1. © 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. 2 © 2010 Cisco Systems, Inc. All rights reserved. Introduction Contact Information  Barry Charterbc_charter@yahoo.com and  Shawn Dennis sdennis@asumh.edu

3. 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. 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. 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. 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 255.255.255.224 128 64 32 16 8 4 2 1 The “Great Divide” The “Magic Number”

7. 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  255.255.255.0 = /24  Use of VLSM requires use of routing protocols that support CIDR  RIPv2  EIGRP  OSPF

8. 8 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Methods Magic Box

9. 9 © 2010 Cisco Systems, Inc. All rights reserved. Magic Box Method

10. 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 100 2 25 50 900 5 10 80 500 15

11. 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/25255.255.255.128126 22 bits/30255.255.255.2522 255 bits/27255.255.255.22430 506 bits/26255.255.255.19262 90010 bits/22255.255.252.01022 53 bits/29255.255.255.2486 104 bits/28255.255.255.24014 807 bits/25255.255.255.128126 5009 bits/23255.255.254.0510 155 bits/27255.255.255.22430

12. 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. 13 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Method Subnetting in a Box

14. 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. 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. 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 0 128 7 host bits /25 126 hosts 127 255

17. 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 0 128 6 host bits /26 62 hosts 7 host bits /25 126 hosts 191 192 127 255

18. 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 0 128 6 host bits /26 62 hosts 7 host bits /25 126 hosts 191 192 224 4 host bits /28 5 host bits /27 239 240 248 30 hosts 243 251 244 127 223 247 255

19. 19 © 2010 Cisco Systems, Inc. All rights reserved. Here is an example VLSM Exercise 1

20. 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. 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. 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 /30 0 128 62 hosts 192.168.10.0 /26 63 64 127 255

23. 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 /30 0 128 62 hosts 192.168.10.0 /26 63 64 96 30 hosts 192.168.10.64 /27 95 127 255

24. 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 /30 0 128 62 hosts 192.168.10.0 /26 63 64 96 14 hosts 192.168.10.96 /28 30 hosts 111 192.168.10.64 /27112 14 hosts 192.168.10.112 /28 95 127 255

25. 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 /30 0 128 136 160 131 139 62 hosts 192.168.10.0 /26 132 140 135 143 144 63 159 191 64 96 192 14 hosts 192.168.10.96 /28 30 hosts 111 192.168.10.64 /27112 14 hosts 192.168.10.112 /28 95 127 255

26. 26 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 2 20 min

27. 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. 28 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 3 20 min

29. 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. 30 © 2010 Cisco Systems, Inc. All rights reserved. Practice Packet Tracer Activities Exercise 4 20 min

31. 31 © 2010 Cisco Systems, Inc. All rights reserved. Start with the largest LAN Working down in LAN size to point-to-point links

32. 32 © 2010 Cisco Systems, Inc. All rights reserved. Teaching Resources

33. 33 © 2010 Cisco Systems, Inc. All rights reserved. Cisco Learning Institute

34. 34 © 2010 Cisco Systems, Inc. All rights reserved. Other Resources  Presentations  http://www.cisco.com/web/learning/le31/le46/cln/clp/fastlane/Su bnet_Calculator/index2.htm http://www.cisco.com/web/learning/le31/le46/cln/clp/fastlane/Su bnet_Calculator/index2.htm  www.learntosubnet.com www.learntosubnet.com  Subnet Calculators  http://www.cisco.com/cgi-bin/Support/IpSubnet/home.pl http://www.cisco.com/cgi-bin/Support/IpSubnet/home.pl  www.solarwinds.com www.solarwinds.com  www.subnet-calculator.com/cidr.php www.subnet-calculator.com/cidr.php  http://www.subnetonline.com/pages/subnet-calculators/ip- subnet-calculator.php http://www.subnetonline.com/pages/subnet-calculators/ip- subnet-calculator.php  http://www.wildpackets.com/resources/free_utilities/ipsubnetcalc http://www.wildpackets.com/resources/free_utilities/ipsubnetcalc

35. 35 © 2010 Cisco Systems, Inc. All rights reserved. Questions? Thank you for attending! DON’T FORGET TO TURN IN EVALUATION