Adtec digital DTA-3050 (version 6.02.14) Manual - Manual (Page 58)

Unicast Support
The support of Unicast is straightforward since Ethernet frames are directed to the DTA-3050’s Ethernet port as a “default
gateway.” As a default gateway, the DTA-3050 will either route the IP datagram, if there is an explicit route for the IP address,
or silently discard the IP datagram if there is no route for the destination.
A unicast packet is one that has a non-broadcast MAC address associated with it, for example, the most significant byte of the
MAC address has the least significant bit set to ‘0’. Unicast IP addresses that may be supported will fall into the standard
class range of A, B, or C. The DTA-3050 has a provision to route unicast IP datagrams based on an IP and subnet mask
structure. Example:
Parameter Value
IP address 10.10.10.0
Mask 255.255.255.0 “C Class”
Resulting IP addresses to be routed 10.10.10.0 to 10.10.10.255
Assigned MAC Address
0x00 00 00 00 00 00 to 0x00 FF FF FF FF FF, and excluding 0xFF FF FF FF
FF FF
For Unicast support, there is no correlation between the IP address and the MAC address as will be described in the Multicast
section.
Multicast Support
MPE support of Multicast is not as straightforward to support, since Linux causes unique challenges. Unlike Unicast, where all
devices communicates to the Multiplexer over the single hardware MAC address assigned to the Multiplexer; the support of
Multicast requires that each Multicast address that is going to be enabled must be statically entered into a list and the Ethernet
port enables a “hash” table, allowing specific Multicast MAC addresses to be enabled. What makes this somewhat daunting is
the fact that there are a finite number of multicast addresses that may be supported.
Multicast is considered as “class D” addressing and falls within the IP address range of 224.0.0.0 to 239.255.255.255. The
corresponding MAC address range is 0x01 00 5E 00 00 00 to 0x01 00 5E 7F FF FF and is derived as follows:
1st three octets and the most significant bit of the 4th byte’s octet are always set to 0x01 00 5E ‘1’. •
The least significant bits of the 4th byte, and bytes five and six are the last three bytes of the multicast IP address. •
Example:
Parameter Value
Multicast IP Address 239.1.1.10
MAC Preamble 0x01 00 5E
Multicast to MAC Mapping:
User Interface 50