© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 1: Introduction to Switched Networks Switched Networks.

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1 © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 1: Introduction to Switched Networks Switched Networks

2 Chapter 1 1.0 Introduction 1.1 LAN Design 1.2 The Switched Environment 1.3 Summary

3 Chapter 1: Objectives  Convergence of data, voice, and video in switched networks  Switched network in a small-to-medium-sized business  Process of frame forwarding in a switched network  Collision domain and broadcast domain

4 © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 4 1.1 LAN Design

5 Converged Networks Growing Complexity of Networks

6 Converged Networks Elements of a Converged Network A converged network solution for a small-to-medium-sized business supports:  Call control - Telephone call processing, caller ID, call transfer, hold, and conference  Voice messaging  Mobility  Automated attendant

7 Converged Networks Borderless Network Architecture

8 Converged Networks Access, Distribution and Core Layers Core Distribution Access

9 Converged Networks Hierarchy in Borderless Switched Networks Borderless switched network design principles:  Hierarchical  Modular  Resiliency  Flexibility

10 Switched Networks Role of Switched Networks Switched networks incorporate the following features:  Layer 3 functionality  Quality of service  IP telephony  Security  Wireless networking  Mobility Meeting the requirements of next generation networks:  Secure  Reliable and always available  Support converged network traffic such as data, voice, video, security systems, and more

11 Switched Networks Form Factors Fixed – pevná konfigurace, nelze snadno dokupovat, rozšiřovat Modular – koupíme rám s minimálním vybavením, pak dokupujeme moduly Stackable – více přepínačů spojených kabely funguje jako jeden

12 Switched Networks Multilayer Switching  Deployed in the core and distribution layers  Can build a routing table  Supports a few routing protocols  Forwards IP packets  With IOS 15.x Catalyst 2960s, can support multiple switched virtual interfaces (SVIs) Multilayer switch – umí přepínat na vrstvě 2 podle MAC adres, ale také na vrstvě 3 podle IP adres.

13 Switch Features = vlastnosti přepínačů, tj. podle čeho vybírat Port Density = počet portů

14 Switch Features = vlastnosti přepínačů, tj. podle čeho vybírat Forwarding Rates = rychlost  How much data the switch can process per second  Switch product lines are classified by forwarding rates

15 Switch Features = vlastnosti přepínačů, tj. podle čeho vybírat Power over Ethernet = napájení přes síť  Power over Ethernet (PoE) allows the switch to deliver power to a device over the existing Ethernet cabling.  PoE pass-through allows you to power PoE devices connected to the switch and the switch by drawing power from specific upstream switches. = průchozí switch nepotřebuje napájení z 230V, je napájen z nadřízeného switche. PoE PoE Pass-Through

16 © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 16 1.2 The Switched Environment

17 Frame Forwarding Switching as a General Concept The fundamental concept of switching refers to a device making a decision based on two criteria: = rozhoduje se podle:  Ingress port = vstupního portu  Destination address = cílové adresy A LAN switch maintains a table that it uses to determine how to forward traffic through the switch = udržuje si tabulku, podle které posílá framy dál.

18 Frame Forwarding Dynamically Populating a Switch MAC Address Table As the switch learns the relationship of ports to devices, it builds a table called = buduje si tabulku, které se říká  MAC address = tabulka MAC adres or  content addressable memory (CAM) table = paměť adresovaná podle obsahu

19 Frame Forwarding Switch Forwarding Methods Application-specific-integrated circuits (ASICs) reduce the packet- handling time, and allow the device to handle an increased number of ports without degrading performance. Two Methods of forwarding frames:  Store-and-Forward - makes a forwarding decision on a frame after it has received the entire frame and checked the frame for errors. = Přijmi celý, zkontroluj, až pak pošli dál  Cut-Through - begins the forwarding process after the destination MAC address of an incoming frame and the egress port has been determined. = Kašli na kontrolu, hned to rvi dál

20 Frame Forwarding Store-and-Forward Switching = Přijmi celý, zkontroluj, až pak pošli dál

21 Frame Forwarding Cut-Through Switching = Kašli na kontrolu, hned to rvi dál

22 Frame Forwarding Fragment Free Switching Fragment free switching is a modified form of cut-through switching - the switch waits for the collision window (64 bytes) to pass before forwarding the frame. Kompromis: Zkontrolujeme prvních 64 bajtů a spoléháme, že dál už chyba nebude.

23 Switching Domains Collision Domains  Each port on the switch represents a new segment.  Each new segment is a collision domain. Mezi jednotlivými porty switche nemůže dojít ke kolizi.

24 Kolizní domény Kolizní doména je část sítě, ve které může dojít ke kolizi kohokoliv s kýmkoliv. Kolizní doména: Počítače propojené koaxiálem Kolizní doména: Počítače propojené hubem

25 Kolizní domény Jedna kolizní doména: A může mít kolizi s B, C, i D Druhá kolizní doména: E může mít kolizi s F, G, i H Switch odděluje obě kolizní domény tak, že mezi nimi nemohou nastat kolize: např. A nemůže mít kolizi s E.

26 Broadcast domény Broadcast je užitečný, když potřebujeme něco sdělit všem, nebo se všech na něco zeptat (viz třeba protokol ARP). Když je ale broadcastů moc, zahlcují síť a otravují většinu účastníků zprávami, které je nezajímají. Proto je dobré broadcast domény omezovat. To umí router. Neumí to switch.

27 Broadcast domény Broadcast doména: Broadcast se zde šíří bez omezení, switch mu nijak nebrání.

28 Broadcast domény Broadcast doména: Broadcast se zde šíří bez omezení, switche mu nijak nebrání.

29 Broadcast domény Router Router odděluje obě domény od sebe tak, že se broadcast mezi nimi nemůže šířit. Jedna broadcast doména: broadcast se v ní šíří bez omezení Druhá broadcast doména: broadcast se v ní šíří bez omezení

30 Broadcast domény Příklad V tomto obrázku jsou 4 kolizní domény (modré rámečky) a 1 broadcast doména (červený rámeček). Hub Switch

31 Alleviating Network Congestion = Jak zabraňovat zácpě v síti  High port density - Large enterprise switches may support many hundreds of ports. Mnoho portů  Large frame buffers - The ability to store many received frames. Velká paměť na framy  Port speed - Depending on the cost of a switch, it may be possible to support a mixture of speeds. Různé, pokud možno velké, přenosové rychlosti  Fast internal switching - Having fast internal forwarding capabilities allows high performance. Rychlé přepínání uvnitř switche  Low per-port cost - Switches provide high-port density at a lower cost. Nízká cena za jeden port

32 © 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 32 1.3 Summary

33 Chapter 1 Summary  The trend is convergence: a single set of wires and devices to handle voice, video, and data transmission.  Network resources must now be available anytime and anywhere.  The three-layer hierarchical design model divides the network into core, distribution, and access layers. It provides modularity, resiliency = nezlomnost, odolnost, and flexibility.  In some networks the core layer and the distribution layer are collapsed together.  It is important to deploy the appropriate types of switches based on network requirements.

34 Chapter 1 Summary (cont.)  The network designer must choose between types of switch: fixed or modular stackable or non-stackable.  A network administrator may choose a multilayer switch.  Multilayer switches build a routing table support routing protocols forward IP packets  Switches use store-and-forward cut-through switching  Every port on a switch forms a separate collision domain

35 Presentation_ID 35 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential