Networking Review – Updated

I needed to review some computer networking concepts this week. I’ve learned and forgotten a lot of this stuff more than once so thought I’d write some of it down here for easy reference. I’ll likely add more as I get to it.

Updated 9/10/20: Just adding a few more bullets from my studies.

1. DNS
   1. Domain Name System
   2. Matches URLs to IPs
   3. Your computer can’t find ‘wordpress.com’
      1. When you try visiting an address, your local DNS cache will be checked first
      2. If the address is not found, then the resolver server cache will be checked with your ISP
      3. If not found with your ISP, then the DNS root server will be checked to match the URL to the IP
2. DHCP
   1. Domain Host Control Protocol
   2. At home it lives in your router
      1. In an office it likely has a dedicated server
   3. Provides hosts in the home network with IP addresses
   4. Also provides subnet mask and default gateway
      1. default gateway is your router, your ‘gateway to the internet’
3. NAT
   1. Network Address Translation
   2. Lives in routers
   3. Translates public & private IP addresses
   4. Inside your network your IPs are private
   5. Outside of your network, IPs are public
4. MAC Address
   1. Media Access Control address
   2. ensures the physical address of the computer
      1. while IP address uniquely identifies the connection
   3. operates on the data link layer
   4. aka physical address
5. WPA2
   1. WiFi Protected Access 2
   2. Security setting that lives in your router
      1. Just navigate to your router’s Admin page to check that out
6. Troubleshooting Network Connectivity Basics (from Windows)
   1. Can you see your router?
      1. Windows key>’cmd’
      2. type ‘ipconfig’
         1. ipconfig is used to display your connection to the internet
      3. look for your gateway/router
         1. will likely be ‘192.168.1.1’
      4. type ‘ping 192.168.1.1’ to check that you can reach your router
      5. You should get back a response like like this:
         • _{Pinging 192.168.1.1 with 32 bytes of data:}
         • _{Reply from 192.168.1.1: bytes=32 time=3ms TTL=64}
      6. If you instead get 0.0.0.0 with ipconfig or the ping, check that your router is on and plugged in etc.
      7. traceroute
         1. coming soon!
7. SCP
   1. Secure Copy Protocol
   2. Based on SSH
   3. Provides file transfers between hosts on a network
   4. It’s faster than SFTP (Secure FTP)
      1. Though SFTP is better at file management
   5. Has a more efficient transfer algorithm
   6. Bonus item as this is not necessarily related to networking 🙂
8. Hardware
   1. Hub
      1. Physical Layer device
      2. connects multiple devices to a network
      3. connects computers to a LAN
      4. basically a repeater
   2. Switch
      1. Data Link Layer device
      2. ‘creates’ networks
      3. used filtering and forwarding
      4. a virtual LAN can be created here
      5. allows different network devices to communicate
   3. Router
      1. Network Layer device
      2. allows different networks to communicate
      3. gateway to the network
9. OSI Model
   1. The OSI model (Open Systems Interconnection) describes the functions of a network system. It’s a more generic description of the TCP/IP Model.
      1. Lots more info here as well!
   2. Within the OSI Model there are 7 layers. I’ve bulleted these out below:
      1. Application Layer
         1. highest level
         2. provides interfaces for users
         3. interacts directly with software applications
         4. uses both TCP/IP and OSI models
         5. presents data to user
         6. ensures receiving device is identified, can be accessed and is available to receive data
         7. ensures effective communication b/n application and network
      2. Presentation Layer
         1. hands data to the application
         2. translates between application and network formats
         3. transforms data into a form that application accepts
         4. de/encryption
         5. data compression
         6. graphic handling
      3. Session Layer
         1. it’s the dialogue controller
         2. establishes, manages, syncs & terminates communication b/n end use application processes
         3. token management
      4. Transport Layer
         1. responsible for end-to-end communication over the network
         2. collects message segments from applications and transmits them on to the network layer
         3. adds a port address to the data packet header
         4. divides messages into smaller segments
      5. Network Layer
         1. allows for connection and transfer of data packets b/n different devices and networks
         2. provides routing paths for data
         3. considered backbone of OSI Model
         4. selects and manages best logical path for transfer of data b/n nodes
         5. assigns destination and source IP addresses to each data segment
         6. responds to requests from transport layer
         7. issues requests to data link layer
      6. Data Link Layer
         1. encodes/decodes data bits
         2. organizes bits into patterns
         3. coordinates data volume
         4. detects and retransmits damaged or lost frames
         5. sub-layers are:
            1. MAC – Media Access Control (see above)
            2. LLC – Logical Link Control
      7. Physical Layer
         1. actual physical connection between devices
         2. info is in the form of bits
         3. transmits individual bits from from one node to the next
         4. receives signal, converts to 1s & 0s and sends them to the Data Link layer for reassembly