There's apparently a new file transfer system, called FSP, gaining
acceptance on the Internet as an alternative to anonymous FTP. The
salient characteristics from a Firewalls point of view are that it is
a connectionless service (it uses UDP rather than TCP), and that there
is apparently no single widely-used well known port for FSP servers.
The software is available for anonymous FTP on ftp.uu.net, file
"networking/archival/fsp.25.tar.Z". I've appended the "INFO" file
Has anybody had any experience with this yet, particularly from a
Firewalls and network security point of view?
Brent Chapman Great Circle Associates
COM 1057 West Dana Street
+1 415 962 0841 Mountain View, CA 94041
Interested party please email
What is the purpose of FSP (V2.5):
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 acceptible 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 or and some impose inconvienent 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 runs 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, flucturations 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 two attributes for that directory:
A) Give all other clients the permission to create files
B) Give all other clients the permission to delete files
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 formuate an attack to force a
shutdown of a FSP site by actions of a rogue site. About the
only way to distrupt 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) 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
Flooding is a ballant 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
The software set:
common_def.h This C header file contains definitions common to
both the server code and the client code.
client_def.h This C header file contains definitions for the
server_def.h This C header file contains definitions for the
udp_io.c This file contains the lowest level routines that
deal with the unix inet sockets. This file is
used by both the server code and the client code.
server_main.c Main routine and dispatch loop for the server.
server_host.c Routines for maintaining client database.
server_file.c Routines for file i/o.
server_lib.c Routines for inet socket i/o.
client_lib.c Core routines of the client library.
client_util.c Supplementry routines of the client library.
client_lock.c udp packet multiplexing mechanism.
bsd_src/ Directory containing additional sources derived
from those in public archive on uunet.uu.net. It
contains a BSD random/srandom routine, a modified
BSD globbing routine, a modified "ls" source.
fcdcmd.c These compiles into individual client utilities.
fgetcmd.c Those with a "cmd" in their name will do their
flscmd.c own globbing on their argv base on directory
fprocmd.c information obtained from the server.
FSP has been compiled and tested on a SS-2 running SunOs 4.1.1,
a HP-9000 running HP UNIX, a VAX-780 running 4.3-tahoe, and a 386
box running system-V UNIX with old Excelan ethernet interface.
It has also been compiled on a variety of machines by over a
hundred users across the net.
To compile the software, you must first successfully complete a
"make" in the bsd_src directory. You may have to change a few
files. In particular, you may have to edit "Makefile" and "tweak.h"
in bsd_src directory.
When that is done, you can edit the Makefile on the top directory
and run "make" in the top directory. You may have to read through
the rest of this document first before making changes to the Makefile.
The only things you need for setting up a FSP server is a work
directory for the service and and the FSP server itself (fspd).
fspd can run independently or it can be run under inetd. When
running independently, fspd waits for messages through a UDP
socket whoes port number is defined in the Makefile. When running
under inetd, fspd is involked as in.fspd. inetd will spawn fspd
when a message arrives for the FSP socket. The fspd process will
take over and stick around to wait on additional messages. After
it has become idle for 2 minutes, fspd will exit and return control
Sample setup for inetd operation:
In /etc/services file:
fsp 21/udp fspd
In /etc/inetd.conf file:
fsp dgram udp wait ftp /usr/etc/fspd in.fspd
In this sample, the same port number for ftp is used for the
fsp socket. There will not be a conflict because ftp uses
stream protocol, and fsp uses UDP protocol. The fspd program
in this example is ran under user 'ftp'.
In addition, fspd will accept these flags:
-h absolute_path Set fsp work directory. Overrides the
-p udp_port_number Set UDP port number. Overrides the
-u uid_number Assume this uid after startup. If present,
fspd will attempt a setuid() to this uid
number. It will exit if setuid() fails.
-d Turn on debug mode. The stdio files will
remain open in debugging mode.
When fspd starts, it chdir to its work directory where it looks
for (and reads in if found) a list of internet numbers in the
standard 4-part form: ddd.ddd.ddd.ddd in the file ".ROGUE_HOSTS".
This file is prepared by the FSP maintainer, and is used to
indicate that fspd should not respond to any requests from these
machines. After that, it begins to service any requests it gets
on the UDP socket.
If a file .OWN.XXXXXXXX, where XXXXXXXX is an 8-digit hex number,
exists in a directory in fspd's work space, the directory is owned
by the machine whoes inet number is XXXXXXXX, where the number
is printed as a hexadecimal number. If no such file exists, the
directory has no owner. (Note, the 'dot' files are hidden from
If the file .FSP_OK_DEL does not exists in a directory, only the
owner is allowed to remove items from that directory.
If the file .FSP_OK_ADD does not exists in a directory, only the
owner is allowed to add items into that directory.
Thus, you typically want to protect the top directory by leaving
out the .FSP_OK_DEL, .FSP_OK_ADD files, and .OWN.XXXXXXXX files
in the top directory.
Clients do not get to read the directory information directly.
Instead, fspd maintains a directory listing in the file .FSP_CONTENT
in each directory. When a client requests information for a
directory, the .FSP_CONTENT file is created if it doesn't exist,
and it is rebuilt if it is out of date. The information is
accessed by having the client read the directory listing file.
Care is taken so that the client will not get corrupted entries
when the directory is changed while the listing is being read.
Files being uploaded are first written to a temporary file in the
work directory: .TXXXXXXXXYYYY where XXXXXXXX is the inet number
of the client, and YYYY is the port number of the client program.
When upload is compelete, the file is moved into the intended
An 'alarm' interrupt will cause fspd to dump its current client
database into the file .HTAB_DUMP in the work directory. This
can be useful for debugging and for catching rogue clients.
All inter-command states are kept in these four shell environment
FSP_PORT Port number of the fspd you wish to contact.
FSP_HOST Host name or number of the fspd.
FSP_DIR Your current working directory in the archive.
When multiple client utilities are run at the same time on the
same client machine, packet multiplexing mechanisms can be used
to enable concurrent access to the same fsp database. If none
of the mechanisms are selected at compile time, FSP_LOCALPORT
can be used to ensure that only once client utility can run at
any time. In this case, FSP_LOCALPORT can be set to any port
number not current used on the client machine.
FSP_TRACE can be set if you want status reports be printed while
files are being transferred. FSP_DELAY variable can be used to
set the retransmit interval for client utilities (in thousandth
of a second). The retransmit rate is adjusted in an exponential
manner, until the retry rate reaches 5 mintes per retry.
FSP_BUF_SIZE can be set to a positive number less than or equal
to 1024. When set, it determines the size of data to be send for
each request during file and directory information transfer. The
default is 1024. Some sites are connected via links that cannot
transmit buffers containing 1024 bytes of data in addition to the
header information. Setting FSP_BUF_SIZE to a lower value will
allow these sites to access fsp archives.
A typical setup looks like this:
setenv FSP_PORT 21
setenv FSP_HOST 18.104.22.168
setenv FSP_DIR /
setenv FSP_DELAY 3000
setenv FSP_BUF_SIZE 1024
(All examples will be in csh. However, it is assumed that similar
things can be done with other shells)
For commands that do globbing using remote directory info, normal
shell globbing needs to be turned off. In csh, it can be done
with a set of aliases:
alias fcd setenv FSP_DIR \`\(set noglob\; exec fcdcmd \!\*\)\`
alias fls \(set noglob\; exec flscmd \!\*\)
alias fget \(set noglob\; exec fgetcmd \!\*\)
alias fgrab \(set noglob\; exec fgrabcmd \!\*\)
alias fcat \(set noglob\; exec fcatcmd \!\*\)
alias frm \(set noglob\; exec frmcmd \!\*\)
alias frmdir \(set noglob\; exec frmdircmd \!\*\)
alias fpro \(set noglob\; exec fprocmd \!\*\)
In addtion, this alias is useful:
alias fpwd echo \$FSP_DIR on \$FSP_HOST port \$FSP_PORT
fver display server's version number.
fcd change current remote directory, like cd.
fls list directory. works like ls.
fget get the named files.
fgrab get the named file and delete it from remote directory.
fput put the named files.
fcat get the named files and send them to stdout.
fmkdir make named directories.
frm delete named files.
frmdir delete named directories.
fpro no arg: display directory protection modes.
+c: give others permission to create new items.
-c: deny others permission to create new items.
+d: give others permission to delete old items.
-d: deny others permission to delete old items.
This is a free software. Be creative; make your own macros and tools
and let me know of any bugs and suggestions.