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

Chapter Introduction 1.1 LAN Design 1.2 The Switched Environment 1.3 Summary

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

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

Converged Networks Growing Complexity of Networks

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

Converged Networks Borderless Network Architecture

Converged Networks Access, Distribution and Core Layers Core Distribution Access

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

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

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

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.

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

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

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

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

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.

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

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

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

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

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.

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.

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

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.

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.

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

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

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

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

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

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

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.

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

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