[clug-talk] nasty problem

Mark Carlson carlsonmark at gmail.com
Wed May 17 19:42:33 PDT 2006

On 5/17/06, Robert Lewko <lewkor at gmail.com> wrote:
> Hi guys:
>  I have a program that sends UDP messages to its server.  Its been working
> just fine for about a week since I delivered it.  At about 2:00pm. my client
> phoned me to say that the server wasn't working.  When I looked at the
> software (putting fprintf''s into it) I could see that it was processing the
> packets that it receives and sending the correct data back.  I can ssh into
> the server and on both the server and the firewall I can use tcpdump to see
> the packet coming in and the packet leaving the server then making its way
> out of the firewall.  However, ethereal does not see the packet return to
> the client.  This affects me at home (shaw) and my client at his work site
> (telus).
>  One other thing.  For brief periods this afternoon I was getting packets
> through without making any changes either to the code, the server or the
> client machines.
>  I am using UDP because the client is using a satellite modem.  The server
> uses UDP port 9608.  When the server gets a packet it just gets the source
> address and returns the response packet to the sender.  Like I said I have
> had no problem with that port both while I have been developing the code and
> for the last week until this afternoon.
>  All the TCP stuff works - ssh, http, https, etc.  Does anyone know how to
> diagnose this?

You could try using a UDP "ping" program to see if your packets are
all getting lost.  Thats about the only thing I can think of that you
haven't tried yet.  Good luck, UDP can get nasty.



P.S. IIRC UDP is highly sensitive to packet loss, since you are going
over satellite, you may want to consider "solar activity"
If you check the past 24 hour conditions right now, you'll see that in
the aural region (north of here) there was some "active intervals."  I
don't know if this would have had an effect... I just think its funny
that the government has a space weather agency.

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