Chapter 9: Subnetting IP Networks - cnacad.com

1 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Presentation_ID 1 Chapter 9: Subnetting IP Networks Introduction to Networking Presentation_ID 2 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Chapter 9 Subnetting an IPv4 network Addressing Schemes Design Considerations for IPv6 Summary Presentation_ID 3 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Chapter 9: Objectives Explain why routing is necessary for hosts on different Networks to communicate. Describe IP as a communication protocol used to identify a single device on a network .

2 Given a network and a subnet mask, calculate the number of host addresses available. calculate the necessary subnet mask in order to accommodate the requirements of a network . Describe the benefits of variable length subnet masking (VLSM) Explain how IPv6 address assignments are implemented in a business network . Presentation_ID 4 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Introduction Subletting IP Networks Consider doing class activity Activity - Call Me Presentation_ID 5 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential network Segmentation Reasons for Subnetting Large Networks need to be segmented into smaller sub- Networks , creating smaller groups of devices and services in order to: Control traffic by containing broadcast traffic within subnetwork Reduce overall network traffic and improve network performance Subnetting - process of segmenting a network into multiple smaller network spaces called subnetworks or Subnets.

3 Communication Between Subnets A router is necessary for devices on different Networks and subnets to communicate. Each router interface must have an IPv4 host address that belongs to the network or subnet that the router interface is connected to. Devices on a network and subnet use the router interface attached to their LAN as their default gateway. Presentation_ID 6 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Why subnet Networks Communication Between Subnets To determine if traffic is local or remote, the router uses the subnet mask.

4 Each subnet is treated as a separate network space. Devices on the same subnet must use an address, subnet mask, and default gateway Presentation_ID 7 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network IP Subnetting is FUNdamental Presentation_ID 8 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network The Plan Address Assignment 8 network bit, 24 host bits 2^24 = 16,777,216 possible hosts 16 network bit, 16 host bits 2^24 = 65,536 possible hosts 24 network bit, 8 host bits 2^8 = 256 possible hosts Problem: Our Public IP address is We have one network that can hold 65,535 hosts!

5 We need many Networks , not one huge one! Presentation_ID 9 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Basic Subnetting Borrowing Bits to Create Subnets Borrowing 1 bit 21 = 2 subnets subnet 1 network Mask: subnet 0 network 127/25 Mask: Borrowing 1 Bit from the host portion creates 2 subnets with the same subnet mask Do the buttons on Presentation_ID 10 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Subnets in Use subnet 0 network 127/25 subnet 1 network Do the buttons on Presentation_ID 11 2008 Cisco Systems, Inc.

6 All rights reserved. Cisco Confidential Subnetting an IPv4 network Subnetting Formulas calculate Number of Subnets calculate Number of Hosts Do the buttons on Presentation_ID 12 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 4 Subnets Borrowing 2 bits to create 4 subnets. 22 = 4 subnets Do the buttons on Presentation_ID 13 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 8 Subnets Borrowing 3 bits to Create 8 Subnets. 23 = 8 subnets Do the buttons on Presentation_ID 14 2008 Cisco Systems, Inc.

7 All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 8 Subnets(continued) Do the buttons on Presentation_ID 15 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 8 Subnets(continued) Do the buttons on Presentation_ID 16 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 8 Subnets(continued) Do the buttons on Presentation_ID 17 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Activity - Determining the network Address Basic Activity - calculate the Number of Hosts Basic Activity - Determining the Valid Addresses for Hosts Basics Activity - calculate the subnet Mask Do Activities , , and in class Students should practice this until mastery.

8 Presentation_ID 18 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Creating 100 Subnets with a /16 prefix In situations where more hosts are required, You must borrow bits from the 3rd octet instead of the 4th. In this example we have 9 host bits for 510 hosts (2^9 -2) Presentation_ID 19 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Calculating the Hosts Do the buttons on Presentation_ID 20 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Subnetting an IPv4 network Calculating the Hosts Do the buttons on Presentation_ID 21 2008 Cisco Systems, Inc.

9 All rights reserved. Cisco Confidential Subnetting an IPv4 network Activity - Determining the network Address Advanced Activity - Calculating the Number of Hosts Advanced Activity - Determining the Valid Addresses for Hosts - Advanced Do activities , 14, 15 in class Presentation_ID 22 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Determining the subnet Mask Subnetting Based on Host Requirements There are two considerations when planning subnets: Number of Subnets required Number of Host addresses required Formula to determine number of useable hosts 2^n-2 2^n (where n is the number the number of host bits remaining) is used to calculate the number of hosts -2 Subnetwork ID and broadcast address cannot be used on each subnet Do animation on Presentation_ID 23 2008 Cisco Systems, Inc.

10 All rights reserved. Cisco Confidential Determining the subnet Mask Subnetting network -Based Requirements calculate number of subnets Formula 2^n (where n is the number of bits borrowed) subnet needed for each department in graphic Presentation_ID 24 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential Determining the subnet Mask Subnetting To Meet network Requirements It is important to balance the number of subnets needed and the number of hosts required for the largest subnet . Design the addressing scheme to accommodate the maximum number of hosts for each subnet .