In Figure ,
there are four PCs connected to a hub. When a hub receives an Ethernet
frame on one port, it forwards (repeats) it out all other ports.
For example, if Host A is sending an Ethernet frame to Host D, Host
A encapsulates the data and upper layer headers into the Layer 2 frame
field known as the “Data.” Normally, when data is being sent from
one computer to another, several frames may be needed to transmit it
all. In the Ethernet frame header, as shown in Figure ,
Host A is the Source MAC address and Host D is the Destination
MAC address.
Question: After Host A sends out the frame, which Hosts
will see this frame, more specifically, where does the frame go?
Answer: The answer is that all of the Hosts on this
network, every host connected to Hub, will see at least part of this
frame.
Explanation: Once the frame is sent out from Host A to the
hub, the hub forwards (repeats) the frame out all ports (except the
port the frame came in on). Therefore, each Host connected to the hub
begins to receive the frame. Each host copies the beginning of the
frame, the MAC Destination Address, into the NIC card. If this
Destination MAC address matches the MAC address of the NIC card, then
the host copies in the rest of the frame. If the Destination MAC
address does not match the NIC card address, then the host ignores the
rest of the frame.
If any other Host on the hub sends an Ethernet frame at the same
time Host A is sending its frame as shown in Figure ,
a collision will occur because all four hosts are on the same
collision domain.
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