Siemens SIMATIC NET S7-300 Manual page 149

Addresses Tab - Connection to all Multicast Nodes
By selecting "all multicast nodes" as the connection partner, you specify that
S sent UDP frames are delivered to all multicast nodes of the multicast group;
S the local device receives multicast frames in the specified multicast group.
The multicast group is specified using the IP address and the port addresses.
In the "Addresses" tab, an IP address in the network valid for multicast groups is
proposed for the partner under IP address (IP). When using multicast, the partner
is always a group of receivers (multicast group).
You must enter a PORT address suitable for all partners you want to reach under
PORT.
In principle, is it possible to address several multicast groups with one IP address.
To achieve this, you can create several UDP connections with the same IP
address but different PORT addresses.
S7-CPs for Industrial Ethernet Configuring and Commissioning
Release 01/2007
C79000-G8976-C182-07
5 Configuring Communication Connections
A -149