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Chapter 19: Local Area Networking (A+ Study Notes)


A+
Study Notebook
You can find my complete study notes in Google Docs format below: https://docs.google.com/document/d/1zcKLWfsns1tqzmXtVRJbcd9NqfaEcjifgIo-oJIbEgc/edit?usp=sharing

References:
M. MEYERS, 2019.  CompTIA A+ All-in-One Exam Guide. 10th ed.

Chapter 19: Local Area Networking

  • IP (4 characters, 0 to 255,  3 dots in-between, never ends in 255) 
  • Types (no longer in use, the current in use system is called CIDR (Classless Inter-Domain Routing. Which means all IP is converted into binary. For e.g. 192.168.0.0/23 . Where /23 means that 1st 23 bits are for the network portion):
    • 1.x.x.x = Class A ( last 3 digit groups can be allocated, millions of hosts) 
      • 1st group can be from 1 to 126
      • 10.X.X.X - private address
    • 128.16.x.x = Class B - (last 2 digit groups can be allocated, 65536 hosts) 
      • 1st group can be from 128 to 191 
      • 172.16.X.X to 172.31.X.X - private addresses 
      • 169.254.0.1 - 169.254.255.254 - APIPA range
    • 192.11.12.x = Class C (only last digit can be allocated, max 254 hosts) 
      • 1st group starts from 192 to 223 
      • 192.168.X.X - private address


  • 224.X.X.X =  Class D-multicast (for presentations) 
  • 240.X.X.X = Class E (reserved / none uses it? ) 
  • 127.0.0.1 = LoopBack

  • Subnet Mask 
    • IP consists of network ID and host ID
    • Subnet mask block out (or masks) the network portion of an IP address.
      IP address: 192.168.4.33
Subnet mask: 255.255.255.0

                Because the first three octets are 255, the network ID is 192.168.4 and the host ID is 33.
  • Subnet masks are binary.
    • default is 255.255.255.0, where 0 will change depending on the number of the machines on your local network. Or it can be 255.255.0.0 where 0 will change depending on how large your network becomes
    • For e.g. if my IP address is 11.12.13.66, and subnet mask is 255.255.255.0 I know that it is Class C and network ID for the local network will be 11.12.13.x . And host 66
    • For e.g. if my IP address is 11.12.13.66, and subnet mask is 255.255.0.0 I know that it is Class B and network ID for the local network will be 11.12.x.x . Host 13.66.

  • Default Gateway (Router & its IP address - it will convert IP addresses which are outside its own LAN network to its own) - it is kind of a gate between yourself on the world wide internet 

  • NAT (Network Address Translation) 
    • Usually built into the routers 
    • Translates private IP into Public and back
      • It allows LANs to stay invisible to the public Internet
  • Static IP address (only 1 IP address which stays constant on you LAN network)
  • DNS (Domain Name Service) - converts IP into its corresponding name. 
    • `nslookup www.website.com` to find  DNS used
  • DHCP (Dynamic Host Configuration Protocol) - automatically assigns IP address
    • DHCP servers are usually within Default Gateway routers  
    • If DHCP server fails, we can use APIPA (Automatically Programmable IP Addressing) - usually it starts to work automatically 
      • Range for APIPA is:
        • 169.254.0.1 - 169.254.255.254
        • APIPA will constantly look for available DHCP 
  • SSH (Secure Shell) - e..g. Used for remote terminal access
  • Protocols
    • TCP/IP (Transmission Control Protocol/Internet Protocol) - most commonly used protocol for the internet 
      • `ping` check if your machine can talk to another 
      • `ping -t` continuous pings until you stop them 
      • `ipconfig` (Windows - view all network connections)
      • `ipconfig /renew` (Windows - get new IP)
      • `ipconfig /release` (Windows - give up IP address) 
      • `ifconfig` (macOS - view all network connections)
      • `nslookup` (info about DNS server)
      • `tracert` (Windows - shows packets route)
      • `traceroute` (macOs - shows packets route) 
      • Change IP address on Windows:
        • Control Panel> Network and Sharing.. > Change Adapter… > Local Area NEtwork > Properties > TCP/IPv4 > Properties 
      • APIPA (Automatic Private IP Addressing) - windows will automatically assign an IP address if it cannot connect eg to DHCP server. 
    • UDP (User Datagram Protocol - One sided communication, without error checking or confirmation checking
    • ICMP - Sends only single packet
    • Handshake - double sided communication - back and forth 

  • IPV6 (8 sets of 4 hexadecimal characters separated by 7 colons)
    • Consists of at least 2 IP addresses: 
      • Link-local address (automatically generated by any IPV6 enabled host) 
        • Always starts with fe80:0000:0000:0000
        • The 2nd half consists of MAC address which converts default 48bit MAC address into 64bit IPV6 interface ID. 
          • EUI-64 (Extended Unique Identifier) 
            • For example: 2a-3b-4f-ff-fe-09-45-01
            • Which means splitting MAC address in half and adding FF-FE in the middle 
            • Then converting 1st 2 hexadecimal characters into binary, find 7th bit, and invert it. E.g.: 0 becomes 1, or if it is 1 then it becomes 0.  Which is actually done automatically. 
        • Final link-local address becomes:  fe80::293b:4fff:fe09:4501
      • Internet address (generated by Gateway Router~) 
    • Global Unicast Address  - when you plug computer to the network, it sends a packet called router solicitation (RS) message , looking for a router. Router responds with Router Advertisement (RA). RA tells computer its network ID, subnet mask and DNS server. 
      • Multicast address - IPv6 uses multicast addresses. Router solicitation message uses the address ff02::2 which can be read only by other computer running IPv6 in the network.

  • To have network connectivity, you need three things in place:
• Connected NIC -  The physical hardware that connects the computer system to the network media.
  • Full-Duplex - all modern NICs run at full-duplex. Meaning they can both send and receive data at the same time. Such NICs also support, older half-duplex. 
  • Half-duplex - means it can send and receive, but not at the same time. 
  • You can adjust it in the NIC settings. Control Panel > etc… 
• Properly configured IP addressing - Your device needs correct IP addressing for your network, either via DHCP or static.
• Switch - Everything connects to a switch in a wired network.
  • Routers
    • They don’t care where packets come from. 
    • Routers filter traffic by the IP addresses.  
    • Routing Table decide where packets will go. By choosing the quickest route. 
    • DOCSIS (Data Over Cable Service Interface Specification)
    • Some use Web connections, some use console
      • Console cable/rollover cable - DB-9 Cable
    • Discoverability (helps with network device identification): 
      • LLDP (Link Layer Discovery Protocol) (on by default) 
      • UPnP (Universal Plug and Play) - enables e.g. router to be discovered on the network 
      • SNMP (Simple Network Management Protocol) 

  • Link Lights (LED lights) 
    • Status indicator  - shows if you have good connectivity or not
    • Activity light - flickers to signify network traffic

  • Wake-on-LAN - ability to wake computers from sleep, even when you are not near the coputer
    • This is achieved by sending a packet that repeats the destination MAC address many times
  • QoS (Quality of Service) - enables busy network to prioritise traffic. Works by tagging the frame. 
  • Switch
    • Unmanaged (smart, automatic device - simply plug and it will communicate via MAC addresses. It simply connect devices)
    • Managed (added security and efficiency. Has an interface which usually can be accessed through an IP address or an app.)
      • VLAN (Virtual Local Area Network) - ability to break up/segment a single physical network into two or more networks. All computers within the same VLAN network can communicate with each other. 
        • Port Security - Lets the Switch memorize the MAC addresses of any machines plugged into it. As such, It won’t let through any other unrecognised addresses. 
  • Sharing and Security:
    • Ability to specify network sharing permissions to be able to: Allow, Restrict Access or Deny Access to shared network resources. 
    • Both NTFS permissions and network permissions need to be set accordingly to allow access to our shared resources. 
      • Network to share the resource
      • NTFS to control permissions 
      • Usually it is best to give full-control over network, and then specify NTFS permissions to specific folders.
  • Network Organization
    • Workgroups (default (works best on small networks <30 pcs) - and most users are usually assigned to this Workgroup when they install Windows)
      • Usernames & Passwords for identification & authentication
      • Problem: User Accounts are stored locally 
    • Domains (for larger networks, with better security and more control)
      • Centralised organisation of user accounts, passwords, and access to resources  
      • One Computer runs a Windows Server and configured as a domain controller.
      • Domain controller - stores a set of domain accounts 
      • As such user connecting to any computer on the domain, can log on to the entire network (single sign-on)
  • Active Directory - As such Domain Servers come very handy, and can become domain servers for printers, printer names, computer names, location information etc. that's where active directory comes into play 
  • Active Directory stores everything about the network. 
    • Computer must run a Windows Server, which then need to be promoted to a domain controller which creates the Active Directory
    • Once a server is set up as a domain controller, each computer on the network needs to join the domain (which kicks you out of Workgroup). When you log on to the computer, you will be prompted to type in Username and Password. You don’t log on to your computer. Instead you log on directly to the domain. 
`domainname.local\username`
  • One way to see the Active Directory is to log on directly to the domain controller and run Active Directory Users and Computers Utility: 
• Builtin (sic) This is where all the built-in domain groups are stored, such as Domain Administrators and Users.
• Computers Every system from servers to workstations are listed in this folder.
• Domain Controllers It’s always a good idea to have more than one domain controller in case one goes down. This folder lists all of them.
• Users This area stores all the non-built-in users for the domain.
  • Ability to reset passwords 
  • Ability to enable/disable accounts
  • Etc. 
  • You can add computer to the domain
  • You can add new users to the domain
  • You can’t add LOCAL users to the domain account (new user account needs to be created on the domain) 
  • You can run scripts, to display e.g. info box, runs special application etc. 
  • You can use organizational units (OUs) - like tags/groups - to seperate users into various organizational divisions
    • HomeGroups (shares libraries, not folders)
      • When you try to connect another computer to the HomeGroup, usually you will receive a password which you can then use to connect other computers to the same HomeGroup
  • Troubleshooting:
    • Physical cabling
    • Lights
    • Cable Testing
      • Time-domain reflectometer (TDR) - it measures impedance in network cabling.
      • Unplugging the patch cable from the PC, attaching a tester, and then going to the telecommunications room. Here you’ll want to unplug the patch cable from the switch and plug the tester into that patch cable.


    • Toner (helps to identify which cable is which) 
      • Tone Generator - it sends an electrical signal along the wire at a certain frequency 
      • Tone probe - emits a sound when it is placed near a cable connected to the tone generator 
  • `net` 
    • `net view` (Windows - displays list of computers on the network)
    • `net view computername` (Windows - will show shares on particular computer)
    • `net use /pathtonetworkshare/` (Windows - will enable a network share to be visible in FIle explorer) 
  • `ifconfig` (macOS) / `arp -a` / `scutil --dns`
  • `nbtstat` (Windows - NetBIOS over TCP/IP)
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