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www.ciscopress.com Networking Basics CCNA 1 Chapter 2
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Networking Basics CCNA 1Chapter 2
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Networking Basics and Terminology
A Brief History of the Networking Universe
• Earliest commercial computers were large mainframes, run by computer scientists
• Terminals were invented, allowing users to interact with the computers
• Eventually (1960s), some terminals were located to allow remote access
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Networking Basics and Terminology
A Brief History of the Networking Universe
• By late 1960s minicomputers entered marketplace
• “Mini’s” were smaller, less powerful and less expensive than mainframes
• Mid 1970s – First personal computers (PCs) built by researchers
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Networking Basics and Terminology
A Brief History of the Networking Universe
• 1977 – Apple introduces the Apple-II
• 1981 – IBM introduces its first PC
• Mid 1980s – Computer users with standalone computers start sharing data through the use of modems connecting to another computer (dialup, point-to-point)
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Networking Basics and Terminology
The Need for Networking Protocols and Standards• 1960s to 1980s – Each vendor set its own
proprietary protocols and standards• Equipment from different vendors would not
interoperate• Eventually, open standards were agreed upon• Open standards allow more competition, which
increases speed of development
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Networking Basics and Terminology
Popular Network Standards Organizations
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Networking Basics and Terminology
Ethernet LANs and LAN Devices• Ethernet LANs originally used coaxial cable
(similar to Cable TV cable)• Network Interface Cards (NICs) would attach to
a length of cable called a segment
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Networking Basics and Terminology
Ethernet LANs and LAN Devices• In early Ethernet LANs, all devices sent their
data on one wire• All other devices on the segment received the
signal• These types of Ethernet are said to be
“broadcast” media, because any signal sent by one device is received by all other devices
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Networking Basics and Terminology
Characteristics of Early Ethernet LANs• Limited to a relatively small geographic area• Allows multiple devices access to high-speed
media• Administrative control rests within a single
company• Provides full-time connectivity• Typically connects devices that are close
together
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Networking Basics and Terminology
Cisco Networking Device Icons
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Networking Basics and Terminology
Ethernet Repeaters• When a signal is sent over a wire, it degrades• 10BASE5 limited a single segment to 500
meters; 10BASE2 to a little less than 200 meters (185 meters) – hence their names (the 5 and the 2; the 10 is for 10Mbps)
• To extend the distance of LANs, repeaters were developed
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Networking Basics and Terminology
Features of Ethernet Repeaters
• Typically had two ports connecting two different Ethernet segments
• Interpreted the incoming signal on one port as 1’s and 0’s
• Sent a regenerated clean signal out the other port
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Networking Basics and Terminology
Repeated Ethernet Signal
See Conceptual View on next slide
• Betty sends a clean signal
• The signal degrades by the time it reaches the repeater
• The repeater regenerates a new, clean signal and sends it out its other port
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Networking Basics and Terminology
Repeated Ethernet Signal
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Networking Basics and Terminology
Ethernet Hubs and 10BASE-T
• Coax cables were expensive and difficult to work with
• If the cable broke, everyone on the LAN had problems
• Lead to the creation of 10BASE-T
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Networking Basics and Terminology
Ethernet Hubs and 10BASE-T• The 10 means it runs at 10Mbps• The T means that it uses twisted-pair cable• The cable is Unshielded Twisted-Pair (UTP),
which is cheaper than coax cable• Smaller diameter than coax cable• Terminated with RJ-45 connectors
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Networking Basics and Terminology
10BASE-T with a Hub – Star Topology
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Networking Basics and Terminology
Functions of a Hub
• Provides RJ-45 jacks so cables with RJ-45 connectors can be attached
• Repeats any incoming signal out all other ports
• Was originally called a “multiport repeater”
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Networking Basics and Terminology
Ethernet Bridges• Examine incoming signal, interpret signal as 0’s
and 1’s, find the destination MAC address listed in the frame
• If destination MAC address is reachable via a different interface than the one on which it was received, then clean, regenerate and forward the frame out that interface
• If the destination is reachable on the same interface on which it was received, discard the frame (this is called “filtering”)
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Networking Basics and Terminology
A Bridge Making a Filtering Decision
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Networking Basics and Terminology
A Bridge Making a Forwarding Decision
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Networking Basics and Terminology
Ethernet Frames
• An Ethernet frame is the data sent by an Ethernet NIC or interface
• The first bits sent are the header; contains info such as the destination and source MAC addresses
• Includes headers from other protocols, such as IP
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Networking Basics and Terminology
Conceptual View of an Ethernet Frame
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Networking Basics and Terminology
Unicast and Broadcast Ethernet Frames and Addresses
• Before the introduction of bridges, the LAN acted as a broadcast medium
• The term unicast MAC address identifies a single NIC or Ethernet interface
• Sometimes a computer needs to send a frame that will reach all devices on the LAN; it uses a broadcast address: FFFF.FFFF.FFFF
• All devices must process data sent to this address
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Networking Basics and Terminology
LAN Switches
• Like a hub, a switch provides a large number of ports/jacks to plug in cables
• Forms a physical star topology
• When forwarding a frame, the switch regenerates a clean signal
• Like bridges, switches use the same filtering/forwarding logic on a per-port basis
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Networking Basics and Terminology
A Switch Making a Forwarding Decision
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Networking Basics and Terminology
Wide-Area Networks (WANs)• Cover a large geographic area• WAN Technologies:
– Modems– Integrated Services Digital Network (ISDN)– Digital Subscribe Line (DSL)– Frame Relay– T1 or E1 leased lines – T1, E1, T3, E3, etc.– Synchronous Optical Network (SONET) – synchronous
transport Level 1(STS-1) optical carrier [OC]-1, STS-3 (OC-3), etc.
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Networking Basics and Terminology
Point-to-Point Leased Lines• A point-to-point leased line extends
between two locations• The line is not owned by the user; it is
leased from a service provider• The service provider is often a telephone
company (telco)• Often, the term link is used to describe a
point-to-point leased line
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Networking Basics and Terminology
Point-to-Point Leased Lines:
Leased lines are drawn like lightning bolts
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Networking Basics and Terminology
Routers and Their Use with LANs• Routers perform a basic but very important
forwarding process in which they receive data packets and then forward the packets toward the destination
• Routers can send and receive traffic on most any kind of physical networking media
• Routers are the perfect device to connect a LAN to a WAN
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Networking Basics and Terminology
Metropolitan Area Networks (MANs)
• A medium-sized network geography, perhaps city-wide
• Usually very high speed
• Optical media used between routers can move data at 10 Gbps or even 40 Gbps
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Networking Basics and Terminology
High-Speed City-Wide MAN
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Networking Basics and Terminology
Storage-Area Networks (SANs)• Allow computers to communicate with storage
devices• Features of SANs:
– Performance: concurrent access of disk or tape arrays
– Availability: used to back up data to offsite locations– Scalability: easy relocation of backup data,
operations, file migration, and data replication between systems
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Networking Basics and Terminology
Typical SAN Used by a Server Farm
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Networking Basics and Terminology
Virtual Private Networks (VPNs)
• Companies can use the Internet to send data between sites, instead of using leased lines
• Often less expensive than leased lines
• Can be less secure than leased lines
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Networking Basics and Terminology
Virtual Private
Networks (VPNs)
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Networking Basics and Terminology
Intranet VPNs
• Packets are encrypted before they leave for the Internet
• Not practical for a hacker to break the encryption
• Intranet VPNs are used inside a single organization
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Networking Basics and Terminology
Intranet VPN
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Networking Basics and Terminology
Comparing Intranet VPNs to Extranetand Access VPNs
• Intranet VPN – A VPN between sites of a single organization
• Extranet VPN – A VPN between sites of different organizations
• Access VPN – A VPN between individual users and an enterprise network, allowing access while working from home or traveling
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Networking Basics and Terminology
Extranet and Access VPNs
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Networking Basics and Terminology
Physical Network Topologies
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Networking Basics and Terminology
Physical Bus Topology
• 10BASE2 and 10BASE5 use a bus topology
• Looks like a city street where each of the computers is a bus stop
• A frame sent by one device is received by all other devices
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Networking Basics and Terminology
Physical Star Topology
• 10BASE-T Ethernet connects with a hub
• The hub is the device at the center, so it resembles a start
• The actual physical layout of the cable may not be in a star pattern
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Networking Basics and Terminology
Logical Bus Topology
• “Logical” refers to how the network operates, not where the cables run
• 10BASE-T is a logical bus, because all devices see any signal sent by other devices on the network
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Networking Basics and Terminology
Physical versus Logical Topology
• Physical Topology – The topology is determined by the physical layout of the cabling and transmission media
• Logical Topology – The topology is determined by the media access control logic and how the devices collectively send traffic over the network
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Networking Basics and Terminology
Typical Modern
LAN and Its Similarities to a Star Topology
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Networking Basics and Terminology
Typical Modern
LAN Design for a Single
Building
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Networking Basics and Terminology
Ring Topologies• Cable is installed from first device to
second device, second device to third device, and so on, until the last device connects to the first device
• Each device cleans up the signal, so fewer repeaters are needed
• Can have single or dual rings
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Networking Basics and Terminology
Ring Topology• R1 and R2 detect that
cable between them is cut
• R1 and R2 loop the primary ring to the backup ring using circuitry in the routers
• One ring still works, assuring connectivity
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Networking Basics and Terminology
Hierarchical and Extended Star Topologies• A central device or site connects to several
other sites• Much like a star topology• The other sites then connect to still more sites• Extended star topologies have the same
features as a hierarchical topology, but are not drawn in a hierarchy
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Networking Basics and Terminology
Hierarchical Network Design
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Networking Basics and Terminology
Mesh: Full and Partial• Most often refers to WAN topologies• Full mesh: all devices connect to all other
devices – highly reliable – Frame Relay is an example
• Partial mesh: Each device connects to many, but not all, other devices
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Networking Basics and Terminology
Mesh: Full and Partial
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Bandwidth
Bandwidth: Number of bits per second that can be sent by a device across a particular transmission medium
Names and Units of Digital bandwidth:
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Bandwidth
LAN and WAN Bandwidth• Actual speed is limited by 3 factors: cabling,
cable length, and the speed at which the devices on the end of the cable try to send data
• Ethernet standards call for Category 5 (Cat 5) UTP cabling, for speeds of 10, 100 and even 1000 Mbps
• The cable can handle higher speeds, but is hardware limited
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Bandwidth
Bandwidths for Various Ethernet Standards and Cables
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Bandwidth
WAN Bandwidths• Vary significantly, as do LAN bandwidths• Engineers need to worry about details such as
cable length restrictions and required equipment • Customers need to worry about how fast the
WAN link is, how much it costs, and the type of technology used
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Bandwidth
WAN Bandwidth Standards
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Bandwidth
WAN Bandwidth Standards (continued)
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Bandwidth
Throughput Versus Bandwidth• Throughput is how many bits are actually
transferred between two computers in a given time
• Two points to consider when comparing throughput to bandwidth:– Throughput rate may vary over time due to network
conditions; bandwidth does not vary over time– Bandwidth defines the speed of a single link;
throughput measures the speed of the end-to-end connection
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Bandwidth
Two Examples of Throughput
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Bandwidth is What You Pay for, Throughput is What You Get
Factors That Affect Throughput• Networking devices in the route being used• Type of data being transferred• Protocols used to transfer the data• Topology of the network• Congestion level in the network• Speed and current workload of the computers• Time of day (# of active concurrent users)
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Bandwidth
Calculating Data Transfer Time: Two Methods
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Bandwidth
Calculating Data Transfer Time:
Four Examples from the “Two Examples of Throughput” Slide
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Bandwidth
Analog Bandwidth• In the analog world, a number of consecutive
frequencies (a “band of frequencies”) defined how much information could be sent with an analog signal
• The wider the band of frequencies, the more information could be sent
• With digital transmission, the range of frequencies does not affect the speed, but the term “bandwidth” is still used to describe the speed of the bits across a link
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Bandwidth
Analog Bandwidth (continued)• Analog transmission requires a set frequency band to
work• The figure below shows a 3-hertz signal
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Bandwidth
Planning for Bandwidth• Neither LAN nor WAN bandwidth is free• On enterprise networks, WAN costs can be
30-40% of the total budget• LAN links cost money, due to wiring costs and
the costs of networking devices such as switches
• Bandwidth is not infinite, and it costs money to upgrade
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Bandwidth
Planning for Bandwidth (continued)
Four reasons why bandwidth is important:• Bandwidth is finite• Bandwidth is not free• Network engineers need to plan for bandwidth• Bandwidth demand is ever-increasing
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The OSI and TCP/IP Networking Models
• Networking models define a related set of standards and protocols
• When used together, these protocols and standards allow the creation of a working network
• The two most commonly used models are the Open Systems Interconnection (OSI) model and the Transmission Control Protocol/Internet Protocol (TCP/IP) model
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The OSI and TCP/IP Networking Models
• In the 1960s, vendors each used their own set of standards and protocols
• These proprietary networking models would not allow equipment from one company to work with equipment from another company
• To overcome this problem, the OSI model was developed beginning in 1984
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The OSI and TCP/IP Networking Models
The OSI Model• Goal was to be the one open networking model that all
vendors would implement• The term “open” means that all vendors have access
to the protocols and rules for building products• Most vendors worked toward adopting the OSI model
in the late 1980s and early 1990s• Many vendors and networking professionals adopted
the OSI terminology to hold meaningful conversations about different networking models, making those conversations a little easier
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The OSI and TCP/IP Networking Models
The OSI Model (continued)• The OSI model might have been the final
standard for networking, but TCP/IP proved to be more widely accepted
• Computers today rarely implement the OSI model as their model for networking
• Why use OSI? The terminology is still used, and it is useful in troubleshooting networking problems
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The OSI and TCP/IP Networking Models
The OSI LayersGeneral networking functions are defined in layers:• Allows better standardization of different components• Opens up competition in marketplace• Standardizes components• Standardizes interfaces between different layers,
allowing companies to focus on one layer• Prevents changes in one layer from affecting other
layers• Breaks network communication into smaller
components
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The OSI and TCP/IP Networking Models
The OSI Layers
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The OSI and TCP/IP Networking Models
Memorizing the Order of the OSI Layers• Starting with Layer 1:
– Please Do Not Take Sausage Pizza Away– Pew! Dead Ninja Turtles Smell Pretty Awful
• Starting with Layer 7:– All People Seem To Need Data Processing
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The OSI and TCP/IP Networking Models
Functions of the OSI Layers• Layer 7 (application layer)
– Provides services to end user’s applications– Does not provide services to any other OSI layer
• Layer 6 (presentation layer)– Ensures info from one system’s application layer can be read
by another system– Translates among multiple data formats– Does encryption and decryption– Handles graphics standards such as PICT, TIFF, JPEG, MIDI
and MPEG
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The OSI and TCP/IP Networking Models
Functions of the OSI Layers (continued)• Layer 5 (session layer)
– Establishes, manages and terminates sessions between two hosts
• Layer 4 (transport layer)– Segments data given to it by the session layer into
smaller chunks– Defines error-recovery services
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The OSI and TCP/IP Networking Models
Functions of the OSI Layers (continued)• Layer 3 (network layer)
– Provides connectivity and path selection between two host systems
– Concerned with logical addressing
• Layer 2 (data link layer)– Provides transit of data across a physical link by defining the
rules about how the link is used– Concerned with physical addressing
• Layer 1 (physical layer)– Defines electrical, mechanical, procedural, and functional
specifications for activating, maintaining, and deactivating the physical link between end systems
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The OSI and TCP/IP Networking Models
Relationship of OSI Layers and Devices
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The OSI and TCP/IP Networking Models
The TCP/IP Networking Model• Began as part of a research project for the US
Dept. of Defense (DoD) in the 1970s.• The structure remains the same today, but
many new protocols have been added• Can be easily compared to the OSI model;
uses 4 layers instead of 7
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The OSI and TCP/IP Networking Models
The TCP/IP Reference Model Layers
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The OSI and TCP/IP Networking Models
Encapsulation1. Application
headers are added
2. Data is segmented
3. IP address information is added
4. Data link header and trailer are added
5. Bits are transmitted
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The OSI and TCP/IP Networking Models
Segments, Packets, Frames, and PDUs• Important to know the terminology for the group
of bytes at each layer• The generic term is protocol data unit (PDU)
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The OSI and TCP/IP Networking Models
De-encapsulation1. Physical layer interprets
incoming electrical signal2. Contents of Ethernet
header and trailer analyzed; IP packet extracted
3. Network layer verifies IP header is okay, extracts contents of data field
4. Segments are reassembled and error recovery performed
5. Data is given to application
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The OSI and TCP/IP Networking Models
Layer Interactions• Same layer interaction – creation of headers, and
possibly trailers, by a protocol at one networking layer on one computer, with the goal of communicating to the same layer and protocol on another computer
• Adjacent layer interaction – On a single computer, the interaction of protocols that sit at adjacent layers of their networking model. Includes exchange of data during encapsulation and de-encapsulation, and how a lower layer protocol provides service to an upper layer protocol
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Networking Fundamentals
Summary• Network devices (hubs, repeaters, bridges, switches, routers)
connect host devices to allow them to communicate• Protocols provide sets of rules for communication• The physical topology is the actual layout of the wire or media• Common physical topologies are bus, ring, star,extended star,
hierarchical, and mesh• A LAN is designed to work in a limited geographical area,
providing multi-access to high-bandwidth media• LANs are controlled privately under local administration• LANs provide full-time connectivity to services and connect
physically adjacent devices
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Networking Fundamentals
Summary• WANs operate over large geographical areas• WANs allow access serial interfaces that operate at lower
speeds, provide full- and part-time connectivity to local services and connect devices separated over large areas
• A MAN is a network that spans a metropolitan area such as a city
• A SAN is a dedicated, high performance network used to move data between servers and storage resources
• SANs are scalable and have disaster tolerance built it• A VPN is a private network constructed with a public network
infrastructure such as the Internet• The three main types of VPNs are access, intranet and
extranet
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Networking Fundamentals
Summary• Access VPNs provide mobile workers connectivity• Intranet VPNs are only available to users who have access
privileges to the internal network of an organization• Extranet VPNs are design to provide applications and services
to external users or enterprises• Bandwidth equals number of bits per second (bps) that can
theoretically be sent through a network connection• Throughput is the amount of data that actually passes through
a connection in a give time, and is constrained by the slowest link between the two end devices
• Analog bandwidth is a measure of how much of the electromagnetic spectrum is occupied by each signal
• Digital bandwidth is measured in bits per second
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Networking Fundamentals
Summary • Layers are used to describe communication from one computer
to another because it:– Reduces complexity– Standardizes interfaces– Facilitates modular engineering– Ensures interoperability– Accelerates evolution– Simplifies teaching and learning
• Two models are the OSI model and the TCP/IP model• The OSI model has seven layers; the TCP/IP model has four –
some layers have the same name but do not correspond exactly
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Networking Fundamentals
Summary• Data is encapsulated with these steps:
– Images and text are converted to data– Data is packaged into segments– Each data segment is encapsulated in a packet with source
and destination addresses– Each packet is encapsulated in a frame with the MAC
address of the next directly connected device– Each frame is converted to a pattern of 1s and 0s and
transmitted on the media
