably accurate explanation. If your looking for info you want to look for NFS and RPC. That should get you a good deal of info.

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