Chapter 4 Network layer

How would you represent 217 in binary? 168?

217 represents 11011001 168 represents 10101000

What is the size of the largest possible IP packet?

65,535

You wish to assign unique labels to 200 objects using binary numbers. What is the minimum number of bits needed?

8

What were the three address classes in early IP networks? How many hosts (computers) could be accommodated in a network in each address class?

Class A: first 8 bits identified the network ID and the remaining 24 bits identified hosts within the network. 16,777,216 hosts. Class B: first 16 bits identified the network ID and the remaining 16 bits identified hosts within each network. 65,536. Class C: the first 24 bits are the network part leaving 8 bits for host part within the network. 2,097,152 are possible.

How many objects can be uniquely labeled with 10-bit address labels?

2 ^10 = 1024 objects.

What requirements must an organization satisfy in order to obtain IP addresses directly from a registry?

Only networks that are connected to two or more networks are allowed to apply to the registries to obtain a network address. Most organizations that need IP addresses with therefore contract with their local ISPs to obtain network addresses. The registries actively try not to allocate IP addresses directly to individuals and very small organizations.

What are the functions of the network layer?

Routing between networks.

What is the need for a computer address at the IP layer when computers also have a MAC address?

Since many of the networks on the Internet use technology that was developed independently of IP, both addresses are necessary. The data-link address allows the packet to be delivered correctly within each individual network on the path of the destination. The IP address retains the address of the actual source and the final destination. Additionally, having addressing handled on two different layers creates great flexibility. The IP protocol could be upgraded without requiring changes to the Data-Link layer and vice versa.

What are the advantages of designing IP as a best-effort protocol?

Best-effort delivery describes a network service in which the network does not provide any special features that recover lost or corrupted packets. These services are instead provided by end systems. By removing the need to provide these services, the network operates more efficiently. In the TCP/IP protocol suite, TCP provides guaranteed services while IP provides best-effort delivery. TCP performs the equivalent of obtaining a delivery confirmation from the recipient and returning it to the sender. Because IP provided basic packet delivery services without guarantees, it is called a best-effort delivery service. It does its best to deliver packets to the destination, but takes no steps to recover packets that are lost or misdirected. With best-effort services, packet discard is acceptable because recovery is handled by other services.

What decimal number does the binary number 10001101 represent? 11011001?

Binary number 10001101 represents 141 Binary number 11011001 represents 217

What is the CIDR notation for IP addesses ?

CIDR is classless inter domain routing . It was introduced in 1993 to address the problem of unavailability of address blocks of reasonable size.

What are the disadvantages of using address classes? How does CIDR overcome these disadvantages?

The A, B, C class system suffers from a problem of allocative efficiency. Half of the available I addresses on the internet could be allocated to 128 networks. Worse more are that there are many unallocated IP addresses. CIDR solves these problems by allowing the network part to be whatever length an organization would need to allocate the right amount of IP addresses. It is a much more flexible scheme for allocation.

What is the need for the time-to-live field in the IP header?

The Time-To-Live field in the IP header specifies a 128 or 256 value when it is created. At each hop, the router will decrement the value by one. This allows "lost" packets to not bounce around the internet indefinitely. Without TTL, sections of the internet could be brought down by DDOS attacks easily.

What information is conveyed by each part of a two-part IP address?

The leftmost part of the IP address is the network part, the subnet, and the rightmost part is the host.

In what way are the 32 bits of an IP address organized similarly to the 10 digits of phone numbers? In what way are they different?

Your phone number is a unique set of numbers that identifies your phone so that other people can call you. Similarly, an IP address is a unique set of numbers that identifies your computer so that it can send and receive data with other computers. Broadly speaking, IP addressed are broken down into two parts. The left part of the IP address represents the network to which the IP address belongs. This called the network part of the IP address. The remaining bits of the IP address identify the computer within this network. This is often called the host part of the IP address. The phone network uses a three-part addressing scheme where the first part identifies the geographical area; the second part identifies the local exchange within the geographical area, and the remaining digits identify the specific user. Unlike phone numbers, IP addresses have limited geographic significance. (IP network addressed identify networks (organizations), but not geographies.

What is an IP address?

a unique string of numbers separated by periods that identifies each computer using the Internet Protocol to communicate over a network.

What is registry in the context of IP addresses?

A database where IP addressed are assigned to different networks.

Which, in your opinion, are the three most important fields in the IP header? Briefly describe the functions of these fields.

Header Length- this field specifies the headers length of the IP. The IP allows the header to include various options, which means the length of the header can be variable. Time to live- this field makes sure no packet can live forever on the Internet. It acts as a safety valve on the Internet. Header Checksum- this field carries error detection information for the packet header.

How are IP addresses similar to MAC addresses? In what ways are the two addresses different?

IP addresses and Mac addresses are both key components to network. They provide unique addressed for computers to send information to each other. Mac is actually a physical address of device which is constant and it is used at a data link layer and IP address is an address of a device which is used at network layer. Throughout the packet's journey from the source to the destination, the destination IP address don't change but the data link layer addressed keep changing as the packet gets transferred from network to network.

How are the 32 bits of an IP address organized in a typical large network?

IP addresses are organized in network Classes A, B, and C depending on the size of the organization. In Class A the first octet is the network part while the rest are the hosts. In Class B, the first and second octets are the network and the rest are hosts. In Class C the first through third octets are the network and the last is the individual host computer.

What is dotted decimal notation?

While computers work with IP addresses as 32-bit binary values, humans normally use the dotted-decimal notation (a presentation format for numerical data. It consists of a string of decimal numbers, each pair separated by a full stop) to convert IP address numbers from binary format so can easily read and remember. A binary address and its dotted-decimal equivalent are shown below. Note that the 32-bit address is divided into four 8-bit fields called octets.

How do you obtain an IP address?

command line ----- ipconfig/all

Briefly describe routing — the primary function of the network layer.

It's the process of moving a packet of data from source to destination. Routing is usually performed by a dedicated device called router. Routing is a key feature of the internet because it enables message to pass from one computer to another and eventually reach the target machine.

What are the advantages of designing the Internet in such a way that specialized devices called routers handle all the details of routing? What may be the possible disadvantages?

Routers are the glue that holds the Internet together. They are placed at the interface between two networks and guide packets across networks in the right direction to their respective destination. It allows even simple devices, such as handheld computers and inexpensive security cameras with limited processing capability, to be connected to the Internet. Each router is only responsible for passing the packet on to a suitable neighboring router. As long as the neighbors are correctly chosen, the packet will reach the destination. Once a router dispatches a data packet on to a neighboring router, the packet is left to its own fate and the router does not worry about the packet anymore. If the neighboring router is unable to process the data packet for any reason, the packet can get lost, but routers do now worry about recovering lost packets. Instead, routers focus on routing the next packet.

What is an IP header ?

is header information at the beginning of an IP packet which contains information about IP version, source IP address, destination IP address, time-to-live, etc.

What is IP version 6 ?

most recent version of the Internet Protocol . IP Version 6 gives an endless supply of IP addresses.