Industrial Managed
Ethernet Switch
User Manual
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2.8 Unicast
/
Multicast MAC
The managed switch is a network device which operate at the OSI layer 2 or medium access control
)
MAC
(
layer
.
It forwards frames of OSI layer 2 based on the MAC addresses
.
Generally, the layer 2 switch will learn about the
destination MAC addresses of the end devices which are connected to the switch over time based on the exchanged
traffic
.
For instance, in the beginning if the switch does not know which port a destination MAC address is, it will
forward or broadcast a frame to all of its ports and wait for a response from end device connected to one of the
ports
.
This way the switch will learn of the MAC address and corresponding port number
.
Later on, the switch will
forward the frame to the destination port only thus saving the traffic on other ports
.
The managed switch typically maintains the learned MAC addresses in its memory which is usually called a MAC
Address table
.
In this section, the managed switch allows the users to control the MAC Address table by adding
static MAC addresses into the table or filtering certain MAC addresses so that they will not be forwarded by the
managed switch
.
Atop
’s manage switch also provides the users with the ability to set the MAC address age
-
out
manually
.
Note that the age
-
out period is a duration of time that a learned MAC address will be maintained in the
MAC address table before it was removed to save the memory.
The MAC addresses that can be managed by the switch can be both Unicast and Multicast MAC addresses
.
This
section will briefly explain the concept of Unicast and Multicastforwardingas well as their benefits
.
Please see Figure
2.71 for illustrations of the Unicast versus the Multicast concept
.
Figure 2.71 Unicast vs
.
Multicast
Unicast
:
This type of transmission sends messages to a single network destination identified by a unique
MAC address
.
This method is simple with one source and one destination
.
Multicast
:
This type of transmission is more complicated
.
It sends messages from one source to multiple
destinations
.
Only those destinations or hosts that belong to a specific multicast group will receive the multicast
packets
.
In addition, networks that support multicast send only one copy of the information across the network
until the delivery path that reaches group members diverges
.
At these diverging points, multicast packets will
be copied and forwarded
.
This method can manage high volume traffic with different destinations while using
network bandwidth efficiently
.
Multicast filtering improves the performance of networks that carry multicast traffic
.
Figure 2.72 shows the Unicast/Multicast MAC dropdown menu which allows the users to manage and view the
status of MAC address table
.
Unicast
Multicast