Complete "Network Foundations" module

README.md

@@ -11,7 +11,7 @@
 | Module Name                                                                  | Status |
 | ---------------------------------------------------------------------------- | ------ |
 | [Introduction to Information Security](./academy/intro-to-infosec/README.md) | ✅     |
-| Network Foundations                                                          |        |
+| [Network Foundations](./academy/network-foundations/README.md)               | ✅     |
 | Introduction to Networking                                                   |        |
 | Linux Fundamentals                                                           |        |
 | Introduction to Bash Scripting                                               |        |

academy/network-foundations/README.md

@@ -0,0 +1,53 @@
+# Network Foundations
+
+### Open Systems Interconnection (OSI)
+
+| Layer | Name         | Addressing                 |
+| ----- | ------------ | -------------------------- |
+| 1     | Physical     |                            |
+| 2     | Data Link    | Media Access Control (MAC) |
+| 3     | Network      | Internet Protocol (IP)     |
+| 4     | Transport    | Port number                |
+| 5     | Session      |                            |
+| 6     | Presentation |                            |
+| 7     | Application  |                            |
+
+### TCP/IP
+
+| Layer | Name        |
+| ----- | ----------- |
+| 1     | Link        |
+| 2     | Internet    |
+| 3     | Transport   |
+| 4     | Application |
+
+### Transmission Modes
+
+- **Simplex mode** allows one-way communication only (keyboard to computer)
+- **Half-duplex mode** allows alternating two-directional communication
+- **Full-duplex mode** allows two-way communication simultaneously
+
+### Dynamic Host Configuration Protocol (DHCP)
+
+| Step        | Source | Destination |
+| ----------- | ------ | ----------- |
+| Discover    | Client | Server      |
+| Offer       | Server | Client      |
+| Request     | Client | Server      |
+| Acknowledge | Server | Client      |
+
+### Network Address Translation (NAT)
+
+- Public IP addresses are assigned by ISPs and can be accessed from anywhere on the internet
+- Private IP addresses are non-routable and assigned to hosts within a LAN
+- Most common form at home is Port Address Translation (PAT) where each connection gets its own port
+- There is also "static NAT" (1:1 public IP address to private IP address) and "dynamic NAT" (a pool of shared public IP addresses)
+
+### Domain Name System (DNS)
+
+1. Search local DNS cache
+2. Query **recursive DNS server** (ISP or i.e. `8.8.8.8`)
+3. Recursive DNS server contacts **root DNS server** which returns the IP address of the Top Level Domain (TLD) name server
+4. Recursive DNS server contact TLD name server which directs the query to the **authoritative name server** for the second-level domain (`example.com`)
+5. Authoritative name server returns IP address for `example.com` to recursive DNS server
+6. Recursive DNS server responds to the requesting host device with the resolved IP address for `example.com`.