Cisco Certified Network Associate (CCNA) - Day Three
Instructor: Imran
Key Concepts Covered:
- Subnetting
- Supernetting
- IP Addressing Schemes
Subnetting
-
Definition: Dividing a network into smaller, manageable subnetworks.
-
Class B Subnetting Example:
- IP Address:
172.16.0.0 with subnet mask 255.255.0.0
- To break into two subnets, borrow 1 bit:
- 1 bit borrowed -> 2^1 = 2 subnets
- Valid hosts per subnet: 2^15 - 2 = 32,766
- First Network ID:
172.16.0.0
- Second Network ID: Add
128 to the third octet.
- Broadcast ID: 1 - next Network ID, e.g.,
128.0 - 1 = 127.255
- Subnet Mask: Changes to
128.0 or /17
-
Class A Subnetting Example:
- IP:
10.0.0.0
- Borrow 1 bit for 2 subnets, Valid hosts: 2^23 - 2 = 8,388,606
- Change subnet mask to
/9
Supernetting
- Definition: Combining multiple smaller networks into a larger network.
- Purpose: Simplifies routing by reducing the number of entries in the routing table.
- Example:
- Four Class C networks can be represented under one supernet by adjusting the subnet mask.
IP Addressing Scheme
- Digital Clock Analogy: Understanding how time rolls over in a digital clock is similar to how IP addresses and subnetting work.
- Essential for calculating network and broadcast IDs.
Magic Table
- Purpose: Used for calculating subnet masks and their corresponding IP ranges.
- Place Values: 1, 2, 4, 8, 16, 32, 64, 128
- Valid Subnet Masks: 128, 192, 224, 240, 248, 252, 254, 255
Practical Examples
- Network Address Calculations:
- /24 Example: Start with
10.0.0.0, increment in the third octet.
- Broadcast IDs: Important to subtract correctly (e.g.,
255 is not always a broadcast ID).
Summary and Homework
- Remember to practice by calculating subnet and supernet addresses.
- Test Questions provided to practice the concepts.
The lecture emphasized the importance of understanding subnetting and supernetting both for exam preparation and practical networking scenarios. The digital clock analogy helps simplify the understanding of network and broadcast ID calculations.