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CompTIA A+

Mar 09, 2024, 7 min read

Parts I felt needed polish

Mobile Devices

  • Laptops
    • Backlight inverter
      • If the monitor is super dim and the brightness doesn’t seem to be able to increase. It’s likely the backlight inverter.
  • Screens
    • LCD (Liquid Crystal Diode)
      • There are two kinds
        • Active
          • Generally faster and brighter
        • Passive
          • Blurry and slow
    • IPS (in-plane switching)
      • Faster
      • Clear
      • Color Accurate
      • High Motion Blur
    • TN (Twisted Neumatic)
      • Cheapest
      • Fastest
      • Low motion blur
      • Bad viewing angles
      • Low color accuracy & contrast ratio
    • VA (Verticle Alignment)
      • Hybrid Tech
      • Better everything
  • Ports
    • Serial
      • Sometimes referred to as COM or RS232 & DB9
  • Mobile Device Application Support
    • Microsoft ActiveSync
      • Gets all devices including iPhones set up from a central location (like gmail and even have corperate control)
    • Mobile Device Management (MDM)
      • This is control of multiple devices in a central place

Networking

Ports and Protocols

  • Standard Port Ranges
    • Well-known Ports
      • 0-1023
    • Register Port Range
      • 1024-49151
    • Dynamic Port Range
      • 49151-65535
  • Protocols
    • Email
      • SMTP (Simple Mail Transfer Protocol): 25
      • IMAP (Internet Message Access Protocol): 143
      • POP3 (Post Office Protocol Version 3): 110
    • File
      • FTP: 20,21
      • TFTP (Trivial FTP): 69
    • Remote Connection
      • Telnet: 23
      • SSH (Secure Shell): 22
      • RDP (Remote Desktop): 3389
    • Network Services
      • DNS (Domain Network System): 53
      • NETBIOS (Network Basic Input/Output System): 137/139 - Outdated
      • DHCP (Dynamic Host Configuration): 67 & 68
      • SNMP (Simple Network Management): 161/162
      • LDAP (Lightweight Directory Access Protocol): 389
      • SMB (Server Message Block): 445

Networking Hardware

  • NIC (Network Interface Card)
  • Hubs - Outdated
  • Switches
    • Managed
    • Unmanaged
  • PoE (Power over Ethernet)
    • PoE = 15.4W (802.3af)
    • PoE+ = 30W (802.3at)
    • PoE++ = 60W (802.3bt, Type 3)
    • PoE++ = 100W (802.3bt, Type 4)
  • Patch Panel
    • Series of Ports (This is what I saw at iCode) that has a bunch of wires coming out the backs.
  • Optical network terminal (ONT)
  • Fios
    • Fiber Optic
  • SDN: Programmatically configure the network

Wireless Protocols

  • 2.4 GHz: Includes Wi-Fi, Bluetooth, Cordless Devices, and Medical Devices
    • 13 Channels: 11 channels in North America, three that don’t overlap
  • 5 GHz: Has less saturation and wider channels through bonding
    • The channels on these don’t overlap like 2.4GHz
  • 802.11:
    • .11a
      • 5 GHz
      • 54 Mbps
    • .11b
      • 2.4 GHz
      • 11 Mbps
    • .11g
      • 2.4 GHz
      • 54 Mbps
    • .11n: Wi-Fi 4
      • 2.4/5 GHz
      • 600 Mbps
    • .11ac: Wi-Fi 5
      • 5 GHz
      • 7 Gbps
    • .11ax: Wi-Fi 6
      • 2.4/5 GHz
      • 10 Gbps
  • Bluetooth:
    • 2.4 GHz frequency: 10 meters or 32.8 feet
    • Standards:
      • 1.1 legacy: First Standardization, 1 Mbps
      • 2.0: Bluetooth + Enhanced Data Rate (EDR), 3 Mbps
      • 3.0: Bluetooth + high speed (HS): 24 Mbps via co-allocated Wi-Fi channel
      • 4.0: Bluetooth + low energy (LE), focus on IoT (Internet of Things).
      • 5.0: Variety of revisions of this standard
  • NFC:
    • 13.56 MHz (megahertz)
  • RFID:
    • Not to be confused with NFC
    • These are tags (Powered and Unpowered)
    • Powered Tags can have up to 100 meters of range

Network Hosts and Services

  • Directory Server: Authentication Servers
    • E.g. Microsoft ActiveDirectory
  • Print Server
    • Central Place to put all printers into so entire building can access the same drivers
  • Internet Appliances
    • Unified Threat Management (UTM) appliance
      • Expensive
      • Takes multiple Security functions into one device
    • Load balancers.
    • Proxy Server
  • SCADA
    • Collection of components
    • E.g. control systems, power grids, water grids, etc

DNS (Domain Name System)

  • FQDN (Fully Qualified Domain Name)
  • Name Resolution Process:
    • Hosts file
    • Local resolver cache.
    • DNS servers: Root first, top-level domain (TLD), system landscape directory (SLD):
      • Locally configured DNS server: private or internet service provider (ISP) DNS server.
      • Root hint.
      • TLD.
      • SLD or host’s domain (SLD, typically organizations)
  • DNS database and records
    • A
      • IPv4
    • AAAA
      • IPv6
    • MX (Mail Exchanger)
      • This is the IP that handles all emails on the domain’s behalf
    • TXT
      • Plain text record
      • Allows for DKIM, DMARC, etc

DHCP (Dynamic Host Configuration Protocol)

  • DHCP Lease Process: Temporary Assignment of an IP to a host
    • Step 1: Discover
      • Send out a signal for all DHCP servers to give a response with configs
    • Step 2: Offer
      • Any DHCP server that hears this request will respond with config
    • Step 3: Request
      • The host tells the first server that responds that it’s requested its config
    • Step 4: Acknowledge
      • DHCP marks it as registered in its system with lease and a timestamp
  • DHCP Scope
    • The range of IP addresses that is allowed to be leased to hosts
  • Reservations
    • Like a static IP but managed by the DHCP server. Allows you to keep specific IPs for specific hosts.

IP Address Configuration

  • Subnet Mask: A binary number to identify what network the computers are on.
    • E.g. 255.255.255.0 192.168.0.10

Note

The highlighted portion is the network ID and the portions after are the “host portion”

  • IPv4 Classes
    • Public Ranges
      • Class A: 1.0.0.0–127.255.255.255
      • Class B: 128.0.0.1–191.255.255.255
      • Class C: 192.0.0.0–223.255.255.255
    • Private Ranges:
      • Class A: 10.0.0.0–10.255.255.255
      • Class B: 172.16.0.0–172.31.255.255
      • Class C: 192.168.0.0–192.168.255.255
    • Reserved Addresses:
      • APIPA address: 169.254.x.y
        • This is used as a fallback if a DHCP connection fails
        • APIPA hosts can only communicate with other APIPA
  • IPv4 vs IPv6
    • IPv4
      • 32-bit
      • dotted decimal
      • 4 octets
      • limited addresses
    • IPv6
      • 128-bit
      • Colon separated hexadecimal
      • 8 blocks
      • Massive address space
  • IPv6 Specifics
    • :: means that 3 continuous blocks of 0000 are truncated
      • This cannot appear twice, if it does, then it’s not IPv6
      • fe80 is also not a part of the first block of IPv6 it’s considered a “link-local” address indicator
      • Leading zeroes in each block can also be left out, and it is still valid
      • E.g. fe80::c53c:41f2:564f:6d3a
    • Types of IPv6 addresses
      • Global
      • Unique Local
      • Link-Local

Internet Connection Types

  • Fiber (Optic)
  • Cable
    • Shared Connection with other people in the area and can slow down when other people in the area use it.
  • Dial-Up
    • Telephone line (Low-speed) but disaster recovery often use this since they’re first to go up.
    • Can’t use phone while using internet
  • DSL
    • This is also a telephone line but allows you to use both phone and internet
    • Max distance of 8000 feet
    • ADSL is different upload and download speeds.
  • Cellular
    • Same internet as smartphones
  • Satellite
  • WISP
    • Like cellular
    • Sses mixed tech
    • Line of sight comms

Network Types

  • Personal Area Network (PAN)
    • E.g. Bluetooth and Phone
  • LAN (Local Area Network)
    • Network in a single geographic location
    • Private Links
  • VLAN (Virtual Local Area Network)
    • A way to divide a switch into multiple switches
    • This allows for only certain devices to be able to communicate with certain other devices within a network.
  • WAN (Wide Area Network)
    • Spans multiple geolocations
    • Using ISP internet links
    • This connects something like 2 homes together
  • MAN (Metropolitan Area Network)
    • This is a network that only stays within city limits
  • SAN (Storage Area Network)
    • Highly optimized fiber comms to combine storage connections
    • Usually in enterprise
  • NAS

Network Tools

  • Cable Stripper
    • Remove coating of cables like shield
  • Cable Crimper
    • These are to hold together wires for things like RJ-45
    • Coaxial crimpers are also a thing
  • Cable Tester
    • You plug ends of a cable like RJ-45 to see if the cables are connected correctly
  • Toner Probe (Wire Tracker)
    • This helps find the correct cable in a bundle of cables in a server closet
  • Punchdown Tool
    • This is for patch panels
    • Make sure you have it facing the correct direction
  • Loopback Plug
    • It’s an RJ-45 connector that connects back in on itself to test that it can send a signal back to itself.
  • Network Tap
    • Expensive device that lets you listen on comms from one destination to another to see the data that’s passing through cable.
  • Wifi analyzer
    • Let’s you read traffic on wifi network

Hardware

  • Copper Media
    • Twisted Pair Cabling
      • 8 Copper Conductors
      • 4 Twisted Pairs
      • Twists are to protect against electromagnetic interference
      • UTP vs. STP
        • Unshielded Twisted Pair
        • Shielded Twisted Pair
      • RJ-45 Jack to connect the pairs
      • Adding something like a RJ-45 is called “terminating”
      • Plenum vs Nonplenum
        • PVC (Polyfenel Chloride?) also known as non plenum jacketing when burnt releases toxic gas
        • Plenum is for firecode non toxic
    • Specs CAT cables
      • CAT5
        • Fast Ethernet
      • CAT5e(nhanced)
        • Gigabit ethernet (actually 350 mbps)
      • CAT6
        • Actual Gigabit ethernet
      • CAT6a
        • 10 Gbps

Graph View

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