An Introduction to IP Addressing

Ways of Communication

Unicasting

·         Communication between two devices is one-on-one. Create least traffic while communicating. Best in when one device want to communicate with one device only as no extra bothering the other hosts on the segment. Cannot be use in one-on-many devices to communicate as one hub device need to send the many copies of the same packet to all the hosts and will get the Acks from them.

Broadcasting

·         Communication between two devices is one-on-all. One-n-all means all the host in the network on the same switch. When host send the packet on broadcast address then the switch will duplicate the packet and will send it on all the host in the network.

Multicasting

·         Communication with one-on-one and one-on-many has too many limitations like large traffic to handle and security breach. It is used when one-on-group one way communication is required. For example live telecasting of video stream on internet, in this case the users are group of people who may need the particular stream but not all the hosts. So the user will join the particular multicast group to get that particular stream.

IP Addressing

One of the most important topics in any discussion of TCP/IP is IP addressing. An IP address is a numeric identifier assigned to each machine on an IP network. It designates the location of a device on the network. An IP address is a software address, not a hardware address—the latter is hardcoded on a network interface card (NIC) and used for finding hosts on a local network. IP addressing was designed to allow a host on one network to communicate with a host on a different network, regardless of the type of LANs the hosts is participating in.

IP stands for Internet Protocol, it's a communications protocol used from the smallest private network to the massive global Internet. An IP address is a unique identifier given to a single device on an IP network. The IP address consists of a 32-bit number that ranges from 0 to 4294967295. This means that theoretically, the Internet can contain approximately 4.3 billion unique objects. But to make such a large address block easier to handle, it was chopped up into four 8-bit numbers, or "octets," separated by a period. Instead of 32 binary base-2 digits, which would be too long to read, it's converted to four base-256 digits. Octets are made up of numbers ranging from 0 to 255. The numbers below show how IP addresses increment.

0.0.0.0
0.0.0.1
...increment 252 hosts...

0.0.0.254
0.0.0.255
0.0.1.0
0.0.1.1
...increment 252 hosts..

0.0.1.254
0.0.1.255
0.0.2.0
0.0.2.1
...increment 4+ billion hosts...

255.255.255.255

IP Terminology

Here are a few of the most important terms: -

Bit One digit; either a 1 or a 0.

Byte 8 bits.

Octet Always 8 bits. Base-8 addressing scheme.

Network address 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

Used by applications and hosts to send information to all nodes on a network. Examples include 255.255.255.255, which is all networks, all nodes; 172.16.255.255, which is all subnets and hosts on network 17.16.0.0; and 10.255.255.255, which broadcasts to all subnets and hosts on network 10.0.0.0.

The Hierarchical IP Addressing Scheme

An IP address consists of 32 bits of information. These bits are divided into four sections, referred to as octets or bytes, each containing 1 byte (8 bits).

You can depict an IP address using one of three methods:

·         Dotted-decimal, as in 172.16.30.56

·          Binary, as in 10101100.00010000.00011110.00111000

·         Hexadecimal, as in 82 39 1E 38

Network Addressing

The network address uniquely identifies each network. Every machine on the same network shares that network address as part of its IP address. In the IP address 172.16.30.56, for example, 172.16 is the network address.

The node address is assigned to, and uniquely identifies, each machine on a network. This part of the address must be unique because it identifies a particular machine—an individual—as opposed to a network, which is a group. This number can also be referred to as a host address. In the sample IP address 172.16.30.56, .30.56 is the node address. The designers of the Internet decided to create classes of networks based on network size. For the small number of networks possessing a very large number of nodes, they created the rank Class A network. At the other extreme is the Class C network, which is reserved for the numerous networks with a small number of nodes. The class distinction for networks between very large and very small is predictably called the Class B network. Subdividing an IP address into a network and node address is determined by the class designation of one’s network.

 Figure summarizes the three classes of networks: -

Network Address Range: Class A

The designers of the IP address scheme said that the first bit of the first byte in a Class A network address must always be off, or 0. This means a Class A address must be between 0 and 127.

Here is how those numbers are defined:

0xxxxxxx: If we turn the other 7 bits all off and then turn them all on, we will find your Class A range of network addresses.

00000000=0

01111111=127

Network Address Range: Class B

In a Class B network, the RFCs state that the first bit of the first byte must always be turned on, but the second bit must always be turned off. If you turn the other six bits all off and then all on, you will find the range for a Class B network:

10000000=128

10111111=191

As you can see, this means that a Class B network can be defined when the first byte is configured from 128 to 191.

Network Address Range: Class C

For Class C networks, the RFCs define the first two bits of the first octet always turned on, but the third bit can never be on. Following the same process as the previous classes, convert from binary to decimal to find the range.

Here is the range for a Class C network:

11000000=192

11011111=223

So, if you see an IP address that starts at 192 and goes to 223, you’ll know it is a Class C IP address.

Network Address Ranges: Classes D and E

The addresses between 224 and 255 are reserved for Class D and E networks.

Class D is used for multicast addresses and Class E for scientific purposes.

Network Addresses: Special Purpose

Some IP addresses are reserved for special purposes, and network administrators shouldn’t assign these addresses to nodes. Table given bellow lists the members of this exclusive little club and why they’re included in it.

Network –Id

·         Can be defined as the Id to represent the no. of host addresses in the same network in the topology. Cannot be assign to any host in the network. When all the host past is zero then it is called network-id. Or simply the first address of the network is always Network-Id

Broadcast-Id

·         Address on which if packets are send these will be receive by all the hosts in the network. T his address is used when all the host in the network are suppose to get the same message. Cannot be assign to any host in the network. When all the host bits are one then it is called broadcast-id. Simply the last address of the network is called broadcast-id.

Class A Addresses

In a Class A network address, the first byte is assigned to the network address and the three remaining bytes are used for the node addresses. The Class A format is Network.Node.Node.Node For example, in the IP address 49.22.102.70, 49 is the network address, and 22.102.70 is the node address. Every machine on this particular network would have the distinctive network address of 49. Class A addresses are one byte long, with the first bit of that byte reserved and the seven remaining bits available for manipulation. As a result, the maximum number of Class A networks that can be created is 128. Why?

Because each of the seven bit positions can either be a 0 or a 1, thus 27 or 128.

To complicate matters further, the network address of all 0s (0000 0000) is reserved to designate the default route. Additionally, the address 127, which is reserved for diagnostics, can’t be used either, which means that you can only use the numbers 1 to 126 to designate Class A network addresses. This means the actual number of usable Class A network addresses is 128 minus 2, or 126. Got it? Each Class A address has three bytes (24-bit positions) for the node address of a machine. Thus, there are 224—or 16,777,216—unique combinations and, therefore, precisely that many possible unique node addresses for each Class A network. Because addresses with the two patterns of all 0s and all 1s are reserved, the actual maximum usable number of nodes for a Class A network is 224 minus 2, which equals 16,777,214.

Class A Valid Host IDs

Here is an example of how to figure out the valid host IDs in a Class A network address: 10.0.0.0 All host bits off is the network address. 10.255.255.255 All host bits on is the broadcast address. The valid hosts are the number in between the network address and the broadcast address: 10.0.0.1 through 10.255.255.254. Notice that 0s and 255s are valid host IDs. All you need to remember when trying to find valid host addresses is that the host bits cannot all be turned off or on at the same time.

Class B Addresses

In a Class B network address, the first two bytes are assigned to the network address, and the remaining two bytes are used for node addresses. The format is Network. Network. Node. Node. For example, in the IP address 172.16.30.56, the network address is 172.16, and the node address is 30.56. With a network address being two bytes (eight bits each), there would be 216 unique combinations. But the Internet designers decided that all Class B network addresses should start with the binary digit 1, then 0. This leaves 14 bit positions to manipulate, therefore 16,384 (214) unique Class B network addresses. A Class B address uses two bytes for node addresses. This is 216 minus thetwo reserved patterns (all 0s and all 1s), for a total of 65,534 possible node addresses for each Class B network.

Class B Valid Host IDs

Here is an example of how to find the valid hosts in a Class B network: 172.16.0.0 All host bits turned off is the network address.172.16.255.255 All host bits turned on is the broadcast address. The valid hosts would be the numbers in between the network address and the broadcast address: 172.16.0.1 through 172.16.255.254.

Class C Addresses

The first three bytes of a Class C network address are dedicated to the network portion of the address, with only one measly byte remaining for the node address. The format is Network.Network.Network.Node. Using the example IP address 192.168.100.102, the network address is192.168.100, and the node address is 102.In a Class C network address, the first three bit positions are always the binary 110. The calculation is such: 3 bytes, or 24 bits, minus 3 reserved positions, leaves 21 positions. Hence, there are 221, or 2,097,152, possible Class C networks. Each unique Class C network has one byte to use for node addresses. This leads to 28 or 256, minus the two reserved patterns of all 0s and all 1s, for a total of 254 node addresses for each Class C network.

Class C Valid Host IDs

Here is an example of how to find a valid host ID in a Class C network: 192.168.100.0 All host bits turned off is the network ID.192.168.100.255 All host bits turned on is the broadcast address. The valid hosts would be the numbers in between the network address and the broadcast address: 192.168.100.1 through 192.168.100.254

So while assigning IP addresses to host, two addresses can never assign one Network-Id and other is Broadcast-Id. Always subtract 2 from the total no of IPs in the network.

Network	Subnet-mask	Total No. of IPs	Usable IPs	Network –Id Broadcast-Id
10.0.0.0	255.0.0.0	2^24	2^24 - 2	10.0.0.0 / 10.255.255.255
172.31.0.0	255.255.0.0	65536	65534	172.31.0.0 / 172.31.255.255
192.168.0.0	255.255.255.0	256	254	192.168.0.0 / 192.168.0.1

Subnetting

The word subnet is short for sub network--a smaller network within a larger one. The smallest subnet that has no more subdivisions within it is considered a single "broadcast domain," which directly correlates to a single LAN (local area network) segment on an Ethernet switch. The broadcast domain serves an important function because this is where devices on a network communicate directly with each other's MAC addresses, which don't route across multiple subnets, let alone the entire Internet. MAC address communications are limited to a smaller network because they rely on ARP broadcasting to find their way around, and broadcasting can be scaled only so much before the amount of broadcast traffic brings down the entire network with sheer broadcast noise. For this reason, the most common smallest subnet is 8 bits, or precisely a single octet, although it can be smaller or slightly larger.

Subnetting is just the concept of borrowing the bits from the host part to reduce the host part and to include it in the network part. With this the no. of available network will be increase and the no of hosts the subnetted will be decreased. This way more efficient assignment of IP addressing in the network is possible with least possible wasting of IPs as they very limited in no .in IPv4

Subnets have a beginning and an ending, and the beginning number is always even and the ending number is always odd. The beginning number is the "Network ID" and the ending number is the "Broadcast ID." You're not allowed to use these numbers because they both have special meaning with special purposes. The Network ID is the official designation for a particular subnet, and the ending number is the broadcast address that every device on a subnet listens to.

With the Subnetting one bigger network can break down into smaller no. of Sub networks. With each sub network they must have their own Network-Id and Broadcast-Id.

For example

192.168.1.0                             255.255.255.0

Network-Id 192.168.0.0   Broadcast-Id 192.168.0.255

By doing binary of last octet we will get following

192.168.0.00000000

Now here we have last 8 digits as host bits and first 24 bits are for network and are reserve.

Lets we have N no. of requirement of IP addresses

Now we have to find out how many bits are suppose to require to reserve for hosts and rest left bits are subnet bits

With N no. of  hosts we require one Network-Id and Broadcast-Id so total no. of IPs required are

N + 2. To generate N options we need M(say) bits to reserve for network.

N + 2 ≤ 2^M (General for all classes)

Now the No. of Subnet Networks will be as given below

2^ (8-M)

 Considering the requirement of 60 people

No. of Ips required are  N + 2 = 62 where N = 60

By putting the values we will get M = 6

So no of Subnets will be 2^(8-6) = 4

And no. of people in the each subnet will be is 2^6 = 64

192.168.0.         00                                          000000

                              Subnet bits                       Host bits

Now Ist  will be

 192.168.0.00 ******    Decimal Form 192.168.0.0

192.168.0.01 ******     Decimal Form 192.168.0.64

192.168.0.10 ******    Decimal Form 192.168.0.128

192.168.0.11 ******    Decimal Form 192.168.0.192

Network-Id                             Broadcast-Id                                          Network-Id      Broadcast- Id

                                                                                                                                   Decimal Form

192.16 8.0.00000000        192.168.0.00111111                           192.168.0.0       192.168.0.63

192.168.0.01000000         192.168.0.01111111                           192.168.0.64     192.168.127

192.168.0.10000000        192.168.0.10111111                            192.168.0.128  192.168.0.191

192.168.0.11000000        192.168.0.11111111                            192.168.0.192  192.168.0.255

IP Variable Length Subnet Masking (VLSM)

Conventional Subnet masking replaces the two-level IP addressing scheme with a more flexible three-level method. Since it lets network administrators assign IP addresses to hosts based on how they are connected in physical networks, subnetting is a real breakthrough for those maintaining large IP networks. It has its own weaknesses though, and still has room for improvement. The main weakness of conventional subnetting is in fact that the subnet ID represents only one additional hierarchical level in how IP addresses are interpreted and used for routing.

The Problem With Single-Level Subnetting

It may seem “greedy” to look at subnetting and say “what, only one additional level”? J However, in large networks, the need to divide our entire network into only one level of subnetworks doesn't represent the best use of our IP address block. Furthermore, we have already seen that since the subnet ID is the same length throughout the network, we can have problems if we have subnetworks with very different numbers of hosts on them—the subnet ID must be chosen based on whichever subnet has the greatest number of hosts, even if most of subnets have far fewer. This is inefficient even in small networks, and can result in the need to use extra addressing blocks while wasting many of the addresses in each block.

For example, consider a relatively small company with a Class C network, 201.45.222.0/24. They have six subnetworks in their network. The first four subnets (S1, S2, S3 and S4) are relatively small, containing only 10 hosts each. However, one of them (S5) is for their production floor and has 50 hosts, and the last (S6) is their development and engineering group, which has 100 hosts.

The total number of hosts needed is thus 196. Without subnetting, we have enough hosts in our Class C network to handle them all. However, when we try to subnet, we have a big problem. In order to have six subnets we need to use 3 bits for the subnet ID. This leaves only 5 bits for the host ID, which means every subnet has the identical capacity of 30 hosts. This is enough for the smaller subnets but not enough for the larger ones. The only solution with conventional subnetting, other than shuffling the physical subnets, is to get another Class C block for the two big subnets and use the original for the four small ones. But this is expensive, and means wasting hundreds of IP addresses.

Network Devices

Network Devices

NIC

Stands for "Network Interface Card." Pronounced "nick," this is the card that physically makes the connection between the computer and the network cable. These cards typically use an Ethernet connection and are available in 10, 100, and 1000 Base-T configurations. A 100 Base-T card can transfer data at 100 Mbps. The cards come in ISA and PCI versions and are made by companies like 3Com and LinkSys. So if you want to connect your computer to a network, you better get yourself a NIC.

ROUTER

A network device that forwards packets from one network to another. Based on internal routing tables, routers read each incoming packet and decide how to forward it. To which interface on the router outgoing packets are sent may be determined by any combination of source and destination address as well as current traffic conditions (load, line costs, bad lines, etc.).

SWITCH
A switch is used to network multiple computers together. Switches made for the consumer market are typically small, flat boxes with 4 to 8 Ethernet ports. These ports can connect to computers, cable or DSL modems, and other switches. High-end switches can have more than 50 ports and often are rack mounted.

Switches are more advanced than hubs and less capable than routers. Unlike hubs, switches can limit the traffic to and from each port so that each device connected to the switch has a sufficient amount of bandwidth. For this reason, you can think of a switch as a "smart hub." However, switches don't provide the firewall and logging capabilities that routers do. Routers can often be configured by software (typically via a Web interface), while switches only work the way the hardware was designed.

The term "switch" can also be used to refer to a small lever or button on computer hardware. And while it has nothing to do with computers, "riding switch" means riding backwards in skateboarding and snowboarding.

BRIDGE

 In communications networks, a device that (a) links or routes signals from one ring or bus to another or from one network to another, (b) may extend the distance span and capacity of a single LAN system, (c) performs no modification to packets or messages, (d) operates at the data-link layer of the OSI--Reference Model (Layer 2), (e) reads packets, and (f) passes only those with addresses on the same segment of the network as the originating user. (188) 2. A functional unit that interconnects two local area networks that use the same logical link control procedure, but may use different medium access control procedures. 3. A balanced electrical network, e.g. , a Wheatstone bridge. Note: A bridge may be used for electrical measurements, especially resistances or impedances..