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Chapter 1Chapter 1

REVIEWREVIEW

}}Semester 2Semester 2

Le Chi TrungLe Chi Trung

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}}ObjectiveObjective

üReinforces the concepts you have already learned related to the OSI reference model, LANs and IP addressing. üUnderstanding these complex topics is the

first step toward understanding the Cisco Internetwork Operating System (IOS), which is a major topic in this curriculum. üYou need to have a firm grasp of the

internetworking principles surveyed in this chapter before attempting to understand the complexities of the Cisco IOS.

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1:00:00The OSI Model à1st

0:15:00Host Layers à1:00:00TCP/IP Addressing à0:30:00LANs à

DurationTopic#Day

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OSI MODELOSI MODEL

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T}}OSI modelOSI model

•• The OSI modelThe OSI model: a framework within which networking standards can be developed.

–– It provided vendors with a set of standards It provided vendors with a set of standards that ensured greater compatibility and that ensured greater compatibility and interoperability between the various types of interoperability between the various types of network technologies that were produced by network technologies that were produced by the many companies around the world.the many companies around the world.

ProprietaryProprietary vs.vs. OpenOpen

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}}7 layers of the OSI reference model7 layers of the OSI reference model

• Layer 7: Application

• Layer 6: Presentation

• Layer 5: Session

• Layer 4: Transport

• Layer 3: Network

• Layer 2: Data Link

• Layer 1: Physical

•All People Seem To Need Data Processing

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T}}Why a layered model?Why a layered model?

• Reduces complexity.

• Standardizes interfaces.

• Facilitates modular engineering.

• Ensures interoperable technology.

• Accelerates evolution.

• Simplifies teaching and learning.

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}}The physical layerThe physical layer

• Transmission of an unstructured bit stream over a physical link between end systems.

– Electrical, mechanical, procedural and functional specifications

– Physical data rate

– Distances

– Physical connector

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T}}The dataThe data--link layerlink layer

• Provides for the reliable transfer of data cross a physical link.

– Frames

– Physical address

– Network topology

– Line discipline

– Synchronization

– Error control

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}}The network layerThe network layer

• Provides connectivity and path selection between two host systems that may be located on geographically separated networks.

– Packets

– Logical address

– Virtual circuits

– Route, routing table, routing protocol

– Fragmentation

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T}}The transport layerThe transport layer

• Provides reliable, transparent transfer of data over networks.

– Segments, data stream, datagram

– Connection oriented and connectionless

– End-to-end flow control

– Error detection and recovery

– Segmentation & reassembly

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}}The session layerThe session layer

• Establishes, manages, and terminates sessions between two communicating hosts.

– Sessions

– Dialog/Conversations

– Data exchange

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T}}The presentation layerThe presentation layer

• Ensures that the information that the application layer of one system sends out is readable by the application layer of another system.

– Format of data

– Data structure

– Data conversion

– Data compression

– Data encryption

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}}The application layerThe application layer

• Is the OSI layer that is closest to the user; it provides network services to the user’s applications.

– File transfer

– Electronic mail

– Terminal access

– Word processing

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T}}Group of LayersGroup of Layers

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}}Devices function at LayersDevices function at Layers

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T}}PeerPeer--toto--peer communicationspeer communications

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}}ProtocolsProtocols

• Is a formal set of rules and conventionsthat governs how computers exchange information over a network medium.

• Implements the functions of one or more of the OSI layers.

• A communication protocol is concerned with exchanging data between two peer layers.

• Protocol Data Units (PDUs) : Block of data that a protocol exchange.

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T}}EncapsulationEncapsulation

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LANsLANs

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T}}LAN mediaLAN media

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}}LAN devicesLAN devices

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T}}Logical TopologiesLogical Topologies

Broadcast

Token Passing

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}}Technology:Technology: Token RingToken Ring

Token Ring

Token Passing

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T}}Technology:Technology: FDDIFDDI

FDDI

Token Passing

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}}Technology:Technology: EthernetEthernet

Ethernet

Broadcast

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T}}Ethernet 802.3Ethernet 802.3

• Ethernet is broadcast topology:– Every devices on the Ethernet segment sees

every frame.

– Frames are addressed with source and destination MAC addresses.

– When a source does not know the destination or wants to communicate with every device, it encapsulates the frame with a broadcast MAC address: FFFF.FFFF.FFFF

•• What is the main network traffic problem What is the main network traffic problem caused by Ethernet topologies ?caused by Ethernet topologies ?

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}}Ethernet 802.3 Ethernet 802.3 –– CSMA/CDCSMA/CD

•• Carrier Sense Multiple Access with Collision Detection.Carrier Sense Multiple Access with Collision Detection.

• A node needing to transmit listens for activity on the media. If there is none, it transmits.

• The node continue to listen. A collision is detected by a spike in voltage (a bit can only be a 0 or a 1; it cannot be a 2)

• The node generates a jam signal to tell all devices to stop transmitting for a random amount of time (back-off algorithm).

• When media is clear of any transmissions, the node can attempt to retransmit.

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T}}Physical and Logical addressPhysical and Logical address

• Physical address:– Data link layer address, MAC addresses.– Unique for each network connection. – Located on the NIC. – Flat address space.– Exist at Layer 2 of the OSI model.

• Logical address:– Network layer address, IP addresses.– Hierarchical address space.– Exist at Layer 3 of the OSI model.

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}}Logical address resolutionLogical address resolution

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TCP/IP ADDRESSINGTCP/IP ADDRESSING

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}}Network addressNetwork address

• The network address helps the router identify a path within the network cloud.

• The router uses the network address to identify the destination network of a packet within an internetwork.

• Network address is assigned by higher-level administrator. Host address is assigned manually or automatically by manager of that network.

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T}}IP network addressIP network address

• Network layer addresses are 32 bits long.

• The are presented as four octets in dotted decimal format.

• The IP address has two components: Network ID and Host ID.

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}}IP address formatIP address format

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T}}Network ID and host IDNetwork ID and host ID

• Network ID :

– Assigned by Internet Network Information Center.

– Assigned by upper organization.

– Identifies the network to which a devices is attached.

• Host ID :

– Assigned by a network administrator.

– Identifies the specific device on that network.

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}}Bits on the IP addressBits on the IP address

• Network Bits :

– Identifies network ID

– Identifies class of the IP address

– All of bits = 0: not allowed

• Host Bits :

– Identifies host ID

– All of bits = 0: reserved for network address

– All of bits = 1: reserved for broadcast address

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T}}IP address classesIP address classes

• Different class addresses reserve different amounts of bits for the Network and Host portions of the address

• Provide the flexibility required to support different size networks

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}}IP address classes:IP address classes: SummarySummary

• 1.0.0.0 - 126.0.0.0 : Class A.

• 127.0.0.0 : Loopback network.

• 128.0.0.0 - 191.255.0.0 : Class B.

• 192.0.0.0 - 223.255.255.0 : Class C.

• 224.0.0.0 < 240.0.0.0 : Class D, multicast.

• >= 240.0.0.0 : Class E, reserved.

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T}}Why we need to divide network?Why we need to divide network?

• Network administrators sometimes need to divide networks, especially large ones, into smaller networks:

– Reduce the size of a broadcast domain.

– Improve network security.

– Implement the hierarchical managements.

• So we need more network addresses for your network. But I want the outside networks see our network as a single network.

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}}SubnettingSubnetting

• Subnetworks are smaller divisions of network.

• Subnet addresses include the Class A, Class B, or Class C network portion, plus a subnet field and a host field.

• To create a subnet address, a network administrator borrows bits from the original host portion and designates them as the subnet field.

• Subnet addresses are assigned locally, usually by a network administrator.

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T}}SubnettingSubnetting

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}}Subnet maskSubnet mask

• “Extended Network Prefix”.

• Determines which part of an IP address is the network field and which part is the host field.

• 32 bits long.

• Divided into four octets.

• Network and Subnet portions all 1’s.

• Host portions all 0’s.

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T}}How many bits can I borrow?How many bits can I borrow?

• All of subnet bits are:– 0 : reserved for network address.

– 1 : reserved for broadcast address.

• The minimum bits you can borrow is:

42 bits.

• The maximum bits you can borrow is:

4A: 22 bits ~ 222 - 2 = 4.194.302 subnets.

4B: 14 bits ~ 214 - 2 = 16.382 subnets.

4C: 06 bits ~ 206 - 2 = 62 subnets.

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}}Purpose of the transport layerPurpose of the transport layer

• Transport and regulate the flow of information from source to destination, reliably and accurately.

• The end-to-end control: – Sliding windows.

– Flow control

– Acknowledgments and sequencing numbers.

– Segmentation.

– Multiplexing.

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T}}Reliable transport Reliable transport

• It ensures that senders receive acknowledgement of delivered segments.

• It provides for retransmission of any segments that are not acknowledged.

• It puts segments back into their correct sequence at the destination device.

• It provides congestion avoidance and control.

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}}Establishing a connection Establishing a connection

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T}}Flow control Flow control

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}}Acknowledgment Acknowledgment

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T}}Windowing Windowing

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}}MultiplexingMultiplexing

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T}}TCP and UDPTCP and UDP

• The emphasis of this curriculum is on TCP/IP Ethernet networks.

• The TCP/IP protocol of the OSI model Layer 4 (transport layer) has two protocols - TCP and UDP.

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}}TCP/IPTCP/IP

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HOST LAYERSHOST LAYERS

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}}Session layerSession layer

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T}}Presentation layerPresentation layer

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}}Application layerApplication layer

• The application layer (Layer 7) supports the communicating component of an application.

• The application layer:– Identifies and establishes the availability of

intended communication partners.

– Synchronizes cooperating applications.

– Establishes agreement on procedures for error recovery and control of data integrity.

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T}}Router Lab TopologyRouter Lab Topology

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