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

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

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

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

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 ) –Broadcast address (e.g )

CIT 384: Network AdministrationSlide #6 Address Classes Class A: bit net ID, 24-bit host ID 2 24 – 2 hosts per network; 126 networks Class B: bit net ID, 16-bit host ID 2 16 – 2 hosts per network; 16,384 networks Class C: bit net ID, 8-bit host ID (2 8 – 2) = 254 hosts per network; 2,097,152 networks Class D: bit multicast group ID Class E: Reserved for future use

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. – /16 = –

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

CIT 384: Network AdministrationSlide #9 Private RFC1918 IP Addresses Private IP NetworksNetwork ClassCount of Networks A through B through C256

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

CIT 384: Network AdministrationSlide #11 Network Mask How do we list subnets in routing table? –Ex: addresses – –Table: netmask 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.

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 A /8 B /16 C /24 D N/A E N/A

CIT 384: Network AdministrationSlide #13 Example IP Address: Address Class: B since 128 < 137 < 191 Default Netmask: Network Address Part: Host Address Part: Broadcast Address: Host Address Range for Network: – through

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.)

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

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. – netmask is identical to /24

CIT 384: Network AdministrationSlide #17 How to find network address? (IP Address) AND (Subnet Mask) AND (convert from binary to decimal)

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 reserves (ambiguity with address of whole B) /24 (ambiguous broadcast )

CIT 384: Network AdministrationSlide #19 Choosing Subnet Mask to meet Design Requirements Requirements –Class B network –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 – –

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? (6 subnet bits, 10 host bits) (7 subnet bits, 9 host bits) (8 subnet bits, 8 host bits) (impossible) –Subnet masks / (6 subnet bits, 10 host bits, 1022 hosts/sub) / (7 subnet bits, 9 host bits, 510 hosts/sub) / (8 subnet bits, 8 host bits, 254 hosts/sub) Do you want to maximize # subnets or # hosts/subnet?

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