interview question for network administrator 8

What is point to point link? - Direct connection between two computers on a network is called as point to point link. - No other network devices other than a connecting cable are required for point to point connection.  - The cable connects the NIC card of both the devices.

When is a switch said to be congested? - Sometimes a switch receives the packets faster than they can be accommodated in the shared link. These packets are stored in the memory for sometime.  - However, after sometime the buffer space will exhaust and some packets will start getting dropped off. - The switch is called as congested in this state.

Explain a.) Uni-casting, b.) Multicasting and c.) Broadcasting a.) Uni-casting - Message is sent from a source to a single destination node.  b.) Multicasting - Message is sent from a source to some subsets of other nodes. c.) Broadcasting - Message is sent from a source to all the nodes in the network.

What are the various types of Multiplexing? The various types of multiplexing are:  a. Frequency Division Multiplexing (FDM) b. Time Division Multiplexing (TDM) i. Synchronous TDM ii. Asynchronous TDM  c. Wave Division Multiplexing (WDM)

Which layers of OSI are referred to as network support layers? The following 3 layers of OSI are referred to as network support layers: a. Physical Layer b. Data link Layer and  c. Network Layers

Which layers of OSI are referred to as user support layers? The block of user support layers consists of:  a. Session Layer b. Presentation Layer and  c. Application Layer

What does the Data Link Layer do? - The Data Link Layer transforms the physical layer to a reliable link.  It takes care of:  a. Node to node delivery.  b. Framing c. Physical Addressing d. Flow Control e. Error Control f. Access Control

What is NIC? - NIC stands for Network Interface Card.  - It is a peripheral card attached to a PC to helps it connect to a network. - The MAC address of the card helps the network in identifying the PC.

What are the responsibilities of Network Layer? - The Network Layer aids in source-to-destination delivery of packet across multiple networks.  - It performs:  a. Logical Addressing b. Routing

Name the various error detection methods. The various error detection methods are:  a. Vertical Redundancy Check (VRC) b. Longitudinal Redundancy Check (VRC) c. Cyclic Redundancy Check (VRC) d. Checksum What is Bit Stuffing? - Bit stuffing means adding one extra 0 whenever five consecutive 1s follow a 0.  - This is done so that the pattern 0111110 is not mistaken for a flag. How does dynamic host configuration protocol aid in network administration? - In a large set up where it is difficult to manually configure the IP address of each system, dynamic host configuration protocol comes very helpful.  - Using this protocol, the administrator can create a pool of IP addresses which are called scopes. These can be then dynamically assigned to the systems. Describe the Packet Format of ARP (Address Resolution Protocol)? The fields of the packet format of ARP are as follows: -Hardware type: It is a 16-bit field . Each LAN has been assigned an integer based on its type. For example, Ethernet is given the type 1. -Protocol type: This is a 16-bit field defining the protocol. For example, the value of this field for IPv4 protocol is 0800. -Hardware length: This is an 8-bit field defining the length of the physical address in bytes. For example, for Ethernet the value is 6. -Protocol length: This is an 8-bit field defining the length of the logical address in bytes. For example, for IPv4 protocol the value is 4. -Operation: This is a 16-bitfield defining the type of packet. Two packet types are defined: ARP request (1), ARP reply (2). -Sender hardware address: This is a variable-length field defining the physical address of the sender. For example, for Ethernet this field is 6 bytes long. -Sender protocol address: This is a variable-length field defining the logical (for example, IP) address of the sender. For the IP protocol, this field is 4 bytes long. -Target hardware address: This is a variable-length field defining the physical address of the target. For example, for Ethernet this field is 6 bytes long. -Target protocol address: This is a variable-length field defining the logical (for example, IP) address of the target. For IPv4 protocol, this field is 4 bytes long. What are the advantages of IPv6 over IPv4? The next generation IP, or IPv6 has some advantages over IPv4 that can be summarized as follows: - Larger Address Space: An IPv6 address is 128 bytes long where IPv4 has 32-bit address only, this is a huge increase in the address space. - Better Header Format: IPv6 uses a new header format which simplifies and speeds up the routing process because most of the options do not need to be checked by routers. - New Options: IPv6 has new options to allow for additional functionalities. - Allowance for extension: In IPv6 new technologies can easily embedded.  -Support For Resource Allocation: In IPv6, flow label has been added to enable the source to request special handling of the packet. This mechanism can be used to support traffic such as real-time audio and video. -Support For More Security: The encryption and authentication options in IPv6 provide confidentiality and integrity of the packet. What are the different design goals of ATM? Asynchronous Transfer Mode (ATM) is the cell relay protocol. The Design Goals of ATM are as follows: - A technology is needed to take advantage of high rate transmission media and less susceptible to noise degradation for maximizing the data rates. -The system must interface with existing systems and provide wide-area inter-connectivity between. -The implementation of design must be cheaper enough so that everyone can afford it. If ATM is to become the backbone of international communications, as indeed, it must be available at low cost to every user who wants it. -The new system must be able to work with and support the existing telecommunication hierarchies. - The new system must be connection-oriented to ensure accurate and predictable delivery. - One objective is to move as many of the functions to hardware as possible (for speed) an eliminate as many software functions as possible (again for speed). In which switching physical path is present and how it is different from packet switching? - Circuit switching uses physical path for transmission of data. - Here initially a physical connection is established between source and destination & then data is sent . - In packet switching data is broken into small parts called packets. - Numbered packets may take any shortest route for transmission. - In packet switching virtual connection is made between source and destination. Give the frame format for data link layer. - Header, payload filled, trailer are the main parts of a frame. - Header contains the number of characters in a frame & source and desitnation address. - Payload filled contains the data to be sent. - Trailer is the end of packet and it also contains the starting and ending bits. - This frame is sent to network layer. Why acknowledged service is better? - When data is sent acknowledgement at reception of data occurs. - If frame is lost, then error is detected and the data is sent again. - Recovery of data takes place easily. - It works for reliable channels where error is minimum. - This is a time saving method and better than unacknowledged service . What are the problems in Character count framing method. - In character count the header gives number of characters in frame. - E.g. 2,3,4,2,5,7, 0,4 - Initially two frames will be sent as header shows 2 i.e. 3 and 4. - Again 2 frames will be sent shown by next header and frames are 5and 7. - 3rd Header is 0 which lead to wastage of time and bandwidth and no frame is sent. - This leads to error and should be avoided. Explain Echoplex - It is a method used to detect error in data link layer and is also called echo checking. - Here reciever retransmits the data back to the transmitter after reception. - It requires a full duplex operation for sending and receiving data. - When data is received at the transmitter,error can be detected by the human operator . - Its disadvantage is that it depends on humans for error detection and correction.