CompTIA exam study guide presentations by instructor Brian Ferrill, PACE-IT (Progressive, Accelerated Certifications for Employment in Information Technology) "Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53" Learn more about the PACE-IT Online program: www.edcc.edu/pace-it

1. Configuring
switches I.

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Instructor, PACE-IT Program – Edmonds Community College
Areas of Expertise Industry Certifications
 PC Hardware
 Network Administration
 IT Project Management
 Network Design
 User Training
 IT Troubleshooting
Qualifications Summary
Education
 M.B.A., IT Management, Western Governor’s University
 B.S., IT Security, Western Governor’s University
Entrepreneur, executive leader, and proven manger
with 10+ years of experience turning complex issues
into efficient and effective solutions.
Strengths include developing and mentoring diverse
workforces, improving processes, analyzing
business needs and creating the solutions
required— with a focus on technology.

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– Unmanaged vs. managed switches.
– Spanning Tree Protocol.
PACE-IT.

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Configuring switches I.

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– Switch basics.
» Most switches operate at Layer 2—the data link layer—of the
OSI (Opens Systems Interconnections) model.
» An application-specific integrated circuit (ASIC) chip is used to
make switching decisions in place of software.
• This allows switches to break-up collision domains.
• This allows switches to run in full-duplex mode.
• This allows switches to make faster decisions than either
bridges or routers.
» When a switch receives a frame on a port, it makes some
simple decisions based on its MAC (media access control)
table.
• Forward: the frame is directed out the port which is
associated with the destination MAC address.
• Filter: the frame is not directed out ports which are not
associated with the destination MAC address.
• Flood: the frame is flooded out all ports (except the port that
received the frame) if the MAC address is not in the MAC
address table.
Configuring switches I.

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Configuring switches I.
An unmanaged switch is a
simple switch—plug it in and
it works. There is no method
provided for configuration.
The unmanaged switch is designed with ease of installation
as its main attribute. Managed switches, on the other hand,
can be configured through either the command line or a
browser based interface. Managed switches provide for a
high degree of network customization and control.
A managed switch can also be set up so that an
administrator can monitor its performance remotely and use
protocols such as SNMP v3 (Simple Network Management
Protocol v3) to make some modifications to its configuration.

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Configuring switches I.

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– Loop avoidance.
» A switching loop can occur on networks where there are
multiple paths to reach destination MAC addresses.
• Can be created when switches are connected together.
» DEC (Digital Equipment Corporation) created the Spanning
Tree Protocol (STP) to reduce the possibility of switching loops.
• The switches elect a root bridge to control the switched
network.
• The switches will shut down ports that are not the best path to
the root bridge—reducing the risk of loops.
• No network can flow until after the STP process has taken
place and a stable state has been achieved. This is called
convergence, which can take a significant amount of time—
up to 50 seconds.
• After convergence, the STP selected switch ports send out
Bridge Protocol Data Unit (BPDU) packets to help maintain
the stable state.
Configuring switches I.

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– STP port states.
» All switch ports in an STP enabled network can be in one of five
states.
• Disabled: administratively shut down.
• Blocking: will not forward packets, but is still receiving BPDU
packets and will drop all other frames.
• Listening: will not forward packets, but listens to BPDU
packets to make sure no loops can occur in preparation for
the next state.
• Learning: will not forward packets, but is learning all of the
paths in the network; it is populating its MAC address table.
• Forwarding: it will forward (send) and receive all packets.
– 802.1d.
» The IEEE version of STP.
• All modern Layer 2 switches run 802.1d by default.
Configuring switches I.

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Configuring switches I.
The slow convergence time
of 802.1d led to the creation
of Rapid Spanning Tree
Protocol (RSTP), which is
also known as 802.1w.
RSTP has a much faster convergence time than 802.1d. With
RSTP enabled on all switches, a network can achieve its stable
state in approximately five seconds. RSTP is not turned on by
default on Layer 2 switches; it must be enabled by an
administrator.
802.1w defines three possible port states. They are as follows:
discarding: the port may be administratively disabled or it may
be in a blocking mode or listening mode; learning: the port is
populating its MAC address table in preparation for forwarding
packets; and forwarding: the port is actively forwarding packets.

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Configuring switches I.
Switches are Layer 2 devices used on networks to move frames (data) from
source to destination based on MAC addresses. Unmanaged switches are
simple and don’t provide a method for configuring their operations.
Managed switches can be configured through the command line or some
other interface. SNMP can be used with managed switches to ease the
management process.
Topic
Unmanaged vs. managed
switches.
Summary
A switching loop can occur on networks when there are redundant paths
between nodes. DEC created STP as a means of preventing switching
loops from occurring on networks. STP defines five port states: disabled,
blocking, listening, learning, and forwarding. STP can take up to 50 seconds
to reach convergence. The IEEE version of STP is 802.1d. RSTP (802.1w)
was created to decrease the convergence time to approximately five
seconds. RSTP defines three port states: discarding, learning, and
forwarding.
Spanning Tree Protocol.

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THANK YOU!

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