© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.1 Computer Networks and Internets, 5e By Douglas E. Comer Lecture PowerPoints By Lami Kaya,

© 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 VLAN Switches Bridging Used with Other Devices

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved 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 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 Uzaklık sınırlaması ve LAN Dizaynı Uzaklık sınırlaması LAN dizaynının temel bölümünü içerir Ağ teknolojisini dizayn ederken, mühendisler verilen maliyete göre kombinasyonların seçimini sağlamıştırlar Kapasite Makimum 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 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 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 Fiber Modem Extensions

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

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

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved 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 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 broadcast ya da multicasti destekliyorsa –köprübroadcast or multicast çerçeveyi göndermelidir Köprü olan LANı sanki tek LANmış gibi işletmek için Köprü hangi bilgisayarların hangi bölümde olduğunu nasıl bilir? –Çoğu köprü adaptif 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 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 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 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 Learning Bridges and Frame Filtering Fig 17.3 Fig 17.4

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved 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 Why Bridging Works Well Bridge ağları tek bir LAN ten daha yüksek performans ortaya koyabilir Bridge 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 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 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 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 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 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 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 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 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 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 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

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved Switching and Layer 2 Switches

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved 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 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 paralelliktir –Hub’ın aynı anda sadece bir iletim yapabilme özelliğine rağmen Switch bir sürü transferi aynı anda destekleyebilir

© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved Switching and Layer 2 Switches

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

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