Networking Protocols and IP

Definition of the term network protocol:

●  In the context of data communication, a network protocol is a formal set of rules, conventions and data structure that governs how computers and other network devices exchange information over a network.

●  In other words, protocol is a standard procedure and format that two data communication devices must understand, accept and use to be able to talk to each other.

The concept of the OSI model: 

● The Open Systems Interconnection model is a set of seven layers that define the different stages that data must go through to travel from one device to another over a network.

The different layers in the OSI model and what they do:

  • [7]: Application → layer that actually interacts with the OS or application whenever the user chooses to transfer files, read messages or perform other network­ related activities.
  • [6]: Presentation → takes the data provided by the Application layer and converts it into a standard format that the other layers can understand.
  • [5]: Session → establishes, maintains and ends communication with the receiving device
  • [4]: Transport → maintains flow control of data and provides for error checking and recovery of data between the devices. Flow control means that the Transport layer looks to see if data is coming from more than one application 
and integrates each application's data into a single stream for the physical network.
  • [3]: Network → Logical protocols, routing and addressing are handled here.
  • [2]: Datalink → the appropriate physical protocol is assigned to the data. Also, the type of network and the packet 
sequencing is defined.
  • [1]: Physical → This is the level of the actual hardware. It defines the physical characteristics of the network such 
as connections, voltage levels and timing.

Is it compulsory that compression, encryption and translation functions will be used during communication?

The sixth OSI model layer is called the presentation layer. Protocols at this layer take care of manipulation tasks that transform data from one representation to another, such as translation, compression and encryption. In many cases, no such functions are required in a particular networking stack; if so, there may not be any protocol active at layer six.

What's the concept of Simplex, Half Duplex and Full Duplex dialogs?

  • Simplex → One direction communication only (e.g megaphone)
  • Half Duplex → Can only communicate one way at a time (but can be from either end...e.g cup and string!)
  • Full Duplex → Communicate from both ends simultaneously (e.g phone call)


What is the definition of Network Congestion?

Network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections (e,g over utilisation of bandwidth).

Definition of IP address:

An IP address is a 32 bit numerical identifier assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."

Can you explain IP protocol?

Internet Protocol (IP) is the primary network protocol used on the Internet, developed in the 1970s. On the Internet and many other networks, IP is often used together with the Transport Control Protocol (TCP) and referred to interchangeably as TCP/IP. IP supports unique addressing for computers on a network. 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. IP functions at layer 3 of the OSI model. It can therefore run on top of different data link interfaces including Ethernet and Wi­Fi.

How many IP addresses can come in IPV4? 

  • IPv4 provides approximately 4.294 billion addresses
  • The anticipated shortage of IPv4 has been the driving factor in creating and adopting several new technologies, 
including Classless Inter­Domain Routing (CIDR) in 1993, network address translation (NAT), and IPv6 in 1998
  • IPv6 (Internet Protocol Version 6), which can support about 3.4×1038 addresses

What is the concept behind a unicast IP address:

A unicast IP address is an IP address uniquely identifying a host in a network. The datagram with a unicast IP address is received and processed by only a single host. For example, the IP address 192.9.205.21 is a unicast IP address.

What is the concept of IP multicasting or multicast IP address?

A multicast address is an IP address identifying a particular group of hosts in network. This group of hosts is called a multicast group. For example, the IP address 225.2.100.1 is a multicast IP address.

What are the IP address ranges for public and private IP address?

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 What is classful IP addressing?

Classful addressing makes it possible to determine the network portion of the IP address by looking at the first four bits of the first octet in the IP address. The first four bits are referred to as the 'most significant bits' of the first octet and are used to determine what class of IP address is being used. The value of the first four bits determines the range of actual numerical values of the first octet of the IP addresses in that class. From this information, a receiving host can determine which part of the IP address is being used to identify the specific network on which the host resides, and which portion of the IP address is used to identify the host.

Can you explain the concept of subnetting?

Subnetting is a method for getting the most out of the limited 32­bit IPv4 addressing space and reducing the size of the routing tables in a large internetwork. With any address class, subnetting provides a means of allocating a part of the host address space to network addresses, which lets you have more networks. The part of the host address space allocated to new network addresses is known as the subnet number.

What are the advantages of using subneting?

In addition to making more efficient use of the IPv4 address space, subnetting has several administrative benefits. Routing can become very complicated as the number of networks grows. A small organization, for example, might give each local network a class C number. As the organization grows, administering a number of different network numbers could become complicated. A better idea is to allocate a few class B network numbers to each major division in an organization. For instance, you could allocate one to Engineering, one to Operations, and so on. Then, you could divide each class B network into additional networks, using the additional network numbers gained by subnetting. This can also reduce the amount of routing information that must be communicated among routers.

1.To divide a large network into smaller segments to reduce traffic and speed up the sections of your network.

2.To connect networks across geographical areas.

3.To connect different topologies such as Ethernet, Token Ring, and FDDI together via routers.

4.To avoid physical limitations such as maximum cable lengths or exceeding the maximum number of computers 
on a segment.

If the host has the subnet ID why do we need a subnet mask?

The subnet mask helps to identify the network portion and the host portion of the address space. It helps us identify the boundaries for that network (network number and broadcast address based on the block size for that class).

How is network address calculated from the subnet?

Use the subnet address to work out the CIDR and it’s block size. The first usable address is the network address and the last available address is the broadcast address.

Classful vs Classless addressing scheme?

In the classful addressing system all the IP addresses that are available are divided into the five classes A,B,C,D and E. The main disadvantage of classful addressing is that it has limited flexibility; you are forced to use a predefined mask which could waste address space. One of the major disadvantage of classful addressing is that it does not send subnet information but it will send the complete network address. The router will supply its own subnet mask based on its locally configured subnets. As long as you have the same subnet mask and the network is contiguous, you can use subnets of a classful network address.

Classless addressing system is also known as CIDR (Classless Inter­Domain Routing). Classless addressing is a way
to allocate and specify IP addresses more flexibly without wasting address space. For example: 192.30.250.0/15 → the "192.30.250.00" is the network address itself and the "15" says that the first 15 bits are the network part of the address, leaving the last 17 bits for specific host addresses. This is much more efficient than using a typical class B address mask (/16) which would waste address space. Another advantage of classless addressing is that the classless protocol sends subnet information. This allows you to create discontiguous networks with any given classful network address.

Can you explain the concept of CIDR?

CIDR ­ Classless Inter­Domain Routing is also called supernetting. It's an IP addressing scheme that replaces the older system based on classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP prefix. For example: 172.200.0.0/16

What is the implication of increasing and decreasing subnet bits?

By increasing the amount of subnet bits, you decrease the amount of hosts on each subnet, with more subnets. By decreasing the amount of subnet bits, you increase the number of hosts on each subnet, with fewer subnets.

Why do we need to subtract two from number of hosts?

We need to subtract 2 to take into account 1) the Network address and 2) Broadcast address

Can you explain the concept of VLSM?

Variable Length Subnet Masks (VLSM) allows an organization to use more than one subnet mask within the same network address space. With VLSM, a network administrator can use a long mask on networks with few hosts, and a short mask on subnets with many hosts. Implementing VLSM is often referred to as "subnetting a subnet", and can be used to maximize addressing efficiency. In order to use VLSM, a network administrator must use a routing protocol that supports it. Cisco routers support VLSM with OSPF, IS­IS, EIGRP, RIP v2, and static routing. VLSM is simply a feature that allows a single autonomous system to have networks with different subnet masks. If a routing protocol allows VLSM, use a 30­bit subnet mask on network connections, 255.255.255.252, a 24­bit mask for user networks, 255.255.255.0, or even a 22­bit mask, 255.255.252.0, for networks with up to 1000 users.