64
Enhanced Features
WAGO-ETHERNET-Zubehör 852
852-1305 8/4-Port 100BASE-T/1000BASE-SX/LX
Manual
1.1.0
7.2.2.2 Multicast Address
A multicast address is associated with a group of interested receivers. According
to RFC 3171, addresses 224.0.0.0 to 239.255.255.255 (formerly Class D
addresses) are reserved as multicast addresses in IPv4.
The first octet (01) includes the broadcast/multicast bit. The lower 23 bits of the
28-bit multicast IP address are mapped to the 23 bits of the available ETHERNET
address space. This means that there is ambiguity in delivering packets. If two
hosts on the same subnet each subscribe to different multicast groups whose
addresses differ only in the first 5 bits, ETHERNET packets for both multicast
groups are sent to both hosts, requiring the network software in the hosts to
discard the unnecessary packets.
Table 18: Multicast Classes and Address Ranges
Class
Address Range
Support
Class A
1.0.0.1 to
126.255.255.254
Supports 16 million hosts on each of 127
networks.
Class B
128.1.0.1 to
191.255.255.254
Supports 65,000 hosts on each of 16,000
networks.
Class C
192.0.1.1 to
223.255.254.254
Supports 254 hosts on each of 2 million
networks.
Class D
224.0.0.0 to
239.255.255.255
Reserved for multicast groups.
Class E
240.0.0.0 to
254.255.255.254
Reserved for future use or research and
development purposes.