Networking

Anonymous FTP

Is a way of granting user access to files in public servers. Users that are allowed access to data in these servers do not need to identify themselves, but instead log in as an anonymous guest.

NOS

Network Operating System, is specialized software whose main task is to provide network connectivity to a computer in order for it to be able to communicate with other computers and connected devices.

Network Topology

Network Topology refers to the layout of a computer network. It shows how devices and cables are physically laid out, as well as how they connect to one another.

Subnet Mask

combined with an IP address in order to identify two parts: the extended network address and the host address. Like an IP address, a subnet mask is made up of 32 bits.

Star Topology

consists of a central hub that connects to nodes. This is one of the easiest to setup and maintain.

Hardware Based Firewall

Its a device like box allows strong security from public network.Mostly used by big networks.

Screening Router Firewall

Its a software base firewall available in router provides only light filtering.

CDMA Code Properties

-If we multiply each code by another, we get zero. -If we multiply each code by itself, we get the number of stations.

LMHOST Files

-It is a text file that resolves NetBIOS names to IP addresses. -It can be compared with the hosts file which is a static method of resolving domain names into IP addresses. -LMHOST files must be manually configured and updated.

Hub vs Switch

- Hub is layer 1 device while switch is a layer 2 device. -Hub works on a single collision and single broadcast domain while switch works on per port collision and single broadcast domain.

Types of Random Access Protocols

-ALOHA -CSMA -CSMA/CD -CSMA/CA

What is a workgroup?

-All computers are peers having no control on each other. -Users need to have an account for every computers. -All computers need to be part of the same local network.

Ring Topology

-All nodes connected with another in a loop. -Each device is connected to one or more devices on either side.

Signal Impairment Causes

-Attenuation -Distortion -Noise

Advantages of IPv6 over IPv4

-Bigger address space. 128 bytes versus 32 bit. -Better header format that speeds up routing process. -Allowance for extension, support for resource allocation and more security.

Which factors make the reliability of a network?

-Frequency of failure -Downtime -Time taken for recovery

Class D

-From Octet 224-239 -Reserved for multicasting -1110

Class E`

-From Octet 240-254 -Experimental; used for research -1111

FQDN

-Fully Qualified Domain -It contains both the host name and a domain name. -It uniquely identifies a host within a DNS hierarchy.

Time to Live - TTL

-It is a value in a data packet of internet protocol. -It communicates to the network router whether or not the packet should be in the network for too long or discarded. -It would specify certain time limit in seconds for transmitting the packet header.

Types of Firewalls

-Packet Filtering Firewall -Screening Router Firewall -Computer Based Firewall -Hardware based Firewall -Proxy Server

Qualities of Effective and Efficient Network

-Performance -Reliability -Security

Different Ways of Data Exchange

-Simplex -Half Duplex -Full Duplex

Bus Topology

-The server is at one end and the clients are connected at different positions across the network.

Class B

-Used for medium size networks. -From octet 128-191 -First bit value of 1, and a second bit value of 0.

Class C

-Used for small to mid size networks. -From Octet 192-223 -110

Class A

-Used for very large networks. -From Octet 1-126 -Account for half of the total available IP addresses.

Characteristics of IMAP4

-User can organize mail. -Multiple mailboxes can be created on the desktop PC as well as on the server. -A user can partially download email. -A whole message will be downloaded only when it is opened for display from its content.

Characteristics of POP3

-User cannot organize their mail on the server. -Only one mailbox/inbox on the server. -A user cannot partially download email. -All email will be downloaded into desktop PC if you want to check new email.

Various Error Detection Methods

-Vertical Redundancy Check -Longitudinal Redundancy Check -Cyclic Redundancy Check -Checksum

Name the factors that tells us about the security of the network?

-Virus attacks on the system -Unauthorized access to the system

Types of Multiplexing

1. Frequency Division Multiplexing FDM 2.Time Division Multiplexing TDM 3.Synchronous TDM 4.Asynchronous TDM 5.Wave Division Multiplexing WDM

5 Types of Wireless Transmission

1.Electromagnetic Transmission 2.Radio Transmission 3.Microwave Transmission 4.Infrared Transmission 5.Light Transmission

3 Approaches for Channelization Protocol

1.FMDA-Frequency Division Multiple Access 2.TDMA-Time Division Multiple Access 3.CDMA-Code Division Multiple Access

Which layers of OSI model are referred to as network support layers?

1.Physical Layer 2.Data Link Layer 3.Network Layers

Which layers of OSI are referred to as user support layers?

1.Session Layer 2.Presentation Layer 3.Application Layer

Link

A link refers to the connectivity between two devices. It includes the type of cables and protocols used in order for one device to be able to communicate with the other.

ARP

Address Resolution Protocol is utilized for mapping IP network address to the hardware address that uses data link protocol.

Proxy Server

Allows all clients to access internet with different access limits. Proxy server has its own firewll which filters the all packet from web server.

What is the User Datagram Protocol UDP?

Allows computer applications to send messages as datagram packets from source to destination on an internet protocol without using prior communications for setting up special transmission paths. -Unreliable service which makes datagram packets may arrive irrespective of order.

Asymmetric Key Cryptography

Also called public key cryptography. Two keys: -Private key and public key Encryption is done through the public key and decryption through private key. Receiver creates both keys and is responsible for distribution.

Passive Route State

An operational route's normal condition. The router will not seek to replace a lost route.

NETBIOS

Network Basic Input Output System allows the applications on different computers to communicate over a LAN.

Network Security -Encryption

Basically designed for confidentiality and data integrity and reversible only if you have the appropriate key.

How can you identify the IP class of a given IP address

By looking at the first octet of any given IP address, you can identify whether it's Class A, B or C. If the first octet begins with a 0 bit, that address is Class A. If it begins with bits 10 then that address is a Class B address. If it begins with 110, then it's a Class C network.

What is the advantage of address sharing?

By using address translation instead of routing, address sharing provides an inherent security benefit. That's because host PCs on the Internet can only see the public IP address of the external interface on the computer that provides address translation and not the private IP addresses on the internal network.

IP Datagram

Can be used to describe a portion of IP data.

Class A 127.0.0.0/ 127.255.255.255

Cannot be used and it is reserved for loopback and diagnostic functions.

Impulse Noise

Comes from power lines, lightning etc

Five IP Classes

Class A, B, C,D & E

What is the goal of information security in an organization?

Confidentiality, integrity and availability.`

What does Data Link Layer do?

It takes care of: -Node to node delivery -Framing -Physical Addressing -Flow Control -Error Control -Access Control

Interior Gateway

Connects LANs within an organization.

Exterior Gateway

Connects the organization to the outside world

Trojan Horse

Consists of two parts: The server and the client. Server is an executable file which runs on victims computer and attacker may take full control.

Symmetric Key Cryptography

It uses a single key for both encryption and decryption. Encryption and decryption algorithm are inverse of each other.

Spanning Tree Protocol

Defined in the IEEE 802.1D is a link management protocol that provides path redundancy while preventing undesirable loops in the network. -For an ethernet network to function properly, only one active path can exist between two stations.

DoS

Denial-of-Service attack, is an attempt to prevent users from being able to access the internet or any other network services. Such attacks may come in different forms and are done by a group of perpetuators. One common method of doing this is to overload the system server so it cannot anymore process legitimate traffic and will be forced to reset.

Define Subnetting

Describes a set of networked computers which have common IP address routing prefix. It prevents ethernet packet collision which has excessive rates in a large network. A router constitute borders among subnets.

PIX Firewall Security

Developed by cisco systems. Private Internet Exchange. It is a popular IP firewall and Network Address Translation NAT appliance. It is used to protect your network with a stateful packet filtering firewall.

What is point to point link?

Direct Connection between two computers on a network. -The cable connects the NIC card of both the devices.

NETBEUI

Extended version of NETBIOS. It is a program that allows computers to communicate within a local area network.

If you have to encrypt as well as compress data during transmission, then which one would you do first?

First compress, then encrypt to keep the data integrity. If you encrypt first, you will have nothing but random data to work with, which will destroy any potential benefit from compression.

Classes of IP Addresses

IP addresses are expressed into decimal format. Every number in each class is represented as binary to computers.

Describe Classful Addressing

IPV4 uses the concept of classes. In classful addressing, the address space is divided into 5 classes: A.B,C,D and E.

POP3 Delete Mode

In this mode the mail is deleted from the mailbox after each retrieval.

Computer Based Firewall

It's a firewall stored in server with an existing operating system like windows and Unix.

How does a nerwork topology affects your decision setting up a network?

It dictates what media you must use to interconnect devices. It also serves as basis on what materials, connector and terminations that is applicable for the setup.

What is the importance of inplementing a fault tolerance system? Are there limitations?

It ensures continuous data availability. This is done by eliminating a single point of failure. However, this type of system would not be able to protect data in some cases, such as in accidental deletions.

10Base5

It is a Ethernet term meaning a maximum transfer rate of 10MBPS that uses baseband signaling, with 5 continuous segments not exceeding 100 meters per segment.

Worm

It is a computer program which makes its copy again and again in the victims computer. They damage the network by using a lot of bandwidth.

Brute Force Attacks

It is a mechanism used by an attacker to break the encryption of data by applying a set of various keys.

Channelization in Networks

It is a multiple access method in which available bandwidth of a link is shared in time, frequency, or through code between different stations.

Multi-homed Host

It is a multiple network interface that requires multiple IP addresses.

What is a firewall?

It is a part of a computer system or network that is designed to block unauthorized access while permitting authorized communications.

RARP

It is a protocol using which a physical machine in a LAN could request to find its IP from ARP table or cache from a gateway server. -Allowing a host to discover its internet address after knowing only its physical address is done by RARP.

RSA

It is a public key encryption algorithm. These are based on the mathematical part that is easy to find and multiply large prime numbers together, but extremely difficult to factor their product.

SMTP

It is a push protocol. It pushes the message from the client to the server. To send email a system must have the client MTA and to receive it must have the server MTA. (Message Transfer Agent).

What is Malware?

It is a software program which is developed to destroy a computer system. Hacked system..

Protocol

It is a standard way of communicating across a network. A protocol is the language of the network. It is a method by which two dissimilar systems can communicate.

10Base2

It is an Ethernet segment which means a maximum transfer rate of 10MBPS that uses baseband signaling with a contiguous cable segment length of 100 meters and a maximum of 2 segments.

10BaseT

It is an Ethernet term meaning a maximum transfer rate of 10MBPS that uses baseband signaling and twister pair cabling.

Fragmentation

It is the process of breaking the IP packets into smaller pieces. It is needed when the datagram is larger than the MTU. Each fragment becomes a datagram in itself and transmitted independently form source. When received by destination they are reassembled.

Latency

It is the time taken by a message to travel from one side to another.

Infrared Transmission

It is used for short-range communication. The remote controls used for televisions, VCRs, and stereos, use infrared communication. They are relatively directional and can not pass through solid objects.

Network Security- Encoding

It is used to protect the integrity of data as it crosses through communication network to keep its original message upon arriving. Insecure form because it is easily reversible.

Resource Reservation Protocol

It is used to reserved resources across a network. used to request a specific QoS from the network.

What is Bit Stuffing?

It means adding one extra 0 whenever 5 consecutive 1s are following a 0.

Bandwidth

It means the number of bits which can be transmitted over the network in a specified time.

Internet Control Message Protocol (ICMP)

Mainly used in OS of networked computers for the purpose of sending error messages. -Used by routers, hosts for communicating the updates or error info to other routers.

MTU

Maximum transmission unit is the size of the largest packet that a communication protocol can pass. Size can be determined by some standard or determined at the time of connection.

What are MAC addresses?

Media Access Control, uniquely identifies a device on the network. It is also known as physical address or Ethernet address. A MAC address is made up of 6-byte parts.

Microwave Transmission

Microwaves travel in a straight line, so if the towers are too far apart, the earth will get in the way. Thus, repeaters are needed periodically. The higher the towers are, the farther apart they can be. Unlike radio waves at lower frequencies, microwaves do not pass through buildings well.

Unicasting

Message is sent from a source to a single destination node.

Broadcasting

Message is sent from a source to all the nodes in the network.

Multicasting

Message is sent from a source to some subsets of other nodes.

Describe MIME

Multipurpose Internet Mail Extensions. A protocol that transforms non-ASCII data at the sender site to network virtual terminal ASCII data and delivers it to the client MTA to be sent through the internet.

NAT

Network Address Translation. This is a protocol that provides a way for multiple computers on a common network to share single connection to the Internet.

How do you use RSA for authentication?

Once can encrypt the hash (MD4/SHA) of the data with a private key. This is known as digital signature.

Disadvantage of a star topology

One major disadvantage of star topology is that once the central hub or switch get damaged, the entire network becomes unusable.

What is a domain?

One or more computers can be a server to manage the network. -Computers can be on differnet local networks. -User doesnt need an account to login on a specific computer if an account is available on the domain.

CDMA

Only one channel occupies the entire bandwidth of the link and also there is no timesharing. -A code is available for every station wanting to send the data.

What is the main purpose of OSPF?

Open Shortest Path First, is a link-state routing protocol that uses routing tables to determine the best possible path for data exchange.

What is OSI and what role does it play in computer networks?

Open Systems Interconnect :serves as a reference model for data communication. It is made up of 7 layers, with each layer defining a particular aspect on how network devices connect and communicate with one another. One layer may deal with the physical media used, while another layer dictates how data is actually transmitted across the network.

Network Security - Hashing

Operation is one way and non reversible. It takes an input (message) and returns a fixed size string, which is called the hash value.

OSI Layers

Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer Application Layer.

POP3

Post office protocol version 3 is used for accessing the message. Simple and limited functionality. A POP3 server listens on port 110. Supports Delete mode and keep mode.

IMAP4

Protocol used in internet for accessing the mail. More powerful and more features than POP3.

Radio Transmission

Radio waves are easy to generate, can travel long distances, and can penetrate buildings easily, so they are widely used for communication. These waves can travel in all directions.

SSL Protocol

Secure socket layer protocol was originally developed by netscape to ensure security of data transported and routed though HTTP, LDAP or POP3 application layer.

Transmission Impairment

Signals need transmission media to travel from one point to another. Transmission media is not perfect and it can provide resistance or signal impairment

When is a switch said to be congested?

Sometimes a switch receives the packets faster they can be accommodated in the shared link. These packets are stored in the memory for some time. After sometime the buffer space will exhaust and some packets will start getting dropped off. In this case the switch is in a congested state.

What does 10Base T means?

The 10 refers to the data transfer rate, in this case is 10Mbps. The word Base refers to base band, as oppose to broad band. T means twisted pair, which is the cable used for that network.

Job of network layer under OSI reference model

The Network layer is responsible for data routing, packet switching and control of network congestion. Routers operate under this layer

What is the equivalent layer or layers of the TCP/IP Application layer in terms of OSI reference model?

The TCP/IP Application layer actually has three counterparts on the OSI model: the Session layer, Presentation Layer and Application Layer.

FDMA

The available bandwidth is divided into frequency bands.

Crosstalk Noise

The effect of one wire on the other.

Octects

The four numbers in an IP address. Divided into two sections: Net and host. First octet represents the network and the host contains the last octet.

POP3 Keep Mode

The mail remains in the mailbox after retrieval.

What is the purpose of cables being shielded or habing twisted pairs?

The main purpose of this is to prevent crosstalk. Crosstalks are electromagnetic interferences or noise that can affect data being transmitted across cables.

Importance of the OSI physical layer

The physical layer does the conversion from data bits to electrical signal, and vice versa. This is where network devices and cable types are considered and setup.

TDMA

The stations share the bandwidth of the channel in time. Each stations allocates a time slot during which it can send data.

Different Types of Malware

Trojan Horse, Worms, Rootkits.

How many layers under TCP/IP?

There are four layers: the Network Layer, Internet Layer, Transport Layer Application Layer.

What are different ways of securing a computer network?

There are several ways to do this. Install reliable and updated anti-virus program on all computers. Make sure firewalls are setup and configured properly. User authentication will also help a lot. All of these combined would make a highly secured network.

Noise

Thermal noise, induced noise, crosstalk noise and impulse noise.

What is a replay attack?

These are network attacks in which an attacker spies the conversation between the sender and receiver and takes the authenticated information. In the replay attack, the attacker gives proof of his identity and authenticity.

Rootkits

These are used to hide the malicious processes from active process.

Light Transmission

These types of wave can easily be effected by wind and temperature. They normally work well on sunny days.

How do you use RSA for secrecy?

This is achieved by encrypting the data with a public key with a private key.

What si the function of the OSI session layer?

This layer provides the protocols and means for two devices on the network to communicate with each other by holding a session. This includes setting up the session, managing information exchange during the session, and tear-down process upon termination of the session.

Packet Filtering Firewall

This type of firewall detects packets and block unnecessary packets and makes the network traffic release.

VPN

Virtual Private Network, a technology that allows a secure tunnel to be created across a network such as the Internet. For example, VPNs allow you to establish a secure dial-up connection to a remote server.

Attenuation

When a signal travels through a medium, and it loses some of its energy due to resistance.

Electromagnetic Transmission

When electrons move, they create electromagnetic waves that can propagate through space and in a vacuum. The electromagnetic waves can be broadcast efficiently and received by a receiver some distance away.

Active Route State

When the feasible successor is not found. The DUAL diffuses the computation by sending the query packets to some other routers as part of attempting to find a replacement path to the network.

Stuck in active route state

When the replies to queries of an active route are not received.

Distortion

When the signal travels through the medium from one point to another it may chance to change the form or shape of signal.

Backbone Network

a centralized infrastructure that is designed to distribute different routes and data to various networks. It also handles management of bandwidth and various channels.

What is a private IP address?

are assigned for use on intranets. These addresses are used for internal networks and are not routable on external public networks. These ensures that no conflicts are present among internal networks while at the same time the same range of private IP addresses are reusable for multiple intranets since they do not "see" each other.

Routers

can connect two or more network segments. These are intelligent network devices that store information in its routing table such as paths, hops and bottlenecks. With this info, they are able to determine the best path for data transfer. Routers operate at the OSI Network Layer.

what is the role of Pseudo tty?

false terminal-it enables external machines to connect through telnet or rlogin. No connection can be made without a pseudo tty.

What is the maximum length allowed for a UTP cable?

has an allowable length of 90 to 100 meters. This limitation can be overcome by using repeaters and switches.

NIC

is short for Network Interface Card. This is a peripheral card that is attached to a PC in order to connect to a network. Every NIC has its own MAC address that identifies the PC on the network.

Data Encapsulation

is the process of breaking down information into smaller manageable chunks before it is transmitted across the network. It is also in this process that the source and destination addresses are attached into the headers, along with parity checks

Internet Group Management Protocol (IGMP)

it allows internet hosts to participate in multicasting. The IGMP messages are used to learn which hosts are part of which multicast groups.

Media Access Control - MAC Address

it is an identifier assigned to most network adapters or NICs by the manufacturer for the purpose of identification. Numbering Spaces managed by IEEE: MAC-48, EUI-48 and EUI-64

Ping

it is particularly used to check if the system is in network or not. It also gives packet lost information. The number of packets sent, received and lost is returned by PING.

How does SSL protect internet users from various threats?

it uses TCP as a communication layer to provide a reliable end to end secure and authenticated connection, which helps internet users to protect from various threats.

What are proxy servers and how do they protect computers?

primarily prevent external users who identifying the IP addresses of an internal network. Without knowledge of the correct IP address, even the physical location of the network cannot be identified. Proxy servers can make a network virtually invisible to external users.

Gateways

provide connectivity between two or more network segments. It is usually a computer that runs the gateway software and provides translation services. This translation is a key in allowing different systems to communicate on the network.

Node

refers to a point or joint where a connection takes place. It can be computer or device that is part of a network. Two or more nodes are needed in order to form a network connection.

Point to Point Link

s to a direct connection between two computers on a network. A point to point connection does not need any other network devices other than connecting a cable to the NIC cards of both computers.

What are firewalls?

serve to protect an internal network from external attacks. These external threats can be hackers who want to steal data or computer viruses that can wipe out data in an instant. It also prevents other users from external networks from gaining access to the private network.

LAN

short for Local Area Network. It refers to the connection between computers and other network devices that are located within a small physical location

RIP

short for Routing Information Protocol is used by routers to send data from one network to another. It efficiently manages routing data by broadcasting its routing table to all other routers within the network. It determines the network distance in units of hops.

WAN

stands for Wide Area Network. It is an interconnection of computers and devices that are geographically dispersed. It connects networks that are located in different regions and countries.