Tài liệu giảng dạy CCNA - module 04 chapter 14-LAN Switching Review and Configuring Cisco 2950 LAN Switches

Module 04 LAN Switching
Chapter 14
LAN Switching Review and Configuring Cisco
2950 LAN Switches

1


Objectives

 Upon completion of this chapter, you will be able to perform the
following tasks:

 Describe Layer 2 switching (bridging) operations
 Describe the Catalyst 2950 switch operations
 Configure Catalyst 2950 switch
 Use show commands to verify Catalyst 2950
switch configuration and operations

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1. LAN SWITCHING REVIEW

3


Three Switch Functions

 Address learning
 Forward/filter decision

 Loop avoidance
4


How Switches Learn Host Locations

MAC address table

A

0260.8c01.1111

C

0260.8c01.2222

B

E0

E1

E2

E3

0260.8c01.3333

D

0260.8c01.4444

• Initial MAC address table is empty

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How Switches Learn Hosts Locations
MAC address table
E0: 0260.8c01.1111
A

0260.8c01.1111

C

B

E0

E1

E2

E3

0260.8c01.2222

0260.8c01.3333

D

0260.8c01.4444

• Station A sends a frame to Station C
• Switch caches station A MAC address to port E0 by learning
the source address of data frames
• The frame from station A to station C is flooded out to all
ports except port E0 (unknown unicasts are flooded)

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How Switches Learn Host Locations
MAC address table
E0: 0260.8c01.1111
E3: 0260.8c01.4444
A

0260.8c01.1111

C

B

E0
E2

0260.8c01.2222

E1
E3

0260.8c01.3333

D

0260.8c01.4444

• Station D sends a frame to station C
• Switch caches station D MAC address to port E3 by learning the
source Address of data frames
• The frame from station D to station C is flooded out to all ports
except port E3 (unknown unicasts are flooded)

7


How Switches Filter Frames
MAC address table

A

0260.8c01.1111

C

0260.8c01.2222

E0:

E2:
E1:
E3:

E0

E2

0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444

B

E1

X
XE3

0260.8c01.3333

D

0260.8c01.4444

 Station A sends a frame to station C
 Destination is known, frame is not flooded
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Broadcast and Multicast Frames

MAC address table

A

0260.8c01.1111

C

0260.8c01.2222

E0:
E2:
E1:
E3:

0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444

E0

E1

E2

E3

B

0260.8c01.3333

D

0260.8c01.4444

• Station D sends a broadcast or multicast frame
• Broadcast and multicast frames are flooded to
all ports other than the originating port
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Transmitting Frames through a
Switch


Cut-through



 Switch checks destination address
and immediately begins forwarding
frame

Frame

 Complete frame is received and

checked before forwarding

Frame
Frame

Fragment free
(modified cut-through)—Cat1900 Default

 Switch checks the first 64 bytes then immediately
begins forwarding frame

Frame



Store and forward

Frame

10


Duplex Overview
Half duplex (CSMA/CD)
• Unidirectional data flow
• Higher potential for collison
• Hubs connectivity

Switch
Hub

Full duplex
• Point-to-point only
• Attached to dedicated switched port
• Requires full-duplex support on both ends
• Collision free
• Collision detect circuit disabled

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2. CONFIGURING CISCO 2950 LAN
SWITCHES

12


Configuring the Switch

 Catalyst 2950
IOS CLI
(command-line interface)
Web-based VSM
(Visual Switch Manager)

13


Catalyst 2950 Default
Configurations

 IP address: 0.0.0.0
 CDP: Enabled
 100baseT port: Auto-negotiate duplex mode
 1000baseT port: Auto-negotiate duplex mode
 Spanning Tree: Enabled
 Console password: none

14


Basic Administrative
configurations

 A switch should be given a hostname, and passwords

should be set on the console and vty lines
 switch(config)#hostname ALSwitch
ALSwitch(config)#line console 0
ALSwitch(config-line)#login
ALSwitch(config-line)#password cisco
ALSwitch(config-line)#line vty 0 4
ALSwitch(config-line)#login
ALSwitch(config-line)#password cisco

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Configuring the Switch IP Address & default
gateway

To allow the switch to be accessible by Telnet
and other TCP/IP applications, IP addresses
and a default gateway should be set
ALSwitch(config)#interface vlan 1
ALSwitch(config-if)#ip address ip_add subnetmask
ALSwitch(config)#ip default-gateway default_gateway

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Speed and Duplex Options

ASLSwitch(config)#interface f0/1
ASLSwitch(config-if)#

duplex {auto | full| half}
Speed {10|100|1000|auto|negociate}

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Enable Web server

 Intelligent networking devices can provide a web-based interface for
configuration and management purposes
 ALSwitch(config)#ip http server
 ALSwitch(config)#ip http port 8080
 Any additional software such as an applet, can be downloaded to the
browser from the switch

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Configuring Static MAC Addresses

 It may be decided that it is desirable for a MAC address to be permanently
assigned to an interface
 To set a static MAC address entry for a switch:
 Switch(config)#mac-address-table static <mac-address of host>
FastEthernet <FastEthernet numer> vlan <vlan number>
 To remove this entry use the no form of the command:
 Switch(config)#no mac-address-table static <mac-address of host>
interface FastEthernet <Ethernet number> vlan <vlan name>

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Configure Port Security

 ALSwitch(config)#interface f0/2
 ALSwitch(config-if)#port security ?
 action
action to take for security violation

max-mac-count maximum mac address count

<cr>
 ALSwitch(config-if)#port security action ?
 shutdown shut down the port from which security violation is detected


trap
send snmp trap for security violaiton

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Showing Duplex Options

21


Duplex Mismatches

 The manually set duplex parameter differs
between connected ports
 The switch port is in autonegotiate and the
attached port is set to full duplex with no autonegotiation capability causing the switch port to
be in half-duplex mode

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FCS and Late Collision Errors
wg_sw_a#show interfaces
Ethernet 0/1 is Enabled
Hardware is Built-in 10Base-T
Address is 0090.8673.3341
MTU 1500 bytes, BW 10000 Kbits
802.1d STP State: Forwarding

Forward Transitions:
Port monitoring: Disabled
Unknown unicast flooding: Enabled
Unregistered multicast flooding: Enabled
Description:
Duplex setting: Half duplex
Back pressure: Disabled
Receive Statistics
------------------------------------Total good frames
44841
Total octets
4944550
Broadcast/multicast frames
31011
Broadcast/multicast octets
3865029
Good frames forwarded
44832
Frames filtered
9
Runt frames
0
No buffer discards
0
Errors:
FCS errors
Alignment errors
Giant frames
Address violations

0
0
0
0

1

Transmit Statistics
------------------------------------Total frames
404502
Total octets
29591574
Broadcast/multicast frames
390913
Broadcast/multicast octets
28478154
Deferrals
0
Single collisions
0
Multiple collisions
0
Excessive collisions
0
Queue full discards
0
Errors:
Late collisions
0
Excessive deferrals

0
Jabber errors
0
Other transmit errors
0

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Managing Mac Address Table

wg_sw_a#show mac-address-table
wg_sw_a#sh mac-address-table
Number of permanent addresses : 0
Number of restricted static addresses : 0
Number of dynamic addresses : 6
Address
Dest Interface
Type
Source Interface List
------------------------------------------------------------------------------------------------00E0.1E5D.AE2F Ethernet 0/2
Dynamic
All
00D0.588F.B604 FastEthernet 0/26 Dynamic
All
00E0.1E5D.AE2B FastEthernet 0/26 Dynamic
All
0090.273B.87A4 FastEthernet 0/26 Dynamic
All
00D0.588F.B600 FastEthernet 0/26 Dynamic

All
00D0.5892.38C4 FastEthernet 0/27 Dynamic
All

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Managing Configuration File
To send the configuration to a TFTP server:

wg_sw_a#

copy nvram tftp://host/dst_file
To download the configuration from a TFTP server:

wg_sw_a#

copy tftp://host/src_file nvram

wg_sw_a#copy nvram tftp://10.1.1.1/wgswd.cfg
Configuration upload is successfully completed
wg_sw_a#copy tftp://10.1.1.1/wgswd.cfg nvram
TFTP successfully downloaded configuration file

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