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Unformatted text preview: stack when a frame is received.
Today most interfaces can also be configured to receive frames whose destination address
is a multicast address, or some subset of multicast addresses. On an Ethernet, a multicast
address has the low-order bit of the high-order byte turned on. In hexadecimal this bit
looks like 01:00:00:00:00:00. (We can consider the Ethernet broadcast address,
ff:ff:ff:ff:ff:ff as a special case of the Ethernet multicast address.)
If the interface card receives the frame, it is passed to the device driver. (One reason the
interface card might discard the frame is if the Ethernet checksum is incorrect.)
Additional filtering is performed by the device driver. First, the frame type must specify a
protocol that is supported (IP, ARP, etc.). Second, additional multicast filtering may be
performed, to check whether the host belongs to the addressed multicast group.
The device driver then passes the frame to the next layer, such as IP, if the frame type
specifies an IP datagram. IP performs more filtering, based on the source and destination
IP addresses, and passes the datagram up to the next layer (such as TCP or UDP) if all is
Each time UDP receives a datagram from IP, it performs filtering based on the destination
port number, and sometimes the source port number too. If no process is currently using
the destination port number, the datagram is discarded and an ICMP port unreachable
message is normally generated. (TCP performs similar filtering based on its port
numbers.) If the UDP datagram has a checksum error, UDP silently discards it. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/broadcas.htm (2 of 12) [12/09/2001 14.47.00] Chapter 12. Broadcasting and Multicasting The problem with broadcasting is the processing load that it places on hosts that aren't
interested in the broadcasts. Consider an application that is designed to use UDP
broadcasts. If there are 50 hosts on the cable, but only 20 are participating in the
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12