© 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