pace-it: configuring switches (part 1)

Configuring switches I.

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.

Brian K. Ferrill, M.B.A.


– Unmanaged vs. managed switches.

– Spanning Tree Protocol.

PACE-IT.

Unmanaged vs. managed switches.Configuring switches I.

Unmanaged vs. managed switches.

– 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.


Unmanaged vs. managed switches.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.

Spanning Tree Protocol.Configuring switches I.

Spanning Tree Protocol.

– 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.



– 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.


Spanning Tree Protocol.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.

What was covered.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.


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