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TCP/IP Concepts (Part 2) January 21, 2010 MIS 4600 - MBA 5880 © Abdou Illia Objectives Explain the basic concepts of IP addressing Explain the binary, octal, and hexadecimal numbering systems 2 IP Addressing The decimal system (base 10) uses 10 digits (0-9) The binary system (base 2) uses 2 digits (0 and 1) to represent numbers. These 0s and 1s are called bits A group of 8 bits is called a byte (or an octet) An IP address consists of four bytes (or four octets) An IP address is a set of 32 bits (4 x 8 bytes) Example: 10000000 00001010 0000010 00000001 For easy reading, IP addresses are represented as 4 decimal numbers separated by dots (e.g. 120.1.2.1) 3 IP addressing (cont.) 10. 133.12.56 139.67. 122.56 An IP address has two components 192.67.122. 56 Network address Network Host Legend: Host address address address IP addresses classified: Class A addresses Class B addresses Class C addresses 4 Class Leftmos t bits Network add. length Address range Number of networks Number of hosts per network A 0xxx 8 bits 0.x.x.x – 127.x.x.x ~ 128 ~ 16 million (255^3) B 10xx 16 bits 128.x.x.x – 191.255.x.x ~ 16000 (64 x 255) ~ 65000 (255^2) C 110x 24 bits 192.x.x.x – 223.255.255.x ~ 2 million (32 x 255 x 255 ~ 254 IP Addressing (continued) Class A Limited number of Class A networks Reserved for large corporations and governments Format: network.node.node.node Class B Supports more than 65,000 host computers Assigned to large corporations and ISPs Format: network.network.node.node Class C Supports up to 254 host computers Available for small business and home networks 5 Format: network.network.network.node Subnetting a TCP/IP network A technique for dividing a network into virtual subnetworks Subnet masks are used to divide networks into virtual subnetworks A subnet mask is a32 bit number, just like an IP address, where all bits in the Network part are set to 1, and all bits in the Host part are set to 0. Examples: 1111111 11111111 11111111 00000000 (or 255.255.255.0 in decimal notation) 192.168.1.130 255.255.255.128 192.168.1.1 255.255.255.128 192.168.1.2 255.255.255.128 192.168.1.3 255.255.255.128 6 1111111 11111111 11111111 10000000 (or 255.255.255.128 in decimal notation) 192.168.1.131 255.255.255.128 Switch 192.168.1.132 255.255.255.128 Subnetting a TCP/IP network (cont) IP addresses cannot contain all 0s or all 1s Accessing entities and services on other networks: Each computer needs IP address of gateway (or router) TCP/IP uses subnet mask to determine destination computer’s network If destination computer is on a different network, sender relays packet to gateway/router Gateway/router forwards packet to its next destination 7 Subnetting Exercise Do Subnetting Exercise posted to the course web site 8 Studying Binary, Octal, Hex Numbering Systems Why study binary, octal, and hex numbering systems? Computer systems operate using binary Some attack codes are written in Hex *NIX (UNIX, Linux) file permissions are represented with bits 0 means removing the permission 1 means granting the permission 111 (rwx) means read, write, execute permission are granted 9 Binary Numbering System Uses the number 2 as its base Binary digits (bits): 0 and 1 Byte Group of 8 bits (example: 00001011) Can represent 28 = 256 different values (from 0 to 255) 128 64 32 16 8 4 2 1 27 26 25 24 23 22 21 20 128 + 64 + 32 5 16 + 8 + 4 + 2 + 1 = 255 10 Binary to Decimal 32-bit IP address and its Decimal version IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101 To convert this to decimal notation, first, divide them into four bytes (also called octets) 10000000 10101010 00010001 00001101 Convert each binary (Base 2) octet into decimal (Base 10) 11 Conversion table Position (N) Binary 10100011 = Decimal 163 Note: Starts with 0 12 Place Value Bit (2N) Decimal 7 128 1 128 6 64 0 0 5 32 1 32 4 16 0 0 3 8 0 0 2 4 0 0 1 2 1 2 0 1 1 1 163 Understanding Nibbles A nibble is half a byte or four bits Helps with reading the number by separating the byte: 1111 1010 Components High-order nibble (left side) Low-order nibble (right side) Converting 1010 1010 to decimal Low-order nibble 1010 = 10 (in base 10) Rule: Odd decimals have last low-order bit turned on (i.e. equal 1). Even decimals have low-order bit off 13 Example:1001 cannot be even. 1110 can’t be odd The Octal Numbering System Uses 8 as its base Supports decimal digits from 0 to 7 Octal digits can be represented with three bits because the largest decimal number is 7 With three bits, there are 23 = 8 possible occurrences: 000, 001, 010, 011, 100, 101, 110, 111 Permissions on UNIX systems Owner permissions (rwx) Group permissions (rwx) Other permissions (rwx) Example: 111 101 001 Octal representation 751 14 (rwxrwxrwx) (rwxr-x--x) 4 1 4 2 1 2 1 1 1 Question: In binary and octal how do you express granting read, write, execute permissions to the Owner of a file, read and write to Group, and just read to Other? 7 Short Case Do Activity 2-4 “Working with binary and Octal numbering” on page 34 of the course textbook. 15 Hexadecimal Numbering System Uses 16 as its base Support numbers from 0 to 15 Hex number consists of two characters Each character represents a nibble Value contains alphabetic letters (A … F) A representing 10 and F representing 15 HEX DECIMAL 0 0 = 0+0+0+0 BINARY 0000 1 1 = 0+0+0+1 0001 2 2 = 0+0+2+0 0010 3 3 = 0+0+2+1 0011 4 4 = 0+2+0+0 0100 5 5 = 0+4+0+1 0101 6 6 = 0+4+2+0 0110 7 7 = 0+4+2+1 0111 8 8 = 8+0+0+0 1000 9 9 = 8+0+0+1 1001 A 10 = 8+0+2+0 1010 B 11 = 8+0+0+1 1011 C 12 = 8+4+0+0 1100 13 = 8+4+0+1 1101 E 14 = 8+4+2+0 1110 F 15 = 8+4+2+1 1111 Sometimes expressed with “0x” in front D Used for MAC address (e.g. 12-34-56-78-9A-BC) To convert hexadecimal F8 to binary, write 16 down the binary for F first, then the binary for 8. F 8 1111 1000