local-area-network (lan) architecture department of computer science southern illinois university...

Local-Area-Network (LAN) Architecture

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2013

Dr. Hiroshi FujinokiE-mail: [email protected]

Switch & Router/000

CS 447 Networks and Data Communication

Switch and Routers

What are the difference between switches and routers?QUESTION

Application

Presentation

Session

Transport

Network

Data-Link

Physical

76

5

4

3

2

1 Repeater

Bridge

Router

Network Connecting Devices

Where is “switch”?

Switch

Switching Hub

Layer-3 Switch

Same

Switch & Router/001


Connecting Devices in LAN

• Bridge

• Router

• RepeaterLow level

High level

Switch & Router/002

IP addressNetwork-layer address

Datalink-layer address MAC address

Physical Ports

Routers: the network devices that forward (or drop) packets by software

Switches: the network devices that forward (or drop) packets by hardware

Simple Definitions

Information used for decision making


• Repeater = signal re-former (+ amplifier)

Input (segment 1) Output (segment 2)Repeater

LAN Segment 2LAN Segment 1

Repeater

One LAN segment

Signal with noise Clean signal

Repeater

Switch & Router/003


Repeater Hub

• Repeater Hub = a multi-port repeater

Ports

Internal shared bus

RepeaterBroadcast messages go through a hub (or Repeater)

Hub

Switch & Router/004

(Repeater-HUB)


• Bridge (switch) = a packet localizer (packet filter)

LAN 1 LAN 2

A B C X Y Z

1 2

Bridge

HOST PORT

A

B

C

X

Y

Z

1

1

1

2

2

2

Bridge (switch)

Switch & Router/005

Switching Table


LAN 1 LAN 2

A B C X Y Z

1 2

Bridge

Bridge Example: if A sends data to B

The bridge will NOT forward packet to LAN2

HOST PORT

A

B

C

X

Y

Z

2

2

2

1

1

1A tries to senddata to Host B

Switch & Router/006


LAN 1 LAN 2

A B C X Y Z

1 2

Bridge

The bridge will forward the packet to LAN2

A tries to senddata to Host Y

HOST PORT

A

B

C

X

Y

Z

2

2

2

1

1

1

Bridge Example: if A sends data to Y

Switch & Router/007


Bridge = a packet localizer (packet filter)

LAN 1 LAN 2

A B C X Y Z

1 2

Bridge

HOST PORT

A

B

C

X

Y

Z

1

2

A CData

Origin

Destination

A CDataA Z Data

A Z Data

Origin

Destination

Switch & Router/008


LAN 1 LAN 2

A B C X Y Z

1 2

Bridge

HOST PORT

A

B

C

X

Y

Z

1

2

Z X Data

Z X Data

Origin

Destination2

Bridge = a packet localizer (packet filter)

Switch & Router/009


Switching Hub

• Switching Hub = a multi-port bridge

Ports

Hub

Switch & Router/010

(Switching-HUB)

Multi-Port Bridge

SwitchingTable

A B C D E

AD BE


Router = intelligent packet forwarding device between two network domains

The problem of repeaters and bridges (what repeaters and bridges can’t do?)

Your destinations must be only one-hop away!

You

Repeater/Bridge

Your Destination

What if your destination is more than one-hop away?

Switch & Router/011

Your Destination

Internet

Request

ResponseRequest (1)

Response with tag (2)

Request (3)Response (4)

Internet

Request

Response

You

Internet

Request

ResponseRequest (1)

Response with tag (2)

Request (3)Response (4)

Internet

Request

Response

Network 1 Network N

Repeater/Bridge

?


Switch & Router/012

Receiver

Sender

Routers exchange routing tablesRouter

Network D

Network C

Network (= LAN or WAN) A

Network B

Router = intelligent packet forwarding device between two network domains


Switch and Routers

Now we know:

Layer-3 Switch

Switch

Router

Bridge

Repeater Switching Hub

Switch & Router/013


Switch and Routers

What is the definition of “switch”, then?

Network connecting device

Packet forwarding is performed by hardware

Cut-Through forwarding (not store-and-forward) forwarding

MAC-address is used as address

Switch & Router/014


MAC Frame

Switch and Routers

What is MAC address?

It’s a hardware address associated to each NIC

(usually hardwired in a ROM chip on a NIC)

The address used in Data-Link layer

Address deeply related to hardware

We can never change it!

Source MAC Address

Source MAC Address

Frame Preamble

Payload8 bytes6 bytes6 bytes64 - 1518 bytes

Switch & Router/015


Switch and Routers

MAC Address (48 bits)

8 bits 8 bits 8 bits 8 bits 8 bits 8 bits

Vendor ID Model # Serial #

http://www.cavebear.com/CaveBear/Ethernet/vendor.html

00 AA 00 47 4E 85

• 00 A0 24 – 3COM• 00 AA 00 -- Intel• 00 00 C0 -- SMC

• 47 – EtherExpress16 • 4E 85 = 20101th card

Switch & Router/016

What is MAC address? How does it look like?


Router

Router_Switch/017

Internal structure of typical router

CPURouting

AlgorithmRoutingTable

RoutingProtocol

Memory

Output Buffer

InputLines

OutputLines



• Definition of the procedure for how to calculate the best path

• Define what is “the best path”

Routing Algorithm

Routing Table

Routing Protocol

• Information the CPU uses to calculate the best path

• It’s implemented as software

• It’s data-structure (usually as “table” format)

• It’s software that constructs and maintains the routing table

• Routing protocol talks to other routers to collect the latest routing information in a network

• Entries in the routing table is network-layer addresses(e.g., IP addresses)

Router_Switch/018


Router


CPU

MemoryInputLines

OutputLines

RoutingAlgorithm

RoutingTable

RoutingProtocol

Router_Switch/019

IP address

DataProcedure


Layer-2 Switch (Bridge)

Internal structure of typical switch

Switching Fabric

Output Buffer

OutputLinesCrossbar switch, TDM switch,

Bus switch, etc.

SwitchControl Unit

InputLines

Switching Table

Short-Term-Buffer (STB)Router_Switch/020


• The component where frames are switched

• Usually implemented by hardware (e.g., crossbar switch and bus switch)

• Checks the packet header• Control switching fabric using the information in the switching table and the packet header

• Tells the switch control unit the correct output port• (Destination MAC Address) + (Output Port #)

STB

Switching Fabric

Switch Control Unit

Switching Table

• Temporary buffer


Router_Switch/021


Layer-2 Switch (Bridge)

InputLines

OutputLines

SwitchControl Unit

Switching Table

Router_Switch/022



SwitchControl Unit

Switching Table

Router_Switch/023

Port #1

Port #2

Port #3

Dest. MAC Port#

Sent to Host X

Copy destinationMAC Address

Host X

MAC=4A3D

4A3D 1

Switching FabricSTB



Layer-3 switches

Router_Switch/024

• Layer-3 switches

= Switches that use layer-3 information (IP address) for forwarding

• The network devices that perform forwarding are traditionally routers

Why not router any more?

- LAN speed keeps increasing

(10Mbps 100Mbps 1,000Mbps)

- Intra-LAN repeaters and switches have been doing a good job in keeping up to the speed (because they are hardware devices)

- Routers become throughput bottleneck

Let switches take care of (replace) routers


Layer-3 switches

Router_Switch/025

LAN Backbone

Leaf-levelEthernet

becomes faster

Routers become performance bottleneck


Layer-3 switches

Router_Switch/026

LAN Backbone

Internet/WAN

We still needa router here.

(why?)


Two different types of Layer-3 switches

- As core switches for virtual-circuit networks (ATM, FrameRelay)

Switching Router

Routing Switch

• It is a router that has built-in switch

• Route first and switch all the rest

• Typical applications:

• It is a switch that has built-in router

• It implements routing protocol (can communicate with other routers)

• Switches that know other networks (or sub-networks) more than one-hop away (this is the difference between L2 and L3 switches)

• It does not implement routing protocol(Routing table must be set up manually)

Router_Switch/027


Internal Structure of Switching Router

CPU RoutingAlgorithm

RoutingTable

RoutingProtocol

Memory SessionMngmnt

Switching Fabric

SW Ctrl UnitSwitchingTable

Router_Switch/028

Switch

Router


(For Virtual Circuit Packet Switching)


RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

SwitchingTable

Router_Switch/029

Internal Structure of Switching Router


Virtual Circuit

Sender S1 S2 Sn Receiver

Time

SignalingMessage

A transmitting station needs to set up a path firstPath set-upat switch S1

Router_Switch/030



RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

Signalingmessagearrived

STEP 1

SwitchingTable

Router_Switch/031



RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

STEP 2

Signalingmessage

stored at STB

SwitchingTable

Router_Switch/032

No switching entryFor this packet



RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

STEP 3

Signalingmessage

sent to memoryRouting willbe performedfor this packet

Router_Switch/033



RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

STEP 4

Router_Switch/034



RoutingTable

RoutingProtocol

Switching Fabric

Memory

SW Ctrl Unit

SessionMngmnt

STEP 5

DestinationHost Address

OutputPort #

SenderHost Address

OutputPort #

Router_Switch/035


Sender S1 S2 Sn Receiver

Path set-upat this switch Path set-up

at this switch Path set-upat this switch

SenderHost Address

OutputPort #

DestinationHost Address

OutputPort #

Router_Switch/036


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