nisttime.carsoncity.k12.mi.us/nisttime.carsoncity.k12.mi.us.tar/nisttime.carsoncity.k12.mi.us/pub/daytime/README.PROXY

Text File | 2001-02-23 | 7KB | 143 lines

   Most of the programs in this directory communicate with our servers using
messages on tcp/ip port 13. Some of the examples use other ports (such as
udp/ip port 37).  Version 3 of the Windows client nistime-32bit.exe can
also be configured to use the Network Time Protocol via udp/ip port 123.

  The communication with our server may fail if your client system
is behind a firewall or proxy server, since these systems can block the
direct communication channel between the client and one of our servers.
The failure usually results in a time-out error message when you try to
run the program, and you should suspect a firewall problem if you get such
a message on a client system that is connected to a network that is
otherwise up and running.

   It is usually possible to configure a firewall system to pass
messages on a particular port or to a particular set of remote servers,
and this configuration change should allow any of the client programs
in this directory to run without modification. This change is the
preferred way of using the programs, since it minimizes the additional
delay introduced by the firewall system.

   If the client is located behind a proxy server, and if the network
configuration cannot be modified to open a direct connection to our
servers on the standard port, it may still be possible to configure the
client software to operate properly in this environment. The following
instructions explain how to do this:

    1.  If you are using nistimew.exe, you must be using version 3.1
or later. This version was compiled on 23 January 1999.  If you are using
nistime-32bit.exe, you must be using version 2.1 or later, which was compiled
on the same date. If you are using older versions, you should upgrade to the
newer releases.  You can copy these newer versions from directory /pub/daytime
on any of our servers. For example, you can copy the files from
ftp://time-b.nist.gov/pub/daytime. These files are not compressed and
should be copied in binary mode to any convenient directory on your
system.

    2. Copy the file nist-srv.lst from our servers to your Windows
directory. This destination directory is usually c:\windows for Win 3.x
and 9x and c:\winnt for Win NT. You can get this file from any of our servers
in directory /pub, and you would copy it using ftp as in 1 above. This
is a simple text file, and should not be copied in binary mode.
You can also get this file by starting the client program (either nistimew.exe
or nistime-32bit.exe) and using the menu command File | Update servers.
This operation will tell you where the file has been stored on your
system.

    3.  Edit the nist-srv.lst file using any convenient text editor,
such as NOTEPAD in Windows or EDIT in DOS. Find the first line after
the $ sign in column 1, and change the ip address on that line to
the ip address of your proxy server.  For example, if the first
few lines in the file look like this:

Server name                     ip address      Note    Location
$
time-b.nist.gov                 129.6.15.28     2       Maryland

and if the ip address of your proxy server is 100.1.2.3, then
edit the ip address on the third line above to match the address
of your proxy server:

time-b.nist.gov                 100.1.2.3       2       Maryland

Be careful not to change anything else in the file. Save this
modified version of the server list in the windows directory.

                           ** Important **
Note that these ip addresses are only examples. You should use the
actual server ip addresses in the nist-srv.lst file and the actual
ip address of your proxy server.

    4. If you are using the daytime format, configure the proxy server
so that a message to it on tcp/ip port 13 is re-transmitted on the same port
to the NIST time server at ip address 129.6.15.28. If you have version 3.0
or later of nistime-32bit.exe and if you plan to use the Network Time
Protocol, then configure the proxy server so that a message to it on
udp/ip port 123 is re-transmitted on the same port to the NIST time server
at the original address.  These changes need only be made once in the
configuration tables of the proxy system.

    5.  When you run the client program and select this
server, it will send a message to the proxy system using the
ip address that you specified.  The proxy system will forward
the message on to our system.  The reply should be re-transmitted
to your client machine, so that the program will appear to be
directly connected to our server even though it is actually going
through the proxy system.

    6.  Some proxy servers require a different port on the
input and output sides of the connection. That is, they will
send messages to our servers on tcp/ip port 13 or udp/ip port 123,
but they listen on some other port for connections from client
systems.  If the inside port number for the daytime service is <j>,
then modify the line above including <j> as shown below:

time-b.nist.gov                 100.1.2.3:<j>      2       Maryland

If you are using Version 3.0 or later of nistime-32bit.exe and if
you also want to re-map the Network Time Protocol to use udp/ip port
<k> instead of the standard value 123, then add this value to
the end of the line as well:

time-b.nist.gov                 100.1.2.3:<j>,<k>  2    Maryland


For example, if the proxy server listens for daytime requests on
port 14, and NTP requests on port 333, then the line above would be:

time-b.nist.gov                 100.1.2.3:14,333       2       Maryland


(In both cases the proxy server must communicate with our systems using
the standard ports: tcp/ip 13 for daytime requests and udp/ip 123 for
NTP requests.)

Note that there can be no space between the ip address, the colon and
the first port number. If you want to re-map the NTP port, the first
value must also be present and the second value must be separated by a
comma as shown above. You can omit the comma and the second value if
you do not use NTP or if you do not have to re-map its port.

These changes are not usually necessary, and you should not use them
if you are in doubt about whether you need them or not.
If you make this change, it will affect all of the servers on the
list -- not just the one whose ip address you have modified.

   Once you have made this change, you may only be able to use the server
whose ip address you have modified.  Requests to other servers probably
will be blocked by the proxy system.

   In addition, note that the proxy server may introduce a significant
delay into the path, and this delay is likely to be different for the
inbound and outbound directions. This asymmetry will tend to bias the
received time, since the software that estimates the delay assumes that
the path delay is symmetrical. (This is true for ALL network-based time
services.) This bias is probably at least 10 milliseconds, and may be
significantly larger that this on a busy system.  You should be concerned
about this problem if you need time stamps with an offset from UTC of
0.1 second or less.

Questions or comments to: [e-mail]

Last changed: 23 February 2001