© 2010 Cisco Systems, Inc. All rights reserved. 1 Academy Conference 2010 Frisco, Texas Teaching VLSM Barry Charter ~ North Arkansas College ~ Newly Retired Shawn Dennis ~ Arkansas State University Mt. Home Arkansas CCNA CCAI July 19, 2010
2 © 2010 Cisco Systems, Inc. All rights reserved. Introduction Contact Information Barry and Shawn Dennis
3 © 2010 Cisco Systems, Inc. All rights reserved. Importance of understanding VLSM IPv4 address availability CCNA exam Further networking classes Networking careers What about IPv6?
4 © 2010 Cisco Systems, Inc. All rights reserved. INTRODUCE IP ADDRESSING AND BINARY THE FIRST DAY!! Do not wait until the chapter on IP Addressing & Subnetting (D1 = Ch 5, E1 = Ch 6) to begin discussing the basics of IP addressing and what a subnet mask is. Review IP Addressing and Binary daily Practice makes perfect!! Note:
5 © 2010 Cisco Systems, Inc. All rights reserved. Binary & IP Addressing Understanding binary is extremely important VLSM Wildcard masks IP Addresses 32 bits Dotted decimal format – 4 octets Conversion for each octect Practice converting IP Addresses from binary to decimal and vice versa. Introduce binary system to students early in first course. I start the second day of class.
6 © 2010 Cisco Systems, Inc. All rights reserved. Dividing Address Space The “Great Divide” Where the division occurs between host bits and network bits The “Magic Number” Decimal value of the bit to the immediate left of “Great Divide” Subnets will be in increments of the “Magic Number” Example Subnet Mask: /27 or The “Great Divide” The “Magic Number”
7 © 2010 Cisco Systems, Inc. All rights reserved. Subnetting vs. VLSM vs. CIDR Subnetting Dividing network address space into equal size subnets VLSM – Variable Length Subnet Mask Divide network address space into unequal size subnets Maximize use of IP address space CIDR – Classless Inter-domain Routing Subnet Mask specified using the prefix size = /24 Use of VLSM requires use of routing protocols that support CIDR RIPv2 EIGRP OSPF
8 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Methods Magic Box
9 © 2010 Cisco Systems, Inc. All rights reserved. Magic Box Method
10 © 2010 Cisco Systems, Inc. All rights reserved. What Length Subnet Mask Should You Use? – Practice, Practice, Practice... Number of Hosts Required # of Host Bits Needed to Support the Required # of Hosts Subnet Mask (CIDR Prefix) Subnet Mask (Dotted Decimal) Number of Usable Hosts Created
11 © 2010 Cisco Systems, Inc. All rights reserved. What Length Subnet Mask Should You Use? – Practice, Practice, Practice... Number of Hosts Required # of Host Bits Needed to Support the Required # of Hosts Subnet Mask (CIDR Prefix) Subnet Mask (Dotted Decimal) Number of Usable Hosts Created 1007 bits/ bits/ bits/ bits/ bits/ bits/ bits/ bits/ bits/ bits/
12 © 2010 Cisco Systems, Inc. All rights reserved. Determine Network Portion of Subnets Start with largest LAN Working down in LAN size to point-to-point links Determine number of bits needed to address the hosts Larger LANs will have smaller CIDR prefixes /30 prefix for point-to-point links Formula: 2 n – 2 n – number of bits 2 unusable addresses Network address – first address in subnet Broadcast address – last address in subnet
13 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Method Subnetting in a Box
14 © 2010 Cisco Systems, Inc. All rights reserved. Subnetting in a Box Method Divide a piece of paper into smaller subnets Value in top left corner of each section – network address Value in bottom right corner of each section – broadcast address Last network address is the value of the appropriate octet for subnet mask As bits are borrowed the network is divided into smaller subnets. New subnet mask is indicated by first address of last
15 © 2010 Cisco Systems, Inc. All rights reserved. Value in top left corner of each section – network address Value in bottom right corner of each section – broadcast address 0 255
16 © 2010 Cisco Systems, Inc. All rights reserved. Value in top left corner of each section – network address Value in bottom right corner of each section – broadcast address host bits / hosts
17 © 2010 Cisco Systems, Inc. All rights reserved. Value in top left corner of each section – network address Value in bottom right corner of each section – broadcast address host bits /26 62 hosts 7 host bits / hosts
18 © 2010 Cisco Systems, Inc. All rights reserved. Value in top left corner of each section – network address Value in bottom right corner of each section – broadcast address host bits /26 62 hosts 7 host bits / hosts host bits /28 5 host bits / hosts
19 © 2010 Cisco Systems, Inc. All rights reserved. Here is an example VLSM Exercise 1
20 © 2010 Cisco Systems, Inc. All rights reserved. Start with largest LAN Working down in LAN size to point-to-point links Example: list LANS in descending order 60 hosts 28 hosts 12 hosts There are 3 WAN links
21 © 2010 Cisco Systems, Inc. All rights reserved. Start with largest LAN Working down in LAN size to point-to-point links Example: Determine number of host bits needed 60 hosts – 6 host bits /26 28 hosts – 5 host bits /27 12 hosts – 4 host bits /28 There are 3 WAN links – 2 host bits /30
22 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links 60 hosts – 6 host bits /26 28 hosts – 5 host bits /27 12 hosts – 4 host bits /28 There are 3 WAN links – 2 host bits / hosts /
23 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links 60 hosts – 6 host bits /26 28 hosts – 5 host bits /27 12 hosts – 4 host bits /28 There are 3 WAN links – 2 host bits / hosts / hosts /
24 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links 60 hosts – 6 host bits /26 28 hosts – 5 host bits /27 12 hosts – 4 host bits /28 There are 3 WAN links – 2 host bits / hosts / hosts /28 30 hosts / hosts /
25 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links 60 hosts – 6 host bits /26 28 hosts – 5 host bits /27 12 hosts – 4 host bits /28 There are 3 WAN links – 2 host bits / hosts / hosts /28 30 hosts / hosts /
26 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 2 20 min
27 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links Ex 2
28 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 3 20 min
29 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links Ex 3
30 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 4 20 min
31 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links
32 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Resources
33 © 2010 Cisco Systems, Inc. All rights reserved. Cisco Learning Institute
34 © 2010 Cisco Systems, Inc. All rights reserved. Other Resources Presentations bnet_Calculator/index2.htm bnet_Calculator/index2.htm Subnet Calculators subnet-calculator.php subnet-calculator.php
35 © 2010 Cisco Systems, Inc. All rights reserved. Questions? Thank you for attending! DON’T FORGET TO TURN IN EVALUATION