CCNA 1.4 Ethernet Networking

• Ethernet is a contention media method that allows all devices on a network to share the bandwidth of a link
• Ethernet utilizes Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to avoid packets collisions
• When collision occurs, a jam signal is send to all device to stop transmission until the backoff timer expire
• Half-duplex Ethernet use one wire pair and share a collision domain
• Full-duplex Ethernet use two wire pairs and has own collision domain (no hub)
• Ethernet at Layer 2 is responsible for Hardware/MAC addressing
• Ethernet MAC address format:

I/G = Individual/Group (broadcast or multicast) bit = 0/1

G/L = Global/Local bit = 0/1

OUI = Assigned by IEEE to org

• Ethernet frame format:

Preamble = provides a 5 MHz clock at start of packet to lock incoming bit stream

DA = Destination Address

SA = Source Address

Type = Network Layer protocol identification

Data = Packet from Layer 3 to 2 (64-1500 bytes)

FCS = Frame Check Sequence (for CRC storing)

• IEEE 802.3 Standard:

10Base2 = 10Mbps, baseband, up to 185m (thinnet)

10Base5 = 10Mbps, baseband, up to 5oom (thicknet)

10BaseT = 10Mbps, category 3 UTP wiring

100BaseTX = 100Mbps, category 5, 6, 7 UTP two-pair wiring, 100m (802.3u)

100BaseFX = 100Mbps, 62.5/125 micron multimode fiber, 412m (802.3u)

1000BaseCX = 1Gbps, copper twisted-pair(twinax), 25 m (802.3z)

1000BaseT = 1Gbps, category 5 UTP four-pair wiring, 100m (802.3ab)

1000BaseSX = 1Gbps, 62.5/50 micron multimode fiber, 220m/550m (802.3z)

1000BaseLX = 1Gbps, 9 micron single mode fiber, 3-9km (802.3z)

CCNA 1.3 The OSI Reference Model

• OSI has seven layers, divide into two groups: Application, Presentation and Session layer; Transport, Network, Data Link and Physical Layer
• The top three layers define applications communication between end stations
• The bottom three layers define data transmission between end points
• Application Layer provides interface between actual application programs
• Presentation Layer presents data to Application layer and responsible for data encryption, compression and translation services
• Session Layer separates different applications' data from other applications' data, provides dialog control between nodes and organize systems communication through simplex, half duplex and full duplex mode.
• Transport Layer provides reliable (TCP) or unreliable (UDP) end-to-end delivery by reassembling data from upper layers into a data stream and performs error correction before retransmit
• Reliable networking (connection-oriented) at the Transport Layer can be achieved through flow control, sequencing and acknowledgment
• Flow control allows receiver to govern the amount of data sent by sender through buffering, windowing and congestion avoidance.
• Buffer acts a memory section of receiver to store data from sender
• Window is the quantity of data (bytes) that the sender is allowed to sent without acknowledgment from receiver
• Acknowledgment requires receiver to send ack to sender when it receives data
• Network Layer provides routing service within an internetwork with two types of packets: data (IP, IPv6) and route update (RIP, RIPv2) packet
• Data Link Layer provides access to device in a LAN through hardware address, format packets into frames and perform error detection
• Data Link Layer has two sublayers: Media Access Control (802.3) and Logical Link Control (802.2)
• MAC defines how packets are placed on the media
• LLC identifies network layer protocol and then encapsulates them
• Physical Layer activates, maintains and deactivates physical link between actual communication media through sending and receiving bits

CCNA 1.2 Internetworking Models

• Open System Interconnection (OSI) was created by International Organization for Standardization (ISO) to standardize internetworking
• OSI model utilizes layered architecture
• Changes in one OSI layer doesn't affect other layers

CCNA 1.1 Internetworking Basics

• Internetwork is created when two or more LANs or WANs are connected via a router
• Network Segmentation involves breaking up a network into a number of smaller portions for network traffic efficiency
• Network Segmentation can be achieved by using devices such as router, switches and bridges (Hub doesn't segment network)
• A switch/bridge can replace the hub, breaking up collision domains
• A router can replace the switch/bridge, breaking up broadcast domains

CCNA: Introduction

• Cisco is the king of internetworking world! =)