Basic switch and switch configuration.pptx

Basic Switching and Switch Configuration

Objectives
CCNA Guide to Cisco Networking Fundamentals 2
• Explain the technology and media access control
method for Ethernet networks
Explain network segmentation and basic traffic
management concepts
Explain basic switching concepts and the operation
of Cisco switches
Perform and verify switch configuration tasks
Implement basic switch security
•
•
•
•

Ethernet
Operations
• Ethernet
– A network access method (or media access
method) originated by the University of Hawaii, later
adopted by Xerox Corporation
– And standardized as IEEE 802.3 in the early 1980s
Ethernet is:
– Most pervasive network access method in use
– Most commonly implemented media access method in
new LANs
•

CSMA/CD
• Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
– Ethernet contention method
Any station connected to a network can transmit
anytime a transmission is not present on the wire
Interframe gap, or interpacket gap (IPG)
– After each transmitted signal, each station must wait a
minimum of 9.6 microseconds before transmitting
another packet
•
•

CSMA/CD
(continued)
• •
Collisions
– Two stations could listen to the wire simultaneously
and not sense a carrier signal
– Both stations might begin to transmit their data
simultaneously
– Once a collision is detected, the first station to detect
the collision transmits a 32-bit jam signal
• Tells all other stations not to transmit for a brief period
– The two stations that caused the collision use an
algorithm to enter a backoff period

CSMA/CD
(continued)
Collision domain
The physical area in which a packet collision might occur
Routers, switches, bridges, and gateways segment networks
And thus create separate collision domains
The 32-bit jam signal that is transmitted when the collision is
discovered prevents all stations on that collision domain from
transmitting
•

CSMA/CD
(continued)
• •
Broadcasts
– Stations on a network broadcast packets to other
stations to make their presence known on the network
• And to carry out normal network tasks
– When a segment has too much broadcast traffic:
• Utilization increases
• Network performance in general suffers
– Simple ways to reduce broadcast traffic:
• Reduce the number of services on your network
• Limit the number of protocols in use on your network

CSMA/CD (continued)
•
•
Broadcast storm
•A sudden rush of network
transmissions that causes all
other network communications
to slow down
•Due to the volume of data
competing for access to the
same bandwidth on the
communications medium
One of the most common
causes of broadcast
storms is a network loop

Latency
• Latency, or propagation delay
– The length of time that is required to forward, send, or
otherwise propagate a data frame
– Latency differs depending on the resistance offered
by the transmission medium, the number of nodes
• And in the case of a connectivity device, the amount of
processing that must be done on the packet
Transmission time
– The amount of time it takes for a packet to be sent
from one device to another
•

Latency (continued)

Latency
(continued)
• Bit time
– Refers to the amount of time required to transmit one
data bit on a network
Slot time (512 bit times)
– An important specification that limits the physical size
of each Ethernet collision domain
– Specifies that all collisions should be detected from
anywhere in a network in less time than is required to
place a 64-byte frame on the network
•

Ethernet Errors
• Frame size errors
– Short frame or runt
– Long frame or giant
– Jabber
Frame check sequence (FCS) error
– Indicates that bits of a frame were corrupted during
transmission
– Can be caused by any of the previously listed errors
•

Ethernet Errors (continued)
•
Collision errors
– Reducing the number of devices per collision domain
will usually solve the problem
• You can do this by segmenting your network with a
router, a bridge, or a switch
– Late collision
• Occurs when two stations transmit more than 64 bytes
of data frames before detecting a collision

Ethernet Errors
(continued)
• Fast Ethernet
– Uses the same CSMA/CD as common 10BaseT
Ethernet
– Provides ten times the data transmission rate—100
Mbps
– Defined under the IEEE 802.3u standard
Implementations
– 100Base-TX
– 100Base-T4
– 100Base-FX
•

Gigabit
Ethernet
• Recent advances in technology have allowed us to
reach even higher speeds than those of Fast
Ethernet
Gigabit Ethernet implementations
– 1000Base-TX (802.3ab)
– 1000Base-SX (802.3z)
– 1000Base-LX (802.3z)
– 1000Base-CX (802.3z)
•

Half- and Full-
Duplex
Communications
•
•
• Half-duplex communications
– Devices can send and receive signals, but not at the
same time
Full-duplex (or duplex) communications
–Devices can send and receive signals simultaneously
Ethernet networks can use equipment that supports
half- and full-duplex communications

Half- and Full-Duplex Communications
(continued)
• Benefits of using full-duplex:
• Time is not wasted retransmitting frames because collisions do not
occur
• The full bandwidth is available in both directions because the send
and receive functions are separate
• Stations do not have to wait until other stations complete their
transmissions because only one transmitter is used for each
twisted pair

Half- and Full-Duplex Communications
(continued)
• On a Cisco Catalyst 2950 switch, you can set the
duplex capabilities port-by-port
The four different duplex options are:
– Auto
– Full
– Full-flow control
– Half
•

A Review of
LAN
Segmentation CCNA Guide to Cisco Networking Fundamentals 20
• You can improve the performance of your Ethernet
network
– By reducing the number of stations per collision
domain
Typically, network administrators implement bridges,
switches, or routers to segment the network and
divide the collision domains
•

Segmenting
with Bridges
• Bridge
– Segments a network by filtering traffic at the Data Link
layer
– Divides a network into two or more segments
• Only forwards a frame from one segment to another if
the frame is a broadcast or has the MAC address of a
station on a different segment
Bridges learn MAC addresses by reading the source
MAC addresses from frames
– As the frames are passed across the bridge
•

Segmenting
with Bridges
(continued) CCNA Guide to Cisco Networking Fundamentals 22
• Bridging table
– Maps the MAC addresses on each segment to the
corresponding port on the bridge to which each
segment is connected
Bridges increase latency, but because they
effectively divide the collision domain
– This does not affect slot time
•

Segmenting with Bridges (continued)
•
Remember these points:
• Bridges reduce collisions on the LAN and filter traffic
based on MAC addresses
• A bridge does not reduce broadcast or multicast
• traffic
• A bridge can extend the useful distance of the Ethernet
LAN
• The bandwidth for the new individual segments is
increased
• Bridges can be used to limit traffic for security purposes

Segmenting
with Routers
• Router
– Operates at layer 3 of the OSI reference model
– Interprets the Network layer protocol and makes
forwarding decisions based on the layer 3 address
Routers typically do not propagate broadcast traffic
– Thus, they reduce network traffic even more than
bridges do
Routers maintain routing tables that include the
Network layer addresses of different segments
•
•

Segmenting with Routers (continued)
• When you segment a LAN with routers, they
will:
• Decrease collisions by filtering traffic
• Reduce broadcast and multicast traffic by blocking or
selectively filtering packets
• Support multiple paths and routes between them
• Provide increased bandwidth for the newly created
segments
• Increase security by preventing packets between hosts
on one side of the router from propagating to the other
side of the router

Segmenting with Routers (continued)
•
When you segment a LAN with routers, they
will: (continued)
• Increase the effective distance of the network by creating
new collision domains
• Provide layer 3 routing, packet fragmentation and
reassembly, and traffic flow control
• Provide communications between different technologies,
such as Ethernet and Token Ring or Ethernet and Frame
Relay
• Have a higher latency than bridges, because routers have
more to process; faster processors in the router can
reduce some of this latency

LAN Switching
Switches Using a switch on a LAN has
a different effect on the
way network traffic is
propagated

Segmentation
with Switches
•
•
Switches are often called multiport bridges
Switch typically connects multiple stations
individually
– Thereby segmenting a LAN into multiple collision
domains
Switches microsegment the network
– By connecting each port to an individual workstation
Switched bandwidth
– Bandwidth is not shared as long as each workstation
connects to its own switch port
•
•

Segmentation with
Switches (continued)

Segmentation with Switches
(continued)
• Switch latency is typically higher than that of a
repeater or hub
– Faster processors and a variety of switching
techniques make switches typically faster than bridges
Switches provide the following benefits:
– Reduction in network traffic and collisions
– Increase in available bandwidth per station
– Increase in the effective distance of a LAN by dividing
it into multiple collision domains
– Increased security, because unicast traffic is sent
directly to its destination
•

Switch
Operations
• A switch learns the hardware address of devices to
which it is attached
– By reading the source address of frames as they are
transmitted across the switch
The switch then matches the source MAC address
with the port from which the frame was sent
– The MAC-to-switch-port mapping is stored in the
switch’s content-addressable memory (CAM)
The switch uses a memory buffer to store frames as
it determines to which port(s) a frame will be
forwarded
•
•

Switch
Operations
(continued) CCNA Guide to Cisco Networking Fundamentals 33
• Types of memory buffering:
– Port-based memory buffering
– Shared memory buffering
Asymmetric switching
– Some switches can interconnect network interfaces of
different speeds
Symmetric switching
– Switches that require all attached network interface
devices to use the same transmit/receive speed
•
•

Switching
Methods
• All switches base frame-forwarding decisions on a
frame’s destination MAC address
The three main methods for processing and
forwarding frames are:
– Cut-through, store-and-forward, and fragment-free
One additional forwarding method, adaptive cut-
through forwarding
– A combination of the cut-through and store-and-
forward methods
•
•

Switching Methods (continued)

Cut-Through
Forwarding
• Switches that use cut-through forwarding start
sending a frame immediately after reading the
destination MAC address into their buffers
The main benefit of cut-through forwarding is a
reduction in latency
The drawback is the potential for errors in the frame
that the switch would be unable to detect
– Because the switch only reads a small portion of the
frame into its buffer
•
•

Cut-Through Forwarding
(continued)

Store-and-
Forward
Forwarding CCNA Guide to Cisco Networking Fundamentals 38
• Store-and-forward switches read the entire frame,
no matter how large, into their buffers before
forwarding
Because the switch reads the entire frame, it will not
forward frames with errors
The store-and-forward method has the highest
latency
•
•

Store-and-Forward Forwarding
(continued)

Fragment-
Free
Forwarding
• Fragment-free forwarding represents an effort to
provide more error-reducing benefits than cut-
through switching
– While keeping latency lower than does store-and-
forward switching
A fragment-free switch reads the first 64 bytes of an
Ethernet frame
– And then begins forwarding it to the appropriate
port(s)
•

Fragment-Free Forwarding
(continued)

Fragment-Free Forwarding
(continued)
•
Adaptive cut-through
– For the most part, the adaptive cut-through switch will
act as a cut-through switch
• To provide the lowest latency
– However, if a certain level of errors is detected, the
switch will:
• Change forwarding techniques
• Act more as a store-and-forward switch

Switch User
Interface
• Two types of operating systems are in use on Cisco
switches: IOS-based and set-based
You can connect to a Cisco switch in the same way
you connect to a Cisco router
The Cisco switch has a console port to which you
can connect your laptop or PC
Once you power on the switch you will be in the
command-line interface
– You can configure anything from the command line
•
•
•

Modes and
Passwords
• You cannot actually configure a switch until you get
to enable mode
To enter enable mode, type enable at the
command-line prompt and then press Enter
The first step in configuring a switch is to set up a
password
To start configuration mode, first type configure
terminal or config t at the command prompt
You can also configure a secret (encrypted)
password
•
•
•
•

Setting the
Host Name
• The actual task of setting the host name on the
Cisco Catalyst switch is identical to setting the host
name on a Cisco router
To configure this name, you would type:
– Switch(config)#hostname name
Once the host name is set, the prompt will change to
reflect the name of the switch
•
•

IP on the
Switch
• By default, Cisco switches are not configured with
IP addresses
– Generally speaking, a switch does not require an IP
address
• Because switches operate mainly on Layer 2
You may want to configure an IP address for your
switch so that you can manage it over the network
Also, you may need to configure an IP address for
your switch if you want to implement VLANs on
your network
•
•

Configuring
Switch Ports
• To enter interface configuration mode for the first
port of a switch named Rm410HL, you would use
the following commands:
– Rm410HL#configure terminal
– Rm410HL(config)#interface f0/1
– Rm410HL(config-if)#
To view the configuration of a port, use the show
command
•

Configuring Switch Ports (continued)
•
Configuring the duplex mode
You would use the following command to set the duplex mode:
•Rm410HL#configure terminal
•Rm410HL(config)#interface f0/24
•Rm410HL(config-if)#duplex full

Securing
Switch Ports
• You can choose from several degrees of security
on a switch
– First, you can configure a permanent MAC address
for a specific port on your switch
– Second, you could define a static MAC address
entry into your switching table
• Which maps a restricted communication path between
two ports
To configure port security, you first must enter the
interface configuration mode
•

Securing
Switch Ports
(continued)
• You can display several options by typing the
following command:
– Rm410HL(config-if)#switchport port-
security ?
– Options include aging, mac-address, maximum,
and violation
To turn switchport security off, use:
– Rm410HL(config-if)#no switchport port-
security
To clear the settings to include erasing the static
MAC addresses, use the clear command:
– Rm410HL(config-if)#clear port-security
•
•

Summary
• Ethernet (CSMA/CD) is a media access method
that was developed in the 1960s
Stations on an Ethernet LAN must listen to the
network media before transmitting to ensure that
no other station is currently transmitting
If two stations transmit simultaneously on the same
collision domain, a collision will occur
The transmitting stations must be able to recognize
the collision and ensure that other stations know
about it by transmitting a jam signal
•
•
•

Summary
(continued)
• The delays caused by collisions on a network can
seriously affect performance when collisions
exceed 5% of the traffic on the collision domain
Switches do the most to divide the collision domain
and reduce traffic without dividing the broadcast
domain
A switch microsegments unicast traffic
Another way to increase the speed at which a LAN
operates is to upgrade from Ethernet to Fast
Ethernet
Full duplex can also improve Ethernet performance
•
•
•
•

Summary
(continued)
• Full duplex allows frames to be sent and received
simultaneously
As with Fast Ethernet, full-duplex operations are
only supported by devices designed for this type of
communication
The two types of operating systems on Cisco
switches are IOS-based and set-based
Configuring a switch is similar to configuring a
router through the CLI
Switches can provide some level of security
through the use of port security commands
•
•
•
•

Basic switch and switch configuration.pptx

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Basic switch and switch configuration.pptx