The University of AkronSummit College

Business Technology Dept.2440: 141

Web Site Administration

IP AddressingInstructor: Enoch E. Damson

Data PacketsComprised of small chunks of data that each layer appends

onto the packet data received from the layer directly above itCommonly referred to as datagramsSent out on the chosen physical medium to its destination

address (included in the packet by the network or IP layerPackets are nothing more than a series of bits (0s and 1s)

If written in binary (bit) format, may take up a lot of space and hard to read

Instead, packets can be displayed in hexadecimal to save space 1 hex digit is equivalent to 4 bits 2 hex digits represents 8 bits (1 byte)

IP Addressing 2

Hexadecimal-Decimal-BinaryComputers use the binary system (base 2) with only two

numeric symbols (0 and 1)Human beings find it easier working with decimal (base

10) values (0-9)Some datagrams are written in hexadecimal (base 16)

values (0-9, a-f)

IP Addressing 3

Numeric ConversionsThere are different methods of conversions between:

Decimal to Binary (and vice versa)Decimal to Hexadecimal (and vice versa)

Adopt a methodology that is easiest or makes most sense to you

IP Addressing 4

Decimal to Hexadecimal ConversionExample #1:172 = 16 * 10 Remainder 12 (12 is c)10 = 16 * 0 Remainder R10 (10 is

a)= AC (10 12)

Example #2:205 = 16 * 12 Remainder 13 (13 is d)12 = 16 * 0 Remainder 12 (12 is c)

= CD (12 13)

Example #3:52 = 16 * 3 Remainder 43 = 16 * 0 Remainder 3

= 34

Hexadecimalsa= 10b= 11c = 12d= 13e = 14f = 15

IP Addressing 5

Hexadecimal to Decimal Conversion

Example #1:AC= (10 x 161) + (12 x 160)

= 160 + 12= 172

Example #2:CD= (12 x 161) + (13 x 160)

= 192 + 13= 205

Example #3:34= (3 x 161) + (4 x 160)

= 48 + 4= 52

Hexadecimalsa= 10b= 11c = 12d= 13e = 14f = 15

IP Addressing 6

Decimal to Binary ConversionExample #1:172 = 2 * 86 Remainder 086 = 2 * 43

Remainder 043 = 2 * 21

Remainder 121 = 2 * 10

Remainder 110 = 2 * 5

Remainder 05 = 2 * 2 Remainder 12 = 2 * 1 Remainder 01 = 2 * 0 Remainder 1

Counting the remainders from the bottom up, the binary equivalent of the decimal value 172 is: 10101100

IP Addressing 7

Decimal to Binary Conversion… Example #2: 125 is converted to binary by finding the integer quotients and the

remainders as follows: 125 divided by 2 equals 62, remainder 1 62 divided by 2 equals 31, remainder 0 31 divided by 2 equals 15, remainder 1 15 divided by 2 equals 7, remainder 1 7 divided by 2 equals 3, remainder 1 3 divided by 2 equals 1, remainder 1 1 divided by 2 equals 0, remainder 1

1111101 For octets: pad with a 0

01111101

IP Addressing 8

Binary to Decimal Conversion One method of converting the binary 11010011 to decimal is

as follows:1. Count the total number of digits in the number (8)2. Subtract one from the total (8 - 1 = 7)3. That number (7) is the power of 2 to associate with the highest

exponent for two in the number4. Convert to exponential notation, using all the digits as multipliers5. 11010011, therefore, converts to:

IP Addressing 9

Binary to Decimal Conversion…

128 64 32 16 8 4 2 1

27 26 25 24 23 22 21 20

0 1 0 1 1 0 1 1

Another method of converting the binary 01011011 to decimals is as follows:Add all the decimals equivalents with the value 1 (for “on”

switches) 64 + 16 + 8 + 2 + 1 = 91

IP Addressing 10

High-Order Bit Patterns

IP Addressing 11

Low-Order Bit Patterns

IP Addressing 12

Hexadecimal-Decimal-Binary Conversion Exampleac.1c.0a.c1 converted to decimal yields 172.28.10.193

hexadecimal decimalac 1721c 280a 10c1 193

Converting the decimals to binary results to: 10101100.00011100.00001010.11000001hexadecimal decimal binary octetsac 172 101011001c 28 11100 (00011100)0a 10 1010 (00001010)c1 193 11000001

The second and third octets are padded with leading 0s to make it 8 bits (1 byte) long

IP Addressing 13

Importance of Numeric ConversionsConverting between number systems is important when:

Calculating IP addressesCalculating SubnetsInterpreting hexadecimal packet representation

IP Addressing 14

IP AddressingAn IP (Internet Protocol) address is a unique identifier

for a node or host connection on an IP networkIP addresses are 32 bits (4 bytes) longEach byte is represented as an octet (decimal number from 0 to 255) –

a grouping of 8 bits usually expressed as decimal numbersThe 4 bytes are usually represented in dotted decimal notation

E.g., 172.24.208.192 IP addresses have two distinct parts:

Network identifier (E.g., 172.24.x.x for IP address above) Host ID identifier (E.g., x.x.208.192 for the IP address above)

IP Addressing 15

IP Addressing…IP address are categorized into ranges referred to as classes:

Classes A, B, C, D, and EOnly IP addresses in the classes A, B, and C are available for

assigning an address to a hostClass system provides a basis for determining which part of the

address is the network and which is the host IDThe first octet of an address denotes its class

IP Addressing 16

IP Addressing Classes Class A:

Intended for large corporations and governmentsAn IP address registry assigns the first octet, leaving the last three

octets for network administrators to assign to hosts First octet between 1-126 16,777,214 hosts per network address

Class B: Intended for use in medium-sized networksFirst two octets are assigned, leaving the last 2 for hosts

First octet between 128-191 65,534 hosts per network address

IP Addressing 17

IP Addressing Classes… Class C:

Intended for small networksFirst three octets are assigned

First octet between 192-223 254 hosts per network address

Class D: Reserved for multicasting – a packet is addressed to allow reception at

more than one destinationApplications using this include streaming media and videoconferencingFirst octet between 224-239Cannot be used to assign IP addresses to host computers

IP Addressing 18

IP Addressing Classes…Class E:

Reserved for experimental useFirst octet between 240-255Cannot be used for IP address assignment

IP Addressing 19

Common IP Classes

Class FirstByte

Subnet mask Number of Networks

Number ofHosts

Class A 1 – 127 255.0.0.0 126 >16,000,000

Class B 128 – 191 255.255.0.0 > 16,000 >65,000

Class C 192 – 223 255.255.255.0 > 2,000,000 254

IP Addressing 20

IP Addressing…IP addresses beginning with 127 (or 01111111) are reserved

for loopback and for internal testing on a local machine127.0.0.0 network is called the loopback address – always

refers to the local computer and used to test the functionality of TCP/IP localhost always corresponds to address 127.0.0.1

To alleviate the problem of IP address scarcity, the TCP/IP’s governing body, Internet Engineering Task Force (IETF), reserved addresses for private networksClass A addresses beginning with 10Class B addresses from 172.16 to 172.31Class C addresses from 192.168.0 to 192.168.255

These addresses cannot be routed across the Internet

IP Addressing 21

IP Addressing…Network Address Translation (NAT) – allows an IP address from one

network to be translated into another address on an internal networkCan be used to translate a single IP address valid on the Internet into

multiple internal addressesUseful if your ISP gives you a single IP address but you have multiple

servers and users on the internal network IPv6 eliminates the need for private addressing

It provides a 128-bit address (vs. IPv4’s 32 bits)A number of public and private companies around the world (IP address

registries) cooperatively manage the total collection of valid IP addressThe activity occurs under the control of the Internet Assigned Numbers

Authority (IANA) – a public nonprofit agency responsible for Internet addressing and address management

IP Addressing 22

Classless Interdomain Routing (CIDR)Addressing by class has been superseded by a more flexible

addressing methodClassless Interdomain Routing (CIDR) – the network and host

demarcation can be made with any number of bits from the beginning of the address E.g., a Class C address’s network section is 24 bits

Using CIDR, an address registry can assign an address with a network section of 26 bits 192.203.187.0/26

The CIDR technique involves “borrowing” bits from the host portion of the address to create two or more network numbers, hence process is called subnetting

Subnetting divides network address in two or more subnetwork addresses (with fewer host IDs for each)

IP Addressing 23

Why Subnet?Subnetting:

Makes more efficient use of available IP addressesEnables dividing networks into logical groupsCan make network communication more efficientReduces broadcast traffic

IP Addressing 24

Subnet MasksSubnet mask (netmask) – determines which part of the IP

address denotes the network and host portions A 32-bit number that is always assigned to a host when the IP address

is assignedA binary 1 signifies that the corresponding bit in the IP address belongs

to the network portionA binary 0 signifies that the bit in the IP address belongs to the host

portionThe default subnet mask uses a 255 (11111111 in binary) in each octet

in the IP address that corresponds to the network portion Class A: 255.0.0.0 Class B: 255.255.0.0 Class C: 255.255.255.0

IP Addressing 25

Calculating a Subnet Mask To build a subnet mask, use the following steps:

1. Decide how many subnets you need Number is usually derived as a result of a network design document Seeing how many network cable segments are connected to router

interfaces can help figure out the needed subnets Each cable segment indicates a required subnet

2. Decide how many bits you need to meet or exceed the number of required subnets Use the formula 2n, with n representing the number of bits you must

add to the starting subnet mask3. Borrow bits from the top of the host portion of the address down4. Ensure that you have enough host bits available to assign to

computers on each subnet Use the formula 2n-2, with n representing the number of host (0) bits in

the subnet (after borrowing the bits from the host)

IP Addressing 26

Calculating a Subnet Mask Example With a Class C address 200.10.10.0 needing 12 subnets:

The default subnet mask will be: 255.255.255.0 11111111.11111111.11111111.00000000 (binary equivalent)

To meet or exceed 12 subnets: The nearest power of 2 is 16 (24) meaning 4 bits will be borrowed from

the host portion of the original subnet mask to the network portion (making them 4 subnet bits)

Borrowing 4 bits from the left of the host creates the following subnet mask: 11111111.11111111.11111111.11110000 255.255.255.240 (decimal equivalent)

To calculate the number of host addresses for each subnet: Count the number of 0s remaining in the subnet mask to determine the

number of bits left for the host address 11111111.11111111.11111111.11110000 (4 bits left for host) 24 – 2 = 14 (host addresses required for each subnet)

IP Addressing 27

Calculating a Subnet Mask Example… After calculating the appropriate subnet mask, determine the network numbers by: Placing the borrowed 4 bits in the network number and cycling the 4

bits through the possible combinations of values they represent (16 possible combinations as shown below, in this case)

IP Addressing 28

Calculating a Subnet Mask Example… After calculating the appropriate

subnet mask, determine the host numbers in each subnet by: Cycling through the 4 host bits Therefore, the subnetwork

address 200.10.10.32 would have host addresses from 200.10.10.33 through 210.10.10.47

However, you cannot use the IP address in which all host bits are 1s (because it is the broadcast address)

So the actual range will be 210.10.10.33 through 210.10.10.46 (14 hosts)

Subnet Host Addresses for 210.10.10.32

200.10.10.33

200.10.10.34

200.10.10.35

200.10.10.36

200.10.10.37

200.10.10.38

200.10.10.39

200.10.10.40

200.10.10.41

200.10.10.42

200.10.10.43

200.10.10.44

200.10.10.45

200.10.10.46

IP Addressing 29

Calculating SupernetsSupernetting “borrows” bits from network portion of an IP

address to “lend” those bits to host portionPermits consecutive IP network addresses to be combined and viewed

in a single logical networkCombining two or more small networks into one larger

network is only one reason to supernetSupernetting can combine multiple routing table entries into a single

entry, which can drastically decrease the table’s size on Internet routersThis reduction in routing table size increases the speed and efficiency of

Internet routers

IP Addressing 30

Calculating Supernets ExampleAssuming a network design has the following four Class C network

addresses available, 192.168.0.0, 192.168.1.0, 192.168.2.0, 192.168.3.0 on the proposed network without the necessary router interfaces to use the numbers: The default subnet mask will be: 255.255.255.0

11111111.11111111.11111111.00000000 (binary equivalent) You may combine the four networks into one by borrowing 2 bits (22 = 4) from

the network portion of the address and adding them to the host portion. You will have a network address of 192.168.0.0 with a subnet mask of 255.255.252.0

11111111.11111111.11111100.00000000 255.255.252.0 (decimal equivalent)

Instead of supporting only 8 bits for the host address portion, the supernet now supports 10 bits (8 + 2) for the host addresses This provides 1022 (210 – 2) host addresses on this supernet

IP Addressing 31