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Open Systems Interconnection (OSI) Model
1) Physical => transmission & receipt of signals via cabling or wireless interface
2) Data Link => transfers data between nodes on the same logical segment
3) Network => moves data round a network of networks, associated with IP
4) Transport => moves frames and datagrams between nodes and networks
5) Session => manages communication between devices
6) Presentation => supports data compression and encryption
7) Application => layer that users see
SOHO Routers
Multifunction network appliance
Modem, switch, wireless AP, router, and firewall
Establishes a LAN and connects it to the Internet WAN
Unshielded Twisted Pair (UTP)
Copper cabling used in telephone wiring and LANs
Low cost
Ease of installation
Shielded Twisted Pair (STP)
Adds an outer covering
Reduce cross-talk, EMI, RFI
More expensive, harder to install
Coaxiale Cable
Built with a metal shield
Designed to block signal interference
Mostly used by TV companies
Twinaxial cable
Two inner conductors
Cost-effective, power efficient, high-speed
Plenum-rated cable
Fire-rated cable jacket
RJ11 connector
6 position, 2 conductor (6P2C)
Some cables will wire additional conductors
Telephone or DSL connection (POTS)
RJ45
8 position, 8 conductor (8P8C)
Modular connector
Ethernet
F-connector
Coaxial connector
Used for cable TV and cable modem connections
BNC (Bayonet Neill-Concelman) connector
Coaxial connector
Secured by an outer ring
High-frequency signals over long distances
Minimal signal loss
Commonly used in video and networking applications
Fiber Optic Cables
Immune to interference
More secure
Longer distances
Multi-mode => short ranges, LED
Single-mode => long ranges, laser
Straight Tip (ST) => bayonet-style twist-and-lock
Subscriber Connector (SC) => push-pull latching mechanism
Local Connector (LC) => snag-free latch, audible click
Mechanical Transfer Registered Jack (MT-RJ)
Small form factor duplex fiber optic connector with a snap-in design
Very efficient, high density, low cost, lightweight
Multi-fiber Push On (MPO)
Multiple fibers in a single physical connector interface
Physical Contact (PC) Connector
Faces of the connector and fiber tip are polished so that they curve slightly and fit together better
Ultra Physical Contact (UPC) => polished to a higher standard than the PC
Angled Physical Contact (APC) => faces are angled for an even tighter connection and better return loss performance
Transceivers
Transmits and receives data over various mediums, including optical fibers, copper cables, and wireless channels
Small Form Factor Pluggable (SFP)
Fiber optic transceiver module type supporting duplex 1 Gbps link
Enhanced Small Form-Factor Pluggable (SFP+)
Fiber optic transceiver module type supporting duplex 16 Gbps link
Quad Small Form Factor Pluggable (QSFP)
Fiber optic transceiver module type supporting four individual duplex lanes at 1 Gbps (QSFP) or 10 Gbps (QSFP+) that can be aggregated into a single 4 Gbps or 40 Gbps channel.
Wavelength Division Multiplexing (WDM)
Means of using a strand to transmit and/or receive more than one channel at a time
Power over Ethernet (PoE)
Allows power to be transmitted over Ethernet cable to remote devices.
Congestion
Network is trying to send and receive more data than its capacity allows
Bottlenecks
Flow of data is slowed or stopped due to a limited capacity or processing point in a network
Single performance metric can slow all of the others down
I/O bus, CPU speed, storage access speed
Bandwidth
Amount of data that can be transmitted over a network in a given amount of time
Throughput
Amount of data successfully transferred through the network
Latency
Delay between the request and response
Amount of time it takes for data packets to travel from one place to another
Jitter
Inconsistency in the time it takes for data packets to reach their destination across a network
Hub
Connects devices in a network
Repeats any data it receives to all devices except the sender
Bridges
Decides whether or not to forward data
Looks at the destination and source MAC address
Segments LANs into smaller sections
Switches
Forwards traffic based on data link address
Has a MAC address table that may pair addresses and corresponding ports
Routers
Connects internal network to outside network
Routes traffic between networks
Access point
Bridge that extends the wired network onto the wireless network
Modem
Allows device to connect to the Internet (ISP) through a physical connection
Converts digital to analog signals that can be transmitted over telephone lines or cable networks
Media converters
Used to transition from one cable type to another
Load Balancer
Distributes network traffic across multiple servers
Proxies
Sits between the users and the external network
Receives the user requests and sends the request on their behalf
Useful for URL filtering, content scanning, access control
Network Attached Storage (NAS)
Network-connected computer dedicated to providing file-based data storage services to other network devices
Storage Area Network (SAN)
Dedicated high-speed network consisting of both hardware and software
Used to connect and manage shared storage devices, such as disk arrays, tape libraries, and optical storage devices
Content Delivery Network (CDN)
System of hardware and software
Stores user data in many different geographical locations and makes those data available on demand
Quality of Service (QoS)
Provide better "priority" service to selected network traffic over various technologies
Spanning Tree Protocol (STP)
A protocol that enables switches to detect and repair bridge loops automatically
Blocking => not forwarding to prevent loop
Listening => not forwarding and cleaning MAC table
Learning => not forwarding and adding to the MAC table
Forwarding => data passes through and is fully operational
Disabled => administrator has turned off the port
Rapid STP (RSTP) => Faster convergence, backwards-compatible
Jump Box
Acts as a secure gateway through which a user can connect before launching any administrative task or connecting to other servers within the network
Burned-in Address (BIA)
The 6-byte address assigned by the vendor making the card
Locally Administered Address (LAA)
MAC address that can be configured on a device
LAA can be used in place of the BIA
Replace a NIC or use a substitute device without changing the address used by the network to access the station
Broadcast Address
The I/G bit of a MAC address determines whether the frame is addressed to an individual (0) or group (1)
Maximum Transmission Unit (MTU)
The largest packet size supported on an interface.
Protocol Analyzer
Tool that allows the inspection of traffic by a host or passing over a network link
Packet Sniffer
Software or hardware used to collect data travelling over a network.
Interrogates the frames received by the network adapter
Switched Port Analyzer (SPAN)
Copies Ethernet frames passing through switch ports and send these frames out to specific port
Monitor communications passing over the switch
Not completely reliable
Passive Test Access Point (TAP)
Box with ports for incoming and outgoing network
Physically copies the signal from the cabling to a monitor port
No logical decisions
Active TAP
Powered device that performs signal regeneration
May become a point of failure
tcpdump
A command-line protocol analyzer
Used to capture packets
Wireshark
Application that captures and analyzes network packets
Nmap
A network utility designed to scan a network and create a map
Find devices and identify open ports
Cisco Discovery Protocol (CDP)
Cisco proprietary Layer 2 protocol to gather information about neighboring Cisco devices
Link Layer Discovery Protocol (LLDP)
A protocol that identifies devices connected on the local area network and allows them to automatically exchange information
ping
A utility that sends an ICMP echo request message to a host
Test reachability
traceroute
Determine the route a packet takes to a destination
netstat
A TCP/IP utility that shows the status of each active connection
Display network statistics
nslookup/dig
Lookup information from DNS servers
arp
Address Resolution Protocol information
View the local ARP table
Ethernet Switch Types
Unmanaged => without configuration
Managed => with configuration
Stackable => combined into a single unit
Fixed => set number of ports
Modular => slots for plug-in cards
Desktop => freestanding units
Rack-mounted => designed to fit on standard-sized racks
MAC Address Table
A switch learns MAC addresses by reading the source address when a frame is received on a port
Port Aggregation / Link Aggregation
Combining two or more separate cabled links into a single logical channel
Link Aggregation Control Protocol (LACP)
Port Mirroring
Copies all packets sent to one or more source ports to a mirror (or destination) port
Capture and analyze network traffic
Jumbo Frames
Supports a data payload of up to 9000 bytes
Reduces the number of frames that need to be transmitted
Flow Control
Allows a server to instruct the switch to pause traffic temporarily to avoid overwhelming its buffer and causing it to drop frames
Network Troubleshooting Methodology
1) Identify the Problem
2) Establish a theory of probable cause
3) Test the theory to determine cause
4) Establish a plan of action to resolve the problem and identify potential effects
5) Implement the solution or escalate as necessary
6) Verify full system functionality, and if applicable, implement preventive measures
7) Document findings, actions, and outcomes
Attenuation
Loss of signal strength
Network Loopback Adapter/Plug
Specially wired RJ-45 plug
Used to test for bad ports and network cards
LED status indicators
Uses LED lights to indicate proper connection and presence of traffic
Cable Testers
Reports detailed information on the physical and electrical properties of the cable
Tests cable conditions such as crosstalk, attenuation, noise, resistance, etc
Time Domain Reflectometer (TDR)
Measure the length of a cable run
Can locate open and short circuits
Wi-Fi Analyzer
Device or software that can report characteristics of a WLAN, such as signal strength and channel utilization
Visual Fault Locator (VFL)
Device that shines light down the fiber to help locate broken glas
Multimeter
A measuring instrument for current, voltage, and resistance
Primarily used to test electrical circuits
Wire Map Tester
Tool to verify termination/pinouts of cable
Identifies continuity, short, incorrect pin-out or termination, reversed pair, crossed pair, etc
Tone Generator
Used to trace a cable from one end to the other
Crosstalk (XT)
Signal on one circuit affects another circuit
Near End (NEXT) => interference at transmitting end
Far End (FEXT) => interference away from the transmitter
Alien (AXT) => interference from other cables
Attenuation to Crosstalk Ratio
Difference between insertion loss and NEXT
Optical Time Domain Reflectometer (OTDR)
Used to measure the length of a fiber optic cable run
Able to locate faults
Optical Spectrum Analyzer (OSA)
Determine whether cable is suitable for reuse with WDM and which wavelengths will support the link distance required
Cyclic Redundancy Check (CRC)
Mathematical algorithm executed on a data string by both sender and receiver
If the calculated CRC values match, data string was not corrupted during transmission
Runts
Frames that are less than 64 bytes
Giants
Frames that are more than 1518 bytes
Port Status
Administratively down => device admin has intentionally "turned off" an interface
Suspended => configuration is not compatible with the current connection
IP Address
Unique address that identifies a device on the internet or a local network
Default gateway
Allows devices to communicate with the outside world, allows digital traffic to leave the network
Automatic Private IP Addressing (APIPA)
Allows a DHCP client to automatically configure an IP Address and subnet mask when a DHCP server is not available
A link-local address
Loopback Address
An IP address that indicates your own computer
Used to test TCP/IP configuration on the computer
Virtual IP addresses (VIP)
Not associated with a physical network adapter
Virtual machine, internal router address
Classless Inter-Domain Routing (CIDR)
Removed the restrictions created by classful subnet masks
Variable Length Subnet Masks (VLSM)
The capability to specify a different subnet mask for the same Class A, B, or C network number on different subnets
Address Resolution Protocol (ARP)
Performs the task of resolving an IP address to a hardware address
Subnet addressing
Has three hierarchical levels: network ID, subnet ID, and host ID
Bits from the host portion of the IP address must be allocated as a subnetwork address
Unicast
A message that is sent from a single sender to a single recipient
One-to-one
Broadcast
Addressing multiple hosts/everyone
One-to-all
Multicast
One host sending to other hosts that identify as interested in receiving
One-to-many
Uses class D
Anycast
An anycast communication flow is a one-to-nearest
Internet Control Message Protocol (ICMP)
Used to report errors and send messages about the delivery of a packet
Can also be used to test and troubleshoot connectivity issues on IP networks
Neighbor Discovery Protocol (NDP)
Part of the IPv6 protocol suite
Used to discover and exchange information about devices on the same subnet
Replaces ARP and ICMP in IPv4