235 lines
4.2 KiB
Markdown
235 lines
4.2 KiB
Markdown
---
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id: 1777971486-WJIG
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aliases:
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- Subnetting (Part 3)
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tags: []
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---
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# Subnetting (Part 3 - VLSM)
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## Class B Reference Table
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| Prefix | Subnets | Hosts |
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|--------|---------|-------|
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| /17 | 2 | 32766 |
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| /18 | 4 | 16382 |
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| /19 | 8 | 8190 |
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| /20 | 16 | 4094 |
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| /21 | 32 | 2046 |
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| /22 | 64 | 1022 |
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| /23 | 128 | 510 |
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| /24 | 256 | 254 |
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---
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## Class C Reference Table
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| Prefix | Subnets | Hosts |
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|--------|---------|-------|
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| /25 | 2 | 126 |
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| /26 | 4 | 62 |
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| /27 | 8 | 30 |
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| /28 | 16 | 14 |
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| /29 | 32 | 6 |
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| /30 | 64 | 2 |
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| /31 | | (0) |
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| /32 | | (0–2) |
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---
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## Quiz Question 1
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You have been given the network **172.30.0.0/16**. Your company requires
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**100 subnets with at least 500 hosts per subnet**.
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**Answer:**
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- Prefix: `/23`
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- Network: `172.30.0.0/23`
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- Subnet mask: `255.255.254.0`
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---
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## Quiz Question 2
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What subnet does host **172.21.111.201/20** belong to?
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```
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10101100.00010101.01101111.11001001 (IP)
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10101100.00010101.01100000.00000000 (Network)
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```
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**Answer:** `172.21.96.0/20`
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---
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## Quiz Question 3
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What is the broadcast address of the network **192.168.91.78/26**?
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```
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11000000.10101000.10110011.01001110 (IP)
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11000000.10101000.10110011.01111111 (Broadcast)
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```
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**Answer:** `192.168.91.127`
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---
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## Quiz Question 4
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You divide the **172.16.0.0/16** network into 4 equal subnets.
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Identify the network and broadcast addresses.
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### Subnet 1
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- Network: `172.16.0.0/18`
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- Broadcast: `172.16.63.255`
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### Subnet 2
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- Network: `172.16.64.0/18`
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- Broadcast: `172.16.127.255`
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### Subnet 3
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- Network: `172.16.128.0/18`
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- Broadcast: `172.16.191.255`
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### Subnet 4
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- Network: `172.16.192.0/18`
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- Broadcast: `172.16.255.255`
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---
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## Quiz Question 5
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You divide the **172.30.0.0/16** network into subnets of **1000 hosts each**.
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**Answer:** 64 subnets
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---
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## Subnetting Class A Networks
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The process of subnetting Class A, B, and C networks is exactly the same.
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---
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## Example 1
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You are given the network **10.0.0.0/8**.
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You must create **2000 subnets**.
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### Solution
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**Answer:**
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- Prefix: `/19`
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- Usable hosts: `8192 - 2 = 8190`
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---
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## Example 2
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PC1 has IP address **10.217.182.223/11**
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### Subnet Details
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- Network: `10.192.0.0/11`
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- Broadcast: `10.223.255.255`
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- First usable: `10.192.0.1`
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- Last usable: `10.223.255.254`
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- Usable hosts: `2,097,150`
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---
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## VLSM (Variable-Length Subnet Masks)
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- Previously, we used **FLSM (Fixed-Length Subnet Masks)**
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- All subnets had the same prefix length
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- VLSM allows **different subnet sizes** for better efficiency
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- More flexible, slightly more complex
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---
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## Example (VLSM Design)
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```
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Tokyo Lan A = 110 Hosts --- Tokyo Lan B = 8 Hosts
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Router
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Router
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Toronto Lan A = 29 Hosts --- Toronto Lan B = 45 Hosts
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```
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We must divide **192.168.1.0/24** into 5 subnets:
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- Tokyo LAN A → 110 hosts
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- Tokyo LAN B → 8 hosts
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- Toronto LAN A → 29 hosts
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- Toronto LAN B → 45 hosts
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- Point-to-point link
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### Steps
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1. Assign largest subnet first
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2. Continue in descending order
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3. Repeat until done
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### Allocation Order
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Tokyo A → Toronto B → Toronto A → Tokyo B → Point-to-point
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---
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### Tokyo LAN A
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- Network: `192.168.1.0/25`
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- Broadcast: `192.168.1.127`
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- Usable: `192.168.1.1 – 192.168.1.126`
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- Hosts: 126
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---
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### Toronto LAN B
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- Network: `192.168.1.128/26`
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- Broadcast: `192.168.1.191`
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- Usable: `192.168.1.129 – 192.168.1.190`
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- Hosts: 62
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---
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### Toronto LAN A
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- Network: `192.168.1.192/27`
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- Broadcast: `192.168.1.223`
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- Usable: `192.168.1.193 – 192.168.1.222`
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- Hosts: 30
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---
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### Tokyo LAN B
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- Network: `192.168.1.224/28`
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- Broadcast: `192.168.1.239`
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- Usable: `192.168.1.225 – 192.168.1.238`
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- Hosts: 14
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---
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### Point-to-Point
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- Network: `192.168.1.240/30`
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- Broadcast: `192.168.1.243`
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- Usable: `192.168.1.241 – 192.168.1.242`
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- Hosts: 2
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---
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## Additional Practice
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- https://www.subnettingquestions.com
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- https://www.subnetting.org
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- https://www.subnettingpractice.com
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```
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