Content • Whats is an IP address. • Whats the type of IP address. • IP Address and virtual hosting • Defintion of IP address. • Internet Address Structure • configure to IP address • Subnet Masks and Subnetting • Primary Address Classes • Unicast.broadcast.multicast • Dotted-Decimal Notation
What is an IP address • Internet Protocol (IP) • An IP (Internet Protocol) address is a unique identifier for a node or host connection on an IP network. • Since these numbers are usually assigned to internet service providers within region-based blocks, an IP address can often be used to identify the region or country from which a computer is connecting to the Internet. An IP address can sometimes be used to show the user's general location.
Type of IP address • Because the numbers may be tedious to deal with,an IP address may also be assigned to a Host name, which is sometimes easier to remember. • Hostnames may be looked up to find IP addresses, and vice-versa. At one time ISPs issued one IP address to each user. These are called static IP addresses. • Because there is a limited number of IP addresses and with increased usage of the internet ISPs now issue IP addresses in a dynamic fashion out of a pool of IP addresses (Using DHCP). These are referred to as dynamic IP addresses. This also limits the ability of the user to host websites, mail servers, ftp servers, etc
IP Address and virtual hosting • Some systems, such as routers which have interfaces to more than one network, must be assigned a unique IP address for each network interface. • In addition to users connecting to the internet, with virtual hosting, a single machine can act like multiple machines (with multiple domain names and IP addresses • Knowing your IP address can allow you (and others you tell) to access services running on your machine such as online games, servers (FTP, web, mail), and remote access utilities (PCAnywhere, GoToMyPC, MS Remote Desktop).
IP Address An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255 (known as octets) separated by decimal points. This is known as "dotted decimal" notation. Example: 22.214.171.124 It is sometimes useful to view the values in their binary form. 140 .179 .220 .200 10001100.10110011.11011100.11001000
IP Address -Every IP address consists of two parts, one identifying the network and one identifying the node. The first part of an Internet address identifies the network on which the host resides, while the second part identifies the particular host on the given network. This created the two-level addressing hierarchy which is illustrated in figure in next slide
Internet Address Structure Figure : Two-Level Internet Address Structure
IP Address …… All hosts on a given network share the same network-prefix but must have a unique host-number. Similarly, any two hosts on different networks must have different network-prefixes but may have the same host-number
Subnet Masks and Subnetting • A subnet allows the flow of network traffic between hosts to be segregated based on a network configuration • By organizing hosts into logical groups, subnetting can improve network security and performance. • a subnet mask contains four bytes (32 bits) .and is often written using the same "dotted-decimal" notation. • All valid subnet masks contain two parts: the left side with all mask bits set to '1' (the extended network portion) and the right side with all bits set to '0' (the host portion)
This means that the standard network masks for the three classes of networks are:- • A Class network mask: 255.0.0.0 • B Class network mask: 255.255.0.0 • C Class network mask: 255.255.255.0 • The network mask is not an IP number - it is used to modify how local IP numbers are interpreted locally.
Masking :- First it ANDs the destination address of the packet with its own subnet mask. If the resulting address matches its own network mask, then the destination is in the same subnet, and the TCP/IP stack tells the card to send the packet directly To the destination machine. (if the address is not in your ARP cache, then your station will send out an ARP to get it). If, however, the calculation shows that the destination is part of another network, then the packet is sent to the default gateway. In effect, the sender is saying, "I do not know how to deliver this packet; can you please deliver it for me?" The gateway accepts the packet and then goes through a similar procedure. (That procedure is known as routing.)
Example 1 Workstation A sends to Workstation B Workstation A knows its own network address/subnet mask is 192.168.16.0/22. Workstation A calculates the local-subnet of the destination packet as follows: • Are A and B in the same subnet? bitwise-AND 11111111 . 11111111 . 11111100 . 00000000 subnet mask of A 11000000 . 10101000 . 00010001 . 00010100 IP addr of dest (B) 11000000 . 10101000 . 00010000 . 00000000 compare 11000000 . 10101000 . 00010000 . 0000000 • They are equal - Both Workstations are on the network 192.168.16.0 • Because the network address of the sender matches the result of this calculation, the packet is sent directly to machine B.
Example 2 • Workstation C sends to Workstation B Workstation C knows its network address/subnet mask is 192.168.30.0/24. Machine C checks to see if the destination packet falls within its subnet. • Are C and B in the same subnet? bitwise-AND (broadcast) 11111111 . 11111111 . 11111111 . 00000000 11000000 . 10101000 . 00010001 . 00010100 subnet mask of C IP addr of dest (B) 11000000 . 10101000 . 00010001 . 00000000 • compare 11000000 . 10101000 . 00011110 . 00000000 network of C • They ARE NOT equal - 192.168.17.0 < not equal to > 192.168.30.0 • In this case, the comparison fails. The sender, C, has no choice but to send packet to its gateway. (If you take the time to do the calculation, you discover the gateway is in machine C's subnet. In fact the gateway must always be in the sender's subnet; otherwise, the sender could not send to it either!)
Primary Address Classes In order to provide the flexibility required to support different size networks, the designers decided that the IP address space should be divided into three different address classes - Class A, Class B, and Class C. This is often referred to as "classful" addressing because the address space is split into three predefined classes, groupings, or categories. Each class fixes the boundary between the network-prefix and the host-number at a different point within the 32-bit address. The formats of the fundamental address classes are illustrated in Figure below
Classful IP Address Figure : Principle Classful IP Address Formats
Address Classes There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address. Class A addresses begin with 0xxx, or 1 to 126 decimal. Class B addresses begin with 10xx, or 128 to 191 decimal. Class C addresses begin with 110x, or 192 to 223 decimal. Class D addresses begin with 1110, or 224 to 239 decimal. Class E addresses begin with 1111, or 240 to 254 decimal.
Class A Networks (/8 Prefixes) Each Class A network address has an 8-bit network-prefix with the highest order bit set to 0 and a seven-bit network number, followed by a 24-bit host-number. Today, it is no longer considered 'modern' to refer to a Class A network. Class A networks are now referred to as "/8s" (pronounced "slash eight" or just "eights") since they have an 8-bit network-prefix. A maximum of 126 (2 ^7 -2) /8 networks can be defined. The calculation requires that the 2 is subtracted because the /8 network 0.0.0.0 is reserved for use as the default route and the /8 network 127.0.0.0 has been reserved for the "loopback" function. Each /8 supports a maximum of 16,777,214 (2^ 24 -2) hosts per network. The host calculation requires that 2 is subtracted because the all-0s ("this network") and all-1s ("broadcast") host-numbers may not be assigned to individual hosts.
Class B Networks (/16 Prefixes) Each Class B network address has a 16-bit network-prefix with the two highest order bits set to 1-0 and a 14-bit network number, followed by a 16-bit host-number. Class B networks are now referred to as"/16s" since they have a 16-bit network-prefix. A maximum of 16,384 (2^ 14 ) /16 networks can be defined with up to 65,534 (2 ^16 -2) hosts per network. Since the entire /16 address block contains 2 30 (1,073,741,824) addresses, it represents 25% of the total IPv4 unicast address space.
Class C Networks (/24 Prefixes) Each Class C network address has a 24-bit network-prefix with the three highest order bits set to 1-1-0 and a 21-bit network number, followed by an 8-bit host-number. Class C networks are now referred to as "/24s" since they have a 24-bit network-prefix. A maximum of 2,097,152 (2 ^21 ) /24 networks can be defined with up to 254 (2^8 -2) hosts per network. Since the entire /24 address block contains 2 ^29 (536,870,912) addresses, it represents 12.5% (or 1/8th) of the total IPv4 unicast address space.
Other Classes In addition to the three most popular classes, there are two additional classes. Class D addresses have their leading four-bits set to 1-1-1-0 and are used to support IP Multicasting. Class E addresses have their leading four-bits set to 1-1-1-1 and are reserved for experimental use.
UnicastUnicast is the term used to describe communication where a piece of information is sent from one point to another point. In this case there is just one sender, and one receiver.
unicast Unicast transmission, in which a packet is sent from a single source to a specified destination, is still the predominant form of transmission on LANs and within the Internet. All LANs (e.g. Ethernet) and IP networks support the unicast transfer mode, and most users are familiar with the standard unicast applications (e.g. http, SMTP, FTP and Telnet) which employ the TCP transport protocol.
Broadcast Broadcast is the term used to describe communication where a piece of information is sent from one point to all other points. In this case there is just one sender, but the information is sent to all connected receivers.
Broadcast Broadcast transmission is supported on most LANs (e.g. Ethernet), and may be used to send the same message to all computers on the LAN Network layer protocols (such as IP) also support a form of broadcast which allows the same packet to be sent to every system in a logical network.
Multicast Multicast is the term used to describe communication where a piece of information is sent from one or more points to a set of other points. In this case there is may be one or more senders, and the information is distributed to a set of receivers.
Multicast Multicasting is the networking technique of delivering the same packet simultaneously to a group of clients. IP multicast provides dynamic many-to-many connectivity between a set of senders (at least 1) and a group of receivers. The format of IP multicast packets is identical to that of unicast packets and is distinguished only by the use of a special class of destination address (class D IP address) which denotes a specific multicast group. Since TCP supports only the unicast mode, multicast applications must use the UDP transport protocol.
Unicast • Multicast • broadcast
Dotted-Decimal Notation To make Internet addresses easier for human users to read and write, IP addresses are often expressed as four decimal numbers, each separated by a dot. This format is called "dotted-decimal notation." Dotted-decimal notation divides the 32-bit Internet address into four 8-bit (byte) fields and specifies the value of each field independently as a decimal number with the fields separated by dots.
This Figure shows how a typical /16 (Class B) Internet address can be expressed in dotted decimal notation. Figure : Dotted-Decimal Notation
Dotted-Decimal Notation This Table displays the range of dotted-decimal values that can be assigned to each of the three principle address classes. The "xxx" represents the host-number field of the address which is assigned by the local network administrator. Table : Dotted-Decimal Ranges for Each Address Class