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L2 Switching Overview. 主讲:孟宁 电话:0512-68839302 E-mail:[email protected] 主页:http://staff.ustc.edu.cn/~mengning 地址:苏州工业园区独墅湖高等教育区仁爱路166号明德楼A302室. 2009年12月. Content. OSI Protocol Stack Network Device Packet Flow Physical Layer Auto Negotiation MII Registers Frame Format Bridging

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L2 switching overview

L2 Switching Overview

主讲:孟宁

电话:0512-68839302

E-mail:[email protected]

主页:http://staff.ustc.edu.cn/~mengning

地址:苏州工业园区独墅湖高等教育区仁爱路166号明德楼A302室

2009年12月


Content
Content

  • OSI Protocol Stack

  • Network Device

  • Packet Flow

  • Physical Layer

  • Auto Negotiation

  • MII Registers

  • Frame Format

  • Bridging

  • Question

  • Reference


Osi protocol stack
OSI Protocol Stack

Application (Message/Stream)

Providing user-application services and procedures

OSI7

Presentation

Arranging data in a mutually agreed format such as

data encryption and data compression

OSI6

Session

Controlling process communication responsible for

buffering, and synchronization

OSI5

Transport (Segment/Datagram)

Proposing end to end control about partitioning and

reassembling messages

OSI4

Network (Packet)

Supporting routing services for transferring user

packet data and network management data

OSI3

Data Link (Frame)

Organizing frame format; provides flow initialization,

flow control, flow termination and error control

OSI2

Physical (Bits)

Transferring data bits across link; defines physical

characteristics of media

OSI1


Network device 1
Network Device(1)

OSI7

OSI7

OSI6

OSI6

OSI5

OSI5

OSI4

OSI4

OSI3

OSI3

OSI2

OSI2

OSI1

OSI1

OSI1

Hub/Repeater


Network device 2
Network Device(2)

OSI7

OSI7

OSI6

OSI6

OSI5

OSI5

OSI4

OSI4

OSI3

OSI3

OSI2

OSI2

OSI2

OSI1

OSI1

OSI1

Bridge/Switch


Network device 3
Network Device(3)

OSI7

OSI7

OSI6

OSI6

OSI5

OSI5

OSI4

OSI4

OSI4

OSI3

OSI3

OSI3

OSI2

OSI2

OSI2

OSI1

OSI1

OSI1

Router/Router Switch


Packet flow
Packet Flow

Telnet FTP POP I MAP SMTP HTTP SNMP

( Presentation Format )

( Session Control )

Email: POP, IMAPSMTP

HTTP: WWW

FTP: File Transfer Protocol

Telnet: Remote Login

SNMP: Network Management

ARP: Address Resolution for MAC

Address based on IP Address

RARP: Address Resolution for IP

Address based on MAC Address

TCP UDP

ICMP

IP ARP RARP

Ethernet FDDI Token Ring Token Bus

Coaxial Cable Twisted Pair Optical Fiber


Physical layer twisted pair 1

PC

Hub

Switch

Router

PC

Hub

Switch

Router

Physical Layer -Twisted Pair(1)

  • Crossover

    • Data Circuit Equipment (DCE)

    • Data Terminating Equipment (DTE)

    • MDI-II/MDI-X


Physical layer twisted pair 2
Physical Layer -Twisted Pair(2)

  • Cable type

Category

Transfer Rate

Description

CAT 1

< 4 Mbps

Voice

CAT 2

Voice and Data

4 Mbps

10 Mbps

Ethernet

CAT 3

CAT 4

Token Ring

16 Mbps

CAT 5

Fast Ethernet

100 Mbps

1 Gbps

CAT 5e

Gigabit Ethernet

1 Gbps

Gigabit Ethernet

CAT 6


Physical layer layout
Physical Layer - Layout

Signal/Pin

TX_CLK

RX_CLK

TX_EN

TXD<3:0>

TX_ER

RX_DV

RXD<3:0>

RX_ER

CRS

COL

MDC

MDIO

LLC

MAC

MII/GMII

即媒体独立接口

PHY (Physical Layer Interface )

IEEE802.3ab


Auto negotiation
Auto Negotiation

  • AN is an optional standard function defined in the 1998 IEEE 802.3 specification.

  • Its purpose is to enable device interface to achieve their highest possible mode of operation over a line segment.

  • It does this by providing a means for the interfaces to exchange information about their capability (such as speed and duplex) over a link.

  • PHY transceiver uses MII to store information about its capability.


Mii registers
MII Registers

  • 32 PHY registers

  • 16-bit value of each register

  • Register table


Frame format 1
Frame Format(1)

Ethernet

Trailer

Ethernet

Trailer

Ethernet Payload

Ethernet Payload

Ethernet Header

Ethernet Header

7 bytes 1 byte 6 bytes 6bytes 2bytes < 1500 bytes 4 bytes

Preamble

Preamble

Delimiter

Delimiter

DA

DA

SA

SA

Type

Type

CRC

CRC

Upper Layer Protocol ( ULP )

Upper Layer Protocol ( ULP )

Maximum Frame size 1518 bytes

Minimum Frame size 64 bytes

Maximum Frame size 1518 bytes

Minimum Frame size 64 bytes

DA: Destination Address

SA: Source Address

Type: EtherType

CRC: Cyclic Redundancy Check

DA: Destination Address

SA: Source Address

Type: EtherType

CRC: Cyclic Redundancy Check


Frame format 2
Frame Format(2)

7 bytes

Preamble: 1010 1010 . . . 1010 1010

Purpose: achieve receiver synchronization with sender

1 byte

Delimiter: 1010 1011

Purpose: denote frame starting point


Frame format 3

A

B

C

Frame Format(3)

DA: MAC Address

SA: MAC Address

( MAC: Media Access Control )

DA SA

mac_c mac_a

mac_a mac_c

mac_a

mac_c

mac_b


Frame format 4
Frame Format(4)

Vendor ID

( e.g. Cisco 00:00:0c )

Serial No

6 bytes

Note: 1. MAC address saved in NIC for PC should not be modified by user.

It is created by NIC vendor.

2. For network device such as bridge or router, it is saved in NVRAM.

There exist a distinct MAC address for each bridge ( or router ) port.


Frame format 5
Frame Format(5)

ICMP

OSI 3

IP

ARP

RARP

Ethernet

OSI 2

EtherType = 0800 for IP

EtherType = 0806 for ARP

EtherType = 8035 for RARP


Bridging
Bridging

  • Filtering Database

  • Forwarding Algorithm

  • Learning Algorithm

  • Operation Process


Filtering database

E

(DA or SA )

Age

MAC Address

Corresponding Port

A 2 53

B 2 40

1

C 2 9

B

D 2 100

2

E 1 65

(DA or SA )

Age

MAC Address

Corresponding Port

A 3 100

1

B 1 65

C 2 44

2

3

D 3 96

E 1 29

C

D

A

Filtering Database


Forwarding algorithm

X equal to

Corresponding Port

Start

Receive frame from incoming port X

DAin

Filtering Database

no

Broadcastincoming frame

to all ports except for X

yes

yes

Filtering

incoming frame

no

Forward incoming frame to

Corresponding Port

End

Forwarding Algorithm


Learning algorithm

Start

SA in

Filtering Database

yes

Reset Age to Default Age

no

Write SA、X and Default Age

into Filtering Database

End

Learning Algorithm


Operation process 1

C

B

A

E

D

Operation Process(1)

Ethernet Header

Ethernet Frame

DA

SA

port

port

port

MAC

MAC

MAC

I

II

III

2

2

3

1

1

1

2


Operation process 2

D

B

A

C

E

A

D

D

D

A

A

A

A

A

A

A

A

A

D

E

E

B

B

B

B

E

B

C

C

C

C

E

C

E

port

port

port

MAC

MAC

MAC

D

I

II

III

2

2

3

1

1

1

2

Operation Process(2)

B -> D

C -> A

E -> A

B 2

B 2

B 1

C 2

C 1

C 1

E 2

E 2

E 3


常见二层协议

  • VLAN 虚拟局域网

  • STP 生成树协议 - RSTP MSTP

  • LA 链路聚合,也称为trunking

  • IGMP Snooping 多播组的二层支持

  • PNAC 基于端口的认证802.1X

  • ......



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