02 - Fundamentals of Ethernet LANs

8/12/2019 02 - Fundamentals of Ethernet LANs

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By Muhammad Asghar [email protected]

02 - Fundamentals of Ethernet LANs

Reference: Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide By WENDELL ODOM

© Cisco Press



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Agenda

www.asghars.blogspot.com

Local Area Networks

Overview of EthernetHistory of EthernetCommon Ethernet StandardsEthernet Media RequirementsEthernet UTP Cabling

UTP Cabling Pinouts for 10BASE-T and 100BASE-TUTP Cabling Pinouts for 1000BASE-T

Ethernet Data Link ProtocolsEthernet AddressingEthernet Type FieldError Detection with FCS

Repeaters, Hubs, Bridges & Switches

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Local Area Networks


LANs interconnect host devices over short distances

LANs can support high speed and a fairly large bandwidthLAN traffic can be controlled with bridges and switches orHubs

Ethernet is the undisputed king of LAN standards todayHistorically speaking, several competing LAN standardsexisted, including Token Ring, Fiber Distributed DataInterface (FDDI), and Asynchronous Transfer Mode (ATM)

Eventually, Ethernet won out over all the competing LANstandardsFigure on next slide shows a simple Ethernet LAN or SmallOffice / Home Office (SOHO) LAN

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Local Area Networks


Figure on next slide shows a conceptual view of atypical enterprise LAN in a three-story buildingTo allow communication between floors, each per-floorswitch connects to one centralized distribution switch

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Local Area Networks


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Overview of Ethernet


The term Ethernet refers to a family of standards that

dene the Physical and Data Link layers of the LANnetworksMost of the standards dene a different variation ofEthernet at the Physical Layer, with differences in speed

and types of cablingAdditionally, for the Data Link Layer, the IEEE separates thefunctions into two sublayers:

The 802.3 Media Access Control (MAC) sublayerThe 802.2 Logical Link Control (LLC) sublayer

Ethernet acts like a single LAN technology because it usesthe same data link layer standard (common Ethernetheader and trailer)over all types of Ethernet physical links

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History of Ethernet


The IEEE in the early 1980s formed two committees that worked

directly on Ethernet —the IEEE 802.3 committee and the IEEE802.2 committeeThe 802.3 committee worked on Physical Layer standards as wellas a subpart of the Data Link Layer called Media Access Control(MAC)

The IEEE assigned the other functions of the Data Link Layer tothe 802.2 committee, calling this part of the data link layer theLogical Link Control (LLC) sublayerThe two early Ethernet standards were 10BASE5 and 10BASE2.

You should not expect to need to implement 10BASE5 or10BASE2 Ethernet LANs today10BASE5 and 10BASE2 had limitations on the total length of acable. With 10BASE5, the limit was 500 m; with 10BASE2, it was185 m

Repeaters were used with 10BASE5 and 10BASE2 standards

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Common Ethernet Standards


• The T refer to the fact that each of these standards denes the use of UTP cabling,with the T referring to the T in twisted pair.

• While X refer to the fact that these standards defines the use of fiber optic

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Ethernet Media Requirements


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Ethernet UTP Cabling


The three most common Ethernet standards used todayare:

10BASE-T (Ethernet)100BASE-T (Fast Ethernet, or FE), and

1000BASE-T (Gigabit Ethernet, or GE)These three standard use UTP cablingTo create electrical circuit, Ethernet defines how to usethe two wires inside a single twisted pair of wires asshown in figureTo send data, the two devices follow an encodingscheme

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Ethernet link has three basic components i.e. cable,connectors on the ends of cable and matching ports onthe devices

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CableCable holds some copper wires, grouped as twisted pairs10Base-T and 100Base-T require two pairs of wires, while1000Base-T requires four pairs

ConnectorsEthernet UTP cables use an RJ-45 connector on both endsRJ-45 connector has eight physical locations into whicheight wires in the cable can be inserted, called pin

positionsPorts

PCs often include the Ethernet ports as part of NIC

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UTP Cable, RJ-45 Connectors and Ports

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Used when the devices on the ends of the cable use

opposite pins when they transmit data10Base -T and 100Base-T use two pair of wires in UTP cable,one for each direction as shown in figure

In the figure on last slide, the PC transmits using the top pair,and the switch on the right transmits using the bottom pair

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As a rule, Ethernet NIC transmitters use the pair connected

to pins 1 and 2, while NIC receivers use a pair of wires at pinposition 3 and 6While the switch knowing those facts do the opposite, theirreceivers use the pins 1 and 2, and their transmitters use the

pins 3 and 6Figure shows the straight through cable pinout

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Crossover Cable PinoutMostly used when connecting like devices like switch toswitchBecause like devices both transmit on over the same pins,therefore; a Crossover cable is used

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It crosses the pair at the transmit pins on each device to the

receive pins on the opposite deviceThe figure shows the crossover cable b/w two switches

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For exam, you should be well prepared to choose which

type of cable is needed in each part of networkHere the key is to know whether a device acts like a PCNIC or like a switch

Table lists the devices and the pin pairs they use

Cisco switches have feature called auto-mdix that noticeswhen the wrong cable is used and automatically changesits logic to make the link work

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UTP Cabling Pinouts for 1000BASE-T

1000BASE-T differs from 10BASE-T and 100BASE-T as far as thecabling and pinoutsStraight-Through Cable Pinouts

The straight-through cable connects each pin with the samenumbered pin on the other side, but it does so for all eight pinsIt keeps one pair at pins 1 and 2 and another at pins 2 and 6,just like in the erlier writing. It adds a pair 4 and 5 and the finalpair at pins 7 and 8

Crossover Cable PinoutsCrossover cables crosses the same two-wire pairs as in theprevious Ethernet standards, but it also crosses the two newpairs as well (pair at pins 4,5 with pair at pins 7,8)

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Ethernet Data Link Protocols


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Ethernet AddressingEthernet LAN addressing identies either individualdevices or groups of devices on a LANEach address is 6 bytes long, is usually written in

hexadecimal, typically is written with periods separatingeach set of four hex digits. For example, 0000.0C12.3456is a valid Ethernet addressEthernet address are also known as Hardware Addresses,

Physical Addresses or MAC AddressesUnicast Ethernet Addresses

Identify a single LAN card

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Each LAN card comes with a burned-in address (BIA) that is

burned into the ROM chip on the cardBIAs sometimes are called universally administeredaddresses (UAA) because the IEEE universally (well, at leastworldwide) administers address assignment

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Group AddressesIdentify more than one LAN interface card. The IEEE denestwo general categories of group addresses for Ethernet Broadcast Addresses: The most often used of the IEEE groupMAC addresses, the broadcast address, has a value ofFFFF.FFFF.FFFF (hexadecimal notation). The broadcastaddress implies that all devices on the LAN should processthe frameMulticast Addresses: Multicast addresses are used to allow a

subset of devices on a LAN to communicate. When IPmulticasts over an Ethernet, the multicast MAC addressesused by IP follow this format: 0100.5exx.xxxx, where anyvalue can be used in the last half of the address

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LAN MAC Address Terminology and Features

Ethernet Type FieldThe Ethernet type field or Ethernet type sits in the Ethernetdata link layer header

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Its purpose is to help the network processing on routers

and hosts i.e. It identifies the type of network layer (Layer3) packet inside the Ethernet frameThe device originating the Ethernet frame insert a value(a hexadecimal number) to identify the type of packetencapsulated inside the Ethernet frameIEEE manages a list of EthernetType valuesAs shown in figure, a host can send one Ethernet frame

with IPv4 packet and the next Ethernet frame with IPv6packet, each of these frame will have different EthernetType field value, reserved by the IEEE

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Error Detection with FCSEthernet Frame Check Sequence (FCS) field gives the

receiving node a way to compare results with the sender,to discover whether errors occurred in the frameNote Error detection does not mean error recovery,Ethernet defines that the errored frame should be

discarded, recovery is task of TCP

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RepeatersRepeaters was used with 10BASE5 and 10BASE2 standardsRepeaters connect to multiple cable segments, receivethe electrical signal on one cable, interpret the bits as 1s

and 0s, and generate a brand-new, clean, strong signalout the other cableA repeater does not simply amplify the signal, becauseamplifying the signal might also amplify any noise picked

up along the wayRepeaters propagate the collisions

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BridgesBridges create one collision domain per port and canforward data frames only on the outbound port thatreaches the destination of the frame, as opposed tohubs, which send the frame out on all portsA bridge is slower than a switch because it uses softwareinstead of hardware application-specific integratedcircuits (ASICs)

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SwitchesCreate one collision domain per port and can forward dataframes only on the outbound port that reaches the destinationof the frame

Switches can buffer frames in memory, switches cancompletely eliminate collisions on switch ports that connect toa single device

As a result, LAN switches with only one device cabled to eachport of the switch allow the use of full-duplex operation. Fullduplex means that anEthernet card can send and

receive concurrently

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02 - Fundamentals of Ethernet LANs

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