Ethernet Star Topology
In a star topology, each host has an individual point-to-point connection to a
centralized hub or switch:
A hub provides no intelligent forwarding whatsoever, and will always
forward every frame out every port, excluding the port originating the frame.
As with a bus topology, a host will only process a frame if it matches the
destination hardware address in the data-link header. Otherwise, it will
discard the frame.
A switch builds a hardware address table, allowing it to make intelligent
forwarding decisions based on frame (data-link) headers. A frame can then
be forwarded out only the appropriate destination port, instead of all ports.
Hubs and switches are covered in great detail in another guide.
Adding or removing hosts is very simple in a star topology. Also, a break in
a cable will affect only that one host, and not the entire network.
There are two disadvantages to the star topology:
• The hub or switch represents a single point of failure.
• Equipment and cabling costs are generally higher than in a bus
topology.
However, the star is still the dominant topology in modern Ethernet
networks, due to its flexibility and scalability. Both twisted-pair and fiber
cabling can be used in a star topology.
In a star topology, each host has an individual point-to-point connection to a
centralized hub or switch:
A hub provides no intelligent forwarding whatsoever, and will always
forward every frame out every port, excluding the port originating the frame.
As with a bus topology, a host will only process a frame if it matches the
destination hardware address in the data-link header. Otherwise, it will
discard the frame.
A switch builds a hardware address table, allowing it to make intelligent
forwarding decisions based on frame (data-link) headers. A frame can then
be forwarded out only the appropriate destination port, instead of all ports.
Hubs and switches are covered in great detail in another guide.
Adding or removing hosts is very simple in a star topology. Also, a break in
a cable will affect only that one host, and not the entire network.
There are two disadvantages to the star topology:
• The hub or switch represents a single point of failure.
• Equipment and cabling costs are generally higher than in a bus
topology.
However, the star is still the dominant topology in modern Ethernet
networks, due to its flexibility and scalability. Both twisted-pair and fiber
cabling can be used in a star topology.
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