IP addressing definition
Internet protocol address or IP address uniquely identifies every network or host on the Internet. An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits. Since each of the 8 positions can have two different states (0 or 1), the total number of combinations per octet is 28or 256.so each octet can contain any value between 0to 255. Each octet is separated by decimal points. For this reason, an IP address is known as “dotted decimal” notation.
For example: 140.179.220.200 is an IP address which is written in dotted decimal format. The actual binary format is 10001100.10110011.11001000.The first octet in this example is 140 and second octet is 179 and so on and the range of decimal number is between 0to 255.
Every IP address consists of two parts, one identifying the network that the computer belongs to known as Network ID and one identifying the host on the network known as Host ID.
Network part of the IP address (Network ID)
Internet is the interconnection of many individual networks. So each network must know its own address on the Internet and that of the other networks with which it communicates. The organization requires a unique network number, which it can request from Network Information center (NIC). This unique network number is added to packet, which is sent from the network onto the Internet.
The Host part of the IP address
In addition to network address or number, information is required to identify which specific host or machine in a network is sending or receiving a message. Therefore, IP address needs unique network number .and this is the part of the IP address.
IP Terminology
It is very important to learn some of the terminology, which is vital to understand Internet protocol. Some of the terms are listed below
- Bit: A bit is one digit; either a 1 or 0
- Byte: A byte is 8 bits.
- Octet: An Octet, mare up of 8 bits, is just an ordinary 8-bit binary number. The terms byte and octet can be used interchangeably.
- Network address: This is the designation used in routing to send packets to a remote network-for example, 10.0.0.0, 172.16.0.0, and 192.168.10.0.
- Broadcast address: The address used by applications and hosts send information to all nodes on a network is called the broadcast address .Examples include 255.255.255.255, which broadcast to all networks, all nodes; 172.16.255.255 which broadcasts to all subnets and hosts on network 10.0.0.0.
Classes of networks
Since networks vary in size, the IP addresses are divided into classes. The most common classes are class A,B and C.The class D(multicast) address and class E (research) addresses exist but end user does not generally use them. The class of an IP address can be identified by looking at its first octet. The size of the host part depends on the size of the network.
The five classes of IP address is shown in the figure
| Class | Leading bits | Start | End | Default Subnet Mask in dotted decimal | CIDR notation |
|---|---|---|---|---|---|
| A | 0 | 0.0.0.0 | 127.255.255.255 | 255.0.0.0 | /8 |
| B | 10 | 128.0.0.0 | 191.255.255.255 | 255.255.0.0 | /16 |
| C | 110 | 192.0.0.0 | 223.255.255.255 | 255.255.255.0 | /24 |
| D | 1110 | 224.0.0.0 | 239.255.255.255 | not defined | not defined |
| E | 1111 | 240.0.0.0 | 255.255.255.254 | not defined | not defined |
The blocks numerically at the start and end of classes A, B and C were originally reserved for special addressing or future features, i.e., 0.0.0.0/8 and 127.0.0.0/8 are reserved in former class A; 128.0.0.0/16 and 191.255.0.0/16 are reserved in former class B; 192.0.0.0/24 and 223.255.255.0/24 are reserved in former class C.
While the 127.0.0.0/8 network is a Class A network, it is designated for loop-back and cannot be assigned to a network.
| CIDR | host bits | Netmask | Hosts in subnet | Classful name | Typical usage |
|---|---|---|---|---|---|
| /8 | 24 | 255.0.0.0 | 16777216 = 224 | Class A (see this list) | Largest block allocation made by IANA |
| /9 | 23 | 255.128.0.0 | 8388608 = 223 | ||
| /10 | 22 | 255.192.0.0 | 4194304 = 222 | ||
| /11 | 21 | 255.224.0.0 | 2097152 = 221 | ||
| /12 | 20 | 255.240.0.0 | 1048576 = 220 | ||
| /13 | 19 | 255.248.0.0 | 524288 = 219 | ||
| /14 | 18 | 255.252.0.0 | 262144 = 218 | ||
| /15 | 17 | 255.254.0.0 | 131072 = 217 | ||
| /16 | 16 | 255.255.0.0 | 65536 = 216 | Class B | |
| /17 | 15 | 255.255.128.0 | 32768 = 215 | ISP / large business | |
| /18 | 14 | 255.255.192.0 | 16384 = 214 | ISP / large business | |
| /19 | 13 | 255.255.224.0 | 8192 = 213 | ISP / large business | |
| /20 | 12 | 255.255.240.0 | 4096 = 212 | Small ISP / large business | |
| /21 | 11 | 255.255.248.0 | 2048 = 211 | Small ISP / large business | |
| /22 | 10 | 255.255.252.0 | 1024 = 210 | ||
| /23 | 9 | 255.255.254.0 | 512 = 29 | ||
| /24 | 8 | 255.255.255.0 | 256 = 28 | Class C | Large LAN |
| /25 | 7 | 255.255.255.128 | 128 = 27 | Large LAN | |
| /26 | 6 | 255.255.255.192 | 64 = 26 | Small LAN | |
| /27 | 5 | 255.255.255.224 | 32 = 25 | Small LAN | |
| /28 | 4 | 255.255.255.240 | 16 = 24 | Small LAN | |
| /29 | 3 | 255.255.255.248 | 8 = 23 | Smallest multi-host network | |
| /30 | 2 | 255.255.255.252 | 4 = 22 | "Glue network" (point to point links) | |
| /31 | 1 | 255.255.255.254 | 2 = 21 | Rarely used, point to point links (RFC 3021) | |
| /32 | 0 | 255.255.255.255 | 1 = 20 | Host route |
In common usage, the "host all zeros" address is reserved for referring to the entire network, while the "host all ones" address is used as a broadcast address in the given subnet; this reduces the number of addresses available for hosts by 2. This explains the reference to /31 networks as "Rarely Used," as the only possible addresses on a /31 network are "host all ones" and "host all zeros." RFC 3021 creates an exception to the "host all ones" and "host all zeros" broadcast usage to make /31 networks usable for point-to-point links. In practice, however, point-to-point links are still typically implemented using /30 networks, or occasionally by /32 and point-to-point explicit host routes. There is generally no technical advantage to /31 versus /32, although one or the other may be more convenient based on other issues. A /30 is always wasteful and has as its sole advantage that it behaves "as expected" for any other subnetwork.
Private IPv4 address spaces
The Internet Engineering Task Force (IETF) has directed the Internet Assigned Numbers Authority (IANA) to reserve the following IPv4 address ranges for private networks, as published in RFC 1918:
| RFC1918 name | IP address range | number of addresses | classful description | largest CIDR block (subnet mask) | host id size |
|---|---|---|---|---|---|
| 24-bit block | 10.0.0.0 – 10.255.255.255 | 16,777,216 | single class A | 10.0.0.0/8 (255.0.0.0) | 24 bits |
| 20-bit block | 172.16.0.0 – 172.31.255.255 | 1,048,576 | 16 contiguous class Bs | 172.16.0.0/12 (255.240.0.0) | 20 bits |
| 16-bit block | 192.168.0.0 – 192.168.255.255 | 65,536 | 256 contiguous class Cs | 192.168.0.0/16 (255.255.0.0) | 16 bits |
Classful addressing is obsolete and has not been used in the Internet since the implementation of Classless Inter-Domain Routing (CIDR) starting in 1993. For example, while 10.0.0.0/8 was a single class A network, it is common for organizations to divide it into smaller /16 or /24 networks.
Broadcast Addresses
Four different types of broadcast addresses are
- Layer 2 broadcasts: These are sent to all nodes or hosts on a LAN.
- Layer 3 broadcasts: These are sent to all hosts or nodes on the network
- Unicast: These are sent to single destination host
- Multicast: These are the packets sent from a single source and transmitted to many devices on
- different networks.
Layer 2 Broadcast:
Layer 2 broadcasts are also known as hardware address. They do not pass the LAN boundary unless they become a Unicast packet. A typical hardware address is 6 bytes and looks something like Oc.43.a4.f3.12.c2. The broadcast would be all 1s in binary and all Fs in hexadecimal, which looks like FF.FF.FF.FF.FF.FF.Layer 3 broadcast addresses:
Broadcast message are meant to reach all hosts on a broadcast domain. These are network broadcast that have all host bits on. The network address of 173. 14.0.0.255.255.0.0 Would have a broadcast address of 173.14.255.255 with all host bits on. Broadcast can also be “all networks and all hosts,” as indicated by 255.255.255.255.Unicast:
A Unicast is different because it’s broadcast that has an actual destination IP address- in other words, it’s sent to a specific host, most commonly a DHCP server. For example: the host on a network sends out an FF.FF.FF.FF.FF.FF.and 255.255.255.255. destination broadcast looking for a DHCP server on the LAN. The router will see that this is a broadcast sent for the DHCP server, and forward the request to the IP address of the DHCP server on another LAN. So, basically, if the DHCP server IP address is 173.14.10.1, the host just sends out a 255.255.255.255 broadcast, and the router changes that broadcast to the specific destination address of 173.14.10.1, the host just sends out a 255.255.255.255 broadcast to the specific destination address of 173.14.10.1.Multicast:
Multicast is point-to-multipoint communication. It is similar to broadcast but this works in a different manner. Multicast works by sending message or data to IP multicast group addesaaes.Routers then forward copies of the packet to every interface that has hosts subscribed to that group address. This is major difference between broadcast and multicast.
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