ndt-users list created

[Richard Carlson <>]

Hi Craig;

The NDT server can run in 2 modes, switchable by the -m flag.

Without the flag (single-client mode), the server handles 1 client at a 
time.  The server uses a FIFO queue to handle client requests.  This allows 
the server to receive multiple requests but it only process one request at 
a time (in a FIFO maner).  The server uses 3 ports to handle the 
communications between the client and server.  By default they are 3001, 
3002, and 3003.
        3001 is the control channel, allowing the client and server to 
exchange
                messages
        3002 is used for the client -> server speed test
        3003 is used for the middlebox and server -> client speed tests

When the flag is set (-m on the command line or multi-client mode)) then 
the server runs in multiple simultaneous client mode.  In this mode the 
server will immediately begin testing to a client, so if multiple requests 
are received, multiple tests will be run.  This means that the server's 
up-link may become congested.  In this mode the server assigns a unique 
pair of ephemeral ports to each client.  There ports will be used for the 
speed and middlebox tests, as described above.  They replace the 3002 and 
3003 ports.  In the example below the server picked 32778 and 32779, but 
those numbers will change every time a client request is received.  The 
debug statement will show you what ports are being used.

When operating in the multi-client mode the server does not use a specific 
port range so you may find it difficult to open up the server ports.  Since 
the single-client mode does FIFO queuing I typically run my servers in this 
mode.


At 09:35 AM 8/31/2005, Pepmiller, Craig E. wrote:

> >At this point the server should have ports 32778 and 32779 in a listen
> >state.  Is that true?  Try running a "netstat -nat" command on the
> >server.  The ports should be in some state (WAITING, LISTEN, or
> something).
>
> Richard:  I'm using iptables also.  Does this mean I should have 32778 &
> 32779 open?  What does "Middlebox testing" do anyway?

No, If you are running in multi-client mode you need to have all port above 
1024 open because the server could pick any 2 open ports.  If you are 
running in single-client mode then ports 3001, 3002, & 3002 open for the 
testing and 7123 open for the web server front end (assuming you use the 
default values).

The middlebox testing opens and closes a TCP connection.  The server sets 
the TCP MSS value to a specific value and examines the Web100 variables to 
see if the client accepted that value.  If not, it assumes that a middlebox 
changed the value.  It also sends the source and dest IP addresses back to 
the client.  The client compares these addresses to the addresses it used 
to see if a NAT box is in the path.

Regards;
Rich
> Thanks-
> -Craig Pepmiller
> -MOREnet, Univ. of MO

------------------------------------



Richard A. Carlson                              e-mail: 

Network Engineer                                phone:  (734) 352-7043
Internet2                                       fax:    (734) 913-4255
1000 Oakbrook Dr; Suite 300
Ann Arbor,  MI  48104