CCNA Routing and Switching Study Guide: Todd Lammle - ICND1

10Base-T (IEEE 802.3)

- 10 Mbps using category 3 unshielded twisted pair (UTP) wiring for runs up to 100 meters - Each device must connect into a hub or switch, and allows only one host per segment or wire - Uses an RJ45 connector (8-pin modular connector) with a physical star topology and a logical bus

Most Common IEEE Ethernet Standards

- 10Base-T (IEEE 802.3) - 100Base-TX (IEEE 802.3u) - 100Base-FX (IEEE 802.3u) - 1000Base-CX (IEEE 802.3z) - 1000Base-T (IEEE 802.3ab) - 1000Base-SX (IEEE 802.3z) - 1000Base-LX (IEEE 802.3z) - 1000Base-ZX (Cisco standard) - 10GBase-T (802.3.an)

1000Base-ZX (Cisco standard)

- A Cisco specified standard for Gigabit Ethernet communication - Operates on ordinary single-mode fiber-optic links with spans up to 43.5 miles (70 km)

Ethernet

- A contention based media access method that allows all hosts on a network to share the same link's bandwidth - Simple to implement and makes troubleshooting straightforward - Readily scalable: eases the process of integrating new technologies into an existing network infrastructure - Uses both Data Link and Physical Layer specifications

Internetwork Switch

- A device sends packets to the Internet - The other devices do not "hear" the frame because they are in diffierent collision domains - The frame goes directly to the default gateway router

MAC Address

- A hexadecimal number identifying the physical connection of a host - Operate at Layer 2 of the OSI model - Enables hosts on the same physical segment to locate one another

Buffer

- A section of memory used to store datagrams that a machine can not readily process because they flooded in too quickly - Can only be successful if the flooded datagrams are part of a small burst - If the datagram deluge continues, eventually exhausting the device's memory, its flood capacity will be exceeded and the device will dump any and all additional datagrams it receives - Operates at the Transport Layer

10GBase-T (802.3.an)

- A standard proposed by the IEEE 802.3an committee to provide 10 Gbps connections over conventional UTP cables, (category 5e, 6, or 7 cables) - Allows the conventional RJ45 used for Ethernet LANs and can support signal transmission at the full 100-meter distance specified for LAN wiring

Positive Acknowledgement with Restransmission

- A technique that requires a receiving machine to communicate with the transmitting source by sending an acknowledgement message back to the sender when it receives data - The sender documents each segment measured in bytes, then sends and waits for the acknowledgement before sending next segments; when it sends a segment, the sender starts a timer and will retransmit if it expires before it gets an acknowledgement back from the receiving end

Characteristics that allow a Service to be considered Connection-Oriented

- A virtual circuit, or "three-way handshake" is set up - It uses sequencing - It uses acknowledgements - It uses flow control

Wireless Access Point

- A wireless device that allows hosts to connect wirelessly using the IEEE 802.11 specification - Don't actually segment the network, only extend them

Transparent Bridging

- After a filter table is built on the layer 2 device, it will forward frames only to the segment where the destination hardware address is located - If the destination device is on the same segment as the frame, the layer 2 device will block the frame from going to any other segments - If the destination is on a different segment, the frame can be transmitted only to that segment

Switches

- An OSI Layer 2 device - Employed to add functionality to network LAN - The main purpose is to optimize LAN performance; Provide more bandwidth to users - Switch frames from one port to another on a switched network - Break up collision domains by default - Create separate collision domains within a single broadcast domain

Routers

- An OSI Layer 3 device - Used to connect networks and route data packets between networks - Employed to efficiently break up a broadcast domain by default; Can break up collision domains as well - Provide connections to wide area network services via a serial interface for WAN connections - Create a separate broadcast domain for each interface - Because each interface represents a separate network, it must be assigned unique network identification numbers, and each host on the network connected must use the same network number

OSI Layer Functions

- Application: File, Print, Message, Database, and Application Services - Presentation: Data Encryption, Compression, and Translation Services - Session: Dialog Control - Transport: End-to-End Connection - Network: Routing - Data Link: Framing - Physical: Physical Topology

Converting from Binary to Hex

- Binary number 01010101: 1. First, break it into nibbles—0101 and 0101—with the value of each nibble being 5 since the 1 and 4 bits are on 2. The hex answer 0x55 3. In decimal format, the number converts to 64 + 16 + 4 + 1 = 85 - Binary number 11001100: 1. Answer would be 1100 = 12 and 1100 = 12 2. Converted to CC in hex 3. The decimal conversion answer would be 128 + 64 + 8 + 4 = 204 - Binary number 10110101: 1. The hex answer would be 0xB5; 1011 converts to B and 0101 converts to 5 2. The decimal equivalent is 128 + 32 + 16 + 4 + 1 = 181

Router Characteristics

- By default, will not forward any broadcast or multicast packets - Each LAN interface is a broadcast domain - Break up broadcast domains by default and provide WAN services - Use the logical address in a Network Layer header to determine the next-hop router to forward the packet to - Can use access lists, created by an administrator, to control security based on the types of packets allowed to enter or exit an interface - Can provide layer 2 bridging functions if needed and can simultaneously route through the same interface - Provide connections between virtual LANs (VLANs) - Can provide quality of service (QoS) for specific types of network traffic

Bytes Examples

- Byte decimal values can add up to a number that's significantly higher than 15 - If every bit is counted as a one (1), then the byte binary value would look like: 11111111; Then count up every bit spot because each is turned on; It would look like: 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 - 10010110; The 128, 16, 4, and 2 bits are on, so we'll just add them up: 128 + 16 + 4 + 2 = 150 - 01101100; The 64, 32, 8, and 4 bits are on: 64 + 32 + 8 + 4 = 108 - 11101000; The 128, 64, 32, and 8 bits are on: 128 + 64 + 32 + 8 = 232

IP Address

- Can be expressed in binary or decimal format - Logical identifiers that are on Layer 3 of the OSI model - Used when hosts reside on different LAN segments or subnets

Key Presentation Layer Functions

- Compression - Decompression - Encryption - Decryption - Multimedia Operations

Hexadecimal Addressing

- Converted by reading nibbles, not bytes - Uses only the characters 0 through 9 - uses the first six letters of the alphabet, A through F, to extend beyond the available 10 characters in the decimal system; used to represent 10, 11, 12, 13, 14, and 15, respectively - Cisco likes to put 0x in front of characters so you know that they are a hex value - Each hex character is one nibble and that two hex characters joined together make a byte - To figure out the binary value, put the hex characters into two nibbles and then join them together into a byte

1000Base-CX (IEEE 802.3z)

- Copper twisted-pair, called twinax, is a balanced coaxial pair that can run only up to 25 meters and uses a special 9-pin connector known as the High Speed Serial Data Connector (HSSDC) - Used in Cisco's new Data Center technologies

Two (2) Types of Packets used at the Network Layer

- Data Packets - Route Update Packets

Data Link Layer Sub-Layer: Media Access Control (MAC)

- Defines how packets are placed on the media - Physical addressing is defined here as well as logical topologies - Line discipline, error notification (but not correction), the ordered delivery of frames, and optional flow control can also be used at this sub-layer

Effects of CSMA/CD Network Collisions

- Delay - Low Throughput - Congestion

Physical Layer (1)

- Does two things: it sends bits and receives bits; Bits come only in values of 1 or 0—a Morse code with numerical values - Communicates directly with the various types of actual communication media - Different kinds of media represent bit values in different ways; Some use audio tones, while others employ state transitions—changes in voltage from high to low and low to high - Specific protocols are needed for each type of media to describe the proper bit patterns to be used, how data is encoded into media signals, and the various qualities of the physical media's attachment interface - Specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating a physical link between end systems - Identifies the interface between the data terminal equipment (DTE) and the data communication equipment (DCE); The DCE is usually located at the service provider, while the DTE is the attached device - The services available to the DTE are most often accessed via a modem or channel service unit/data service unit (CSU/DSU) - Responsible for taking 1s and 0s and encoding them into a digital signal for transmission on the network segment

Benefits of using Switches vs. Hubs

- Each switch port is actually its own collision domain - Hubs create one large collision domain - Each device on every segment plugged into a switch can transmit simultaneously as there's only one host on each port and there isn't a hub plugged into a switch port - Hubs only allow one device per network segment to communicate at a time

Reliable Data Transport in Flow Control

- Employs a connection-oriented communications session between systems - Protocols involved ensure that the following will be achieved: - Segments delivered are acknowledged back to send upon receipt - Any segments not acknowledged are retransmitted - Segments are sequenced back into proper order upon arrival at destination - A manageable data flow is maintained in order to avoid congestion, overloading, or data loss

Ethernet at the Physical Layer

- Ethernet was first implemented by a group called DIX, which stands for Digital, Intel, and Xerox - They created and implemented the first Ethernet LAN specification, which the IEEE used to create the IEEE 802.3 committee - This was a 10 Mbps network that ran on coax and then eventually twisted-pair and fiber physical media - The IEEE extended the 802.3 committee to three new committees known as 802.3u (Fast Ethernet), 802.3ab (Gigabit Ethernet on category 5) and then finally one more, 802.3ae (10 Gbps over fiber and coax)

Session Multiplexing

- Evnet that occurs when the Transport Layer, working in tandem with the Session Layer, separates data from different applications - Takes place when a client connects to a server with multiple browser sessions open

Flow Control

- Fail-safe solution in place at the Transport Layer that ensures data integrity by allowing applications to request reliable data transport between systems - Prevents a sending host on one side of the connection from overflowing the buffers in the receiving host - Purpose is to provide a way for the receiving device to control the amount of data sent by the sender

Examples of Application Layer Events

- File Transfers - Email - Enabling Remote Access - Network Management Activities - Client/Server Processes - Information Location

Half-Duplex and Full-Duplex Points to Remember

- Full-duplex Ethernet requires a point-to-point connection when only two nodes are present - Half-duplex Ethernet shares a collision domain and provides a lower effective throughput than full-duplex Ethernet, which typically has a private per-port collision domain plus a higher effective throughput - There are no collisions in full-duplex mode - A dedicated switch port is required for each full-duplex node - The host network card and the switch port must be capable of operating in fullduplex mode - The default behavior of 10Base-T and 100Base-T hosts is 10 Mbps half-duplex if the autodetect mechanism fails, so it is always good practice to set the speed and duplex of each port on a switch if you can

Nibble Examples

- If a 1 is placed in each spot of a nibble, add up 8 + 4 + 2 + 1 to get a maximum value of 15 - A nibble binary value of 1001 means that the 8 bit and the 1 bit are turned on, which equals a decimal value of 9 - A nibble binary value of 0110 means that the decimal value would be 6, because the 4 and 2 bits are turned on

Collision Event

- If two devices on a single physical segment just happen to transmit simultaneously, it will cause a collision and require these devices to retransmit - A situation where each device's digital signals totally interfere with one another on the wire

Transmitting Segments with Flow Control

- Instead of dumping and losing data, the Transport layer can issue a "not ready" indicator to the sender, or potential source of the flood - This mechanism works kind of like a stoplight, signaling the sending device to stop transmitting segment traffic to its overwhelmed peer - After the peer receiver processes the segments already in its memory reservoir—its buffer—it sends out a "ready" transport indicator - When the machine waiting to transmit the rest of its datagrams receives this "go" indicator, it resumes its transmission

Benefits of using the OSI Layered Model

- It divides the network communication process into smaller components, facilitating component development, design, and troubleshooting - It allows multiple-vendor development through network component standardization - It encourages industry standardization by clearly defining what functions occur at each layer - It allows various types of network hardware and software to communicate - It prevents changes in one layer from affecting other layers to expedite development

Layer 2 Bridging and Switching

- Layer 2 switching is considered hardware-based bridging because it uses specialized hardware called an application-specific integrated circuit (ASIC) - ASICs can run up to high gigabit speeds with very low latency rates - Bridges and switches read each frame as it passes through the network, the device then puts the source hardware address in a filter table and keeps track of which port the frame was received on - This information (logged in the bridge's or switch's filter table) is what helps the machine determine the location of the specific sending device - Primarily, Layer 3 machines (such as routers) need to locate specific networks, whereas Layer 2 machines (switches and bridges) need to eventually locate specific devices - Networks are to routers as individual devices are to switches and bridges - Routing tables that "map" the internetwork are for routers, as filter tables that "map" individual devices are for switches and bridges

Network Layer (3)

- Manages logical device addressing, tracks the location of devices on the network, and determines the best way to move data - Transports traffic between devices that aren't locally attached - Routers are specified at this layer, and provide the routing services within an internetwork

100Base-TX (IEEE 802.3u)

- Most commonly known as Fast Ethernet, uses EIA/TIA category 5, 5E, or 6 UTP two-pair wiring - One user per segment - Up to 100 meters long - Uses an RJ45 connector with a physical star topology and a logical bus

Routing Table Information

- Network Addresses (NET) : Protocol-specific network addresses; A router must maintain a routing table for individual routing protocols because each routed protocol keeps track of a network with a different addressing scheme - Interface (INT): The exit interface a packet will take when destined for a specific network - Metric (Metric): The distance to the remote network; Different routing protocols use different ways of computing the distance (i.e. hop count, delay of the line, tick count)

Devices that Operate at All Seven Layers of the OSI Model

- Network Management Stations (NMS's) - Web and Application Servers - Gateways (Not Default Gateways) - Servers - Network Hosts

Binary Values

- Nibble Values: 8 4 2 1 - Byte Values: 128 64 32 16 8 4 2 1

Four (4) Ways Routers Function in Networks

- Packet Switching - Packet Filtering - Internetwork Communication - Path Selection

Presentation Layer (6)

- Presents data to the Application Layer and is responsible for data translation and code formatting - Serves as OSI Model's translator, providing coding and conversion services - Ensures that data transferred from the Application Layer of one system can be read by the Application Layer of another

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

- Protocol used by ethernet networks which helps devices share bandwidth evenly while preventing two devices from transmitting simultaneously on the same network medium - Created to overcome the problem of the collisions that occur when packets are transmitted from different nodes at the same time - When a host wants to transmit over the network, it first checks for the presence of a digital signal on the wire; If all is clear and no other host is transmitting, the host will then proceed with its transmission - The transmitting host constantly monitors the wire to make sure no other hosts begin transmitting; If the host detects another signal on the wire, it sends out an extended jam signal that causes all nodes on the segment to stop sending data (think busy signal) - The nodes respond to that jam signal by waiting a bit before attempting to transmit again - Backoff algorithms determine when the colliding stations can retransmit; If collisions keep occurring after 15 tries, the nodes attempting to transmit will then time out

Data Link Layer (2)

- Provides for the physical transmission of data and handles error notification, network topology, and flow control - Will ensure that messages are delivered to the proper device on a LAN using hardware addresses and will translate messages from the Network Layer into bits for the Physical Layer - Formats the message and adds a customized header containing the hardware destination and the source address; the added information forms a sort of capsule that surrounds the original message - Responsible for the actual unique identification of each device that resides on a local network - Uses hardware addressing to allow a host to send packets to individual hosts on a local network as well as transmit packets between routers - Uses Ethernet and IEEE standards - Frames a packet with control information each time it is sent between routers, but the information is stripped off at the receiving router and only the original packet is left completely intact - Packet framing continues at each hop until the packet is finally delivered to the correct receiving host - The packet itself is never altered along the route, it's only encapsulated with the type of control information required for it to be properly passed on to the different media types - As data is encoded with control information at each layer of the OSI model, the data is named with something called a Protocol Data Unit (PDU): At the Transport layer the PDU is called a Segment, Network layer is Packet, Data Link is Frame, and Physical layer is Bits

Hubs at the Physical Layer

- Really multiple-port repeaters; A repeater receives a digital signal, reamplifies or regenerates that signal, then forwards the signal out the other port without looking at any data - Does the same thing across all active ports: any digital signal received from a segment on a port is regenerated or reamplified and transmitted out all other ports on the hub - All connected devices are in the same collision domain as well as in the same broadcast domain - Do not examine any of the traffic as it enters or before it's transmitted out to the other parts of the physical media - Every connected device must listen if a device transmits - Creates physical star network topology, and is a central device and cables extend in all directions out from it,

Broadcast Domain

- Refers to a group of devices on a specific network segment that hear all the broadcasts sent out on that specific network segment - Usually a boundary delimited by physical media like switches and routers - Can also refer to a logical division of a network segment, where all hosts can communicate via a Data Link Layer, hardware address broadcast

Ethernet at the Data Link Layer

- Responsible for Ethernet addressing, commonly referred to as MAC or hardware addressing - Also responsible for framing packets received from the Network Layer and preparing them for transmission on the local network through the Ethernet contention-based media access method

Data Link Layer Sub-Layer: Logical Link Control (LLC)

- Responsible for identifying Network Layer protocols and then encapsulating them - The LLC header tells the Data Link Layer what to do with a packet once a frame is received - the host receives a frame and it looks in the LLC header to find out where the packet is destined - Can also provide flow control and sequencing of control bits

Session Layer (5)

- Responsible for setting up, managing, and dismantling sessions between Presentation Layer entities and keeping user data separate - Dialogue control between devices - Coordinates and organizes communication between hosts' various applications, as from a client to a server, via three different modes: Simplex, Half-Duplex, and Full-Duplex

Transport Layer (4)

- Segments and reassembles data into a single data stream - Services take all the various data received from upper-layer applications, combine it into the same concise data stream - Protocols provide end-to-end data transport services and can establish a logical connection between the sending host an destination host on an internetwork - TCP and UDP are integral protocols - Responsible for providing mechanisms for multiplexing upper-layer applications, establishing sessions, and tearing down virtual circuits - Can also hide details of network-dependent information from the higher layers as well as provide transparent data transfer - Can be either be connectionless or connection-oriented

Three (3) Modes used to Coordinate and Organize Data at the Session Layer

- Simplex - Half-Duplex - Full-Duplex

Ethernet Frames

- The Data Link Layer is responsible for combining bits into bytes and bytes into frames - Frames are used at the Data Link Layer to encapsulate packets handed down from the Network Layer for transmission on a type of media access - The function of Ethernet stations is to pass data frames between each other using a group of bits known as a MAC frame format - This provides error detection from a cyclic redundancy check (CRC); This is error detection, not error correction

Binary Numbering

- The digits used are limited to either a 1 or a 0, and each digit is called a bit, which is short for binary digit - Typically, you group either 4 or 8 bits together, with these being referred to as a nibble and a byte, respectively - The typical decimal format is the base-10 number scheme - The numbers are placed in a value spot, starting at the right and moving left, with each spot having double the value of the previous spot - If a one digit (1) is placed in a value spot, then the nibble or byte takes on that decimal value and adds it to any other value spots that have a 1 - If a zero (0) is placed in a bit spot, you don't count that value

1000Base-SX (IEEE 802.3z)

- The implementation of 1 Gigabit Ethernet running over multimode fiber-optic cable instead of copper twisted-pair cable, using short wavelength laser - Multimode fiber (MMF) using 62.5- and 50-micron core - Uses an 850 nanometer (nm) laser and can go up to 220 meters with 62.5-micron, 550 meters with 50-micron

Window

- The quantity of data segments, measured in bytes, that the transmitting machine is allowed to send without receiving an acknowledgement - The size controls how much information is transferred from one end to the other before an acknowledgement is required - The sending host can improve the communications session if the receiving host fails to receive all the bytes that it should acknowledge by reducing the size

Backoff on an Ethernet Network

- The retransmission delay that's enforced when a collision occurs - When that happens, a host will resume transmission only after the forced time delay has expired - After the backoff has elapsed, all stations have equal priority to transmit data

Reliable Delivery

- The sending machine transmits the first set of segments - The receiving node acknowledges that it has received them by requesting the segment it is expecting next - When it receives the acknowledgment, the sender then transmits the next set of segments - If one of the segments doesn't make it to the destination, the receiving node acknowledges that event with a request for the segment to be re-sent - The sending machine will then resend the lost segment and wait for an acknowledgment, which it must receive in order to move on to the transmission of the last segment

EIA/TIA (Electronic Industries Alliance and the newer Telecommunications Industry Association)

- The standards body that creates the Physical layer specifications for Ethernet - Specifies that Ethernet use a registered jack (RJ) connector on unshielded twisted-pair (UTP) cabling (RJ45) - Every Ethernet cable type that's specified has inherent attenuation - The cabling used in corporate and home markets is measured in categories; A higher-quality cable will have a higher-rated category and lower attenuation

Windowing

- There are two window sizes, one set to 1 and one set to 3 - If you've configured a window size of 1, the sending machine will wait for an acknowledgment for each data segment it transmits before transmitting another one but will allow three to be transmitted before receiving an acknowledgement if the window size is set to 3 *In reality, the transmission isn't based on simple numbers but in the amount of bytes that can be sent*

Data Packets

- These are used to transport user data through the internetwork - Protocols used to support data traffic are called Routed Protocols (i.e. IP and IPv6)

Two (2) Advantages of using Routers

- They do not forward broadcasts by default - They can filter a network based on OSI Layer 3 information such as an IP address

Causes of LAN Traffic Congestion

- Too many hosts in a collision or broadcast domain - Broadcast storms - Too much multicast traffic - Low bandwidth - Adding hub for network connectivity - A bunch of ARP broadcasts

Half-Duplex

- Two-way communication - Can take place in only one direction at a time, preventing the interruption of the transmitting device

Full-Duplex

- Two-way communication - Devices can transmit and receive at the same time

Connection-Oriented Communication

- Used by the Transport Layer to ensure reliable data transport - The process in which a device establishes a connection-oriented communication session with a remote device - its peer system - known as a call setup or a three-way handshake - Once this process is complete, the data transfer occurs, and when it's finished, a call termination takes place to tear down the virtual circuit - Virtual circuit setup also known as Overhead

Virtual LANs (VLANs)

- Used to create small broadcast domains in modern switched networks - Employed to increase bandwidth available to individual users - Can be used to easily control both collision and broadcast domains

Route Update Packets

- Used to update neighboring routers about the networks connected to all routers within the internetwork - Used to help build and maintain routing tables - Protocols that send route update packets are called Routing Protocols - Most critical protocols for CCNA: RIP, RIPv2, EIGRP, and OSPF

100Base-FX (IEEE 802.3u)

- Uses fiber cabling 62.5/125-micron multimode fiber - Point-to-point topology - Up to 412 meters long - Uses ST and SC connectors, which are media-interface connectors *Fiber-optic cable provides a more secure, long-distance cable that is not susceptible to EMI (Electromagnetic Interference) at high speeds*

Half-Duplex Ethernet

- Uses only one wire pair with a digital signal running in both directions on the wire - Uses the CSMA/CD protocol to help prevent collisions and to permit retransmitting if one occurs - If a hub is attached to a switch, it must operate in half-duplex mode because the end stations must be able to detect collisions - The network can only run half-duplex, and if two hosts communicate at the same time there will be a collision - Half-duplex Ethernet is only about 30 to 40 percent efficient because a large 100Base-T network will usually only give you 30 to 40 Mbps, at most, due to overhead

Ethernet Addressing

- Uses the Media Access Control (MAC) address burned into each and every Ethernet network interface card (NIC) - The MAC, or hardware, address is a 48-bit (6-byte) address written in a hexadecimal format

Full-Duplex Ethernet

- Uses two pairs of wires at the same time instead of a single wire pair like half-duplex - Uses a point-to-point connection between the transmitter of the transmitting device and the receiver of the receiving device - Transfers happen a lot faster when compared to half-duplex transfers - Because the transmitted data is sent on a different set of wires than the received data, collisions won't happen - Can be used with any device except a hub - Supposed to offer 100-percent efficiency in both directions; Rate is known as an aggregate rate (not guaranteed)

Auto-Detect Mechanism

- When a full-duplex Ethernet port is powered on, it first connects to the remote end and then negotiates with the other end of the Fast Ethernet link - The mechanism first decides on the exchange capability, which means it checks to see if it can run at 10, 100, or even 1000 Mbps - It then checks to see if it can run full-duplex, and if it can't, it will run half-duplex

Layer 2 Switching

- When a switch interface receives a frame with a destination hardware address that isn't found in the device's filter table, it will forward the frame to all connected segments - If the unknown device that was sent the "mystery frame" replies to this forwarding action, the switch updates its filter table regarding that device's location - In the event the destination address of the transmitting frame is a broadcast address, the switch will forward all broadcasts to every connected segment by default - All devices that the broadcast is forwarded to are considered to be in the same broadcast domain - This can be a problem because Layer 2 devices propagate Layer 2 broadcast storms that can seriously choke performance - The only way to stop a broadcast storm from propagating through an internetwork is with a Layer 3 device—a router

Application Layer (7)

- Where users communicate to the computer and comes into play only when it's clear that access to the network will be needed soon - The interface between the actual application program and the next layer down by providing ways for the application to send information down through the protocol stack - Identification and confirmation of the communications partner's availability and verification of the required resources to permit the specified type of communication to take place

Six Situations in which Full-Duplex Ethernet can be used

- With a connection from a switch to a host - With a connection from a switch to a switch - With a connection from a host to a host - With a connection from a switch to a router - With a connection from a router to a router - With a connection from a router to a host

Steps in CSMA/CD Operation

1. A jam signal informs all devices that a collision occurred 2. The collision invokes a random backoff algorithm 3. Each device on the Ethernet segment stops transmitting for a short time until its backoff timer expires 4. All hosts have equal priority to transmit after the timers have expired

MAC Address Composition

1. Organizationally Unique Identifier (OUI) - assigned by the IEEE to an organization; composed of 24 bits, or 3 bytes, and it in turn assigns a globally administered address also made up of 24 bits, or 3 bytes, that's supposedly unique to each and every adapter an organization manufactures 2. Individual/Group (I/G) bit - high-order bit; when it has a value of 0, we can assume that the address is the MAC address of a device and that it may well appear in the source portion of the MAC header; when it's a 1, the address represents either a broadcast or multicast address in Ethernet 3. Global/Local (G/L) bit - next bit; when set to 0, this bit represents a globally administered address, as assigned by the IEEE, but when it's a 1, it represents a locally governed and administered address 4. Locally Administered or Manufacturer-Assigned Code - low-order 24 bits of an Ethernet address; commonly starts with 24 0s for the first card made and continues in order until there are 24 1s for the last (16,777,216th) card made

Ethernet Frame Format

1. Preamble: 7 Bytes; An alternating 1,0 pattern provides a 5 MHz clock at the start of each packet, which allows the receiving devices to lock the incoming bit stream 2. Start Frame Delimiter (SFD)/Synch: 1 Byte; The preamble is seven octets and the SFD is one octet (synch); The SFD is 10101011, where the last pair of 1s allows the receiver to come into the alternating 1,0 pattern somewhere in the middle and still sync up to detect the beginning of the data 3. Destination Address (DA): 6 Bytes; This transmits a 48-bit value using the least significant bit (LSB) first; Used by receiving stations to determine whether an incoming packet is addressed to a particular node; Can be an individual address or a broadcast or multicast MAC address; A broadcast is all 1s—all Fs in hex— and is sent to all devices; A multicast is sent only to a similar subset of nodes on a network 4. Source Address (SA): 6 Bytes; a 48-bit MAC address used to identify the transmitting device, and it uses the least significant bit first; Broadcast and multicast address formats are illegal within the SA field 5. Length or Type: 2 Bytes; 802.3 uses a Length field, but an Ethernet_II frame uses a Type field to identify the Network layer protocol; The old, original 802.3 cannot identify the upper-layer protocol and must be used with a proprietary LAN—IPX, for example 6. Data: 46 - 1500 Bytes (Packet); A packet sent down to the Data Link layer from the Network layer; The size can vary from 46 to 1,500 bytes 7. Frame Check Sequence (FCS): 4 Bytes; A field at the end of the frame that's used to store the cyclic redundancy check (CRC) answer; When a receiving host receives the frame and runs the CRC, the answer should be the same; If not, the frame is discarded, assuming errors have occurred

Steps in Connection-Oriented Communication (TCP Handshake)

1. The first "connection agreement' segment is a request for synchronization (SYN) 2. The next segments acknowledge (ACK) the request and establish connection parameters - the rules - between hosts; These segments request that the receiver's sequencing is synchronized here as well so that a bidirectional connection can be formed 3. The final segment is also and acknowledgement, which notifies the destination host that the connection agreement has been accepted and that the actual connection has been established; Data transfer can now begin

Ethernet_II Frame Examples

1. The frame below has only three fields: Destination, Source,and Type, which is shown as Protocol Type - Destination: 00:60:f5:00:1f:27 Source: 00:60:f5:00:1f:2c Protocol Type: 08-00 IP The Type field is IP, or 08-00, mostly just referred to as 0x800 in hexadecimal 2. The next frame has the same fields, so it must be an Ethernet_II frame as well - Destination: ff:ff:ff:ff:ff:ff Ethernet Broadcast Source: 02:07:01:22:de:a4 Protocol Type: 08-00 IP This frame was a broadcastbecause the destination hardware address is all 1s in binary, or all Fs in hexadecimal 3. In the next example, the Ethernet frame is the same Ethernet_II frame used with the IPv4 routed protocol - Destination: IPv6-Neighbor-Discovery_00:01:00:03 (33:33:00:01:00:03) Source: Aopen_3e:7f:dd (00:01:80:3e:7f:dd) Type: IPv6 (0x86dd) The Type field has 0x86dd when the frame is carrying IPv6 data, and when we have IPv4 data, the frame uses 0x0800 in the protocol field Because of the Type field, we can run any Network Layer routed protocol and the frame will carry the data because it can identify the Network Layer protocol

Ethernet Cabling

3 Types: - Straight-through cable - Crossover cable - Rolled cable

Open Systems Interconnection (OSI) Model

7. Application (Upper Layer) - Provides user interface 6. Presentation (Upper Layer) - Presents data; Handles processing such as encryption 5. Session (Upper Layer) - Keeps different applications' data separate 4. Transport (Lower Layer) - Provides reliable or unreliable delivery; Performs error correction before retransmit 3. Network (Lower Layer) - Provides logical addressing, which routers use for path determination 2. Data Link (Lower Layer) - Combines packets into bytes and bytes into frames; Provides access to media using MAC address; Performs error detection not correction 1. Physical (Lower Layer) - Moves bits between devices; Specifies voltage, wire speed, and pinout of cables

Cyclic Redundancy Check (CRC)

A mathematical algorithm that's run when each frame is built based on the data in the frame

Network Segmentation

Breaking up a massive network in to smaller networks

Category 5 Enhanced Unshielded Twisted Pair (UTP) Cable

Can handle speeds up to a gigabit with a distance of up to 100 meters

1000Base-T (IEEE 802.3ab)

Category 5, four-pair UTP wiring up to 100 meters long and up to 1 Gbps

Tunneling

Encapsulating a frame within a different type of frame

Collision Domain

Network in which a device sends out a packet on a network segment, and all other devices on the segment are forced to pay attention no matter what

Bridges

Reduce collisions in broadcast domains; Increase number of collision domains in a network

Collision Domain

Refers to a network scenario wherein one device sends a frame out on a physical network segment forcing every other device on the same segment to pay attention to it

Simplex

Simple one-way communication

1000Base-LX (IEEE 802.3z)

Single-mode fiber that uses a 9-micron core and 1300 nm laser and can go from 3 kilometers up to 10 kilometers

Attenuation

The loss of signal strength as it travels the length of a cable and is measured in decibels (dB)

Broadcast Domain

The set of all devices on a network segment which are allowed to hear all broadcasts sent out on that specific segment

Crosstalk

The unwanted signal interference from adjacent pairs in the cable