where each falls within the spectrum as well as the potential applications.
applications and hosts, protocol methods and procedures are discussed. For
example, it covers the methods by which hosts join and leave multicast
groups, and it also covers group advertisements and multicast forwarding.
added to the IP header. These are the source and destination IP addresses.
They specify a particular originating and receiving host. After the layer 3
PDU is formed, it is passed to layer 2 to create the layer 2 PDU, or frame. The
frame consists of all of the previous layers' headers in addition to the layer
2 header. With an Ethernet frame, for example, the two 48-bit source and
destination MAC addresses are specified in the layer 2 header. Other proto-
cols such as IEEE 802.5 (Token Ring) and FDDI also have headers that con-
tain specific host source and destination addresses.
everyone. A MAC address must
address for each host. With the specific address, any source host should be
able to contact the destination host without confusion.
wishes to communicate with. This may not be done on a host-by-host basis.
The normal operation is that the host has a default gateway assigned for use
when the logical destination address does not reside on the same subnet as
the source host. Figure 9.1 depicts how unicast traffic works on the same
subnet.