B.2.2 Multicast Routing; Figure B-1. Multicast Mapping (Ip To Mac - Comtech EF Data CMR-5995 Installation And Operation Manual

Digicast Media Router S2 Receiver CMR-5995 (MR-S2-ASI)
IP Routing Support

B.2.2 Multicast Routing

Multicast routing provides point-to-multipoint delivery of IP datagrams. Routes for multicast IP
packets are configured according to the following:
• IP Addresses, which fall into class D (224.0.0.0 to 239.255.255.255)
• Medium Access Control (MAC) Addresses, which identifies the frames as multicast. The
least-significant bit of the first byte of the six-byte MAC address is a '1'. For example, 0x01
00 5E 00 00 01 is a multicast address
•
Broadcast frames are identified by the MAC Address
Multicast IP addresses are related to multicast MAC addresses as follows:
The lower 23 bits of the IP address are mapped into the lower 23 bits of the MAC address as
shown in Figure B-1. Examples of the relationship are:
1) Received IP: 239.1.1.10 = MAC: 0x01 00 5E 01 01 0A
2) Received IP: 224.10.10.10 = MAC: 0x01 00 5E 0A 0A 0A
3) Received IP: 228.63.10.10 = MAC: 0x01 00 5E 3F 0A 0A
Note that the upper 5 bits of the multicast IP address are ignored in the MAC so that 32 Multicast
group IP addresses map to a single MAC address. This implies further filtering is required at the
end device.

Figure B-1. Multicast Mapping (IP to MAC)

B–3
MN-CMR5995-IOM
0x FF FF FF FF FF FF
Revision 1
.