Chabot College
ELEC 99.05
Ethernet Switches
CISCO NETWORKING ACADEMY
Ethernet Switch Basics
• Layer 2 device
• Uses MAC addressing to control traffic flow
• Supports multiple simultaneous
conversations
• Reduces needless LAN traffic
CISCO NETWORKING ACADEMY
Basics: Layer 2 Device
• Switch understands layer 2 addresses
(MAC addresses):
00-C0-F0-56-BD-98
CISCO NETWORKING ACADEMY
Basics: MAC Address Use
• Switch does not act like hub!
• Switch forwards frames based on
MAC address tables.
MAC Address
Table
A
B
C
D
G
H
I
CISCO NETWORKING ACADEMY
E
F
Basics: MAC Address Use
• Switch “learns” MAC addresses of hosts
connected to switch ports as it receives frames
from those ports:
MAC Address
Table
A
B
C
A
C
E
D
G H
G
H
I
CISCO NETWORKING ACADEMY
E
F
Basics: Multiple Data Paths
• Switch can create several simultaneous data
paths or “conversations”:
A
B
CISCO NETWORKING ACADEMY
C
D
E
F
G
I
Switches Reduce Needless
LAN Traffic
• Each switch port defines a collision domain.
• Users on hub A
only see traffic
from/to their
workgroup.
CISCO NETWORKING ACADEMY
Switch - 1 port per hub
Hub
Hub
Advanced Features
•
•
•
•
•
•
•
•
Switching matrix
Addressing
Multiple data rates
Full duplex
Port trunking
VLANs
Inter-switch communications
Modular Chassis
CISCO NETWORKING ACADEMY
Switching Matrix (Fabric)
• Store & Forward
– stores entire incoming frame in memory buffer
– performs error detection
– drops bad frames
– forwards good frames to destination port
based on MAC address
– takes time - “high latency”
CISCO NETWORKING ACADEMY
Switching Matrix (Fabric)
• Cut-through (cross-point)
– reads frame only as far as destination
address field
– immediately forwards all frames to destination
port based on MAC address
– no error checking; forwards bad frames
(usually not a serious problem)
– fast - “low latency” (“wire speed”)
CISCO NETWORKING ACADEMY
Addressing Capability
• 1 MAC address per port
– used with “port
switching”
– microsegmentation
CISCO NETWORKING ACADEMY
Switch - 1 port per PC
Addressing Capability
• 1 MAC address per port
– used with “port
switching”
– microsegmentation
• Multiple MAC addresses
per port
– used with “segment
switching”
CISCO NETWORKING ACADEMY
Switch - 1 port per PC
Switch - 1 port per hub
Hub
Hub
Multiple Data Transfer Rates
• Ports at 10mb/s and 100 mb/s
• Requires “flow control”
Server
Otherwise, a fast server
on a 100 mb port
could overflow the
buffer of a 10 mb port.
100
10 10 10 10 10 10 10
B
C
D
E
F
G
I
CISCO NETWORKING ACADEMY
Full Duplex Ports
• Ports can transmit & receive simultaneously.
• Useful mainly for servers.
• Possible only when there is one host per port
(no collisions).
• Modern NICs “auto-sense” a full-duplex
switch port
& turn on FD.
CISCO NETWORKING ACADEMY
Port Trunking
• Ports can “trunked” (linked together) to form a
high bandwidth channel between switches:
Campus
Core
Switch
300
Building
Switch
CISCO NETWORKING ACADEMY
Tiered Bandwidth
• Bandwidth can be placed where it is needed
most:
Campus
Core
Switch
300
Building
Switch
100
100
Workgroup Switch
10 10 10 10 10
D
E
F
G
I
CISCO NETWORKING ACADEMY
Workgroup Switch
10
10 10 10 10
J
K
L
M
N
VLANs
• Switch ports can be separated into groups
called VLANs (virtual LANs)
LAN1
D
E
same
as
LAN2
F
CISCO NETWORKING ACADEMY
G
I
J
VLAN1
D
E
F
VLAN2
G
I
J
VLANs
• Each VLAN forms a broadcast domain.
• Each VLAN is a separate Local Area Network
LAN1
D
E
same
as
LAN2
F
CISCO NETWORKING ACADEMY
G
I
J
VLAN1
D
E
F
VLAN2
G
I
J
VLANs
• VLAN can be cross-connected by routers.
(just like LANs)
LAN1
D
E
same
as
LAN2
F
CISCO NETWORKING ACADEMY
G
I
J
VLAN1
D
E
F
VLAN2
G
I
J
Inter-Switch Communication
• Vendor-specific frame technologies allow
switches to communicate.
• Cisco’s version is ISL (Inter Switch Link)
• Allows VLANs to span several switches.
• Hosts G, I, J, K are all part of VLAN 2:
VLAN1
D
E
CISCO NETWORKING ACADEMY
F
VLAN2
G
I
VLAN2
ISL
J
K
VLAN3
L
M
N
Modular Chassis
• Large switches often use a modular chassis
that accepts various:
– “switching engines”
– interface modules
– power supplies
• The Cisco Catalyst 5000 and 5505 are
examples used on the Chabot campus
CISCO NETWORKING ACADEMY
Catalyst 5000 Chassis
SD
POWER
115/230 VAC
9.8/4.9 A
60/50Hz
s
bp
0M
10 K
N
I
L
TXRX
TXRX
TXRX
TXRX
IX
MD
6
5
4
3
2
1
US
AT RX
ST
TXRX
s
bp
TXRX
9
IX
MD
SUPERVISOR ENGINE
1
0M
10 K
LIN
TXRX
TXRX
TXRX
TXRX
XX
TR
12
1%
11
CHD
0% WITOA
10
S L
10
T
SE
RE
8
1
N
FA
2
PS 1
PS
7
US
AT
ST
POWER
115/230 VAC
9.8/4.9 A
60/50Hz
TX
1
TXRX
TXRX
9
8
7
6
TXRX
TXRX
TXRX
TXRX
TXRX
ETHERNET SWITCHING MODULE
1
US 1-4
AT
ST
4
-2
21
0
-2
17
6
-1
13
12
9-
8
5-
1
ETHERNET SWITCHING
US 1-4
AT
ST
ETHERNET SWITCHING
CISCO NETWORKING ACADEMY
8
5-
12
9-
6
-1
13
0
-2
17
4
-2
21
XX
TR
12
TXRX
11
TXRX
10
TXRX
5
4
3
2
US
AT RX
ST
1
ETHERNET SWITCHING MODULE
TX