How to detect blocked UDP multicast port

  • Thread starter Thread starter Andy Bates
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A

Andy Bates

Hi -

Can't see another newsgroup to post this in; so thought I'd post here.

I have a C# application that relies on multicast UDP to detect how many PCs
the application is executing on concurrently. This works okay providing the
port is open but fails miserably if the port is blocked by a firewall.

All applications provide a server listening on the port for the ping but for
some reason on the PC sending the ping irrespective of whether the port is
open or blocked the request is still received. So I cannot even use this to
detect that the port has been blocked.

Any ideas on how to workaround this or an alternative would be greatly
appreciated?

TIA

- Andy
 
Pete -

Thanks for your reply. I'll take a look for the other groups.

The problem is with the firewall. When the applicaiton first starts it asks
if the port should be unblocked; if you say Yes then all is well. If you say
no then the behaviour above is exhibited.

In order to control licensing this obviously causes problems in that if all
users say No then the application only sees itself as running and defeats
the concurrent user checking.

What we need to be able to ascertain is that the port is open prior to
attempting the ping. I'll post this in one of the networking forums. Thanks
again.

Regards

- Andy
 
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