[sclug] Distributed computing

[Jonathan H N Chin]

Tony Sumner <whittycat at ntlworld.com> wrote:
> I am trying to sign up to a worthy distributed computing group that
> is working on how to fold proteins. Everyone else has got the program
> running except me. The whole story is a bit involved but I'd like to
> start by asking a narrow specific question. What happens is that I
> can send stuff to their server but I can't get anything back. Some
> packets arrive back but they seem to vanish. The log says that the
> source port is 80 and the destination port is 1026. My question is:
> should I have an entry in /etc/services referring to port 1026?

I shall assume that there is a central server somewhere that doles
out jobs to participating clients and saves the results, rather than
the system being properly distributed.

Connections between server and client may either be initiated by the
server, or by the client.

Since this is a client-server system, it would seem likely that the
client is expected to initiate contact with the server. Doing it the
other way doesn't seem likely to scale very well.[1]

Given that you say "the source port is 80", it seems likely that the
server is using an http-like protocol for communicating with clients.

You say that you "can send stuff to their server". What do you mean?
Do you have a client program (supplied by them?) running?
If so, it is probably just connecting to the remote port 80 from a
"random" local port (1026 in this case). Since the client initiates
the connection, it doesn't matter if the port is in /etc/services:
the server will just reply to wherever the connection came in from.

You say that "packets arrive back but they seem to vanish".
I don't understand what this means. If they have arrived back then,
ipso facto, they have not vanished. Please clarify.


-jonathan

[1] If the server does in fact poll clients, then you *will* need have
    the service on your machine advertised in some way. One way would be
    to register the service with the portmapper. In that case, you would
    expect to see incoming connections to the portmapper port. However,
    the most likely method would be that the protocol assumes some fixed
    port and only tries to connect to that. This port could be chosen
    when the client first registers as part of the group.

-- 
Jonathan H N Chin, 1 dan | deputy computer | Newton Institute, Cambridge, UK
<jc254 at newton.cam.ac.uk> | systems mangler | tel/fax: +44 1223 335986/330508

                "respondeo etsi mutabor" --Rosenstock-Huessy