> For the complete documentation index, see [llms.txt](https://riteshs4hu.gitbook.io/infosec-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://riteshs4hu.gitbook.io/infosec-notes/networking-fundamentals/ip-address-internet-protocol-address.md). # IP Address (Internet Protocol Address) An IP address is a unique identifier for devices on a network, not for the network itself. Each device connected to a network is assigned a unique IP address, which is used to identify and communicate with that device. *** ### **Types of IP Addresses:-** 1. **IPv4 (Internet Protocol version 4)** 2. **IPv6 (Internet Protocol version 6)** *** ## **IPv4 (Internet Protocol version 4)** **IPv4** (Internet Protocol version 4) is the fourth version of the Internet Protocol, which is widely used for identifying devices on a network. * **Structure**: 32-bit address. * **Sections**: 4 sections, each 8 bits. * **Range per section**: 0 to 255. * **Address range**: `0.0.0.0` to `255.255.255.255`. * **Total addresses**: (2^32 = 4,294,967,296). ### **Structure of IPv4 Address** 1. **Bit Size**: * IPv4 uses **32 bits** to represent an IP address. * This is a fixed length, meaning every IPv4 address is 32 bits long. 2. **Sections (Octets)**: * IPv4 addresses are divided into **4 sections**, each consisting of **8 bits**. * Each section is separated by a dot (`.`). 3. **Value Range for Each Section**: * Each 8-bit section can store values ranging from **0 to 255** (decimal). * This is because the maximum value of 8 bits in binary is `11111111`, which equals **255** in decimal. **Address Range:** * **Smallest IPv4 Address**: `00000000.00000000.00000000.00000000` (Binary) = `0.0.0.0` (Decimal). * **Largest IPv4 Address**: `11111111.11111111.11111111.11111111` (Binary) = `255.255.255.255` (Decimal). #### **Example: IPv4 Address** Let’s convert the binary IPv4 address **`11000000.10101000.00000001.00000001`** into decimal. #### **Explanation** 1. Each bit in the binary number represents a power of 2, starting from (2^0) (rightmost bit) to (2^7) (leftmost bit) for an 8-bit binary number. 2. Multiply each bit by its corresponding power of 2. 3. Add the results of all bits to get the decimal value of the binary number. *** **Step 1: Break into Octets** The binary address consists of four 8-bit sections: * Octet 1: `11000000` * Octet 2: `10101000` * Octet 3: `00000001` * Octet 4: `00000001` *** **Step 2: Convert Each Octet** | **Bit Position** | (2^7) (128) | (2^6) (64) | (2^5) (32) | (2^4) (16) | (2^3) (8) | (2^2) (4) | (2^1) (2) | (2^0) (1) | **Decimal Value** | | ---------------------- | ----------- | ---------- | ---------- | ---------- | --------- | --------- | --------- | --------- | -------------------- | | **Octet 1 (11000000)** | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | (128 + 64 = 192) | | **Octet 2 (10101000)** | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | (128 + 32 + 8 = 168) | | **Octet 3 (00000001)** | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | (1 = 1) | | **Octet 4 (00000001)** | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | (1 = 1) | *** **Step 3: Combine the Decimal Values** Now, write the decimal values of all four octets together to get the full IPv4 address: `[ 11000000.10101000.00000001.00000001 = 192.168.1.1 ]` *** ### **Classful and Classless IP Addressing** IP addressing can follow two models: **Classful** (fixed structure) and **Classless** (flexible structure). Below is an in-depth explanation with examples. *** #### **Classful IP Addressing** In **classful addressing**, IP addresses are divided into fixed classes: A, B, C, D, and E. Each class has a predefined number of **network bits** and **host bits**, limiting the number of available networks and hosts per network. #### **Class A** **Purpose:** Reserved for governments, large corporations, and ISPs requiring very large networks. **Binary Range:** ``` 0 0000000 . 00000000 . 00000000 . 00000000 (0.0.0.0) to 0 1111111 . 11111111 . 11111111 . 11111111 (127.255.255.255) ``` The first bit is always `0`. **IP Range:** ``` 0.0.0.0 to 127.255.255.255 ``` **Structure:** ``` OFFNNNNNNN . HHHHHHHH . HHHHHHHH . HHHHHHHH N.H.H.H ``` * `N`: Network bits (7 bits) * `H`: Host bits (24 bits) **Network and Host Bits:** * **Network Bits:** 7 * **Host Bits:** 24 **Number of Networks:** ``` 2^7 - 2 = 126 (0 is reserved for default routing, 127 is reserved for loopback testing) ``` **Number of Hosts per Network:** ``` 2^24 - 2 = 16,777,214 (Subtract 2 for network and broadcast addresses) ``` **Decimal Octet | Binary Representation | Explanation:** | Decimal Octet | Binary Representation | Explanation | | ------------- | --------------------- | -------------------------- | | 0 | 00000000 | Starting range for Class A | | 127 | 01111111 | Ending range for Class A | | Remaining | HHHHHHHH | Host portion (24 bits) | *** #### **Class B** **Purpose:** Designed for medium-sized networks like multinational companies. **Binary Range:** ``` 10 000000 . 00000000 . 00000000 . 00000000 (128.0.0.0) to 10 111111 . 11111111 . 11111111 . 11111111 (191.255.255.255) ``` The first two bits are always `10`. **IP Range:** ``` 128.0.0.0 to 191.255.255.255 ``` **Structure:** ``` ONOFFNNNNNN . HHHHHHHH . HHHHHHHH . HHHHHHHH N.N.H.H ``` * `N`: Network bits (14 bits) * `H`: Host bits (16 bits) **Network and Host Bits:** * **Network Bits:** 14 * **Host Bits:** 16 **Number of Networks:** ``` 2^14 = 16,384 ``` **Number of Hosts per Network:** ``` 2^16 - 2 = 65,534 (Subtract 2 for network and broadcast addresses) ``` **Decimal Octet | Binary Representation | Explanation:** | Decimal Octet | Binary Representation | Explanation | | ------------- | --------------------- | -------------------------- | | 128 | 10000000 | Starting range for Class B | | 191 | 10111111 | Ending range for Class B | | Remaining | HHHHHHHH | Host portion (16 bits) | *** #### **Class C** **Purpose:** Allocated for small companies with smaller networks. **Binary Range:** ``` 110 00000 . 00000000 . 00000000 . 00000000 (192.0.0.0) to 110 11111 . 11111111 . 11111111 . 11111111 (223.255.255.255) ``` The first three bits are always `110`. **IP Range:** ``` 192.0.0.0 to 223.255.255.255 ``` **Structure:** ``` ONONOFFNNNNN . HHHHHHHH . HHHHHHHH . HHHHHHHH N.N.N.H ``` * `N`: Network bits (21 bits) * `H`: Host bits (8 bits) **Network and Host Bits:** * **Network Bits:** 21 * **Host Bits:** 8 **Number of Networks:** ``` 2^21 = 2,097,152 ``` **Number of Hosts per Network:** ``` 2^8 - 2 = 254 (Subtract 2 for network and broadcast addresses) ``` **Decimal Octet | Binary Representation | Explanation:** | Decimal Octet | Binary Representation | Explanation | | ------------- | --------------------- | -------------------------- | | 192 | 11000000 | Starting range for Class C | | 223 | 11011111 | Ending range for Class C | | Remaining | HHHHHHHH | Host portion (8 bits) | *** #### **Class D** **Purpose:** Reserved for multicast communication (e.g., streaming services). **Binary Range:** ``` 1110 0000 . 00000000 . 00000000 . 00000000 (224.0.0.0) to 1110 1111 . 11111111 . 11111111 . 11111111 (239.255.255.255) ``` The first four bits are always `1110`. **IP Range:** ``` 224.0.0.0 to 239.255.255.255 ``` **Structure:**\ No network/host division; used for group communication. *** #### **Class E** **Purpose:** Reserved for experimental and future use. **Binary Range:** ``` 1111 0000 . 00000000 . 00000000 . 00000000 (240.0.0.0) to 1111 1111 . 11111111 . 11111111 . 11111111 (255.255.255.255) ``` The first four bits are always `1111`. **IP Range:** ``` 240.0.0.0 to 255.255.255.255 ``` **Structure:**\ Reserved for future use or research purposes. *** #### **Summary Table** | **Class** | **IP Range** | **Network Bits** | **Host Bits** | **Networks** | **Hosts/Network** | | --------- | --------------------------- | ---------------- | ------------- | ------------ | -------------------------- | | A | 0.0.0.0 - 127.255.255.255 | 7 | 24 | 126 | 16,777,214 | | B | 128.0.0.0 - 191.255.255.255 | 14 | 16 | 16,384 | 65,534 | | C | 192.0.0.0 - 223.255.255.255 | 21 | 8 | 2,097,152 | 254 | | D | 224.0.0.0 - 239.255.255.255 | Multicast | Multicast | Multicast | Multicast | | E | 240.0.0.0 - 255.255.255.255 | Experimental | Experimental | Experimental |

Experimental

| *** ### Private and Public IPs **Private IPs** * Used for internal communication in LAN. * Free of cost. * Cannot access the internet directly. * **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` **Public IPs** * Used to communicate over the internet. * Assigned by ISPs and not free. * **Ranges**: * **Class A**: `1.0.0.0` – `126.255.255.255` * **Class B**: `128.0.0.0` – `191.255.255.255` * **Class C**: `192.0.0.0` – `223.255.255.255` *** ### **Principles for Assigning IPs** 1. Never assign IPs without enabled network or host bits (e.g., `0.0.0.0`). 2. Avoid IPs where no host bits are enabled (e.g., `1.0.0.0`). 3. Avoid IPs with all host bits enabled (e.g., `1.255.255.255`). 4. Ensure IPs are unique within a network. *** ## **Subnet Mask / Netmask / Network Mask** A **Subnet Mask** (also called **Netmask** or **Network Mask**) is used in IP networking to divide an IP address into **network** and **host** portions. It tells which part of the IP address identifies the **network** and which part identifies the **device (host)**. *** ### **Network Mask Structure** * **Total Bits**: 32 bits (just like an IPv4 address) * **Sections**: 4 sections (octets) * **Bits per Section**: 8 bits each * **Representation**: Binary or Decimal (e.g., `11111111.00000000.00000000.00000000` = `255.0.0.0`) * **Binary Pattern**: * **Network part**: All bits are `1` * **Host part**: All bits are `0` *** ### **Subnet Masks by IP Class** #### **Class A** * **Example IP**: `1.0.0.1` * **Structure**: `N.H.H.H` (Network.Host.Host.Host) * **Binary Mask**: `11111111.00000000.00000000.00000000` * **Decimal Mask**: `255.0.0.0` #### **Class B** * **Example IP**: `128.0.0.1` * **Structure**: `N.N.H.H` (Network.Network.Host.Host) * **Binary Mask**: `11111111.11111111.00000000.00000000` * **Decimal Mask**: `255.255.0.0` #### **Class C** * **Example IP**: `192.0.0.1` * **Structure**: `N.N.N.H` (Network.Network.Network.Host) * **Binary Mask**: `11111111.11111111.11111111.00000000` * **Decimal Mask**: `255.255.255.0` *** ### **Purpose of a Subnet Mask** * **Identifies** how many bits are used for the network and how many for hosts. * **Helps routers** understand where to send packets. * **Enables subnetting**, which breaks large networks into smaller, manageable parts.