                                    Interested parties about FSP please email
                                                               to Radim Kolar
                                                         hsn at cybermail.net
                                                        visit our homepage on
                                                  http://fsp.sourceforge.net/
                                                                 and join us!
    
        For more than 7 years benefits of FSP protocol were unnoticed
        and FSP software was not maintained...

    FSP today
        Written by Radim Kolar

        FSP uses UDP datagrams and it is reliable even when there is high
        number of packet loss. It is usable on WiFi network with 60% packet
        loss. 
        
        Unlike TCP, FSP has a fast restart when line comes up.

        FSP server do not sends any data out unless is asked for. This
        solves problem with transfering duplicate data when using
        TCP protocol on overloaded lines. About 30% are dupes, thrown
        out by client.

        UDP ports are not often port scanned today. Nobody notice that
        you are running a server.

        FSP uses UDP which is unnoticed by many firewalls. FSP server
        runs on 21 port by default, if you move it to port 53 (dns)
        even strictly configured firewall can be worked around.

        You want to run anonymous archive and want to keep lamers out.

        You want to share something without ruining your valueable bandwidth.

        You have overloaded archive site.
         
        You do want to share large data files (movies, ISO images) on
        slow (or you do not want to waste valuable bandwidth) lines.
        Ideal for sharing files on modem lines.

        FSP daemon is a very light server.
                                                 
    What is the purpose of FSP (V2.8.1):
        
        Written by A.J.Doherty@reading.ac.uk
    
        FSP is a set of programs that implements a public-access archive
        similar to an anonymous-FTP archive.  It is not meant to be a
        replacement for FTP; it is only meant to do what anonymous-FTP
        does, but in a manner more acceptable to the provider of the
        service and more friendly to the clients. 

        Providing anonymous-FTP service can be costly --- each active
        session consumes one process slot in the OS and one stream socket
        entry in the network sub-system.  The servers can also run
        concurrently, adding to the system load.  A popular archive site
        can easily be overwhelmed as a result.  Some were forced to
        shutdown and some impose inconvenient access restrictions. 

        Unlike FTP, FSP is connection-less and virtually state-less.  One
        server handles requests from all clients machines.  Each active
        client machine takes up 16-bytes in a dynamically extensible
        table.  Since only one server exists on a server machine at any
        time, the load added to the server machine is no more than one. 

        In exchange for allowing site operators to keep their sites open
        and do away with cumbersome access restrictions, this is what the
        clients accept with FSP: 

         1) Lower transfer rate.  The maximum rate is 1 kbyte per UDP
            message round-trip time between the client and the server.
        
        In addition to the potential for more abundant sites and more
        accessible sites, this is what the clients gain with FSP:

         1) Robustness.  Since FSP is connectionless, fluctuations in
            the network will not abort a FSP transaction.  Furthermore,
            the 16-bytes of data for each client can be regenerated at
            any point during any transaction.  Thus, if the server goes
            down at any point during a transaction, the transaction will
            resume when the server is restarted.  (like NFS) 

         2) Friendlier user interface.  FSP does not have its own command
            interpretor like FTP.  Since it is connectionless, there is
            no reason to carry much information from one command to the
            next, and the commands can all be made into individual Unix
            programs.  For instance, there is one program you run to list
            the directory and another you run to download a file. 

         3) Client protection.  FSP oversees a directory structure similar
            to that of an anonymous-FTP.  However, a directory created
            via FSP transaction is owned by the client machine that issued
            the creation request.  The client can create and delete files
            and subdirectories in that directory.  In addition, the client
            can enable any of the four attributes for that directory: 

                A) Give all other clients the permission to create files.

                B) Give all other clients the permission to delete files
                   or subdirectories.

                C) Give all other clients the permission to read files.
                   (this is true by default)

                D) Give all other clients the permission to create sub-
                   directories.

            Note: A subdirectory can be deleted if it is empty and the
                  client owns the subdirectory.

         4) Server protection.  FSP server does not spawn sub-programs.
            It will accept only paths that are downward relative to its
            designated working directory.  On systems with symbolic links,
            the server will follow symbolic links, but it does not follow
            uplinks ("..").  Clients cannot create symbolic links and
            care should be taken so that other users on the server machine
            cannot create symbolic links in the server's work space. 

            It is also fairly difficult to formulate an attack to force a
            shutdown of a FSP site by actions of a rogue site.  About the
            only way to disrupt a FSP service is to flood the FSP site
            with network packets.  FSP server prevents itself from
            'counter-flooding' by filtering for legitimate requests using
            the following method:

                A) Each request message contains a key.  For each client,
                   server database contains the keys to be used for the
                   next client request and for the previous client request.

                B) If the next request does not contain a key that matches
                   either of the two keys, it is accepted only if at least
                   one minute has elapsed since the last time a request
                   is accepted.  If the key does match the old key
                   (retransmit by client) it is accepted if the elapse time
                   is greater than 3 seconds.

                C) Every request message accepted is acknowledged with
                   one reply message.  The reply message contains a new
                   key to used for the next request.  The new key is
                   computed by the server with a pseudo-random number
                   generator. 

            Flooding is a blatant violation of network etiquette because
            a site can be subjected to flooding attack whether it has FSP
            running or not, and flooding congests every link and gateway
            between the rogue client and the server.  As a further measure
            of protection, the server loads a table of rogue clients on
            startup.  The server will not respond to requests from any of
            those clients.

    ***********************************************************************

    This is a free software.  Be creative; make your own macros and tools
    and let me know of any bugs and suggestions. 
   
    ***********************************************************************
    
    Source code uses several BSD-like licenses; Whole FSP is distributed
    under 2-point BSD license, also known as MIT X11 License.
