Chapter 2: Cơ bản về Switch các khái niệm và cấu hình pot

•After a collision occurs and all stations allow the cable to become idle each waits the Randomly Backoff Time become idle each waits the full inter-frame spacing •The stations that coll

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Chapter 2: Basic switch concepts

and configurations

CCNA Exploration 4.0

1

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Học viện mạng Bach Khoa - Website: www.bkacad.com 2

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Media Access Control (MAC)

•MAC refers to protocols that determine which computer

logical bus topology and

Deterministic, Non-Deterministic

on a shared-medium environment, or collision domain, is allowed to transmit the data

topology and physical star or extended star

transmit the data.

•MAC, with LLC, comprises the IEEE version of the OSI Layer 2

logical ring topology and a Layer 2

•There are two broad categories of Media Access Control, deterministic ( taking

physical star topology

turns ) and non-deterministic

( first come, first served)

logical ring topology and physical dual ring

physical dual-ring topology

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Transmitting&

layers of the OSI model

3 Detecting errors within data packets or on the

listening Why ???

p network

???

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Flow chart

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•After a collision occurs and all stations allow the cable to become idle (each waits the

Randomly Backoff Time

become idle (each waits the full inter-frame spacing)

•The stations that collided must wait an additional and

must wait an additional and potentially progressively longer period of time before attempting to retransmit the p g collided frame

•The waiting period is intentionally designed to be random

•If the MAC layer is unable to send the frame after sixteen attempts it gi es p and

attempts, it gives up and generates an error to the network layer

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Ethernet Communications

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Ethernet frame structure

•At the data link layer the frame

structure is nearly identical for

all speeds of Ethernet from 10

all speeds of Ethernet from 10 Mbps to 10,000 Mbps

•At the physical layer almost all versions of Ethernet are

substantially different from one another with each speed having a distinct set of

architecture design rules

•The Ethernet II Type field is incorporated into the current

802 3 frame definition The

802.3 frame definition The

which higher-layer protocol is present in an incoming frame

present in an incoming frame

by examining the Length/Type field

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•The Preamble is used for timing synchronization in the

Synchronization, Address types

slower implementations of Ethernet Faster versions of Ethernet are synchronous, and this timing information is

multicast (group), or (g p), broadcast

(all nodes)

•The source address is generally the unicast address

of the transmitting Ethernet node (can be virtual entity – group or multicast)

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•The type value specifies the upper-layer protocol to

receive the data after

Length if value < 1536 decimal, (0x600) Î need LLC to identify receive the data after

Ethernet processing is completed.

•The length indicates the

(0x600) Î need LLC to identify upper protocol

number of bytes of data that follows this field (so contents

of the Data field are decoded per the protocol indicated)

•The maximum transmission unit (MTU) for Ethernet is

1500 octets so the data

1500 octets, so the data should not exceed that size

•Ethernet requires that the frame be not less than 46

4 bytes CRC

frame be not less than 46 octets or more than 1518 octets (Pad is required if not enough data)

Type if value => 1536 decimal, (0x600) Î it identify upper protocol

CRC

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Naming on Ethernet

MAC ADDRESS

Ethernet uses MAC addresses that are 48 bits in length and expressed as

•Ethernet uses MAC addresses that are 48 bits in length and expressed as

12 hexadecimal digits

•Sometimes referred to as burned-in addresses ( BIA ) because they are

burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes

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Ethernet in full duplex

Full duplex Full duplex

• If the attached station is operating in full duplex then the station may

send and receive simultaneously and collisions should not occur Full

send and receive simultaneously and collisions should not occur duplex operation also changes the timing considerations and

Full-eliminates the concept of slot time

• In half-duplex if no collision the sending station will transmit 64 bits

In half-duplex, if no collision, the sending station will transmit 64 bits

(timing synchronization) preamble, DA, SA, certain other header

information, actual data payload, FCS

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• Fast Ethernet and 10/100/1000 ports: default is auto

• 100BASE-FX ports: default is full p

• 10/100/1000 ports operate in either half- or full-duplex

mode when they are set to 10 or 100 Mb/s, but when set to

1 000 Mb/s they operate only in full duplex mode

1,000 Mb/s, they operate only in full-duplex mode

• Default: when Default: when autonegotiation fails autonegotiation fails ÆCatalyst switch sets ÆCatalyst switch sets the corresponding switch port to half-duplex mode

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releases between Cisco IOS Release 12.1(14)EA1 and ( )

12.2(18)SE, the auto-MDIX feature is disabled by default

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MAC Addressing and Switch MAC Address

Tables

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Bandwidth and Throuhgput

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Collision Domains

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Collision Domains

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Broadcast Domains

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Broadcast Domains - Example

When a switch receives a broadcast frame, it forwards the frame to each of its ports, except the incoming port where the switch received the broadcast frame Each attached device recognizes the broadcast frame and processes it

it.

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Broadcast Domains - Example

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Network Latency

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Network Congestion

• Causes of network congestion: g

– Increasingly powerful computer and network

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LAN Segmentation

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Controlling Network Latency

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Removing Network Bottlenecks

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Switch Packet Forwarding Methods

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Switch Packet Forwarding Methods

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Symmetric and Asymmetric Switching

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Port Based and Shared Memory Buffering

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Layer 2 and Layer 3

Switching

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Layer 3 Switch and Router Comparison

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Review you understanding

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Review you understanding

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Switch configuration

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The Command Line Interface Modes

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GUI-based Alternatives to the CLI

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Context Sensitive Help

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Console Error Messages

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The Command History Buffer

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Configure the Command History Buffer

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Describe the Boot Sequence

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Prepare to Configure the Switch

Step 1

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Step 2

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Step 3

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Management Interface Considerations

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Configure Duplex and Speed

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Configure a Web Interface

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Managing the MAC Address Table

show mac-address-table

show mac address table

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Show Commands

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Show running-config

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Show interfaces

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Backing Up the Configuration

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Restoring the Configuration

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Back up Configuration Files to a TFTP Server

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Clearing Configuration Information

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Config Password g

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Configure Console Access

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Secure the vty Ports

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Configure EXEC Mode Passwords

Clear text password

Encrypted, Priority than enable password

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Configure Encrypted Passwords

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Enable Password Recovery

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Password Recovery

• Step 1 Connect a terminal or PC with terminal-emulation software to the switch console port.

• Step 2 Set the line speed on the emulation software to 9600 baud.

• Step 3 Power off the switch Reconnect the power cord to the switch and within 15 seconds, press the Mode button while the System LED is still flashing green Continue pressing the Mode button until the System LED turns briefly amber and then solid green Then release the Mode button.

• Step 4 Initialize the Flash file system using the flash_init command.

• Step 5 Load any helper files using the load helper command.

Step 5 Load any helper files using the load_helper command.

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• 16128000 bytes total (10003456 bytes free)

• Step 7 Rename the configuration file to config.text.old, which contains the password definition, using the rename flash:config.text

the password definition, using the rename flash:config.text

flash:config.text.old command.

• Step 8 Boot the system with the boot command

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Password Recovery

• Step 9 You are prompted to start the setup program Enter N at the prompt, and then when the system prompts whether to continue with the configuration dialog, enter N.

• Step 10 At the switch prompt enter privileged EXEC mode using the enable command

• Step 10 At the switch prompt, enter privileged EXEC mode using the enable command.

• Step 11 Rename the configuration file to its original name using the rename

flash:config.text.old flash:config.text command.

• Step 12 Copy the configuration file into memory using the copy flash:config.text

system:running-config command After this command has been entered, the follow is displayed on the console:

– Source filename [config.text]?

– Destination filename [running-config]?

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• Step 15 Return to privileged EXEC mode using the exit command.

• Step 16 Write the running configuration to the startup configuration file Step 16 Write the running configuration to the startup configuration file using the copy running-config startup-config command.

• Step 17 Reload the switch using the reload command.

• Note: The password recovery procedure can be different depending on the Cisco switch series, so you should refer to the product

documentation before you attempt a password recovery.

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Configure a Login Banner

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Configure a MOTD Banner

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Telnet and SSH

• Remote control tool of switch and router

• SSH encrypt data before transmit yp

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Configuring Telnet

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Configuring SSH

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Configuring SSH

• The switch supports SSHv1 or SSHv2 for the server component The

switch supports only SSHv1 for the client component

• To implement SSH, you need to generate RSA keys

– Step 1. Enter global configuration mode using the configure terminal

– Step 5. Return to privileged EXEC mode using the end command.

– Step 6 p Show the status of the SSH server on the switch using the show ip g p ssh or show ssh command.

– To delete the RSA key pair, use the crypto key zeroize rsa global

configuration command After the RSA key pair is deleted, the SSH server

is automatically disabled

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Configuring the SSH Server

• Step 1 Enter global configuration mode using the configure terminal command

• Step 2 (Optional) Configure the switch to run SSHv1 or SSHv2 using Step 2 (Optional) Configure the switch to run SSHv1 or SSHv2 using the ip ssh version [1 | 2] command

– If you do not enter this command or do not specify a keyword, the If you do not enter this command or do not specify a keyword, the SSH server selects the latest SSH version supported by the SSH client For example, if the SSH client supports SSHv1 and SSHv2, the SSH server selects SSHv2

• Step 3 Configure the SSH control parameters:

– Specify the time-out value in seconds: default of 10 minutes

– Specify the number of times that a client can re-authenticate to the server The default is 3; the range is 0 to 5

– Command: ip ssh {timeoutseconds | authentication-retriesnumber}.

Tiêu đề	Chapter 2: Basic switch concepts and configurations
Trường học	Học viện mạng Bách Khoa
Chuyên ngành	Networking
Thể loại	Chương

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