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www.ciscopress.com Networking Basics CCNA 1 Chapter 5
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Networking Basics CCNA 1Chapter 5
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Cabling LANs
Line Styles for Cables Used in Network Diagrams
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Cabling LANs
Ethernet LAN Physical Layer• Earliest Ethernet standards used coaxial cabling• Today’s standards called for twisted-pair (usually
UTP) or fiber-optic cabling• IEEE separated Ethernet into two standards
– IEEE 802.2 - Logical Link Control (LLC) sublayer defines part of the OSI data link layer
– IEEE 802.3 – Media Access Control (MAC) sublayer also defines part of the OSI data link layer
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Cabling LANs
Ethernet LAN Physical Layer (continued)
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Cabling LANs
Ethernet LAN Physical Layer Design Considerations
• Does maximum cable length allowed meet segment requirements
• Cost of cable• Cost of equipment on ends of cable• Which cables support which Ethernet speeds• Ease of installation• Susceptibility to interference
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Cabling LANs
Choosing Ethernet Types (Speeds) in the Campus
• Network engineers must consider speed of Ethernet types
• Most current PCs have 10/100 Mbps NICs – means a current design would use 100 Mbps Ethernet on the LAN
• Most new PCs come with 10/100/1000 Mbps NICs – must consider expense of upgrading LAN switches to 1000 Mbps (1 Gbps)
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Cabling LANs
Three Types of Ethernet Links• End-user level – Links between a hub/switch
and end users’ computers• Workgroup level – Links between the
hub/switch that attach to end users’ computers and other hubs/switches in the LAN core
• Backbone level – Links between the hubs/switches in the LAN core
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Cabling LANs
Campus LAN with Online
Curriculum’s LAN Level
Terms
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Cabling LANs
Ethernet Types and Speeds Used on Various Link Types per Online Curriculum
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Cabling LANs
Ethernet Types and Speeds Used on Various Link Types – Best Practices
• End-user level: 100 Mbps
• Workgroup level: 1 Gbps
• LAN Core (Backbone): 1 Gbps or 10 Gbps
• Remember, speeds will increase as the technology evolves
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Cabling LANs
Components of the Campus Design Model• Access switches and links – end-user devices
connect to access switches (LAN switches), with Ethernet links called access links
• Distribution switches and uplinks – a large number of access switches connect to a smaller number of distribution switches; the links between them are called uplinks
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Cabling LANs
Components of the Campus Design Model (continued)
• Building block – a single building’s design with access and distribution switches
• Core switches and links – in large campuses, each building block is connected to very fast core switches, using core links
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Cabling LANs
Ethernet Types, Media and Segment Lengths
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Cabling LANs
Ethernet Types, Media and Segment Lengths (continued)
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Cabling LANs
Ethernet Types, Media and Segment Lengths• Using the charts is important to the LAN planning
process• Most paths between devices are not straight line• After media are selected, cables with appropriate
connectors must be ordered or made• Some older NICs and networking devices use
attachment user interface (AUI) connectors
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Cabling LANs
Common LAN Cable Connectors
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Cabling LANs
Picking UTP Cable Pinouts• Straight-through – use TIA/EIA-T568-A or
TIA/EIA-T568-B on both ends• Crossover (10BASE-T and 100BASE-TX) - use
TIA/EIA-T568-A on one end and TIA/EIA-T568-B on the other end
• Crossover (1000BASE-TX) – use TIA/EIA-T568-A on one end and swap the orange/green (pairs 1 and 2) and blue/brown pairs (pairs 3 and 4) on the other end
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Cabling LANs
TIA/EIA-T568-A and TIA/EIA-T568B Pinouts
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Cabling LANs
10BASE-T and 100BASE-TX Crossover Cable
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Cabling LANs
1000BASE-T Crossover Cable
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Cabling LANs
Crossover Cables• Many products, including Cisco switches,
us Auto Medium-independent Crossover (Auto-mdix)
• Detects when a cable with wrong pinouts is connected
• Automatically makes internal changes to make connection work
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Cabling LANs
Choosing When to Use Straight-Through and Crossover Cables
• Devices that transmit at pins 1 and 2: PCs, routers, servers, wireless access points’ Ethernet ports
• Devices that transmit at pins 3 and 6: hubs, switches, bridges, repeaters
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Cabling LANs
Choosing When to Use Straight-Through and Crossover Cables
• Use a straight-through cable to connect– Switch to router– Switch to PC or server– Hub to PC or server
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Cabling LANs
Choosing When to Use Straight-Through and Crossover Cables
• Use a crossover cable to connect– Switch to switch– Switch to hub– Hub to hub– Router to router– PC to PC– Router to PC
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Cabling LANs
Choosing When to Use Straight-Through and Crossover Cables
• Cisco prints an “X” on ports that transmit on pins 3 and 6 instead of pins 1 and 2
• This denotes they are internally crossed over
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Cabling LANs
Choosing When to Use Straight-Through and Crossover Cables
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Cabling LANs
Connecting Ethernet Networking Devices• Must play close attention to distances between
devices• Must consider how extending the length of the
network by adding devices has an impact
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Cabling LANs
Connecting Ethernet Networking Devices
• Repeaters– Extend the distances over which an Ethernet
network can send data– Receives a degraded signal, cleans it up and
retimes it, and sends it out the other port– Cannot indefinitely extend a LAN
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Cabling LANs
Connecting Ethernet Networking Devices
• Repeaters– 5-4-3 rule
• At most 5 cables in the LAN• At most 4 repeaters• At most 3 cables can have PCs attached
– Allows for maximum distance of 500 meters
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Cabling LANs
Basic Function of a Repeater
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Cabling LANs
Connecting Ethernet Networking Devices• Hubs
– IEEE created 10BASE-T and hubs to overcome problems with older Ethernet standards
– Old standard called for a physical bus topology– New standard allows a physical star topology– Thinner cable makes installation easier– Maximum single cable length of 100 m, versus 185 m
and 500 m
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Cabling LANs
Connecting Ethernet Networking Devices• Hubs (continued)
– 10BASE-T allows the use of hubs and repeaters– Similar to repeaters, hubs receive a signal on one
port, regenerate it, and send it out all other ports– Hubs contain multiple RJ-45 jacks to provide a place
to connect multiple UTP cables, which creates the physical star topology
– Hubs are sometimes called “multiport repeaters” or “concentrators”
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Cabling LANs
10BASE-T with Hub Operation
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Cabling LANs
Comparing the Three Types of Ethernet Hubs
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Cabling LANs
Connecting Ethernet Networking Devices• Bridges
– Use logic to decide whether to forward frames– This logic is closely matched to OSI Layer 2, so
bridges are considered to be Layer 2 devices– Bridges use this process:
• Examine incoming frame, look at destination MAC address• If destination MAC is reachable via a different interface than
the one one which it was received, regenerate and forward out that interface (forward)
• If destination MAC is on the same interface it arrived on, discard the frame (filter)
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Cabling LANs
Bridge Making a Filtering Decision
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Cabling LANs
Bridge Making a Forwarding Decision
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Cabling LANs
Connecting Ethernet Networking Devices
• Ethernet switches– Provide all the benefits of repeaters, hubs and
bridges– Most LANs use switches instead of hubs or
bridges– LANs need repeaters only when very long
runs are needed
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Cabling LANs
Connecting Ethernet Networking Devices• Functions of an Ethernet Switch
– Like a hub, provides a large number of ports for making a physical star topology
– Like repeaters, hubs and bridges, regenerates a clean signal
– Like bridges, uses filtering/forwarding logic– Like bridges, separates a LAN into multiple collision
domains, increasing LAN bandwidth– Beyond the functions of hubs, repeaters, and bridges, offers
advanced features such as virtual LANS (VLANs) and much faster performance
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Cabling LANs
Switch Making a Forwarding
Decision
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Cabling LANs
Connecting Ethernet Networking Devices• Functions of an Ethernet Switch (continued)
– Uses a switching table much the same way a bridge uses a bridging table - Cisco switching table is sometimes referred to as Content Addressable Memory (CAM) table
– Allows devices to send data at the same time without collisions by using full-duplex logic
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Cabling LANs
Switch with Four 100 Mbps Ports – 400 Mbps
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Cabling LANs
Wireless Communications and Wireless Access Points
• “Wireless” does not mean just WLANs or Wi-Fi
• Includes most every type of electromagnetic (EM) energy– Radio waves– Microwaves– Infrared light
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Cabling LANs
Wireless Communications and Wireless Access Points
• Infrared (IR) and radio frequencies (RF) are both popular for wireless communication today
• IR requires line-of-sight between sending and receiving devices (TV remote control and TV)
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Cabling LANs
Wireless Communications and Wireless Access Points
• RF has been used for communications for more than a century: AM/FM radio, Airplane to control tower, Police and fire departments
• Does not require line-of-sight• Wireless devices designed for two-way communication
need a transmitter and a receiver• WLAN standards use a range of frequencies called a
spread spectrum
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Cabling LANs
WLAN Review• Wireless Access Points (APs)
– Have much in common with hubs and switches– Provide a centralized connection point (without wires)– Have limitations on distance– Like hubs, create a shared medium– PCs and laptops use wireless cards, so no networking
cables are needed– The AP connects to the rest of the network with a
cable
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Cabling LANs
AP, Switch, and Hub Used for End-User Device Access
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Cabling LANs
Ethernet NICs• NICs – expansion PC cards that create a way for
the PC to connect to a network• Must operate and OSI Layers 1 and 2• Layer 1 – send and receive signals over an
attached cable• Layer 2 – they frame data inside a header and
trailer, with header including Layer 2 address called the Media Access Control (MAC) address
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Cabling LANs
Ethernet NICs• Network diagrams do not usually show the NIC
as it is assumed each PC has one• On laptops, the NIC might be built in or in a small
expansion slot called a PC card slot
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Cabling LANs
Ethernet NIC: Circuit Board Internal to the PC
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Cabling LANs
Ethernet NIC: External Portion with RJ-45 Connector
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Cabling LANs
Ethernet NICs• Most NICs use an RJ-45 connector• Older NICs can be replaced or an adapter can be
used (older routers, e.g., may need an AUI connector for their Ethernet ports
• The use of an AUI means the device does not need to have an internal transceiver
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Cabling LANs
Using the LAN: Models for PC Communication
• Computers on a network need to share information
• Client/server model– Client: uses some resource on another
computer– Server: provides that service
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Cabling LANs
Using the LAN: Models for PC Communication
• Peer-to-peer model– A computer acts as a peer with other
computers by acting as a client in some cases and a server in other cases
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Cabling LANs
Using the LAN: Models for PC Communication
• Peer-to-peer networking– Computers act as equals, providing services
to each other– To act as a server, a computer must decide to
share some or all of its resources with other peers
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Cabling LANs
PC Constellation Shares a Folder
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Cabling LANs
Another PC Shares Constellation’s Folder
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Cabling LANs
Using the LAN: Models for PC Communication
• Peer-to-peer networking– Have several advantages over client/server
networks• Simple to install• No special hardware required• Users control their own resources• No network administrator required
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Cabling LANs
Using the LAN: Models for PC Communication
• Peer-to-peer networking– Have several disadvantages compared to
client/server networks• Lack centralized security controls• Individuals must perform own backups• When user’s PC is acting as a server, performance
may suffer• Don’t work well with lots of users (limit of 10 or so)
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Cabling LANs
Using the LAN: Models for PC Communication
• Client/server networking– End users all act as clients– Dedicated computers, called servers, provide
all services– Use of multiple servers is common
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Cabling LANs
Client/Server Networking Model
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Cabling LANs
Using the LAN: Models for PC Communication
• Client/server networking– End user PCs are typically less expensive– Servers use a network operating system (NOS) that is
more expensive– Servers are more expensive and powerful– Centralized security is available– Centralized backups can be done
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Cabling LANs
Comparing Peer-to-Peer and Client Server Networking
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Cabling WANs
Simple Internetwork with Two Routers
Jagged line is a WAN link; often called a “lightning bolt”
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Cabling WANs
WAN Physical and Data Link Layers
• Routers can have both LAN and WAN interfaces– LAN interface requirements are more obvious
• RJ-45 jack needs a cable with an RJ-45 connector
– Some WAN interfaces are less obvious• Might be ISDN, DSL or cable
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Cabling WANs
WAN Physical and Data Link Layers• Router Serial Interfaces
– A serial interface connects to channel service unit/data service unit (CSU/DSU) with a serial cable
– The proper serial cable must be selected by the network engineer
– Router has WAN interface cards that have particular types of connectors
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Cabling WANs
Different Connectors on Router WAN Interface Cards
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Cabling WANs
WAN Link with Serial Cables, CSU/DSUs, and the Telco Shown
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Cabling WANs
Routers and WAN Cables• Many WAN links require a CSU/DSU• Connection to the CSU/DSU from router is with a
serial cable• Different CSU/DSU vendors use different cables• After selecting the CSU/DSU, order the correct
serial cable
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Cabling WANs
WAN Serial Cables Used with a Router
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Cabling WANs
Routers and WAN Cables• The CSU/DSU connects to a cable provided by
the Telco – usually an RJ-45 connector but with a different pinout
• Most companies standardize on connectors• Some routers have the CSU/DSU built in, so no
serial cable is needed• Network engineer must also consider what
protocol is being used
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Cabling WANs
OSI Layers 1 and 2 for Router Serial Links
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Cabling WANs
Cable, DSL and ISDN
• ISDN– Allows a WAN connection to be dialed like a
phone call– WAN link is not up and working all the time– Often used as a backup to a full-time, always-
on link
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Cabling WANs
Cable, DSL and ISDN• Several varieties of ISDN
– Basic Rate Interface uses already-installed phone lines
– Allows two concurrent 64 Kbps WAN links called “B channels”
– Has a signaling channel, the “D channel”
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Cabling WANs
Cable, DSL and ISDN• DSL and cable modems are now popular
– DSL uses phone lines– Cable modems use cable TV coaxial cable
• All three methods use a variation of Point-to-Point Protocol (PPP)
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Cabling WANs
ISDN, DSL and Cable: Cables and Connectors
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Cabling WANs
WAN Speeds• WAN links provided by Telcos can run at a large
variety of speeds– 2400 bps to multiples of 64 Kbps, up to 1.544 Mbps (a
T1 connection)– Traditional WAN speeds go above T1
• A T3 circuit runs at 28 times the speed of a T1• Synchronous Optical Network (SONET) can exceed 10 Gbps
• Faster links cost more money• Maximum length between devices is based in
part on speed
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Cabling WANs
Serial Cable Lengths in Comparison to Speed
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Cabling WANs
Choosing DCE and DTE Cables• Devices on both ends of a link must be synchronized• The telco provides clocking (synchronization)• The CSU/DSU monitors the clocking from the telco• Data communications equipment (DCE) - a device that
supplies clocking to another device• Data terminal equipment (DTE) – a device that receives
clocking from another device and adjusts its clock as needed
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Cabling WANs
DCE and DTE on a Typical WAN Link
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Cabling WANs
Choosing DCE and DTE Cables• In some cases, the router needs to operate as a
DCE device• This is common in lab situations like ours• We do this so we do not have to buy two
CSU/DSUs.
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Cabling WANs
Router as DCE: Back-to-Back Serial Communication
The connection between the two routers is a crossover serial connection.
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Cabling WANs
Fixed and Modular Routers• Cisco routers with permanently installed
interfaces are called “fixed-function” routers
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Cabling WANs
Fixed and Modular Routers• Cisco routers with the capability to add and
remove cards are called “modular” routers• Most current Cisco routers support at least some
modular interfaces• Each interface type has a unique number
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Cabling WANs
Cisco 1841 Modular Router
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Cabling WANs
Cisco 1841 Modular Router
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Cabling WANs
Router Console Cabling• Technically isn’t a LAN or WAN cable• To gain access to a Cisco switch or router for initial
configuration, you need to know about console ports and cables
• To configure or troubleshoot a Cisco router or switch– Connect a PC to the console port of the router or switch by using
a rollover cable– Configure a terminal emulator on the PC with the proper settings– Log into the router or switch by using the terminal emulator on
the PC
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Cabling WANs
Console Cabling
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Cabling WANs
Router Console Cabling• Many PCs have a nine-pin connector (DB-9)
which is used for serial communications• May be called a “serial port” or a “COM port”• Most routers and switches have an RJ-45 port for
a console port• Connect a PC to a router or switch using a
rollover cable and two RJ-45 connectors• Use an RJ-45 to DB-9 adapter on the PC end
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Cabling WANs
Router Console Cabling• Configure HyperTerminal or another terminal
emulator– 9600 bps– 8 data bits– No parity– 1 stop bit– No flow control
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Cabling WANs
Router Auxiliary Port• Routers also have an auxiliary port• Used for “out of band” (not through the network)
management• A modem may be connected to the auxiliary port• The network engineer may call the router and
make changes and troubleshoot problems over the phone line
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Summary
• Ethernet is the most widely used LAN technology
• Ethernet technologies provide a variety of speeds from 10 Mbps to 10 Gbps
• A NIC’s connector must match the media– Coax typically uses BNC connectors– STP and UTP use RJ-45 connectors– Fiber-Optic uses ST, SC or MT-RJ connectors
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Summary
• Twisted-pair cabling must use the correct pinout to work properly
• A crossover cable is used to connect two similar devices, such as switches
• A straight-through cable connects two different devices, such as a PC and a switch
• A rollover cable connects a PC to the console port of a router or a switch
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Summary
• Repeaters regenerate and retime network signals and let them travel a longer distance
• Hubs act as multiport repeaters and provide a central device to connect devices in a star physical topology
• Hubs are sometimes called concentrators• Bridges and switches use logic at Layer 2 of the
OSI model to decide when to forward frames or when not to forward (filter) them
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Summary
• Bridges and switches examine the destination MAC address of the frame and compare it to a list of MAC addresses and ports
• Because bridges and switches do not forward traffic unless necessary, they provide more bandwidth than hubs and repeaters and greatly improve network performance
• LAN switches provide the same basic functions as a bridge, but have a large number of ports that act as a concentration point
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Summary
• Today’s switches are so much faster than bridges that vendors such as Cisco no longer sell bridges
• Switches support a large variety of extra features, such as VLANs
• Wireless networks can be created with much less cabling than other networks
• Wireless AP’s connect to the rest of the network with an Ethernet cable
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Summary
• Wireless devices use transmitters and receivers to convert bits to EM waves (transmitter) and then back to bits at the destination (receiver)
• Two most common types of wireless technologies used for networking are IR and RF
• Typically computers use a peer-to-peer or client/server network model
• In both models, one computer acts as a client and another acts as a server
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Summary
• In peer-to-peer networks, networked computers act as equal partners
• In client/server networks, network services are located on a computer called a server and end-user computers always act as clients
• Routers are responsible for routing packets from source to destination computers
• Routers typically connect to a wide range of networking media, including different WAN (ISDN, DSL, CABLE) and LAN (Ethernet) types
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Summary
• Each WAN type requires some type of media and connector
• When a router’s serial interface is used, the cable type is determined by– Physical connector on the router– Physical interface on the CSU/DSU
• Router interface can be DCE or DTE, but is usually a DTE interface
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Summary
• A router serial WAN link can be DCE or DTE
• DCE provides clock synchronization; DTE adjusts its clock to match DTE end
• Traditionally, a router is a DTE device and a CSU/DSU is a DCE device (except in lab situations where no CSU/DSUs are used)
