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NETWORK BASICS

Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  


Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

INTRODUCTION TO IP (INTERNET PROTOCOL)

INTRODUCTION TO IP (INTERNET PROTOCOL)IP is a connection-less protocol, which means that there is no continuing connection between the end points that are communicating. Each packet that travels through the Internet is treated as an independent unit of data without any relation to any other unit of data. (The reason the packets do get put in the right order is because of TCP, the connection-oriented protocol that keeps track of the packet sequence in a message.) In the Open Systems Interconnection (OSI) communication model, IP is in layer 3, the Networking Layer. The most widely used version of IP today is Internet Protocol Version 4 (32 bit) .However, IP Version 6 (IPv6) is also beginning to be supported. IPv6 provides for much longer addresses and therefore for the possibility of many more Internet users. IPv6 includes the capabilities of IPv4 and any server that can support IPv6 packets can also support IPv4 packets. The newer Internet Protocol version 6 (IPv6) standard features addresses 16 bytes (128 bits) in length. Data on an Internet Protocol network is organized into packets. Each IP packet includes both a header (that specifies source, destination, and other information about the data) and the message data itself. 
Think of an analogy with the postal system. IP is similar to the U.S. Postal System in that it allows a package (a data-gram) to be addressed (encapsulation) and put into the system (the Internet) by the sender (source host). However, there is no direct link between sender and receiver. The package (data-gram) is almost always divided into pieces, but each piece contains the address of the receiver (destination host). Eventually, each piece arrives at the receiver, often by different routes and at different times. These routes and times are also determined by the Postal System, which is the IP. However, the Postal System (in the transport and application layers) puts all the pieces back together before delivery to the receiver (destination host). 
Internet Protocol version 4 (IPv4) was the first major version of IP. This is the dominant protocol of the Internet. However, iPv6 is active and in use, and its deployment is increasing all over the world. Addressing and routing are the most complex aspects of IP. However, intelligence in the network is located at nodes (network interconnection points) in the form of routers which forward data-grams to the next known gateway on the route to the final destination. The routers use interior gateway protocols (IGPs) or external gateway protocols (EGPs) to help with making forwarding route decisions. Routes are determined by the routing prefix within the data-grams. The routing process can therefore become complex. But at the speed of light (or nearly so) the routing intelligence determines the best route, and the data-gram pieces and data-gram all eventually arrive at their destination. 
Internet protocol transmits the data in form of a data-gram as shown in the following diagram: 


  • The length of Data-gram is variable. 
  • The Data-gram is divided into two parts: header and data. 
  • The length of header is 20 to 60 bytes. 
  • The header contains information for routing and delivery of the packet. 

IPv4 is the most widely used version of the Internet Protocol. It defines IP addresses in a 32-bit format, which looks like 123.123.123.123. Each three-digit section can include a number from 0 to 255, which means the total number of IPv4 addresses available is 4,294,967,296 (256 x 256 x 256 x 256) 
Each computer or device connected to the Internet must have a unique IP address in order to communicate with other systems on the Internet. Because the number of systems connected to the Internet is quickly approaching the number of available IP addresses, IPv4 addresses are predicted to run out soon. When you consider that there are over 6 billion people in the world and many people have more than one system connected to the Internet (for example, at home, school, work, etc.), it is not surprising that roughly 4.3 billion addresses is not enough. To solve this problem, a new 128-bit IP system, called IPv6, has been developed and is in the process of replacing the current IPv4 system. During this transitional process from IPv4 to IPv6, systems connected to the Internet may be assigned both an IPv4 and IPv6 address. 


Every computer system and device connected to the Internet is located by an IP address. The current system of distributing IP addresses is called IPv4. This system assigns each computer a 32-bit numeric address, such as 120.121.123.124. However, with the growth of computers connected to the Internet, the number of available IP addresses are predicted to run out in only a few years. This is why IPv6 was introduced. IPv6, also called IPng (or IP Next Generation), is the next planned version of the IP address system. (IPv5 was an experimental version used primarily for streaming data.) While IPv4 uses 32-bit addresses, IPv6 uses 128-bit addresses, which increases the number of possible addresses by an exponential amount. For example, IPv4 allows 4,294,967,296 addresses to be used (2^32). IPv6 allows for over 340,000,000,000,000,000,000,000,000,000,000,000,000 IP addresses. That should be enough to last awhile. 


                                          IPv4
                                          IPv6
IPv4 addresses are 32 bit length.
IPv6 addresses are 128 bit length.
IPv4 addresses are binary numbers represented in decimals.
IPv6 addresses are binary numbers represented in hexadecimals.
IP-Sec support is only optional.
Inbuilt IP-Sec support.
Fragmentation is done by sender and forwarding routers.
Fragmentation is done only by sender.
No packet flow identification.
Packet flow identification is available within the IPv6 header using the Flow Label field.
Checksum field is available in IPv4 header
No checksum field in IPv6 header.
Options fields are available in IPv4 header.
No option fields, but IPv6 Extension headers are available.
Address Resolution Protocol (ARP) is available to map IPv4 addresses to MAC addresses.
Address Resolution Protocol (ARP) is replaced with a function of Neighbor Discovery Protocol (NDP).
Internet Group Management Protocol (IGMP) is used to manage multicast group membership.
IGMP is replaced with Multicast Listener Discovery (MLD) messages.
Broadcast messages are available.
Broadcast messages are not available. Instead a link-local scope "All nodes" multicast IPv6 address (FF02::1) is used for broadcast similar functionality.
Manual configuration (Static) of IPv4 addresses or DHCP (Dynamic configuration) is required to configure IPv4 addresses.
Auto-configuration of addresses is available


TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extra-net). When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.  
TCP/IP is a two-layer program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination. Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination. TCP/IP uses the client/server model of communication in which a computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network. TCP/IP communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer. TCP/IP and the higher-level applications that use it are collectively said to be "stateless" because each client request is considered a new request unrelated to any previous one (unlike ordinary phone conversations that require a dedicated connection for the call duration). Being stateless frees network paths so that everyone can use them continuously. (Note that the TCP layer itself is not stateless as far as any one message is concerned. Its connection remains in place until all packets in a message have been received.) 


UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact. TCP has emerged as the dominant protocol used for the bulk of Internet connectivity owing to services for breaking large data sets into individual packets, checking for and resending lost packets and reassembling packets into the correct sequence. But these additional services come at a cost in terms of additional data overhead, and delays called latency. In contrast, UDP just sends the packets, which means that it has much lower bandwidth overhead and latency. But packets can be lost or received out of order as a result, owing to the different paths individual packets traverse between sender and receiver. UDP is an ideal protocol for network applications in which perceived latency is critical such as gaming, voice and video communications, which can suffer some data loss without adversely affecting perceived quality. In some cases, forward error correction techniques are used to improve audio and video quality in spite of some loss. UDP can also be used in applications that require lossless data transmission when the application is configured to manage the process of re-transmitting lost packets and correctly arranging received packets. This approach can help to improve the data transfer rate of large files compared with TCP.In the Open Systems Interconnection (OSI) communication model, UDP, like TCP, is in layer 4, the Transport Layer. UDP works in conjunction with higher level protocols to help manage data transmission services including Trivial File Transfer Protocol (TFTP), Real Time Streaming Protocol (RTSP), and Simple Network Protocol (SNP) and Domain Name System (DNS) lookups. 


Data encapsulation refers to sending data where the data is augmented with successive layers of control information before transmission across a network. The reverse of data encapsulation is de capsulation, which refers to the successive layers of data being removed (essentially unwrapped) at the receiving end of a network. In telecommunication, encapsulation is the inclusion of one data structure within another structure so that the first data structure is hidden for the time being. For example, a TCP/IP-formatted data packet can be encapsulated within an ATM frame (another kind of transmitted data unit). Within the context of transmitting and receiving the ATM frame, the encapsulated packet is simply a stream of bits between the ATM data that describes the transfer. 
The computer in the above picture needs to send some data to another computer. The Application layer is where the user interface exists, here the user interacts with the application he or she is using, and then this data is passed to the Presentation layer and then to the Session layer. These three layer add some extra information to the original data that came from the user and then passes it to the Transport layer. Here the data is broken into smaller pieces (one piece at a time transmitted) and the TCP header is an added. At this point, the data at the Transport layer is called a segment. 
Each segment is sequenced so the data stream can be put back together on the receiving side exactly as transmitted. Each segment is then handed to the Network layer for network addressing (logical addressing) and routing through the internet network. At the Network layer, we call the data (which includes at this point the transport header and the upper layer information) a packet. The Network layer add its IP header and then sends it off to the Data-link layer. Here we call the data (which includes the Network layer header, Transport layer header and upper layer information) a frame. The Data-link layer is responsible for taking packets from the Network layer and placing them on the network medium (cable). The Data-link layer encapsulates each packet in a frame which contains the hardware address (MAC) of the source and destination computer (host) and the LLC information which identifies to which protocol in the previous layer (Network layer) the packet should be passed when it arrives to its destination. Also, at the end, you will notice the FCS field which is the Frame Check Sequence. This is used for error checking and is also added at the end by the Data-link layer. If the destination computer is on a remote network, then the frame is sent to the router or gateway to be routed to the destinations. To put this frame on the network, it must be put into a digital signal. Since a frame is really a logical group of 1's and 0's, the Physical layer is responsible for encapsulating these digits into a digital signal which is read by devices on the same local network. 


To change the computer’s IP address in Windows, type network and sharing into the Search box in the Start Menu and select Network and Sharing Center when it comes up. If you are in Windows 8.x it will be on the Start Screen itself, like the screenshot at the top of this article. If you’re in Windows 7 or 10 it’ll be in the start menu. Then when the Network and Sharing Center opens, click on Change adapter settings. This will be the same on Windows 7 or 8.x or 10. 

Right-click on your local adapter and select Properties. 

In the Local Area Connection Properties window highlight Internet Protocol Version 4 (TCP/IPv4) then click the Properties button. 

Now select the radio button Use the following IP address and enter in the correct IP, Subnet mask, and Default gateway that corresponds with your network setup. Then enter your Preferred and Alternate DNS server addresses. Here we’re on a home network and using a simple Class C network configuration and Google DNS. 
Check Validate settings upon exit so Windows can find any problems with the addresses you entered. When you’re finished click OK. 

Step 6: 

Now close out of the Local Area Connections Properties window. 

Step 7: 

Windows will run network diagnostics and verify the connection is good. Here we had no problems with it, but if you did, you could run the network troubleshooting wizard. 

Step 8: 

Now you can open the command prompt and do an ipconfig to see the network adapter settings have been successfully changed. 


Classless Inter Domain Routing (CIDR) was invented to keep the Internet from running out of IP Addresses. The IPv4, a 32-bit, addresses have a limit of 4,294,967,296 (232) unique IP addresses. The classful address scheme (Class A, B and C) of allocating IP addresses in 8-bit increments can be very wasteful. With classful addressing scheme, a minimum number of IP addresses allocated to an organization is 256 (Class C). Giving 256 IP addresses to an organization only requiring 15 IP addresses is wasteful.  
Also, an organization requiring more than 256 IP addresses (let's say 1,000 IP addresses) is assigned a Class B, which allocates 65,536 IP addresses. Similarly, an organization requiring more than 65,636 (65,634 usable IPs) is assigned a Class A network, which allocates 16,777,216 (16.7 Million) IP addresses. This type of address allocation is very wasteful. With CIDR, a network of IP addresses is allocated in 1-bit increments as opposed to 8-bits in classful network. The use of a CIDR notated address can easily represent classful addresses (Class A = /8, Class B = /16, and Class C = /24). The number next to the slash (i.e. /8) represents the number of bits assigned to the network address. The example shown above can be illustrated with CIDR as follows:  
 216.3.128.12, with subnet mask of 255.255.255.128 is written as 216.3.128.12/25 

Similarly, the 8 customers with the block of 16 IP addresses can be Written as: 

   216.3.128.129/28, 216.3.128.130/28, and etc. 

With an introduction of CIDR addressing scheme, IP addresses are more efficiently allocated to ISPs and customers; and hence there is less risk of IP addresses running out anytime soon. For detailed specification on CIDR, please review RFC 1519. With introduction of additional gaming, medical, appliance and telecom devices requiring static IP addresses in addition to more than 6.5 billion (July 2006 est.) world population, the IPv4 addresses with CIDR addressing scheme will eventually run out. To solve shortage of IPv4 addresses, the IPv6 (128-bit) address scheme was introduced in 1993.  


MAC, Media Access Control, address is a globally unique identifier assigned to network devices, and therefore it is often referred to as hardware or physical address. MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes are ID number of the manufacturer, which is assigned by an Internet standards body. The second 3-bytes are serial number assigned by the manufacturer. MAC layer represents layer 2 of the TCP/IP (adopted from OSI Reference Model), where IP represents layer 3. MAC address can be thought of as supporting hardware implementation whereas IP address supports software implementation.  
MAC addresses are permanently burned into hardware by hardware manufacturer, but IP addresses are assigned to the network devices by a network administrator. DHCP relies on MAC address to assign IP addresses to network devices. To check the pc or laptop mac address just type “ getmac ”& hit enter. To check your IP address or physical address type” ipconfig/all “in cmd. 


A loopback test is a test in which a signal in sent from a communications device and returned (looped back) to it as a way to determine whether the device is working right or as a way to pin down a failing node in a network. One type of loopback test is performed using a special plug, called a wrap plug that is inserted in a port on a communications device. The effect of a wrap plug is to cause transmitted (output) data to be returned as received (input) data, simulating a complete communications circuit using a single computer. To apply loopback test type” ping 127.0.0.1 “in CMD.127.0.0.1 is known as loopback address.  

  • Smart Loopback - Analyses incoming traffic, automatically detects and swaps Source and Destination MAC, IP, and UDP addresses before sending back the packet.  
  • Layer 1 – Loops back incoming packets as is  
  • Ethernet – Swaps Source and Destination MAC addresses before sending back the packet  
  • IP – Swaps Source and Destination MAC addresses, IP addresses before sending back the packet.  
  • UDP - Swaps Source and Destination MAC addresses, Destination IP addresses, and UDP ports before sending back the packet. 

Loopback helps in easy test setup, especially in end-to-end testing, when the other end is in a remote place. In such cases, one Packet Expert™ can be put in constant Loopback at the remote end, and BERT tests can be started / stopped anytime at the local end. 


A MAC address table, sometimes called a Content Addressable Memory (CAM) table, is used on Ethernet switches to determine where to forward traffic on a LAN. Now let's break this down a little bit to understand how the MAC address table is built and used by an Ethernet switch to help traffic move along the path to its destination. 


A switch is surrounded by a number of common devices. Let's assume that all of the devices are powered on but have not sent any traffic. In this case, the MAC address table of the switch would be empty (ignoring any system MAC addresses shown in the table by default). Now suppose PC1 wants to send traffic to the server that has a MAC address of 00:00:00:00:00:01. It would encapsulate an Ethernet frame and send it off toward the switch. The first thing the switch would do when receiving the traffic is create a new entry in its MAC address table for PC1's MAC address (PC1 -> Fa0/3). The switch would then perform a lookup on its MAC address table to determine whether it knows which port to send the traffic to; since no matching entries exist in the switch's tables, it would flood the frame out all of its interfaces (except the receiving port). Because the frame was sent out to all of the switch's other ports, it would be received by the target server. Assuming that the server wants to respond to PC1, it would sent a new frame back toward the switch. The switch would receive the frame and create a new entry in its MAC address table for the server's MAC address (Server -> Fa0/2). It would then perform a lookup of its MAC address table to determine whether it knows which port to send the server's traffic to; in this case it does, so it sends the return traffic out only its Fa0/3 port (PC1), without flooding. The below image shows what the MAC address table would look like at this point. 


This process repeats as devices continue to send traffic to each other. An important detail to remember is that the MAC address table timeout is typically short (Cisco's default is five minutes), so an entry is left in the table itself only for that specified amount of time before the timeout expires and the entry is removed from the table.   

  • Check out your MAC address 
  • Find out your IP address. 



a) DNS  
b) ICMP  
c) UDP  
d) TCP  


a) Network Interface  
b) Internetwork  
c) Transport  
d) Application  


a) A packet  
b) A header  
c) A data-gram  
d) An FTP  


a) Physical and logical 
b) Network and subnet  
c) Network and host (or node)  
d) Physical and emotional  


a) 192.168.1.1  
b) 127.0.0.1  
c) 10.10.10.10  
d) 255.255.255.255 

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