S4 Ch01

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Chapter 1Chapter 1

REVIEWREVIEW

Semester 4Semester 4

Nguyen Tam TrungNguyen Tam Trung

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ObjectiveObjective

The advantages of LAN switching and VLANS along with how they should be implemented. Gathering the users requirements and designing the physical topology.Selecting a routing protocol to be used in the network. Implementing a method for controlling data packet flow across the network for security. Understanding the requirements for multiple protocols such as IPX and IP.

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TopicTopic

1. LAN Switching2. Virtual LANs3. LAN Design4. Routing Protocols5. Access List Overview6. IPX Routing Overview

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LAN SWITCHINGLAN SWITCHING

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Congestion and bandwidthCongestion and bandwidth

Technology advances are producing faster and more intelligent desktop computers and workstations.

Need More BANDWIDTH

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Multimedia bandwidth requirementMultimedia bandwidth requirement

Increase in the transmission of large graphic files, images, full-motion video and multimedia applications

Need More BANDWIDTH

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Multimedia ScalabilityMultimedia Scalability

Share large files, network congestion occurs; Slower response times; Longer file transfersRelieve network congestion

Need More BANDWIDTH

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LAN SegmentationLAN Segmentation

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Why segment LANs?Why segment LANs?

• Isolate traffic between segments.• Achieve more bandwidth per user by

creating smaller collision domains.• LANs are segmented by devices like

bridges, switches, and routers.• Extend the effective length of a LAN,

permitting the attachment of distant stations.

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Segmentation with bridgesSegmentation with bridges

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Segmentation with bridges (cont.)Segmentation with bridges (cont.)

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LAN SwitchesLAN Switches

• Switching is a technology that decreases congestion LANs by reducing traffic and increasing bandwidth.

• LAN switches often replace shared hubs and are designed to work with existing cable infrastructures.

• Perform two basic operations:– Switching data frames: Frame arrives on an

input and is transmitted to an output media. – Maintaining switching operations: Switches

build and maintain switching tables.

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MicroMicro--segmentationsegmentation

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Content addressable memory (CAM)Content addressable memory (CAM)

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Learn addressesLearn addresses

• Learn a station’s location by examining the source address.

• Sends out all ports when destination address is a broadcast, multicast or an unknown address.

• Forwards when the destination is located on a different interface.

• Filters when the destination is located on the same interface.

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Benefits of switchingBenefits of switching

• Number of collisions reduced.• Simultaneous, multiple communications.• High-speed uplinks.• Improved network response.• Increased user productivity.• Maximizes the bandwidth available.• Combined with software to configure

LANs give great flexibility in managing.

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Symmetric switchingSymmetric switching

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Asymmetric switchingAsymmetric switching

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Memory bufferingMemory buffering

• Buffering is an Ethernet technique to store and forward packets to the correct port or ports.

• Buffering may also be used when the destination port is busy.

• The buffer is the area of memory where the switch stores the data.

• The memory buffer can use two methods for forwarding packets:– port-based memory buffering– shared memory buffering

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In portIn port--based memory bufferingbased memory buffering

• Packets are stored in queues that are linked to specific incoming ports.

• A packet is transmitted to the outgoing port only when all the packets ahead of it in the queue have been successfully transmitted.

• It is possible for a single packet to delay the transmission of all the packets in memory because of a busy destination port.

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Shared memory bufferingShared memory buffering

• All packets are stored in a common memory buffer that is shared by all the ports on the switch. This is called dynamic allocation of buffer memory.

• The packets in the buffer are then linked dynamically to the transmit port.

• This allows the packet to be received on one port and transmitted on another port, without moving it into a different queue.

• The packet is restricted by the size of the entire memory buffer, not just the allocation to one port.

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Two switching methodsTwo switching methods

• Store-and-forward: – The entire frame is received before forward.– The latency is greater with larger frames. – Error detection is high.

• Cut-through: – The switch reads the destination address

before receiving the entire frame. – The frame is then forwarded before the entire

frame arrives. – Fast-forward and Fragment-free switching.

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CutCut--through switching methodsthrough switching methods

• Fast-forward switching: – offers the lowest level of latency by

immediately forwarding a packet after receiving the destination address.

• Fragment-free switching: – filters out collision fragments by forwarding

a packet after receiving first 64 bytes.– Waits until the received packet has been

determined not to be a collision fragment before forwarding the packet.

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ForwardingForwarding

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VIRTUAL LANVIRTUAL LAN

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Logical LAN SegmentationLogical LAN Segmentation

• Logically segment the physical LAN infrastructure into different subnets or broadcast domainsrather than physical location

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VLAN IntroductionVLAN Introduction

• A VLAN is a logical grouping of devices or users.

• These devices or users can be grouped by function, department, or application, regardless of their physical segment location.

• VLAN configuration is done at the switch via software.

• VLANs are not standardized and require the use of proprietary software from the switch vendor.

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VLAN ImplementationVLAN Implementation

• Each port can be assigned to a VLAN. – Ports assigned to the same VLAN share

broadcasts. – Ports that do not belong to that VLAN do

not share these broadcasts.

• Two methods that can be used to assign a switch port to a VLAN: – Static – Dynamic

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Static VLANStatic VLAN

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Dynamic VLANDynamic VLAN

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Transport of VLANsTransport of VLANs

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Frames TaggingFrames Tagging

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TrunkingTrunking ProtocolProtocol

• ISL: (Cisco)– Inter-Switch Link– Fast Ethernet

• 802.1q (IEEE)– Fast Ethernet

• 802.10 (IEEE)– FDDI

• LANE (ATM Forum)– LAN Emulation– ATM

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Router in the VLANsRouter in the VLANs

• Traditionally provide firewalls, broadcast management etc…

• Provide connected routes between different VLANs

• Cost effectively integrate external routers into switching architecture by using one or more high speed backbone connection

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LAN DESIGNLAN DESIGN

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IntroductionIntroduction

• Designing a network can be a challenging task, and involves more than just connecting computers together.

• Learning how to design networks is comprised of four basic areas: hardware, cabling, protocols and routing.

• There is no single book or manual that can teach you how to properly design computer network.

• This chapter will assist you with learning the basic foundations of network design.

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LAN Design GoalsLAN Design Goals

• The first step in designing a LAN is to establish and document the goals of the design.

• There are requirements in most network designs: – Functionality– Scalability– Adaptability– Manageability

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Design MethodologyDesign Methodology

1. Gathering the users' requirements and expectations

2. Analyzing requirements3. Designing the Layer 1, 2, and 3 LAN

structure (that is, topology)4. Documenting the logical and physical

network implementation

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Develop LAN topologyDevelop LAN topology

• Decide on an overall LAN topology that will satisfy the user requirements.

• We concentrate on the star topology and extended star topology.– The reason that this curriculum focuses on a

CSMA/CD star topology is that it is by far the dominant configuration in the industry.

• The major pieces of a LAN topology design can be broken into three unique categories of the OSI reference model.

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LAN topologyLAN topology

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Layer 1 design Layer 1 design -- GoalGoal

• Choose cable type.• Identify work area and HCC.• Identify MDF, IDF, HCC, VCC and POP.• Choose Ethernet or Fast Ethernet.• Documentation and physical diagrams.

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HCC and VCCHCC and VCC

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Layer 2 design Layer 2 design -- GoalGoal

• The purpose of Layer 2 devices in the network is to provide flow control, error detection, error correction, and to reduce congestion in the network.

• Devices at this layer determine the size of the collision domains and broadcast domains.

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Using switch in MDF and IDFUsing switch in MDF and IDF

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Layer 3 design Layer 3 design -- Goal Goal

• Determines traffic flow between unique physical network segments based on Layer 3 addressing.

• Stops broadcasts from reaching other LAN segments.

• By using VLANs, you can limit broadcast traffic to within a VLAN and thus create smaller broadcast domains.

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Diagramming a LAN that uses routers Diagramming a LAN that uses routers

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ROUTING PROTOCOLSROUTING PROTOCOLS

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Routing processRouting process

• Routing information can be configured by the administrator or collected dynamically

• Provides best-effort end-to-end packet delivery across interconnected networks

• The network layer uses the IP routing table to send packets from the source network to the destination network

• Takes the packet that it accepted on one interface forwards to another interface

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Routing tableRouting table

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How distances are determinedHow distances are determined

• Primary objective of routing protocol is to determine the best information to include in the routing table.

• Each routing algorithm interprets what is best in its own way.

• Routing algorithm generates a number, called the metric value, for each path through the network.

• Typically, the smaller the metric number, the better the path.

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Distance in MetricsDistance in Metrics

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How the metric is calculatedHow the metric is calculated

• You can calculate metrics based on a single characteristic of a path.

• You can calculate more complex metrics by combining several characteristics.

• The metrics most commonly used by routers are as bandwidth, delay, load, reliability, hop count, ticks and cost.

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Routing protocolsRouting protocols

• Routing is the process of determining where to send data packets destined for addresses outside the local network.

• Routers gather and maintain routing information.

• Routing information takes the form of entries in a routing table, with one entry for each identified route.

• Routing protocols allow a router to create and maintain routing tables dynamically and to adjust to network changes.

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The goals of routing protocols The goals of routing protocols

• The Optimal Route • Simplicity and Efficiency• Robustness• Rapid Convergence• Flexibility

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Classes of routing protocolsClasses of routing protocols

• Most routing algorithms can be classified as one of two basic algorithms distance vector and link state.

• The distance-vector routing approach determines the direction and distance to any link in the internetwork.

• The link-state approach re-creates the exact topology of the entire internetwork.

• The balanced hybrid approach combines aspects of the link-state and distance-vector algorithms.

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Choosing a routing protocol Choosing a routing protocol

• Network size and complexity • Network traffic levels • Security needs • Reliability needs • Network delay characteristics • Organizational policies • Organizational acceptance of change

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Distance vector algorithm Distance vector algorithm

• Routing algorithms pass periodic copies of a routing table from router to router.

• These regular updates between routers communicate topology changes.

• Each router receives a routing table from its directly connected neighbors.

• Distance-vector algorithms do not allow a router to know the exact topology of an internetwork.

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Distance vector concepts Distance vector concepts

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The problem of routing loops The problem of routing loops

• Routing loops can occur if a network's slow convergence on a new configuration causes inconsistent routing entries.

• Solutions:– Defining a Maximum– Split Horizon– Split Horizon with Poison Reverse– Route Poisoning– Hold-down Timers

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Problem:Problem: Routing LoopRouting Loop

Network 1 unreachable Network 1

Distance 3

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Problem:Problem: Counting to InfinityCounting to Infinity

Network 1 Distance 3



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Loop prevention: Loop prevention: Defining a MaximumDefining a Maximum

Maximum Metric is 16 Network 1

unreachable



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Loop prevention: Loop prevention: Split horizonSplit horizon


Network 1 unreachable

CRouter

21DistanceNetwork

ARouter

31DistanceNetwork

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Loop prevention: Loop prevention: Poison reversePoison reverse



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Loop prevention: Loop prevention: Route poisoningRoute poisoning


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Loop prevention: Loop prevention: HoldHold--down timerdown timer



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ACCESS LIST OVERVIEWACCESS LIST OVERVIEW

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IntroductionIntroduction

• ACLs are lists of instructions you apply to a router's interface.

• These lists tell the router what kinds of packets to accept and what kinds of packets to deny.

• Acceptance and denial can be based on certain specifications, such as source address, destination address, and port number.

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Reasons to create Reasons to create ACLsACLs

• Limit network traffic and increase network performance.

• Provide traffic flow control. • Provide a basic level of security for

network access.• Decide which types of traffic are

forwarded or blocked at the router interfaces.

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ACLsACLs check the packet and headercheck the packet and header

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Testing packets with Testing packets with ACLsACLs

• The order in which you place ACL statements is important.

• IOS software tests the packet against each condition statement, in the order in which the statements were created.

• Note: After a match is found, no more condition statements are checked.

• You can create an ACL for each protocol you want to filter for each router interface.

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Order of ACL statementsOrder of ACL statements

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How the ACL work? How the ACL work?

• An ACL is a group of statements that define how packets: – Enter inbound interfaces – Relay through the router – Exit outbound interfaces of the router

• ACL statements operate in order. If a condition match is true, the rest of the ACL statements are not checked.

• If all the ACL statements are unmatched, an implicit "deny any" statement is imposed.

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How the ACL work? (cont.)How the ACL work? (cont.)

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ACL numbersACL numbers

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Wildcard mask bitsWildcard mask bits

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Wildcard Wildcard anyany

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Wildcard Wildcard hosthost

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ExampleExample

• Router(config)# access-list 1 permit 0.0.0.0 255.255.255.255

• Router(config)# access-list 1 permit any

• Router(config)# access-list 1 permit 172.30.16.29 0.0.0.0

• Router(config)# access-list 1 permit host 172.30.16.29

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Placing Placing ACLsACLs

• Put the extended ACLs as close as possible to the source of the traffic denied.

• Put the standard ACL as near the destination as possible.

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Placing Placing ACLsACLs

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IPX ROUTING OVERVIEWIPX ROUTING OVERVIEW

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ArchitectureArchitecture

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ProtocolsProtocols

• IPX (Internetwork Packet Exchange), connectionless, layer 3 and defines the network and node addresses.

• SPX (Sequenced Packet Exchange), service for Layer 4 connection-oriented services.

• SAP (Service Advertising Protocol), to advertise network services.

• NCP (Netware Core Protocol), to provide client-to-server connections and applications.

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Routing ProtocolsRouting Protocols

• RIP: Routing Information Protocol,– Distance Vector Protocol.– Uses ticks (network delay) and hop count as

its routing metric.– Sends routing updates every 60 seconds.– Maximum hop count is 15.

• NLSP: Novell Link State Protocol, – Link State Protocol.

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IPX AddressingIPX Addressing

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IPX network addressIPX network address

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Encapsulation namesEncapsulation names

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IPX RIPIPX RIP

• Distance vector routing protocol.• Uses two metrics: Tick and hop count.

– Ticks: a time measure 1/18 of a second.– If ticks are equal, hop count is used.– If both ticks a hop count are equal, the router

load shares.– By default, a Cisco router treats a link as

having a certain number of ticks. (Ethernet 1 tick and Serial 6 ticks)

• Routing table updates every 60 seconds.Th

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RIPRIP

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Service AdvertisementsService Advertisements

• SAP allows file and print servers, to advertise their network addresses and the services they provide.

• Each service is identified by a number, called a SAP identifier. – 4 NetWare File server– 7 Print server– 24 Remote bridge server (router)

• SAP updates are sent every 60 seconds.

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SAPSAP

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Get Nearest ServerGet Nearest Server

• The client/server interaction begins when the client powers up and runs its client startup programs.

• These programs initiate the connection sequence for the NetWare command shell to use.

• The connection sequence, a client sends a broadcast using SAP. The nearest file server responds with another SAP.

• Now, the client can log in to the target server, make a connection, set the packet size and proceed to use server resources.

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GNSGNS

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Get Nearest Server (cont.)Get Nearest Server (cont.)

• If a server is located on the segment, it responds to the client request. The router does not respond to the GNS request.

• If there are no servers on the local network, the router responds with a server address from its own SAP table.

• Cisco IOS software allows NetWare clients to be located on LAN segments where there are no servers.

• In responding to GNS requests, Cisco IOS software can also distribute clients evenly among the available servers.

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GNS ProtocolGNS Protocol

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Router Lab TopologyRouter Lab Topology

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S4 Ch01

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