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© 2000, Cisco Systems, Inc. 6-1
Chapter 6
Catalyst Switch Operations
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-2
• Address learning
• Forward/filter decision
• Loop avoidance
Three Switch Functions Three Switch Functions
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-3
How Switches Learn Host Locations
How Switches Learn Host Locations
• Initial MAC address table is empty.
MAC Address Table
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0 E1
E2 E3
A B
C D
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-4
How Switches Learn Host Locations
How Switches Learn Host Locations
• Station A sends a frame to station C.
• Switch caches the 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).
MAC Address Table
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0: 0260.8c01.1111
E0 E1
E2 E3DC
BA
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-5
How Switches Learn Host Locations
How Switches Learn Host Locations
• Station D sends a frame to station C.
• Switch caches the 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).
MAC Address Table
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0: 0260.8c01.1111E3: 0260.8c01.4444
E0 E1
E2 E3 DC
A B
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-6
How Switches Filter FramesHow Switches Filter Frames
• Station A sends a frame to station C.
• Destination is known; frame is not flooded.
E0: 0260.8c01.1111
E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0 E1
E2 E3
XXXX DC
A B
MAC Address Table
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-7
Broadcast and Multicast Frames
Broadcast and Multicast Frames
• Station D sends a broadcast or multicast frame.
• Broadcast and multicast frames are flooded to all ports other than the originating port.
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0 E1
E2 E3 DC
A B
E0: 0260.8c01.1111
E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444
MAC Address Table
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-8
Redundant Topology Redundant Topology
• Redundant topology eliminates single points of failure.
• Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems.
Segment 1
Segment 2
Server/Host X Router Y
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-9
Broadcast StormsBroadcast Storms
Segment 1
Segment 2
Server/Host X Router Y
Broadcast
Switch A Switch B
Host X sends a Broadcast
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-10
Broadcast StormsBroadcast Storms
Segment 1
Segment 2
Server/Host X Router Y
Broadcast
Switch A Switch B
Host X sends a Broadcast
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-11
Broadcast StormsBroadcast Storms
Segment 1
Segment 2
Server/Host X Router Y
Broadcast
• Switches continue to propagate broadcast traffic over and over.
Switch A Switch B
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-12
• Complex topology can cause multiple loops to occur.
• Layer 2 has no mechanism to stop the loop.
Server/Host
Workstations
Loop
Loop
Loop
Multiple Loop ProblemsMultiple Loop Problems
Broadcast
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-13
Solution: Spanning-Tree ProtocolSolution: Spanning-Tree Protocol
• Provides a loop-free redundant network topology by placing certain ports in the blocking state.
Blockx
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-14
Spanning-Tree Protocol Path Cost
Spanning-Tree Protocol Path Cost
Link Speed Cost (Reratify IEEE Spec) Cost (Previous IEEE Spec)----------------------------------------------------------------------------------------------------10 Gbps 2 11 Gbps 4 1100 Mbps 19 1010 Mbps 100 100
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-15
Blocking (20 Seconds)Listening (15 Seconds) Learning (15 Seconds)Forwarding
Spanning-Tree Port StatesSpanning-Tree Port States
• Spanning-tree transits each port through several different states:
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-16
• Primarily software based
• One spanning-tree instance per bridge
• Usually up to 16 ports per bridge
Bridging
• Primarily hardware-based (ASIC)
• Many spanning-tree instances per switch
• More ports on a switch
LAN Switching
Bridging Compared with LAN Switching
Bridging Compared with LAN Switching
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-17
Transmitting Frames Through a Switch
Transmitting Frames Through a Switch
Cut-Through
• Switch checks destination address and immediately begins forwarding frame.
Frame
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-18
Transmitting Frames Through a Switch
Transmitting Frames Through a Switch
Store and Forward
• Complete frame is received and checked before forwarding.
Cut-Through
• Switch checks destination address and immediately begins forwarding frame.
Frame FrameFrame F
rame
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-19
Transmitting Frames Through a Switch
Transmitting Frames Through a Switch
Cut-Through
• Switch checks destination address and immediately begins 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
• Complete frame is received and checked before forwarding.
Frame
Fram
e
Frame
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-20
Duplex OverviewDuplex Overview
Half Duplex (CSMA/CD)
• Unidirectional data flow• Higher potential for collision• Hubs connectivity
Switch
Hub
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-21
Duplex OverviewDuplex Overview
Half Duplex (CSMA/CD)
• Unidirectional data flow• Higher potential for collision• 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
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-22
Configuring the SwitchConfiguring the Switch
•Catalyst 1900 Switch–Menu-driven interface
–Web-based Visual Switch Manager
–Cisco IOS® CLI (command line interface)
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-23
Catalyst 1900 Series Default Configurations
Catalyst 1900 Series Default Configurations
• IP address: 0.0.0.0
• CDP: enabled
• Switching mode: fragment-free
• 100baseT port: autonegotiate duplex mode
• 10baseT port: half duplex
• Spanning tree: enabled
• Console password: none
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-24
Ports on the Catalyst 1900 Switch
Ports on the Catalyst 1900 Switch
Catalyst 1912 Catalyst 1924
10BaseT ports
AUI port
100BaseT uplink ports
e0/1 to e0/12 e0/1 to e0/24
e0/25 e0/25
fa0/26 (port A)fa0/27 (port B)
fa0/26 (port A)fa0/27 (port B)
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-25
Ports on the Catalyst 1900Switch (cont.)
Ports on the Catalyst 1900Switch (cont.)
wg_sw_d#sh run
Building configuration...Current configuration:!!interface Ethernet 0/1!interface Ethernet 0/2
wg_sw_d#sh span
Port Ethernet 0/1 of VLAN1 is Forwarding Port path cost 100, Port priority 128 Designated root has priority 32768, address 0090.8673.3340 Designated bridge has priority 32768, address 0090.8673.3340 Designated port is Ethernet 0/1, path cost 0 Timers: message age 20, forward delay 15, hold 1
wg_sw_a#show vlan-membership
Port VLAN Membership Type Port VLAN Membership Type ------------------------------------------------------------------ 1 5 Static 13 1 Static 2 1 Static 14 1 Static 3 1 Static 15 1 Static
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-26
Configuring the SwitchConfiguring the Switch
Configuration Modes• Global configuration mode – wg_sw_a# conf term
– wg_sw_a(config)#
• Interface configuration mode– wg_sw_a(config)# interface e0/1
– wg_sw_a(config-if)#
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-27
Configuring the Switch IP Address
Configuring the Switch IP Address
wg_sw_a(config)#ip address {ip address} {mask}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-28
wg_sw_a(config)#ip address 10.5.5.11 255.255.255.0
Configuring the Switch IP Address
Configuring the Switch IP Address
wg_sw_a(config)#ip address {ip address} {mask}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-29
wg_sw_a(config)# ip default-gateway {ip address}
Configuring the Switch Default Gateway
Configuring the Switch Default Gateway
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-30
wg_sw_a(config)#ip default-gateway 10.5.5.3
Configuring the Switch Default Gateway
Configuring the Switch Default Gateway
wg_sw_a(config)# ip default-gateway {ip address}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-31
Showing the Switch IP AddressShowing the Switch IP Address
wg_sw_a#show ip IP address: 10.5.5.11Subnet mask: 255.255.255.0Default gateway: 10.5.5.3Management VLAN: 1Domain name: Name server 1: 0.0.0.0Name server 2: 0.0.0.0HTTP server: EnabledHTTP port: 80RIP: Enabledwg_sw_a#
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-32
Showing Duplex OptionsShowing Duplex Options
wg_sw_a#sh interfaces
Ethernet 0/1 is EnabledHardware is Built-in 10Base-TAddress is 0090.8673.3341MTU 1500 bytes, BW 10000 Kbits802.1d STP State: Forwarding Forward Transitions: 1Port monitoring: DisabledUnknown unicast flooding: EnabledUnregistered multicast flooding: EnabledDescription:Duplex setting: Half duplexBack pressure: Disabled
Receive Statistics Transmit Statistics------------------------------------- -------------------------------------Total good frames 44841 Total frames 404502Total octets 4944550 Total octets 29591574Broadcast/multicast frames 31011 Broadcast/multicast frames 390913Broadcast/multicast octets 3865029 Broadcast/multicast octets 28478154Good frames forwarded 44832 Deferrals 0Frames filtered 9 Single collisions 0Runt frames 0 Multiple collisions 0No buffer discards 0 Excessive collisions 0 Queue full discards 0Errors: Errors: FCS errors 0 Late collisions 0 Alignment errors 0 Excessive deferrals 0 Giant frames 0 Jabber errors 0 Address violations 0 Other transmit errors 0
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-33
Duplex MismatchesDuplex 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 auto negotiation capability, causing the switch port to be in half-duplex mode.
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-34
wg_sw_a#show interfaces
Ethernet 0/1 is EnabledHardware is Built-in 10Base-TAddress is 0090.8673.3341MTU 1500 bytes, BW 10000 Kbits802.1d STP State: Forwarding Forward Transitions: 1Port monitoring: DisabledUnknown unicast flooding: EnabledUnregistered multicast flooding: EnabledDescription:Duplex setting: Half duplexBack pressure: Disabled
Receive Statistics Transmit Statistics------------------------------------- -------------------------------------Total good frames 44841 Total frames 404502Total octets 4944550 Total octets 29591574Broadcast/multicast frames 31011 Broadcast/multicast frames 390913Broadcast/multicast octets 3865029 Broadcast/multicast octets 28478154Good frames forwarded 44832 Deferrals 0Frames filtered 9 Single collisions 0Runt frames 0 Multiple collisions 0No buffer discards 0 Excessive collisions 0 Queue full discards 0Errors: Errors: FCS errors 0 Late collisions 0 Alignment errors 0 Excessive deferrals 0 Giant frames 0 Jabber errors 0 Address violations 0 Other transmit errors 0
FCS and Late Collision Errors
FCS and Late Collision Errors
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-35
Managing the MAC Address Table
Managing the MAC Address Table
wg_sw_a#show mac-address-table
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-36
Managing the MAC Address Table
Managing the MAC Address Table
wg_sw_a#sh mac-address-tableNumber of permanent addresses : 0Number of restricted static addresses : 0Number of dynamic addresses : 6
Address Dest Interface Type Source Interface List------------------------------------------------------------------00E0.1E5D.AE2F Ethernet 0/2 Dynamic All00D0.588F.B604 FastEthernet 0/26 Dynamic All00E0.1E5D.AE2B FastEthernet 0/26 Dynamic All0090.273B.87A4 FastEthernet 0/26 Dynamic All00D0.588F.B600 FastEthernet 0/26 Dynamic All00D0.5892.38C4 FastEthernet 0/27 Dynamic All
wg_sw_a#show mac-address-table
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-37
Setting a Permanent MAC Address
Setting a Permanent MAC Address
wg_sw_a(config)#mac-address-table permanent{mac-address type module/port}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-38
Setting a Permanent MAC Address
Setting a Permanent MAC Address
wg_sw_a(config)#mac-address-table permanent 2222.2222.2222 ethernet 0/3
wg_sw_a(config)#mac-address-table permanent{mac-address type module/port}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-39
Setting a Permanent MAC Address
Setting a Permanent MAC Address
wg_sw_a#sh mac-address-tableNumber of permanent addresses : 1Number of restricted static addresses : 0Number of dynamic addresses : 4
Address Dest Interface Type Source Interface List------------------------------------------------------------------00E0.1E5D.AE2F Ethernet 0/2 Dynamic All2222.2222.2222 Ethernet 0/3 Permanent All00D0.588F.B604 FastEthernet 0/26 Dynamic All00E0.1E5D.AE2B FastEthernet 0/26 Dynamic All00D0.5892.38C4 FastEthernet 0/27 Dynamic All
wg_sw_a(config)#mac-address-table permanent 2222.2222.2222 ethernet 0/3
wg_sw_a(config)#mac-address-table permanent{mac-address type module/port}
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-40
wg_sw_a#show version
Cisco Catalyst 1900/2820 Enterprise Edition SoftwareVersion V8.01.01Copyright (c) Cisco Systems, Inc. 1993-1998ROM: System Bootstrap, Version 3.03wg_sw_d uptime is 8day(s) 17hour(s) 53minute(s) 25second(s)cisco Catalyst 1900 (486sxl) processor with 2048K/1024K bytes of memoryHardware board revision is 1Upgrade Status: No upgrade currently in progress.Config File Status: File wgswd.cfg downloaded from 10.1.1.127 Fixed Ethernet/IEEE 802.3 interface(s)Base Ethernet Address: 00-90-86-73-33-40wg_sw_a#
show versionshow version
© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.1—6-41
Review QuestionsReview Questions
1. What function does the Spanning-Tree Protocol provide?
2. What are the different spanning-tree port states?
3. Describe the difference between full-duplex and half-duplex operations. What is the default duplex setting on the Catalyst 1900 switch 10-Mbps port and 100-Mbps port?
4. What is the default switching mode on the Catalyst 1900 switch?