udp port binding

[killkolor]

hello

i am trying to make a simple udp application and encountered a problem with the port binding. i isolated the critical part in an console application with some try and catche's and came to this conclusions

if i only bind the udp client to a port this works fin
if i don't bind the udp client to an explicit port (overload constructor without arguments) the JoinMulticastGroup works fin
--> if i bind the udp client to a specific port and try the JoinMulticastGroup, i get an exception (code: 10049) that says: the adress is not valid in this contex

what i did is to turn off my firewall and disconnect everything from the internet, so it's really local. unfortunately still the same exception

is there something i have to set in my system to allow a multicast on a specific port

is there alternatively a way to find out what port i get, if i don't use an argument in the constructor, so i can send it as an endpoint to other multicast clients

th
killkolor