以太交換機(jī)原理講解

C

培不需要stp了,改為以太網(wǎng)工作原理以太網(wǎng)交換機(jī)原理中心機(jī)房數(shù)據(jù)專業(yè)李世發(fā)課程目標(biāo)通過本章的學(xué)習(xí),你可以有以下收獲:掌握交換機(jī)的工作原理和過程了解環(huán)路的危害了解交換機(jī)避免環(huán)路的方式目錄交換機(jī)的工作原理環(huán)路帶來的問題解決環(huán)路問題的方法交換機(jī)的工作原理Station

ASegment

A1/1Segment

B

1/2Station

BSlide1of1Purpose:Emphasize:Thenextfewslidesdiscussthebasicfunctionofabridge/switch.1.Howitlearnsthelocationofthehostsbyreadingthesourcemacaddressofincomingframes.2.Howitmakesforwarding/filteringdecisions.Threeconditionswhenaswitchwillfloodaframeoutonallportsexcepttotheportwheretheframecameinon:UnknownunicastaddressBroadcastframeMulticastframe3.HowSTPisusedtoavoidloopsinaswitched/bridgednetwork.交換機(jī)的三個功能地址學(xué)習(xí)轉(zhuǎn)發(fā)/過濾避免環(huán)路Slide1of1Purpose:Emphasize:The1900enmaxmacaddresstablesizeis1024.Oncethetableisfull,itwillfloodallnewaddressesuntilexistingentriesageout.Thecommandtochangethemacaddresstableagingtimeis:wg_sw_a(config)#mac-address-tableaging-time?<10-1000000>AgingtimevalueThedefaultis300sec.TheMACaddresstableisalsoreferredtoastheCAMtable(ContentAddressMemory)onsomeswitches.地址學(xué)習(xí)最開始的地址表是空的MAC地址表A:00d0.d001.1111C:00d0.d001.2222B:00d0.d001.3333D:00d0.d001.4444E0E1E2E3Slide

1

of

1Purpose:Emphasize:Station

A發(fā)送一個幀（frame）給StationC交換機(jī)從端口E0學(xué)習(xí)到station

A的MAC地址將該幀做“洪泛（flooding）”轉(zhuǎn)發(fā)。C:00d0.d001.2222B:00d0.d001.3333D:00d0.d001.4444MAC地址表E0:

00d0.d001.1111E0E1E2E3地址學(xué)習(xí)A:00d0.d001.1111Slide

1

of

1Purpose:Emphasize:

Once

C

replies,

the

switch

will

also

cache

station

C’s

MAC

address

to

port

E2

as

shown

in

the

next

slide.A:00d0.d001.1111B:00d0.d001.3333MAC地址表E0:

00d0.d001.1111E2:

00d0.d001.2222E0E1E2E3地址學(xué)習(xí)C:00d0.d001.2222 D:00d0.d001.4444StationC回應(yīng)一個幀（frame）給StationA交換機(jī)從端口E2學(xué)習(xí)到stationC的MAC地址Slide

1

of

1Purpose:Emphasize:過濾StationA發(fā)送一個幀（frame）給stationC目標(biāo)地址已經(jīng)知道,不再“洪泛”發(fā)送,直接從E2端口發(fā)送出去。A:00d0.d001.1111C:00d0.d001.2222B:00d0.d001.3333D:00d0.d001.4444E0E1E2XXE3MAC地址表E0:

00d0.d001.1111E2:

00d0.d001.2222E1:

00d0.d001.3333E3:

00d0.d001.4444Slide

1

of

1Purpose:Emphasize:A:00d0.d001.1111C:00d0.d001.2222B:00d0.d001.3333D:00d0.d001.4444MAC

address

table

E0:

00d0.d001.1111E2:

00d0.d001.2222E1:

00d0.d001.3333E3:

00d0.d001.4444E0

E1E2

E3廣播和多播幀Station

D發(fā)送一個廣播或多播幀（frame）給C

交換機(jī)將廣播（broadcast）或多播（multicast）幀“泛洪”轉(zhuǎn)發(fā)給其他所有端口（不包括進(jìn)來的那個端口)。課程大綱交換機(jī)的工作原理環(huán)路帶來的問題解決環(huán)路問題的方法Purpose:Thisisanintroductorygraphictotellstudentsthatredundantconnectionsintheswitchblockareverynecessaryinordertoprovidearedundant,fault-tolerantnetwork.WewillbediscussingthechallengesofredundantconnectionsinaLayer2networkandthesolutionstothosechallenges.Emphasize:Theinstructorshouldtakethestudentsthroughsomeofthepossiblescenariosthatareonthegraphic.Emphasizethepossibilitiesfordisasterifthephysicalredundancywasnotalreadyinplaceandhowthatisonlyapartialsolution.Bridgingandswitchingaretermsthatareusedinterchangeablyinthischapter.Forthepurposesofspanningtreetheyareconsideredtobethesamething.Transition:Wearegoingtostartwithanoverviewoftransparentbridgingandlookatwhathappenswhenaredundantlinkcausesaloop.AccessLayerDistributionLayerSW

1Link

ALink

BSW

2保證網(wǎng)絡(luò)的可靠性Slide

1

of

1Purpose:Emphasize:

Layer

2

has

no

mechanism(like

a

TTL)

to

stop

loops.Segment

1Server/host

XRouter

YSegment2在冗余拓?fù)渲?出現(xiàn)了環(huán)路（loop）冗余拓?fù)銼lide

1

of

1Purpose:Emphasize:

Layer

2

has

no

mechanism(like

a

TTL)

to

stop

loops.冗余拓?fù)銼egment

1Segment2環(huán)路（loop）帶來的問題:·廣播風(fēng)暴·幀的重復(fù)復(fù)制·交換機(jī)MAC地址表的不穩(wěn)定Server/host

XRouter

YSlide

1

of

3Purpose:Emphasize:

Broadcast

frames

are

flooded.Segment

1Server/host

XRouter

YBroadcastSwitch

ASwitch

BSegment

2Host

X發(fā)送一個廣播幀廣播風(fēng)暴Slide

2

of

3Purpose:Emphasize:Segment

1Server/host

XRouter

YBroadcastSwitch

ASwitch

BSegment

2Host

X發(fā)送一個廣播幀廣播風(fēng)暴Slide

3

of

3Purpose:Emphasize:

Layer

2

has

no

TTL

mechanismto

stop

loopingframes.Segment

1Server/host

XRouter

YBroadcastSegment

2交換機(jī)不斷的轉(zhuǎn)發(fā)該廣播幀Switch

ASwitch

B廣播風(fēng)暴Slide

1

of

2Purpose:Emphasize:

This

slide

assumes

Router

Y

Mac

address

has

not

been

learned

by

Switch

Aand

Switch

B

yet

so

the

unknown

unicast

frame

toRouter

Y

will

be

flooded.Segment

1Segment

2Server/host

XRouter

YUnicastSwitch

ASwitch

B復(fù)制出多個重復(fù)的幀Host

X發(fā)送一個單播幀到Router

Y

任何一臺交換機(jī)都沒有學(xué)到過Router

Y的MAC地址Slide

2

of

2Purpose:Emphasize:Segment

1Server/host

XRouter

YUnicastSwitch

ASwitch

BUnicastUnicast復(fù)制出多個重復(fù)的幀Segment

2Host

X發(fā)送一個單播幀到Router

Y任何一臺交換機(jī)都沒有學(xué)到過Router

Y的MAC地址Router

Y將收到兩個完全一樣的重復(fù)幀Slide

1

of

2Purpose:Emphasize:

This

slide

assumes

Router

Y

Mac

address

has

not

been

learned

by

Switch

Aand

Switch

B

yet

so

the

unknown

unicast

frame

toRouter

Y

will

be

flooded.Server/host

XRouter

YUnicastSegment

1UnicastSwitch

APort

0Port

1Port

0Switch

B

Port

1MAC地址表的不穩(wěn)定Segment

2Host

X發(fā)送一個單播幀到Router

Y任何一臺交換機(jī)都沒有學(xué)到過Router

X的MAC地址Switch

A和B從各自的port

0學(xué)到Router

X的MAC地址Slide

2

of

2Purpose:Emphasize:Segment

1Segment

2Server/host

XRouter

YUnicastUnicastSwitch

APort

0Port

1Port

0Switch

BPort

1MAC地址表的不穩(wěn)定任何一臺交換機(jī)都沒有學(xué)到過Router

Y的MAC地址該幀被洪泛（flooding）轉(zhuǎn)發(fā)Switch

A和B錯誤的從port

1學(xué)到Router

X的MAC地址Slide

1

of

1Purpose:Emphasize:環(huán)路問題面對這么多的環(huán)路，怎么辦？WorkstationsLoopLoopServer/hostLoopBroadcast課程大綱交換機(jī)的工作原理環(huán)路帶來的問題解決環(huán)路問題的方法環(huán)路解決辦法1:網(wǎng)絡(luò)結(jié)構(gòu)采用星型結(jié)構(gòu)組建交換網(wǎng)絡(luò),從根本上防范物理環(huán)路的產(chǎn)生BRAS園區(qū)交換機(jī):T40G/3228/3252/3206/3928/3952/3906等匯聚交換機(jī):T160G/T64G/T40GGEGEFE/GEIP城域網(wǎng)以太匯聚層用戶接入層駐地網(wǎng)DSLAM:8220/9210等FE/GESRPESlide1of1Purpose:Emphasize:Aloopedtopologyisoftendesiredtoprovideredundancy,butloopedtrafficisundesirable.TheSpanningTreeprotocolwasoriginallydesignedforbridges.Today,itisalsoappliedtoLANswitchesandroutersoperatingasabridge.STPensuresallbridgedsegmentsarereachablebutanypointswhereloopsoccurwillbeblocked.生成樹協(xié)議能夠發(fā)現(xiàn)并自動消除冗余網(wǎng)絡(luò)拓?fù)渲械沫h(huán)路。Blockx環(huán)路解決辦法2:生成樹協(xié)議

(Spanning-Tree

Protocol)加加4條條Slide1of1Purpose:Emphasize:ThethreegeneralruleswhendealingwithSTP:1.Onerootbridgepernetwork.TherootisthebridgewiththelowestBridgeID.Alltheportsontherootbridgearedesignatedports(forwarding).2.Foreverynonrootbridge,thereisarootport(forwarding).Therootportistheportwiththelowestaccumulatedpathcosttotherootbridge.3.Foreverysegment,thereisonlyonedesignatedport.Thedesignatedportforwardstrafficforthesegment.Thedesignatedporthasthelowestaccumulatedpathcosttotherootbridge.xDesignated

port

(F)Root

port

(F)Designated

port

(F)Nondesignated

port

(B)Root

bridgeNonroot

bridge100baseTSpanning-Tree的運(yùn)作10baseT1.選出一個根橋Root（rootbridge）2.在一個鏈路上選出指定端口DP（designatedport）3.在非根網(wǎng)橋上選出根端口RP（rootport) 4.未成為指定端口或根端口的端口被阻塞,即阻隔端口,Blocked(blockedport）。ABZXR10配置STPzte#

configure

terzte(config)#

spanning-tree

enablezte(config)#

spanning-tree

mode

sstp在全局配置模式下啟動生成樹協(xié)議STP配置生成樹協(xié)議的當(dāng)前模式為sstpSTP的配置實(shí)例ABC1211212Switch

AZXR10-A#

configure

tZXR10-A(config)#

spanning-tree

enableZXR10-A(config)#

spanning-tree

mode

sstpSwitch

BZXR10-B#

configure

tZXR10-B(config)#

spanning-tree

enableZXR10-B(config)#

spanning-tree

mode

sstpSwitch

CZXR10-C#

configure

tZXR10-C(config)#

spanning-tree

enableZXR10-C(config)#

spanning-tree

mode

sstpSTP的配置實(shí)例ZXR10-A(config)#show

spanning-tree

instance

0Spanning

tree

enabled

protocolMSTPRoot

ID:

Priority 32768;

Address

00d0.d0c2.0101Hello-Time 2sec;

Max-Age

20

secForward-Delay

15

sec;RegRootID:

PriorityBridgeID:

Priority32768;

Address

00d0.d0c2.010132768;

Address

00d0.d0c2.0101Hello-Time 2sec;

Max-Age

20

secForward-Delay

15

sec;

Max-Hops

20Message-Age

1

sec;

RemainHops

20Interface

Prio.NbrName

Port

ID

Cost

Sts

Role

LinkType

Boundfei_1/1

128.41fei_1/2

128.42200000

ForwardDesignated

p2p200000

Forward

Designated

p2pSSTPSSTPABC1211212ZXR10-B(config)#show

spanning-tree

instance

0Name PortID

Cost

Sts

Role

LinkType

Boundfei_1/1fei_1/2200000

Forward

Root

p2p200000

Forward

Designated

p2pSSTPSSTPZXR10-B(config)#show

spanning-tree

instance

0Name PortID

Cost

Sts

Role

LinkType

Boundfei_1/1128.41200000Forward

Rootp2p

SSTPfei_1/2128.42200000Discard

Alternatep2p

SSTPSTP的問題收斂速度慢 RSTP大型網(wǎng)絡(luò)中的分組問題 MSTP需要大量的計(jì)算,嚴(yán)重耗費(fèi)內(nèi)存、CPU資源環(huán)路解決辦法3:單端口環(huán)路檢測作用: 此功能能檢測到交換機(jī)下接的用戶或者交換機(jī)上的環(huán)回，從而對此端口進(jìn)行處理，避免因下面用戶或者設(shè)備的環(huán)回導(dǎo)致交換機(jī)廣播風(fēng)暴等異常，將影響限制到某個端口。單端口環(huán)路檢測的工作原理 交換機(jī)從某個端口發(fā)送一個檢測報(bào)文,如果這個檢測報(bào)文原封不動（或者僅打了一個tag頭）地從這個端口接收回來,說明這個端口存在環(huán)路,交換機(jī)將自動關(guān)閉該端口。單端口環(huán)路檢測的配置實(shí)例switchAswitchBFei_1/1ZXR10(config)#interface

fei_1/1ZXR10(config-if)#switchport

mode

trunkZXR10(config-if)#switchport

trunk

vlan

1-2ZXR10(config-if)#exitZXR10(config)#loop-detect

interface

f