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Chapter 12 Port Channel Configuration
12.1 Introduction to Port Channel
To understand Port Channel, Port Group should be introduced first. Port Group is a group of
physical ports in the configuration level; only physical ports in the Port Group can take part in
link aggregation and become a member port of a Port Channel. Logically, Port Group is not a
port but a port sequence. Under certain conditions, physical ports in a Port Group perform port
aggregation to form a Port Channel that has all the properties of a logical port, therefore it
becomes an independent logical port. Port aggregation is a process of logical abstraction to
abstract a set of ports (port sequence) with the same properties to a logical port. Port Channel
is a collection of physical ports and used logically as one physical port. Port Channel can be
used as a normal port by the user, and can not only add network's bandwidth, but also provide
link backup. Port aggregation is usually used when the switch is connected to routers, PCs or
other switches.
As shown in the above, S1 is aggregated to a Port Channel, the bandwidth of this Port
Channel is the total of all the four ports. If traffic from S1 needs to be transferred to S2 through
the Port Channel, traffic allocation calculation will be performed based on the source MAC
address and the lowest bit of target MAC address. The calculation result will decide which port
to convey the traffic. If a port in Port Channel fails, the other ports will undertake traffic of that
port through a traffic allocation algorithm. This algorithm is carried out by the hardware.
Switch offers two methods for configuring port aggregation: manual Port Channel creation and
LACP (Link Aggregation Control Protocol) dynamic Port Channel creation. Port aggregation
Figure 12-1: Port aggregation
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S1
S2
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