B.2.1 Unicast Routing; B.2.2 Multicast Routing - Comtech EF Data MR-S2 Installation And Operation Manual

Digicast Media Router S2 Receiver CMR-5975 (MR-S2)
IP Routing Support

B.2.1 Unicast Routing

Unicast routing provides point-to-point delivery of IP datagrams. Routes for Unicast IP packets
are configured according to the following:
• IP Addresses, which fall into three classes:
A (0.0.0.0 to 127.255.255.255)
B (128.0.0.0 to 191.255.255.255)
C (192.0.0.0 to 223.255.255.255)
•
Medium Access Control (MAC) Addresses, which identifies the destination device (next-
hop) to which the packets are sent. The least-significant bit of the first byte of the six-byte
MAC address is a '0'. For example, 0x00 11 22 33 44 55 is a Unicast address.
Unicast is supported by the MR-S2 as it would be in any routed network. Packets received by the
MR-S2 are routed to the Ethernet if they meet the subnet criteria or the MR-S2 is configured to
route non-local packets to a default gateway.
The MR-S2 uses Classless Inter-Domain Routing (CIDR) notation in which a 'slash' followed by
a decimal number is used to represent the number of bits for the mask, e.g. /32 is
255.255.255.255 and /24 is 255.255.255.0.
As stated above, part of the route configuration is a MAC address that is assigned for delivery of
the packet when it is encapsulated into MPE. The MAC address typically identifies the remote
receiver (physical device), e.g. satellite terminal, DTV terminal, or cable receiver.

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.
0x FF FF FF FF FF FF
B–2
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