Ethernet Frame PreambleDestination Address Source Address Length/ Type LLC/ Data Frame Check Sequence.

Ethernet Frame

Preamble DestinationAddress

SourceAddress

Length/Type

LLC/Data

FrameCheck Sequence

Ethernet Addresses

48 bit normally shown in HEX

e.g.: 02-60-8C-44-59-E0 first 24 bits are obtained from IEEE by hardware manufacturers

one bit is used to distinguish unicast from multicast addresses

one bit is used to distinguish locally assigned addresses(rare) from globally assigned addresses (typical)

Transmission Types

Unicast - intended for one specific station Broadcast - intended for all stations Multicast - intended for a group of stations

CSMA/CD

Carrier Sense, Multiple Access with Collision Detection

Carrier sense - don't transmit if there is already a signal

Collision detection - if a collision is detected jam, wait, and retransmit

No Carrier

Transmission

Transmission

End of Transmission

Transmission

Second Transmission

Collision

Collision detected

Wait

Ethernet HUB(repeater)

• Layer 1 device

• Repeat signal on all ports

• Enforce collision on all segments (jam)

• Restore amplitude of the signal

• Retime the signal

• Single speed

• May mix media

Repeater Hub

Repeater Hubone station transmits

Repeater Hubsignal repeated on all other ports

Repeater Hubsignal repeated on all other ports

Repeater Hubend of transmission

Repeater Hub

Matrix Module

Collision Domain

• Devices connected by hubs

• Only one device can transmit at a time

• Collisions detected by all devices in the domain

Hub

Hub Hub

One Collision Domain

Broadcast Domain

• Devices connected by switches• Can contain multiple collision domains• One transmission in each collision domain• Collisions do not propagate between collision

domains• Broadcast frames do propagate to all collision

domains• Can be full duplex if only two devices in collision

domain and both devices are full duplex cabable

Switch

Hub Hub

Three Collision Domains

One Broadcast Domain

H – Ethernet Hub

S – Ethernet Switch

R – IP Router

W – Workstation

_____ Ethernet Segment

R

S

H

W

S

S

H

H

W

W

H

W WW

W WW

H – Ethernet Hub

S – Ethernet Switch

R – IP Router

W – Workstation

_____ Ethernet Segment

R

S

H

W

S

S

H

H

W

W

H

W WW

W WW

H – Ethernet Hub

S – Ethernet Switch

R – IP Router

W – Workstation

_____ Ethernet Segment

R

S

H

W

S

S

H

H

W

W

H

W WW

W WW

H – Ethernet Hub

S – Ethernet Switch

R – IP Router

W – Workstation

_____ Ethernet Segment

R

S

H

W

S

S

H

H

W

W

H

W WW

W WW

Ethernet switch

• Function (old name) “bridge”

• Forwards or Filters unicasts

• Floods (forwards to all ports) all broadcasts

• Learns address locations

• Can be full duplex if only two devices in collision domain and both devices are full duplex cabable

• Can mix speeds and media

switch

HubHubHub

E1 E2 E3 E4 E5 E6

1 2 3

DA SA Action

FF E2

E2 E3

E3 E2

FF E5

E5 E6

E6 E5

E4 E1

ADDRESS PORT

Switch Light Videos

• Switch Lights(3.5 MB)

• Switch Lights – more(5.9 MB)

Cut-Through Mode andStore and Forward Mode

• Cut-through mode– Switching mode in which switch reads a frame’s header and

decides where to forward the data before it receives the entire packet

– Can detect runts, or packet fragments

• Store and forward mode– Switching mode in which switch reads the entire data frame

into its memory and checks it for accuracy before transmitting it

Using Switches to Create VLANs

• Virtual local area networks (VLANs)– Means by which a

switch can logically group a number of ports into a broadcast domain

• Broadcast domain– Combination of ports

that make up a Layer 2 segment and must be connected to a Layer 3 device FIGURE 6-24 Simple VLAN design

Trunk Aggregation

Resilient Links

Higher-Layer Switches

• Switch capable of interpreting Layer 3 is called a Layer 3 switch

• Switch capable of interpreting Layer 4 is called a Layer 4 switch

• Higher-layer switches may also be called routing switches or application switches

Routers

• Multiport device• Can connect dissimilar LANs and WANs running

at different transmission speeds and using a variety of protocols

Router Features and Functions

• Filter out broadcast transmission to alleviate network congestion

• Prevent certain types of traffic from getting to a network• Support simultaneous local and remote activity• Provide high network fault tolerance through redundant

components• Monitor network traffic and report statistics to a MIB• Diagnose internal or other connectivity problems and trigger

alarms

Routers

FIGURE 6-26 Placement of routers on a LAN

Routing Protocols

• Means by which routers communicate with each other about network status– Convergence time

• The time it takes for a router to recognize a best path in the event of a change or outage

– Bandwidth overhead• Burden placed on an underlying network to support the

routing protocol

Routing Protocols

• RIP (Routing Information Protocol) for IP and IPX

• OSPF (Open Shortest Path First) for IP– Best path refers to the most efficient route from one

node on a network to another

• EIGRP (Enhanced Interior Gateway Routing Protocol) for IP, IPX, and AppleTalk

• BGP (Border Gateway Protocol) for IP

Gateways

• Combination of networking hardware and software that connects two dissimilar kinds of networks– E-mail gateway

– IBM host gateway

– Internet gateway

– LAN gateway