Chabot College

ELEC 99.05

Ethernet Switches

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Ethernet Switch Basics

• Layer 2 device • Uses MAC addressing to control traffic flow • Supports multiple simultaneous conversations • Reduces needless LAN traffic

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Basics: Layer 2 Device

• Switch understands layer 2 addresses (MAC addresses): 00-C0-F0-56-BD-98

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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 E F G H I

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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 C E A B C D E F G H G H I

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Basics: Multiple Data Paths

• Switch can create several simultaneous data paths or “conversations”: A

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B 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.

Hub Switch - 1 port per hub Hub CISCO NETWORKING ACADEMY

Advanced Features

• Switching matrix • Addressing • Multiple data rates • Full duplex • Port trunking • VLANs • Inter-switch communications • Modular Chassis

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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”

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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”)

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Addressing Capability

• 1 MAC address per port – used with “port switching” – microsegmentation

Switch - 1 port per PC CISCO NETWORKING ACADEMY

Addressing Capability

• 1 MAC address per port – used with “port switching” – microsegmentation

Switch - 1 port per PC

• Multiple MAC addresses per port – used with “segment switching”

Hub Switch - 1 port per hub Hub CISCO NETWORKING ACADEMY

Multiple Data Transfer Rates

• Ports at 10mb/s and 100 mb/s • Requires “flow control” Otherwise, a fast server on a 100 mb port could overflow the buffer of a 10 mb port .

Server 100

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10 B 10 C 10 D 10 E 10 F 10 G 10 I

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.

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Port Trunking

• Ports can “trunked” (linked together) to form a high bandwidth channel between switches: Campus Core Switch 300 Building Switch

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Tiered Bandwidth

• Bandwidth can be placed where it is needed most: Campus Core Switch 300 Building Switch 100 100 Workgroup Switch

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10 D 10 E 10 F 10 G 10 I Workgroup Switch 10 J 10 K 10 L 10 M 10 N

VLANs

• Switch ports can be separated into groups called VLANs (virtual LANs) LAN1 LAN2 D E F G I J same as VLAN1 VLAN2 D E F G I J

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VLANs

• Each VLAN forms a broadcast domain.

• Each VLAN is a separate Local Area Network LAN1 LAN2 D E F G I J same as VLAN1 VLAN2 D E F G I J

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VLANs

• VLAN can be cross-connected by routers.

(just like LANs) LAN1 LAN2 D E F G I J

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same as VLAN1 VLAN2 D E F G I J

Inter-Switch Communication

• Vendor-specific frame technologies allow switches to communicate.

• Cisco’s version is ISL ( I nter S witch L ink) • Allows VLANs to span several switches.

• Hosts G, I, J, K are all part of VLAN 2: VLAN1 VLAN2 D E

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F G I ISL VLAN2 VLAN3 J K 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

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Catalyst 5000 Chassis

POWER 115/230 VAC 9.8/4.9 A 60/50Hz POWER 115/230 VAC 9.8/4.9 A 60/50Hz SD 1 ST AT US FA PS PS N 2 1 SUPERVISOR ENGINE RE SE T 10 0% SW IT CH LO AD 1% 1 2 3 1 ST AT US R X TX R X TX R X TX R X 1 ETHERNET SWITCHING MODULE 1 ST AT US R X TX R X 2 TX R X ETHERNET SWITCHING MODULE 3 TX X 4 4 TX R X TX R X 5 5 10 0M bp s LI NK M DI X 6 TX R X TX R X 7 TX R X 8 TX R X 9 10 0M bp s LI NK M DI X TX R X 1 0 TX R X 1 1 TX R X 1 2 TX TX X 6 TX R X 7 TX R X 8 TX X 9 TX X 1 0 TX X 1 1 TX X 1 2 TX 1 5 8 9 12 13 -1 6 17 -2 0 21 -2 4 ST AT US 1 4 1 ETHERNET SWITCHING 5 8 9 12 13 -1 6 17 -2 0 21 -2 4 ST AT US 1 4 ETHERNET SWITCHING

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