ch17.pp

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© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

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Computer Networks and Internets, 5e


By Douglas E. Comer

Lecture PowerPoints


By Lami Kaya, LKaya@ieee.org

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

2

Chapter 17



LAN
Uzantıları
:

Fiber Modems, Repeaters, Bridges,
ve

Switches

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

3

Topics Covered


17.1 Introduction


17.2 Distance Limitation and LAN Design


17.3 Fiber Modem Extensions



17.4 Repeaters


17.5 Bridges and Bridging


17.6 Learning Bridges and Frame Filtering


17.7 Why Bridging Works Well


17.8 Distributed Spanning Tree


17.9 Switching and Layer 2 Switches


17.10 VLAN Switches


17.11 Bridging Used with Other Devices


© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

4

17.1 Introduction


This chapter


discusses two important concepts: mechanisms that can extend a
LAN across a longer distance and LAN switching


introduces repeaters, bridges, and the spanning tree algorithm used
to prevent forwarding loops

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

5

17.2 Distance Limitation and LAN Design


Distance limitation is a fundamental part of LAN designs


When designing a network technology, engineers choose a
combination of factors that can be achieved at a given cost


Capacity


Maximum delay


Distance




Hardware is designed to emit a fixed amount of energy


if wiring is extended beyond the design limits


stations will not receive a sufficiently strong signal, and errors will
occur

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

6

17.2
Uzaklık sınırlaması ve LAN Dizaynı



Uzaklık sınırlaması LAN dizaynının temel bölümünü içerir


Ağ teknolojisini dizayn ederken, mühendisler verilen
maliyete göre kombinasyonların seçimini sağlamıştırlar


Kapasite


Ma
kimum gecikme


Uzaklık




Donanım sabit büyüklükteki enerjiyi yaymak için dizayn
edilmiştir


Eğer kablolama dizayn sınırlarının uzağına genişletilmişse


Birimler yeterince güçlü sinyaller alamazlar, ve hatalar oluşmaya
başlar

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

7

17.3 Fiber Modem Extensions


Extension mechanisms do not increase the signal strength


nor do they merely extend cables


Most extension mechanisms use standard interface


and insert additional hardware components that can relay signals
across longer distances


The simplest LAN extension mechanism consists of an
optical fiber and a pair of fiber modems


used to connect a computer to a remote Ethernet


Figure 17.1 illustrates the interconnection


Each of the fiber modems contains hardware to perform two chores:


accept packets over the Ethernet interface and send them over the optical
fiber


and accept packets that arrive over the optical fiber and send them over the
Ethernet interface

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

8

17.3 Fiber Modem Extensions


Genişletme mekanizması sinyal gücünü arttırmaz


Nede kabloları çok nadiren uzatmatır


Çoğu uzatma mekanizması standart arayüzünü kullanır


Ve ek donanım komponent’i ekler ve böylelikler sinyalleri daha uzun
mesafelere iletir


En basit LAN uzatma mekanizması optik fiber ve ikili fiber
modemleri içerir


Bilgisayarı uzaktaki ethernet’e bağlamak için kullanılır


Şekil

17.1
bu bağlantıyı şekillendirir


Her fiber modemlerinden biri iki küçük işi yapabilmek için donanım
gerektirir


accept packets over the Ethernet interface and send them over the optical
fiber


and accept packets that arrive over the optical fiber and send them over the
Ethernet interface

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

9

17.3 Fiber Modem Extensions

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

10

17.4 Repeaters


A
repeater

is an analog device used to propagate LAN
signals over long distances


A repeater does not understand packets or signal coding


Instead, it merely amplifies the signal received


and transmits the
amplified

version as output


Repeaters were used extensively with the original Ethernet,
and have been used with other LAN technologies


Recently, repeaters have been introduced with infrared receivers


to permit a receiver to be located at a longer distance from a computer


Consider a situation in which the infrared receiver for a cable
television controller must be in a different room than the controller


A repeater can extend the connection, as Figure 17.2
illustrates

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

11

17.4 Repeaters


Repeaterlar analog cihazlardır ve LAN sinyallerinin uzun
mesafelere iletilmesi için kullanılır


Repeater

paketten yada sinyalden anlamaz


Bunun yerine, nadiren alınan sinyali amplify eder


and transmits the
amplified

version as output


Repeaterlar orjinal Ethernette çok kullanılır, ve diğer LAN
teknolojilerinde kullanılır


Nadiren, Repeaterlar infrared alıcılar ile birleştirilir


to permit a receiver to be located at a longer distance from a computer


Consider a situation in which the infrared receiver for a cable
television controller must be in a different room than the controller


Repeaterlar bağlantıyı genişletir, Şekil 17.2 de
şekillendirilmiştir

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

12

17.4 Repeaters

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13

17.5 Bridges and Bridging


A
bridge
is a mechanism that connects two LAN segments


The bridge listens in
promiscuous

mode on each segment


i.e., receives all packets sent on the segment


When it receives an intact frame from one segment


the bridge forwards a copy of the frame to the other segment


Two LAN segments connected by a bridge appear to
behave like a
single LAN


a computer connected to either segment can send a frame to any
computer on the both segments


A broadcast frame is delivered to all computers


Thus, computers do not know whether they are connected to a single
LAN segment or a bridged LAN


Figure 17.3 illustrates the conceptual architecture

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

14

17.5 Bridges and Bridging


İki LAN segment’ini birleştirmek için kullanılan mekanizmaya
bridge

denir


Bridge

her segment’i karmakarışık mod’u dinler


Mesela, alıcı aldığı bütün paketleri segment şeklinde gönderir


Geldiği zaman bozulmamış frame bir segmentten alınır


Bridge frame’in kopyasını diğer segment’e iletir


İki LAN segmenti bridge’ı bağlar ve tek bir LAN gibi görünür


a computer connected to either segment can send a frame to any
computer on the both segments


Broadcast frame’i bütün bilgisayalara iletir


Böylelikle, bilgisayarlar tek LAN segment’i ile bağlantısını bilmez
yada bridge LAN


Şekil

17.3

bu kavramsal mimariyi gösterir

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

15

17.5 Bridges and Bridging

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16

17.6 Learning Bridges and Frame
Filtering


Bridges do not
blindly

forward a copy of each frame from
one LAN to another


Instead, a bridge uses MAC addresses to perform
filtering


A bridge examines the destination address in a frame


and does not forward the frame onto the other LAN segment unless
necessary


If the LAN supports broadcast or multicast


the bridge must forward a copy of each broadcast or multicast frame



to make the bridged LAN operate like a single LAN


How can a bridge know which computers are attached to
which segments?


Most bridges are called
adaptive

or
learning bridges


because they learn the locations of computers automatically


To do so, a bridge uses source addresses

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

17

17.6 Learning Bridges and Frame
Filtering


Köprüler her çerçevenin kopyasını
körce

bir LANdan
diğerine forwardlamaz



Onun yerine MAC adresleri kullanarak
filtreleme

yaparlar


Köprü varış adresine bakar


Ve gerekmedikçe çerçeveyi başka LAN segmentine göndermez


Eğer LAN broadca
st
ya da

multicast
i destekliyorsa


köprübroadcas
t or multicast
çerçeveyi göndermelidir


Köprü olan LANı sanki tek

LAN
mış gibi işletmek için


Köprü hangi bilgisayarların hangi bölümde olduğunu nasıl
bilir?



Çoğu köprü
adapti
f

yada

öğrenen köprüdür



Çünkü bilgisayarların yerini otomatik öğrenirler


Böyle yapmak için köprü kaynak adreslerini kullanır.

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

18

17.6 Learning Bridges and Frame
Filtering


When a frame arrives from a given segment


the bridge
extracts

the
source address
from the header


and
adds

the address to a list of computers attached
to the segment


Bridge must then extract the MAC address from the frame


and use the address to determine whether to forward the frame


A bridge
learns

that a computer is present on a segment as
soon as the computer transmits a frame


Consider the bridge in Figure 17.3


Consider also Figure 17.4, which


lists a sequence of packet transmissions


the location information that the bridge has accumulated at each step


and the disposition of the packet


(i.e., the segments over which the packet is sent)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

19

17.6 Learning Bridges and Frame
Filtering


When a frame arrives from a given segment


the bridge
extracts

the
source address
from the header


and
adds

the address to a list of computers attached
to the segment


Bridge must then extract the MAC address from the frame


and use the address to determine whether to forward the frame


A bridge
learns

that a computer is present on a segment as
soon as the computer transmits a frame


Consider the bridge in Figure 17.3


Consider also Figure 17.4, which


lists a sequence of packet transmissions


the location information that the bridge has accumulated at each step


and the disposition of the packet


(i.e., the segments over which the packet is sent)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

20

17.6 Learning Bridges and Frame
Filtering


Bir çerçeve bir bölümden geldiğinde


Bridge header’dan kaynak adresi çıkarır


Ve ulaşılan segmentlerde adreslerine listedeki bilgisayarları ekler


Bridge MAC adresini frame’den çıkarmak zorundadır


Ve bu adresi kullanarak frame’in iletileceği yere iletir


Bridge, bilgisayar frame gönderiri göndermez bilgisayarı
öğrenir


Şekil 17.3 teki bridge’ı hesaba katın


Paket iletimlerini sıralama listesini


Bridge her adımda Yer bilgisi biriktirir


Ve paket işleme durumunu gösterir

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

21

17.6 Learning Bridges and Frame Filtering

Fig 17.3

Fig 17.4

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22

17.7 Why Bridging Works Well


A
bridged network
can exhibit higher overall performance than
a single LAN


A bridge permits simultaneous transmission on each segment


In Figure 17.3, for example


computer
A

can send a packet to computer
B



at the same time computer
X

sends a packet to computer
Y


Although it receives a copy of each packet


the bridge will not forward either of them


because each packet has been sent to a destination on the same segment as
the source


the bridge merely

discards
the two frames without forwarding them


A bridge permits simultaneous activity on attached segments


a pair of computers on one segment can communicate at the same
time as a pair of computers on another segment

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

23

17.7 Why Bridging Works Well


Bridge ağları tek bir LAN ten daha yüksek performans ortaya
koyabilir


B
ridge

her segment için eş zamanlı iletimi kabul eder


Şekil 17.3 te, mesela


A bilgisayarı B bilgisayarına paket gönderebilir


Aynı zamanda X bilgisayarı Y bilgisayarına paket gönderebilir


He paketin bir kopyasını almasına rağmen


the bridge will not forward either of them


because each packet has been sent to a destination on the same segment as
the source


Bridge iki frame’i nadiren atar, onları iletmeden


Ulaşılan segmentlere, bridge eş zamanlı activiteye izin verir


Her segmentteki Bilgisayar çifti eş zamanlı iletişim kurabilir

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

24

17.8 Distributed Spanning Tree


Şekil 17.5 teki şekli düşünün(aşağıdaki)


Şekil dört LAN segmentlerinin aynı anda üç bridge’e bağlandığını
gösteriyor


Biz bilgisayarların hublara bağlandığını farzediyoruz


© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

25

17.8 Distributed Spanning Tree


Before the fourth bridge is inserted


the network operates as expected


any computer can send a unicast frame to another computer


or send a broadcast or multicast frame to all computers


If a fourth bridge is inserted


a problem arises because a
loop

will exist


Unless at least one bridge is prevented from forwarding
broadcasts


copies of a broadcast frame will continue to flow around the
cycle

forever


And computers attached to hubs will receive many copies


To prevent cycles, a
Distributed Spanning Tree

(DST) is used


the algorithm views bridges as nodes in a graph


and imposes a
tree

on the
graph

(a tree is a graph that does not
contain cycles)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

26

17.8 Distributed Spanning Tree


Dördüncü bridge araya eklenmeden önce


Ağ işlendiği gibi çalışır


any computer can send a unicast frame to another computer


or send a broadcast or multicast frame to all computers


Eğer dördüncü bridge eklendiği zaman


Problem meydana geliyor çünkü loop (halka) oluşuyorsa


İletim broadcastlerden en az bir bridge önlenmedikçe


Broadcast edilen frame kopyaları döngü etrafında sonsuza kadar
döner durur


Ve hublara ulaşan bilgisayarlar frame’in çok kopyasını alırla


Dögüyü önlemek için,
Distributed Spanning Tree

(DST)

kullanılır


Algoritma brigleri graftaki node olarak görürler


Ve graf’a ağaç’ı empoze eder (tree aynı anda graftır, fakat döngü
içermez)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

27

17.8 Distributed Spanning Tree


The original (DEC in 1985) was designed for Ethernet
networks


known as
Spanning Tree Protocol

(STP)


STP consists of three steps:



Root

election


bridges multicast a packet that contains their
bridge ID
, and the bridge with
the smallest ID is chosen


To permit a manager to control the election, a bridge ID consists of two
parts: a

16
-
bit
configurable
priority number
and a
48
-
bit MAC
address



Shortest path
computation


Each bridge computes a shortest path to the root bridge.


Links included in the shortest paths of all bridges form the spanning tree


Forwarding


An interface that connects to the shortest path is
enabled

for forwarding
packets; an interface that does not lie on the shortest path is
blocked,


In STP, Ethernet bridges communicate amongst themselves
using a multicast address that is reserved for STP

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

28

17.8 Distributed Spanning Tree


Orjinal’i Ethernet ağlarına göre dizayn edilmiştir (1985 te)


Spanning Tree Protocol

(STP)

olarak bilinir


STP üç adım içerir:


Root (Kök) Seçimi


bridges multicast a packet that contains their
bridge ID
, and the bridge with
the smallest ID is chosen


To permit a manager to control the election, a bridge ID consists of two
parts: a

16
-
bit
configurable
priority number
and a
48
-
bit MAC
address


En Kısa yol’un hesaplanması


Each bridge computes a shortest path to the root bridge.


Links included in the shortest paths of all bridges form the spanning tree


İletim


An interface that connects to the shortest path is
enabled

for forwarding
packets; an interface that does not lie on the shortest path is
blocked,


STP’de, Ethernet bridge’ler kendi aralarında STP’lere tahsis
edilmiş multicast adresleri üzerinden haberleşirler

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

29

17.8 Distributed Spanning Tree


Variations of STP have been designed and standardized


IEEE created a standard named
802.1d
(in 1990)


the standard was updated in 1998


IEEE standard 802.1q provides a way to run STP on a set of
logically independent networks


that share a physical medium without any confusion or interference


Cisco created a proprietary version of STP,
Per
-
VLAN
Spanning Tree

(PVST) for use on a VLAN switch


IEEE standard 802.1w introduced the
Rapid STP

(RSTP)
has been incorporated in 801.1d
-
2004 (in 1998), and now
replaces STP, some versions are


Multiple Instance STP (MISTP)


Multiple STP (MSTP)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

30

17.8 Distributed Spanning Tree


STP’nin Değişik versiyonları tasarlanmış ve standartlaşmıştır


IEEE
802.1d
(in 1990)

standartını oluşturmuştur


Ve standart 1998’de güncellenmeştir


IEEE standartında
802.1q

STP’in mantıksal bağımsız ağlar üzerinde
çalışabilecek yolu vardır


Aynı fiziksel ortam’ı herhangi bir karışıma maruz kalmadan ve kafa
karışıklığına sebebiyet vermeden paylaşır


Cisco STP’nin tescilli versiyonunu oluşturmuştur,
Per
-
VLAN Spanning
Tree

(PVST)
VLAN switch’lerinde kullanılacak şekilde


IEEE standart’ı
802.1w
de
Rapid STP

(RSTP)

tanıtmıştır, ve
801.1d
-
2004

birleştirilmiştir (1998 de), ve şimdi STP ile yer değiştirmiştir , ve
bazı versiyonları şunlardır


Multiple Instance STP (MISTP)


Multiple STP (MSTP)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

31

17.9 Switching and Layer 2 Switches


An
Ethernet switch
, sometimes called a
Layer 2 switch
is an
electronic device that resembles a hub


a switch provides multiple ports that each attach to a single computer


and a switch allows computers to send frames to one another


The difference between a hub and a switch arises from the
way the devices operate:


a hub operates as an analog device that forwards signals among
computers


while a switch is a digital device that forwards packets


We can think of a hub as simulating a shared transmission medium


We think of a switch as simulating a bridged network that has one
computer per LAN segment


Figure 17.6 illustrates the conceptual use of bridges in a
switch


© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

32

17.9 Switching and Layer 2 Switches


Ethernet switch

bazen Layer 2 switch (2 katman switch’i) olarak
adlandırılır, ve bu elektronik cihaz hubları birleştirir


Bağlanan her bilgisayara bir port ayırımı yapar, ve br çok port girişi mevcuttur
switch’te


Ve
switch
bilgisayarların diğer bilgisayarlara frame göndermelerine izin verir


Hub ile switch arasındaki fark, çalışmış oldukları ortamlar arası farklılık
gösterir


Hub analog cihaz olarak çalışır ve bilgisayarlar arasında sinyaleri iletir


Switch dijital bir cihazdır ve paketleri iletir


Biz hub’ı paylaşılan iletim ortamı olarak düşünebiliriz


Switch’i de ağlar arasında bir köprü (bridge) olarak görebiliriz, ve her LAN
segmentinde bir bilgisayar olduğunu farzedin


Şekil
17.6

switch’in köprü şeklinde kavramsal kullanımını gösterir

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33

17.9 Switching and Layer 2 Switches

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34

17.9 Switching and Layer 2 Switches


A switch does not contain separate bridges


a switch consists of an
intelligent interface

attached to each port


and a
central fabric
that provides simultaneous transfers


An interface contains


a processor, memory, and other hardware needed to accept a packet


consult a forwarding table


and send the packet across the fabric to the correct output port


An interface can buffer arriving packets when an output port is busy


Figure 17.7 illustrates the architecture


Physically, switches are available in many sizes (ports)


Advantage of using a switched LAN instead of a hub is parallelism


Although a hub can only support one transmission at a time


a switch permits
multiple transfers
to occur at the same time, provided the transfers are
independent

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

35

17.9 Switching and Layer 2 Switches


Switch, ayrı bridgeler içermez


Switch

akıllı arayüzler içerir ve bu arayüzler her port’a ulaşabilir


Ve merkezi kumaştır, eşzamanlı transferler gerçekleştirir



Arayüz şunları içerir


İşlemci, hafıza, ve paket kabul etmek için gereken diğer donanım


Ve paketi doğru yer üzerinden doğru çıkış portuna gönderir



Arayüz gelen paketleri çıkış portları meşgulken buffer’layabilir



Şekil
17.7
bu mimariyi gösterir


Fiziksel olarak, switchler herhangi büyüklükte olabilir (port sayısı olarak)



LAN’da hub yerine switch kullanmanın avantajı
paralellik
tir


Hub’ın aynı anda sadece bir iletim yapabilme özelliğine rağmen


Switch bir sürü transferi aynı anda destekleyebilir

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36

17.9 Switching and Layer 2 Switches

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37

17.10 VLAN Switches


Virtual Local Area Network (VLAN) switches


The concept is straightforward:


allow a manager to configure a single switch to emulate multiple,
independent switches


A manager can specify a set of ports on the switch and
designates them to be on virtual LAN 1


designates another set of ports to be on virtual LAN 2, and so on


When a computer on virtual LAN 2 broadcasts a packet


only those computers on the same virtual LAN receive a copy


(i.e., once configured, a VLAN switch
makes it appear
that there are
multiple switches
)

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

38

17.10 VLAN Switches


Virtual Local Area Network (VLAN) switches


Konsept olarak açıktır:


Sistem sorumlusunun tek bir
switch
konfigüre ederek birden çok
switch’i taklit ederbilir


Sistem sorumlusu switch üzerinden port kümesi
tanımlayabilir ve bunları sanal LAN 1 olması için dizayn
edebilir


Diğer port kümesini de sanal LAN 2 olarak ta atayabilir, böyle devam
edebilir


Sanal LAN 2 deki bir gisayar paket’ini broadcast ettiği
zaman


Sadece aynı sanal LAN daki bilgisayarlar paketin kopyasını alır


( mesela bir kere düzenler, VLAN
switch

bir sürü
switch

gibi görünür
ve iş görür )

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39

17.10 VLAN Switches


Dividing computers into separate
broadcast domains
does
not appear important


until one considers a large company or a service provider


In each case, it may be important to guarantee that a set of
computers can communicate


without others receiving the packets and without receiving packets
from outsiders


For example, a company may choose to provide a firewall
between computers in the CEO's office and other computers
in the company

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

40

17.10 VLAN Switches


Bilgisayarları farklı broadcast domainlerine bölmek önemli
görünmeyebilir


Taki bir tanesi büyük bir şirket veya servis sağlayıcısı olarka
düşünüldüğünde


Her durumda, bazı bilgisayar kümelerinin haberleşebiliyor
olması önemli olabilir


Diğerlerinin paketleri almaması ve dışarıdaki bilgisyarlardan da paket
alınmaması


Mesela, şirket CEO’ların offisi ile diğer bilgisayarlar arasında
firewall desteği sağlamayı düşünüyor ve istiyorsa