Configuring communications connections
5.7 Configuring UDP connection properties
Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13
109
Note
Within a multicast group, assign identical port addresses for the local port and the partner
port. This is the only way that frames can be sent and also received by the
CP within a
Note the following example of three nodes in the multicast group:
IP addresses for IP multicast
● Range of values
IP addresses from 224.0.0.0 to 239.255.255.255 can be used for IP multicast.
Since the IP addresses from 224.0.0.0 to 224.0.0.255 are reserved for special purposes,
we recommend that you use IP addresses starting at 224.0.1.0 (default) for IP multicast.
● Clear identification of the multicast group
On Ethernet (Internet protocol), the IP addresses of the multicast group are converted to
MAC addresses by a special mechanism.
When it receives a frame, the CP, however, checks the complete multicast IP address.
This ensures clear identification of the addressed multicast group.
– Background information for obtaining the resulting MAC address
A multicast group is not identified initially using the entire IP address; the first address
byte and the most significant bit of the second address byte are ignored. As illustrated
in the following example, seemingly different IP addresses can address the same
multicast group due to the resulting MAC address.
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