Re: Firewall question

[Scott Klement <sk@xxxxxxxxxxxxxxxx>]

Hi James,

OS/400 buffers output data...   So HTTPAPI can write data to to be sent 
to the server, and the operating system will stick it into a buffer -- 
and not return any error to HTTPAPI -- while it's waiting for the data 
to be sent to the server.

So if a firewall is blocking this outgoing data, HTTPAPI won't realize 
it, since it was successfully sent to the buffer.  Unfortunately TCP (on 
any platform) never knows whether the data was sent successfully or not, 
until it gets a acknowledgement.  If a firewall is blocking data, it 
won't know that the data wasn't received until it times out waiting for 
that acknowledgement.  (If that makes sense?)

Anyway... the point is... it's quite common to not detect any errors 
until HTTPAPI tries to RECEIVE something... which is what it sounds like 
you're experiencing.   Typically, you'd only get an error during the 
connect, or during a receive.  (And using a proxy may eliminate the 
error on the connect -- so you'd only get it on the receive...)

Unless you mean that the request has actually ARRIVED on the server, and 
the server folks can see the request?   In that case, ignore everything 
I've said :)

James Lampert wrote:
> Are there firewalls out there, such that the request goes out fine, but 
> the reply from the server is blocked?
> 
> I've seen things happen with our new web service, for which this sort of 
> thing, if it actually happens in the real world, is the most plausible 
> explanation.
> 

-----------------------------------------------------------------------
This is the FTPAPI mailing list.  To unsubscribe, please go to:
http://www.scottklement.com/mailman/listinfo/ftpapi
-----------------------------------------------------------------------