1. CIT 384: Network AdministrationSlide #1 CIT 384: Network Administration Subnetting

2. CIT 384: Network AdministrationSlide #2 Topics 1.IP Addresses 2.Classful and classless addressing 3.Subnet Masks and Prefixes 4.Subnet Math 5.Subnet Problems

3. CIT 384: Network AdministrationSlide #3 IP Addresses 32-bit integers One for each network interface. Dotted decimal notation: ii.jj.kk.ll 172. 16. 254. 1 10101100000100001111111000000001 1 byte 32 bits = 4 bytes

4. CIT 384: Network AdministrationSlide #4 Grouping IP Addresses Groups of consecutive IP addrs are called networks. Routing table would only need 3 entries below.

5. CIT 384: Network AdministrationSlide #5 Network and Host Parts IP addresses are divided into two parts –Network ID (like zip code) –Host ID (like street address) Network IDHost ID Two special IP addresses –Network address (e.g. 130.4.0.0) –Broadcast address (e.g. 130.4.255.255)

6. CIT 384: Network AdministrationSlide #6 Address Classes Class A: 0.0.0.0-127.255.255.255 8-bit net ID, 24-bit host ID 2 24 – 2 hosts per network; 126 networks Class B: 128.0.0.0-191.255.255.255 16-bit net ID, 16-bit host ID 2 16 – 2 hosts per network; 16,384 networks Class C: 192.0.0.0-223.255.255.255 24-bit net ID, 8-bit host ID (2 8 – 2) = 254 hosts per network; 2,097,152 networks Class D: 224.0.0.0-239.255.255.255 28-bit multicast group ID Class E: 240.0.0.0-255.255.255.255 Reserved for future use

7. CIT 384: Network AdministrationSlide #7 CIDR Classless Inter-Domain Routing –Classful routing wastes most IP addresses. –Allocate addresses on bit boundaries instead of byte boundaries. –Allow ISPs/users to decide on boundaries instead of basing on IP addresses. Prefix notation –/x indicates that first x bits are shared. –192.168.0.0/16 = 192.168.0.0 – 192.168.255.255

8. CIT 384: Network AdministrationSlide #8 Public IP Addresses ICANN assigns network numbers. –Internet Corporation for Assigned Network Numbers. –ICANN gives authority to regional orgs, e.g. ARIN (American Registry for Internet Numbers) –Typically to ISPs, universities, corporations. ISP assigns IP addresses within network

9. CIT 384: Network AdministrationSlide #9 Private RFC1918 IP Addresses Private IP NetworksNetwork ClassCount of Networks 10.0.0.0A1 172.16.0.0 through 172.31.0.0 B16 192.168.0.0 through 192.168.255.0 C256

10. CIT 384: Network AdministrationSlide #10 IPv4 vs IPv6 Addresses FeatureIPv4IPv6 Size of Address32 bits128 bits Example Address10.1.1.10000:0000:0000: 0000:FFFF:FFFF :0A01:0101 Abbreviated Address -::FFFF:FFFF:0A 01:0101 Localhost127.0.0.1::1/128 Possible Addresses 2 32 (~4 billion)2 128 (~3.4 x 10 38 )

11. CIT 384: Network AdministrationSlide #11 Network Mask How do we list subnets in routing table? –Ex: addresses 150.150.4.0 – 150.150.4.255 –Table: 155.155.4.0 netmask 255.255.255.0 Subnet mask indicates range –Binary 1s indicate network part of address. –Binary 0s indicate host part of address. –Always consists of 1s followed by 0s. Prefix notation –Humanly readable form of subnet mask. –Just counts the number of binary 1s in mask.

12. CIT 384: Network AdministrationSlide #12 Classful Address Ranges and Masks Class A NNNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH Class B NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH Class C NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH ClassLeading Bits StartEndSubnet MaskCIDR A00.0.0.0126.255.255.255255.0.0.0/8 B10128.0.0.0191.255.255.255255.255.0.0/16 C110192.0.0.0231.255.255.255255.255.255.0/24 D1110224.0.0.0239.255.255.255N/A E1111240.0.0.0255.255.255.0N/A

13. CIT 384: Network AdministrationSlide #13 Example IP Address: 137.201.18.42 Address Class: B since 128 < 137 < 191 Default Netmask: 255.255.0.0 Network Address Part: 137.201.0.0 Host Address Part: 0.0.18.42 Broadcast Address: 137.201.255.255 Host Address Range for Network: –137.201.18.1 through 137.201.255.254

14. CIT 384: Network AdministrationSlide #14 Why Subnet? Allows admin to create more networks for: 1.Address conservation. 2.Organization of hosts. 3.Different physical media. 4.Security. 5.Performance (smaller broadcast domains.)

15. CIT 384: Network AdministrationSlide #15 IP Addresses with Subnets Route on network + subnet part of address.

16. CIT 384: Network AdministrationSlide #16 Subnet Math Binary Decimal Conversion –Convert each byte of dotted quad into binary. –Convert binary byte into 4 decimal values. Boolean AND operation –0 AND 0 = 0 –0 AND 1 = 0 –1 AND 0 = 0 –1 AND 1 = 1 Convert between dotted quad and prefix. –255.255.255.0 netmask is identical to /24

17. CIT 384: Network AdministrationSlide #17 How to find network address? (IP Address) AND (Subnet Mask) 137.201.18.42 10001001.11001001.00010010.00101010 AND 255.255.0.0 11111111.11111111.00000000.00000000 --------------------------------------------------- 10001001.11001001.00000000.00000000 (convert from binary to decimal) 137.201.0.0

18. CIT 384: Network AdministrationSlide #18 How to find number of networks? Address divided between network and host. –If there are s subnet bits and h host bits, then –Number of subnets = 2 s –Number of hosts = 2 h – 2 Subnet zero –Classful routing reserves 2 subnets so only have 2 s – 2. Lowest and highest subnet numbers. –For Class B network 150.150.0.0 reserves 150.150.0.0 (ambiguity with address of whole B) 150.150.255.0/24 (ambiguous broadcast 150.150.255.255)

19. CIT 384: Network AdministrationSlide #19 Choosing Subnet Mask to meet Design Requirements Requirements –Class B network 130.1.0.0 –Number of subnets: 200 –Max hosts per subnet: 200 Problem 1: how many host bits? –Find h, # of host bits, such that 2 h >= 200. –2 7 = 128, 2 8 = 256, therefore h = 8. Problem 2: how many subnet bits? –Find s, # of subnet bits, such that 2 s >= 200, yields s = 8. –NNNNNNNN.NNNNNNNN.SSSSSSSS.HHHHHHHH Problem 3: find subnet mask –11111111 11111111 11111111 00000000 –255.255.255.0

20. CIT 384: Network AdministrationSlide #20 Multiple Possible Subnet Masks In some problems, many subnet masks exist. Ex: change # of subnets from 200 to 50. –Find s, # of subnet bits, such that 2 s >= 50, yields s = 6. –NNNNNNNN.NNNNNNNN.SSSSSSxx.HHHHHHHH –How many possible subnets exist? 11111111 11111111 11111100 (6 subnet bits, 10 host bits) 11111111 11111111 11111110 (7 subnet bits, 9 host bits) 11111111 11111111 11111111 (8 subnet bits, 8 host bits) 11111111 11111111 11111101 (impossible) –Subnet masks /22 255.255.252.0 (6 subnet bits, 10 host bits, 1022 hosts/sub) /23 255.255.254.0 (7 subnet bits, 9 host bits, 510 hosts/sub) /24 255.255.255.0 (8 subnet bits, 8 host bits, 254 hosts/sub) Do you want to maximize # subnets or # hosts/subnet?

21. CIT 384: Network AdministrationSlide #21 References 1.James Boney, Cisco IOS in a Nutshell, 2 nd edition, O’Reilly, 2005. 2.Cisco, Cisco Connection Documentation, http://www.cisco.com/univercd/home/home.htm http://www.cisco.com/univercd/home/home.htm 3.Cisco, Internetworking Basics, http://www.cisco.com/univercd/cc/td/doc/cisintw k/ito_doc/introint.htm http://www.cisco.com/univercd/cc/td/doc/cisintw k/ito_doc/introint.htm 4.Matthew Gast, 802.11 Wireless Networks: The Definitive Guide, O’Reilly, 2005. 5.Wendell Odom, CCNA Official Exam Certification Library, 3 rd edition, Cisco Press, 2007.