add ipv4 addressing part 1 notes

Author: laaraujo

README.md

@@ -9,6 +9,7 @@ Personal notes for learning [CCNA](https://www.cisco.com/site/us/en/learn/traini
 * [OSI model and TCP/IP suite](./contents/osi_model_and_tcp_ip_suite/)
 * [Intro to Cisco IOS CLI](./contents/intro_to_cisco_cli/)
 * [Ethernet LAN Switching](./contents/ethernet_lan_switching/)
+* [IPv4 Addressing](./contents/ipv4_addressing/)
 
 
 ## Network node icons

contents/ipv4_addressing/README.md

@@ -0,0 +1,78 @@
+# IPv4 Addressing
+
+
+## Table of contents
+* [IPv4 Address](#ipv4-address)
+* [Decimal and Binary](#decimal-and-binary)
+* [IPv4 Address Classes](#ipv4-address-classes)
+
+
+## IPv4 Address
+
+* `32 bits` / `4 bytes`
+* We use **dotted decimal** instead of binary for ease of use
+    * `192.168.1.254` = `11000000.10101000.00000001.11111110`
+* **CIDR notation**: `/24` after the IP number indicates `24` out of the `32` bits in an IP address correspond to the network portion. Possible values are `1 > n > 32` where `n` is an integer. 🔥🔥🔥
+    * i.e `192.168.1.0/24`
+
+## Decimal and Binary
+
+![Min/Max binary octet](docs/min_max_octet_1.png)
+
+![](docs/min_max_octet_2.png)
+
+### Binary to Decimal
+
+![](docs/binary_to_decimal.png)
+
+### Decimal to Binary
+
+![](docs/decimal_to_binary.png)
+
+
+## IPv4 Address Classes
+
+| Class | First octet | First octet numeric range |
+| :-: | :-: | :-: |
+| **A** | 0xxxxxxx | 0-127 |
+| **B** | 10xxxxxx | 128-191 |
+| **C** | 110xxxxx | 192-223 |
+| **D** | 1110xxxx | 224-239 |
+| **E** | 1111xxxx | 240-255 |
+
+* `A` class range end is usually considered `126` because `127` first octet is used to test the **network stack (l3)** on the local device
+* We will focus on `A`, `B` and `C`.
+* `D` are multicast addresses
+* `E` are reserved (experimental)
+
+| Class | First octet | First octet numeric range | Prefix Length |
+| :-: | :-: | :-: | :-: |
+| **A** | 0xxxxxxx | 0-127 | /8 |
+| **B** | 10xxxxxx | 128-191 | /16 |
+| **C** | 110xxxxx | 192-223 | /24 |
+
+![](docs/ipv4_address_classes.png)
+
+### Netmask
+
+| Class | Prefix Length | Netmask | Binary octets |
+| :-: | :-: | :-: | :-: |
+| **A** | /8 | 255.0.0.0 | 11111111 00000000 00000000 00000000 |
+| **B** | /16 | 255.255.0.0 | 11111111 11111111 00000000 00000000 |
+| **C** | /24 | 255.255.255.0 | 11111111 11111111 11111111 00000000 |
+
+### Network address
+
+`192.168.1.0/24`
+
+* `/24` means `192.168.1` is the network portion and `.0` is the host portion
+* Since the **host portion** is `0` it means it is the network address
+* it is the first address with a **host portion** of all `0`s
+
+### Broadcast address
+
+`192.168.1.255/24`
+
+* last address in the network
+* with `/24` net mask it would be the last octet `.255`
+* cannot be assigned to a host