At 09:12 AM 6/28/01, Ramesh c wrote:
>1) Does a Network Interface card support 2^47 ethernet multicast address.
The first three bytes are still a vendor code (with the multicast bit
turned on). So that reduces the number of possible multicast addresses.
>If
>so how are the Addresses generated or stored?
The Ethernet driver keeps track of which multicasts to listen to.
>2)How are the Ip Multicast address mapped to Ethernet multicast address?
IP multicasting transmits IP data to a group of hosts that are identified
by a single Class-D IP address. In dotted-decimal notation, host group
addresses range from 224.0.0.0 to 239.255.255.255. Network stations
recognize an address as being a Class-D address because the first four bits
must be 1110 in binary.
A multicast group is also identified by a MAC-layer multicast address.
The Internet Assigned Numbers Authority (IANA) owns a block of MAC-layer
addresses that are used for group multicast addresses. The range of
addresses for Ethernet is 01:00:5E:00:00:00 -- 01:00:5E:7F:FF:FF. When a
station sends a frame to an IP group that is identified by a Class-D
address, the station inserts the low-order 23 bits of the Class-D address
into the low-order 23 bits of the MAC-layer destination address. The top 9
bits of the Class-D address are not used. The top 25 bits of the MAC
address are 01:00:5E followed by a zero, or, in binary:
00000001 00000000 01011110 0
Cheers,
Priscilla
>Cheers
>
>
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