68482545-Network-Engineer-Interview-Questions-Answers.pdf

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Transport

Layer 4) This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end

error recovery and flow control. It ensures complete data transfer.

Network

Layer 3) This layer provides switching and routing technologies, creating logical paths, known as virtual circuits , for

transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing,

internetworking, error handling, congestion control and packet sequencing.

Data Link

Layer 2)

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and

management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided

into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer

controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame

synchronization, flow control and error checking.

Physical

Layer 1) This layer conveys the bit stream – electrical impulse, light or radio signal — through the network at the electrical

and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables,

cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Application Layers Usage Example :

7. Application Layer NNTP · SIP · SSI · DNS · FTP · Gopher · HTTP · NFS · NTP · SMPP · SMTP · SNMP · Telnet (more)

6. Presentation Layer : MIME · XDR ·

5. Session Layer : Named Pipes · NetBIOS · SAP

4. Transport Layer : TCP · UDP · PPTP · SCTP · SSL · TLS

3. Network Layer : IP · ICMP · IPsec · IGMP · IPX · AppleTalk

2. Data Link Layer ARP : · CSLIP · SLIP · Ethernet · Frame relay · ITU-T G.hn DLL · L2TP · PPP

1. Physical Layer : RS-232 · V.35 · V.34 · I.430 · I.431 · T1 · E1 · POTS · SONET/SDH · OTN · DSL · 802.11a/b/g/n PHY ·

ITU-T G.hn PHY

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wiki/MIMEhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/External_Data_Representationhttp://en.wikipedia.org/wiki/External_Data_Representationhttp://en.wikipedia.org/wiki/External_Data_Representationhttp://en.wikipedia.org/wiki/Session_Layerhttp://en.wikipedia.org/wiki/Session_Layerhttp://en.wikipedia.org/wiki/Session_Layerhttp://en.wikipedia.org/wiki/Named_Pipeshttp://en.wikipedia.org/wiki/Named_Pipeshttp://en.wikipedia.org/wiki/Named_Pipeshttp://en.wikipedia.org/wiki/NetBIOShttp://en.wikipedia.org/wiki/NetBIOShttp://en.wikipedia.org/wiki/NetBIOShttp://en.wikipedia.org/wiki/Session_Announcement_Protocolhttp://en.wikipedia.org/wiki/Session_Announcement_Protocolhttp://en.wikipedia.org/wiki/Session_Announcement_Protocolhttp://en.wikipedia.org/wiki/Transport_Layerhttp://en.wikipedia.org/wiki/Transport_Layerhttp://en.wikipedia.org/wiki/Transport_Layerhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/Stream_Control_Transport_protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transport_protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transport_protocolhttp://en.wikipedia.org/wiki/Secure_Sockets_Layerhttp://en.wikipedia.org/wiki/Secure_Sockets_Layerhttp://en.wikipedia.org/wiki/Secure_Sockets_Layerhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Network_Layerhttp://en.wikipedia.org/wiki/Network_Layerhttp://en.wikipedia.org/wiki/Network_Layerhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Control_Message_Protocolhttp://en.wikipedia.org/wiki/Internet_Control_Message_Protocolhttp://en.wikipedia.org/wiki/Internet_Control_Message_Protocolhttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/IGMPhttp://en.wikipedia.org/wiki/IGMPhttp://en.wikipedia.org/wiki/IGMPhttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/CSLIPhttp://en.wikipedia.org/wiki/CSLIPhttp://en.wikipedia.org/wiki/CSLIPhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/IEEE_802.3http://en.wikipedia.org/wiki/IEEE_802.3http://en.wikipedia.org/wiki/IEEE_802.3http://en.wikipedia.org/wiki/Frame_relayhttp://en.wikipedia.org/wiki/Frame_relayhttp://en.wikipedia.org/wiki/Frame_relayhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/Layer_2_tunneling_Protocolhttp://en.wikipedia.org/wiki/Layer_2_tunneling_Protocolhttp://en.wikipedia.org/wiki/Layer_2_tunneling_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Physical_Layerhttp://en.wikipedia.org/wiki/Physical_Layerhttp://en.wikipedia.org/wiki/Physical_Layerhttp://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/V.35http://en.wikipedia.org/wiki/V.35http://en.wikipedia.org/wiki/V.35http://en.wikipedia.org/wiki/V.34http://en.wikipedia.org/wiki/V.34http://en.wikipedia.org/wiki/V.34http://en.wikipedia.org/wiki/I.430http://en.wikipedia.org/wiki/I.430http://en.wikipedia.org/wiki/I.430http://en.wikipedia.org/wiki/I.431http://en.wikipedia.org/wiki/I.431http://en.wikipedia.org/wiki/I.431http://en.wikipedia.org/wiki/T1%28Networking%29http://en.wikipedia.org/wiki/T1%28Networking%29http://en.wikipedia.org/wiki/T1%28Networking%29http://en.wikipedia.org/wiki/E-carrier#E1http://en.wikipedia.org/wiki/E-carrier#E1http://en.wikipedia.org/wiki/E-carrier#E1http://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/SONET/SDHhttp://en.wikipedia.org/wiki/SONET/SDHhttp://en.wikipedia.org/wiki/SONET/SDHhttp://en.wikipedia.org/wiki/OTNhttp://en.wikipedia.org/wiki/OTNhttp://en.wikipedia.org/wiki/OTNhttp://en.wikipedia.org/wiki/DSLhttp://en.wikipedia.org/wiki/DSLhttp://en.wikipedia.org/wiki/DSLhttp://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/DSLhttp://en.wikipedia.org/wiki/OTNhttp://en.wikipedia.org/wiki/SONET/SDHhttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/E-carrier#E1http://en.wikipedia.org/wiki/T1%28Networking%29http://en.wikipedia.org/wiki/I.431http://en.wikipedia.org/wiki/I.430http://en.wikipedia.org/wiki/V.34http://en.wikipedia.org/wiki/V.35http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/Physical_Layerhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Layer_2_tunneling_Protocolhttp://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/Frame_relayhttp://en.wikipedia.org/wiki/IEEE_802.3http://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/CSLIPhttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/IGMPhttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/Internet_Control_Message_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Network_Layerhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Secure_Sockets_Layerhttp://en.wikipedia.org/wiki/Stream_Control_Transport_protocolhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Transport_Layerhttp://en.wikipedia.org/wiki/Session_Announcement_Protocolhttp://en.wikipedia.org/wiki/NetBIOShttp://en.wikipedia.org/wiki/Named_Pipeshttp://en.wikipedia.org/wiki/Session_Layerhttp://en.wikipedia.org/wiki/External_Data_Representationhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Presentation_Layerhttp://en.wikipedia.org/wiki/Category:Application_layer_protocolshttp://en.wikipedia.org/wiki/Telnethttp://en.wikipedia.org/wiki/Simple_Network_Management_Protocolhttp://en.wikipedia.org/wiki/SMTPhttp://en.wikipedia.org/wiki/SMPPhttp://en.wikipedia.org/wiki/Network_Time_Protocolhttp://en.wikipedia.org/wiki/Network_File_System_%28protocol%29http://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/Gopher_%28protocol%29http://en.wikipedia.org/wiki/FTPhttp://en.wikipedia.org/wiki/Domain_name_systemhttp://en.wikipedia.org/wiki/Simple_Sensor_Interface_protocolhttp://en.wikipedia.org/wiki/Session_Initiation_Protocolhttp://en.wikipedia.org/wiki/NNTPhttp://en.wikipedia.org/wiki/Application_Layerhttp://www.webopedia.com/TERM/p/protocol.htmlhttp://www.webopedia.com/TERM/A/ATM.htmlhttp://www.webopedia.com/TERM/R/RS_232C.htmlhttp://www.webopedia.com/quick_ref/Fast_Ethernet.htmlhttp://www.webopedia.com/TERM/H/hardware.htmlhttp://www.webopedia.com/TERM/n/network.htmlhttp://www.webopedia.com/TERM/D/data_synchronization.htmlhttp://www.webopedia.com/TERM/L/Logical_Link_Control_layer.htmlhttp://www.webopedia.com/TERM/M/MAC_address.htmlhttp://www.webopedia.com/TERM/T/TCP_IP.htmlhttp://www.webopedia.com/TERM/E/encoding.htmlhttp://www.webopedia.com/TERM/C/congestion.htmlhttp://www.webopedia.com/TERM/I/internetworking.htmlhttp://www.webopedia.com/DidYouKnow/Internet/2002/IPaddressing.asphttp://www.webopedia.com/TERM/M/node.htmlhttp://www.webopedia.com/quick_ref/virtual_circuit.htmlhttp://www.webopedia.com/TERM/R/routing.htmlhttp://www.webopedia.com/TERM/P/packet_switching.htmlhttp://www.webopedia.com/TERM/F/flow_control.htmlhttp://www.webopedia.com/TERM/h/host.html


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What is the difference between a repeater, bridge, router? Relate this to the OSI model

Bridges:

(sometimes called ―Transparent bridges‖ ) work at OSI model Layer 2. This means they don‘t know anything about protocols,

but just forward data depending on the destination address in the data packet. This address is not the IP address, but theMAC (Media Access Control) address that is unique to each network adapter card. Bridges are very useful for joining networks

made of different media types together into larger networks, and keeping network segments free of data that doesn‘t belong

in a particular segment.

Switches:

Switches are the same thing as Bridges, but usually have multiple ports with the same ―flavor‖ connection (Example:

10/100/10000BaseT).

Switches can be used in heavily loaded networks to isolate data flow and improve performance. In a switch, data between two

lightly used computers will be isolated from data intended for a heavily used server, for example. Or in the opposite case, in

―auto sensing‖ switches that allow mixing of 10 and 100Mbps connections, the slower 10Mbps transfer won‘t slow down the

faster 100Mbps flow.

Repeater:

Forwards every frame it receives

it is a generator,not an amplifier(i.e i t removes noise & regenerates signal )

Bi-directional in nature

Useful in increasing ethernet size/length

Maximum of 5 Repeaters in an Ethernet

Routers

Links dissimilar n/ws

not transparent to end stations

acts on a network layer frame

isolates LAN to subnets to manage & control traffic


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A VLAN (Virtual LAN) is a grouping of ports on switches which is considered as one broadcast domain. All the ports on a

VLAN act as if they were all on the same wire. Therefore, broadcasts are propagated across a VLAN ,and anything

communication outside that VLAN must be routed or bridged.

The ELAN is a mechanism used to link VLANs across a wide area network. ATM is a good candidate for ELANs. With ELANs,

you could have 2 VLANs at different sites which are linked together via an ELAN. The ELAN links the two VLANs

Together, forming one big broadcast domain. The advantage of ELANs over straight bridging is that membership into ELANsis dynamic, and that multiple ELANs can be handled by one single WAN link.

v Describe Ethernet packet contents: min./max. size, header.

Ethernet frame consists of:

7 bytes – Preamble

1 byte – SOF Delimiter

6 bytes – DA

6 bytes – SA

2 bytes – Type\Length

46-1500 bytes – Data \ 802.2 Header + Data

4 bytes – FCS

Min amount of bytes is 72. Ethernet frame minimal size is 64 = 72 bytes of frame – 7 bytes of preamble – 1 byte of SOF.

The ethernet frame size upper limit of 1500 bytes goes up to the history of DIX Ethernet – physical limit of memory size used

in NICs because of it‘s cost. Actually there is no strict requirements by used algorythms or standarts.

Lower limit of frame size has the following reasons:

1. To make transmission error detection more easy – smaller size of binary sequence leads to lower reliability of error

detection.

2. The most important reason: If frame size is less than 64 bytes (512 bits), host may finish transmission before receiving

noise signal and can think that frame transmitted successfully, while another host sent collision notification.

For 10 Mbps rate min frame size should be at least 500 bits – that‘s the only guarantee that collision can be detected

anywhere in the cable. For reliability min size was increased up to 512 (power of 2) and became 512 bits = 64 bytes.

the min size was to make sure that it contains enough ethernet headers.

the max size also has something to do with the data written in the headers.


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v Describe TCP/IP and its protocols.

The TCP/IP suite of protocols is the set of protocols used to communicate across the internet. It is also widely used on many

organizational networks due to its flexibility and wide array of functionality provided. Microsoft who had originally developed

their own set of protocols now is more widely using TCP/IP, at first for transport and now to support other services.

IP – Internet Protocol. Except for ARP and RARP all protocols‘ data packets will be packaged into an IP data packet. IP provides

the mechanism to use software to address and manage data packets being sent to computers.

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 – A reliable connection oriented protocol used to control the management of application level services between computers. It is used for transport by some

applications.

UDP – An unreliable connection less protocol used to control the management of application level services between computers. It is used for transport by some

applications which must provide their own reliability.

Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet. These

include the World Wide Web‘s Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets

you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP). These and other protocols are often packaged

together with TCP/IP as a ―suite.‖

v Describe ATM and what are its current advantages and disadvantages.

Describe SONET

ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte

cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed

asynchronously relative to other related cells and is queued before being multiplexed over the transmission path.

Because ATM is designed to be easily implemented by hardware (rather than software), faster processing and switch speeds

are possible. The prespecified bit rates are either 155.520 Mbps or 622.080 Mbps. Speeds on ATM networks can reach 10

Gbps. Along with Synchronous Optical Network (SONET) and several other technologies, ATM is a key component of

broadband ISDN (BISDN).

ATM also stands for automated teller machine , a machine that bank customers use to make transactions without a human

teller.

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Advantages and Disadvantages of ATM

ATM Advantages

ATM supports voice, video and data allowing multimedia and mixed services over a

single network.

High evolution potential, works with existing, legacy technologies

Provides the best multiple service support

Supports delay close to that of dedicated services

Supports the broadest range of burstiness, delay tolerance and loss performance through the implementation of multiple QoS classes

Provides the capability to support both connection-oriented and connectionless traffic using AALs

Able to use all common physical transmission paths like SONET.

Cable can be twisted-pair, coaxial or fiber-optic

Ability to connect LAN to WAN

Legacy LAN emulation

Efficient bandwidth use by statistical multiplexing

Scalability

Higher aggregate bandwidth

High speed Mbps and possibly Gbps

ATM disadvantages

Flexible to efficiency‘s expense, at present, for any one application it is usually possible to find a more optimized technol ogy

Cost, although it will decrease with time

New customer premises hardware and software are required

Competition from other technologies -100 Mbps FDDI, 100 Mbps Ethernet and fast Ethernet

Presently the applications that can benefit from ATM such as multimedia are rare

The wait, with all the promise of ATM‘s capabilities many details are still in the standards process

v What are the maximum distances for CAT5 cabling?

A good standard answer is 100 meters (300 feet) with patch cords,90 meters (270 feet) without patch

cords. That goes pretty much for everything up to and including CAT 7/Class Fa UTP.


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Maximum cable lengh for ethernet depends on what kind of ethernet you are talking

about! Here are some details on the most popular kinds of ethernet. (UTP = unshielded twisted

air)

Gigabit Ethernet over copper), 1000baseT

Speed: 1000 Mbps

Max Len: 100 Meters

Cable: UTP, RJ-45 connectors

Fast Ethernet, 100baseT

Speed: 100 Mbps

Max Len: 100 Meters


Twisted Pair Ethernet, 10baseT

Speed: 10 Mbps

Max Len: 100 Meters


Thin Ethernet , 10 base 2

Speed: 10 Mbps

Max Len: 185 Meters

Cable: RG-58 type coax, 50 ohm impedance

Thick Ethernet, 10 base 5

Speed: 10 Mbps

Max Len: 500 Meters

Cable: RG-58 type coax, 50 ohm impedance

v Describe UDP and TCP and the differences between the two.

TCP – A reliable connection oriented protocol used to control the management of application level services between

computers. It is used for transport by some applications.

UDP – An unreliable connection less protocol used to control the management of application level services between

computers. It is used for transport by some applications which must provide their own reliability.


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Multilayer switching is usually implemented through a fast hardware such as a higher-density ASICs (Application-Specific

Integrated Circuits), which allow real-time switching and forwarding with wirespeed performance, and at lower cost than

traditional software-based routers built around general-purpose CPUs.

The following are some basic architecture approaches for the multiplayer switches:

Generic Cut-Through Routing:

In the multi-layer switching architecture Layer 3 routing calculations are done on the first packet in a data flow. Followingpackets belonging to the same flow are switched at Layer 2 along the same route. In other words, route calculation and frame

forwarding are handled very differently here.

ATM-Based Cut-Through Routing:

This is a variation of generic cut-through routing which is based on ATM cells rather than frames. ATM-based cut-through

routing offers several advantages such as improved support of LAN emulation and multi-vendor support in the form of the

Multiprotocol Over ATM (MPOA) standard. Products referred to as IP switches and tag switches generally fall into this

category.

Layer 3 Learning Bridging CIn this architecture, routing is not provided. Instead, it uses IP ―snooping‖ techniques to le arn theMAC/IP address relationships of endstations from true routers that must exist elsewhere in the network. Then it redirects

traffic away from the routers and switches it based on its Layer 2 addresses.

Wirespeed Routing:

Wirespeed architecture routes every packet individually. It is often referred to as packet-by-packet Layer 3 switching. Using

advanced ASICs to perform Layer 3 routing in hardware, it implements dynamic routing protocols such as OSPF and RIP. In

addition to basic IP routing, it supports IP multicast routing, VLAN segregation, and multiple priority levels to assist in quality

of service.

Network Troubleshooting

v Explain how traceroute, ping, and tcpdump work and what they are used for?

Traceroute;

Traceroute works by increasing the ―time-to-live‖ value of each successive batch of packets sent. The first three packets sent

have a time-to-live (TTL) value of one (implying that they are not forwarded by the next router and make only a single hop).

The next three packets have a TTL value of 2, and so on. When a packet passes through a host, normally the host decrements

the TTL value by one, and forwards the packet to the next host. When a packet with a TTL of one reaches a host, the host

discards the packet and sends an ICMP time exceeded (type 11) packet to the sender. The traceroute utility uses these

returning packets to produce a list of hosts that the packets have traversed en route to the destination. The three timestamp


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values returned for each host along the path are the delay (aka latency) values typically in milliseconds (ms) for each packet in

the batch. If a packet does not return within the expected timeout window, a star (asterisk) is traditionally printed. Traceroute

may not list the real hosts. It indicates that the first host is at one hop, the second host at two hops, etc. IP does not

guarantee that all the packets take the same route. Also note that if the host at hop number N does not reply, the hop will be

skipped in the output.

Ping:

It works by sending ICMP ―echo request‖ packets to the target host and listening for ICMP ―echo response‖ replies. Ping

estimates the round-trip time, generally in milliseconds, and records any packet loss, and prints a statistical summary when

finished.

TCPDUMP:

traceroute and ping work on the ICMP protocol and are used for network connectivity testing. but TCPDUMP is different its a

NETWORK PACKET ANALYZER. tcpdump uses libpacp / winpcap to capture data and uses it extensive protocol definitions

build inside to analyze the captured packets. Its mainly used to debug the protocol of the captured packet which in turn

reveals the network traffic charachterstics.

v What is a metric?

Metrics is a property of a route in computer networking, consisting of any value used by routing algorithms to determine

whether one route should perform better than another (the route with the lowest metric is the preferred route). The routing

table stores only the best possible routes, while link-state or topological databases may store all other information as well.

For example, Routing Information Protocol uses hopcount (number of hops) to determine the best possible route.

A Metric can include:

measuring link utilisation (using SNMP)

number of hops (hop count)

speed of the path

packet loss (router congestion/conditions)

latency (delay)

path reliability

path bandwidth

throughput [SNMP - query routers]

load

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The actual encryption logic in RC4 is very simple. The plain text is XOR-ed with an infinitely long keystream. The security of

RC4 comes from the secrecy of the packet key that‘s derived f rom the keystream.

v Describe what a VPN is and how it works.

A VPN connection is the extension of a private network that includes links across shared or public networks, such as the

Internet. VPN connections (VPNs) enable organizations to send data between two computers across the Internet in a manner

that emulates the properties of a point-to-point private link.

Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users

together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses ―virtual‖ connections routed

through the Internet from the company‘s private network to the remote site or employee.

VoIP

Describe how VoIP works.

Voice over Internet Protocol (VoIP), is a technology that allows you to make voice calls using a broadband Internet connection

instead of a regular (or analog) phone line. Some VoIP services may only allow you to call other people using the same service,

but others may allow you to call anyone who has a telephone number – including local, long distance, mobile, and

international numbers. Also, while some VoIP services only work over your computer or a special VoIP phone, other services

allow you to use a traditional phone connected to a VoIP adapter.

Describe methods of QoS.

Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a

certain level of performance to a data flow.

QOS is Quality of Service: A set of metrics used to measure the quality of transmission and service available of any giventransmission system

Are you familiar with IPv6? If so, what are the major differences between IPv4 and IPv6?

IPv6 is based on IPv4, it is an evolution of IPv4. So many things that we find with IPv6 are familiar to us. The main differences

are:

1.Simplified header format. IPv6 has a fixed length header, which does not include most of the options an IPv4 header can

include. Even though the IPv6 header contains two 128 bit addresses (source and destination IP address) the whole header

has a fixed length of 40 bytes only. This allows for faster processing.

Options are dealt with in extension headers, which are only inserted after the IPv6 header if needed. So for instance if a

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packet needs to be fragmented, the fragmentation header is inserted after the IPv6 header. The basic set of extension

headers is defined in RFC 2460.

2.Address extended to 128 bits. This allows for hierarchical structure of the address space and provides enough addresses

for almost every ‗grain of sand‘ on the earth. Important for security and new services/devices that will need multiple IP

addresses and/or permanent connectivity.

3.A lot of the new IPv6 functionality is built into ICMPv6 such as Neighbor Discovery, Autoconfiguration, Multicast Listener

Discovery, Path MTU Discovery.

4.Enhanced Security and QoS Features.

IPv4 means Internet Protocol version 4, whereas IPv6 means Internet Protocol version 6.

IPv4 is 32 bits IP address that we use commonly, it can be 192.168.8.1, 10.3.4.5 or other 32 bits IP addresses. IPv4 can

support up to 232 addresses, however the 32 bits IPv4 addresses are finishing to be used in near future, so IPv6 is developed

as a replacement.

IPv6 is 128 bits, can support up to 2 128 addresses to fulfill future needs with better security and network related features.

Here are some examples of IPv6 address:

1050:0:0:0:5:600:300c:326b

ff06::c3

0:0:0:0:0:0:192.1.56.10

What authentication, authorization ad accounting AAA) mechanisms are you familiar with? Which ones have you

implemented??

RADIUS Server (Remote Access Dialin User Service)

MS IAS (Internet Authenticaion Service)

14. What is DHCP, and what is needed on a router interface to allow DHCP to function on a subnet? 15. Describe what a stateful firewall is? 16. What is HSRP?

Is this an open standard? 17. In a PIX/ASA, what are security levels used for? 18. What two things are needed in a PIX/ASA firewall to allow traffic to pass from a

higher security level to a lower security level? 19. In IPSec VPNs, what is diffe helman? What is it used for? 20. In an IPSec tunnel, what is main mode?

How does computer get IP from DHCP.

Explain MAC Address?

Difference between Private and Public IP.


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explain framing or channelizing a T1

what's a PRI

what's PSTN?

What is ping? Why you use ping?

PING Stands for Packet InterNet Gopher. PING is used for connectivity checking of any network or any host or device of any or other networks.

Routers are always preferrable for routing services. Routers work at which OSI layers?

Router works at network layer for providing routing services between or among several networks.

A gateway works in which layer?

Transport layer of OSI model.

How can you check the connectivity of any network?

By using ping command.

What is a gateway?

A gateway acts a door for the packet to reach the ‘outside’ of the internal network.

What are the differences among router, switch, bridge and hub?

Router, switch, bridge and hub are network devices. Yet there are some differences among them. The main differences are:

Router: A layer 3 device, can work on physical, data and network layer.

Switch: A layer 2 device, can work on data link layer


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Bridge: A layer 2 device, can work on data link layer.

Hub: A layer 1device, just a multi-port repeater and works on physical layer

What is the range of class A address?

0-127 is the range of class A address.

Tell an IP which has class C range. Also tell why that IP is an class C address.

IP of Class C: 193.1.1.1

Why this is a class C address: Class C addresses have the range of 192 - 223

Name a device which can operate at physical layer of OSI model.

Hub.

Note: Remember, hub is the device that can work only into the physical layer of OSI model. But switch, router can also be used instead of a hub. So, all the

answers hub, switch or router are all correct.

What is the major differences between a router and a switch?

A router can divide the broadcast domain and collision domain. But a switch can only divide the collision domain. Router can communicate among different

networks where as the switch can not communicate different networks.

Hub operates at which layers of OSI model? Is it wise to use a hub for huge networks? Why or why not?

Hub operates at only physical layer of OSI model.

No, it's not so wise to use hub for a huge network.

Hubs can't divide the broadcast domain or the collision domain. So, if we use hubs then there creates huge broadcast domain. When there are huge broadcast,

the network gets problem time to time. So, it's not wise to use hubs to support a huge network.


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How many layers are in OSI model? Name them

There are seven layers of OSI model. The layers are:

Application layer

Presentation layer

Session layer

Transport layer

Network layer

Data link layer

Physical layer

Note: You can remember the seven layer model by a simple sentence. Please Do Not Touch Steven's Pet Alligator. See, the starting of each word forms the layer.

Why do you need to use a router?

Router can easily divide the broadcast domain and collision domain. So, to communicate among several networks, routers are used.

What is the second layer of OSI model?

Data Link layer.

Name two network devices which can work as layer 2 device.

Switch and router

What is OSI model?

OSI revers for Open System Interconnection Reference Model. It is an abstract model for layered communications and computer network protocol design. There

are seven layers of OSI model which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers.

OSI model also referred as OSI layered model, OIS layered technology, 7 layer model, OSI seven layer model, OSI reference model.


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What is the data unit of Data Link layer?

Frame

What are the difference between TCP and UDP?

TCP: Connection oriented protocol, acknowledged one, Point to point communication.

UDP: Connection less protocol, unreliable, less traffic

What is the port no of DNS and Telnet?

DNS port no: 53

Telnet port no: 23

What is the port no of SMTP and POP3?

SMPT port no: 25

POP3 port no: 110

What is the functionality of network layer? Name the data unint of network layer.

Functionality of network layer: Path determination and logical addressing

Data unit of network layer: Packet

Which three layers of OSI model is treated as "Media Layers"?

Physical layer, data link layer and network layer are treated as "Media Layers".


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What is deadlock?

Deadlock is a situation when two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting processes. The

implementation of a semaphore with a waiting queue may result in this situation.

Mention the advantages and disadvantages of a router.

Advantages:

Router can limit the collision domain and broadcast domain

Router can function both on LAN & WAN.

Different media & architectures can be connected among themselves through router.

Router can determine best path/route for data to reach

the destination.

Router can filter the broadcasts.

For communicating different networks, routers must be used.

Disadvantage:

Router is more expensive than any other networking devices like Hub, Bridge & Switch.

Router only work with routable protocols.

Routing updates consume some bandwidth.

Increase latency due to greater degree of packet

filtering.

Routers function as software based and so it's slower compared to switch.


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Mention the private IP address rannge of class B and C.

For Class B: 172.16.0.0 – 172.31.255.255

For Class C: 192.168.0.0 – 192.168.255.255

What is the IP range of class C IP address?

240.0.0.0 255.255.255.255

What is the default subnet mask of class C IP address?

255.255.255.0

Why do you need subnet mask?

Subnet mask is required to divide a large network into several small networks.

Tell the full name: DNS, FTP

DNS: Domain Name System

FTP: File Transfer Protocol

What is the functionality or ARP?

ARP refers to Address Resolution Protocol. ARP is a computer networking protocol for determining a network host's link layer or hardware address when only its

Internet Layer (IP) or Network Layer address is known.

Which one is reliable: TCP or UDP?

TCP is reliable and UDP is an unreliable service.


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How DHCP works?

DHCP works by four-steps: (1) IP request, (2) IP offer (3) IP selection and (d) Acknowledgement.

What is POP3? Why you require POP3?

POP stands for Post Office Protocol. This is used to describe how e-mail clients interact with mail servers. The POP3 Server is a type of mail server used for

incoming mail. POP is only used to receive messages.

What is the difference between Layer 2 Switch and Layer 3 Switch?

Layer 2 switch is based on MAC addresses which operates on Data Link Layer of OSI mode. And Layer 3 switching is based on network topology table populated

and works on Network layer.

Recommended Reading

Cheat Charts of Networking Engineering

Final words

In this page, I try to integreate some of the basic and useful questions which are really helpful for your networking related jobs. I personally suggest to read at

least once before going to the written exam or interview of Networking related jobs or Network Engineer jobs. Hope, you have a basic idea of the sample

questions. One thing, you can also add your own questions after interviewing your job in the comment section. It will helpful for others also.

Interviewing candidates for network administrators is a bit like opening up the door to a herd of Chihuahuas. Sit them down and start talking and all you hear is

Yip! Novell? Yip! VPN services? Yip! MCSE? Yip! CCNA? Yip! Yip!

IT managers need to bring on the best talent to run their networks; the company’s infrastructure relies on productive, capable staff. How do you cut through all

the Yipping? What questions do you ask to find that stately Shepherd amidst the dog pack?

Whether you are a technical hands-on manager or a business-centric CIO doing that final “check for a fit with the company” job interview, the questions you ask

a network admin candidate should check on seven aspects of what makes a good employee: Knowledge, Tinkering, Honesty, Ethics, Community, Discretion, and

the all important Sanity Check. We asked network specialists to share their favorite questions (and best answers) to help you eliminate those annoying Yippies.


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Knowledge Check: What is a TCP Three-Way Handshake?

Let’s go right for the jugular. By now, you’ve asked a few questions, sniffed through the resume looking for fudged qualifications, determined a level of

expertise, and found out how many years she has spent using the technologies on which your organization relies. But do you know what your candidate really

knows? Asking a simple question rather than a tough one can be revealing.

Only 5-10% of IT professionals have very strong technical skills, says Robert Brockway, a system and network administrator at a software development company

based in Toronto. “I would rather ask them, ‘Describe a three-way handshake.’ That is really an introductory question for a network administrator.”

“Maybe one in 10 people get it right,” he says, “And sometimes these [candidates] are for senior positions.” If someone gets the answer right, Brockway can ask

harder questions. “But more often than not, they get that question wrong, and that troubles me,” he says.

The right answer? SYN SYN/ACK ACK. The candidate can go into more detail, Brockway adds, but if the interviewee says that phrase, he gives them high marks.

“When you are diagnosing network problems you have to understand the network or you don’t know what you are looking at,” Brockway says.

Tinkerer Check: What is Your Home Network Like?

A good employee manages his own mindset. He has to do what is necessary to keep that elan for the work. A true love of technology helps, especially on the

days when you have to slog through one too many worst-case scenarios.

“We’re looking for someone who can bring enthusiasm and curiosity to the office. What we’re looking for the most is someone who has a tinkerer’s mentality.

Someone who wants to try out things at home, because they can’t get enough of the technology at work,” says Scott Sherrill, senior systems engineer for the

Regional Educational Media Center, a Michigan nonprofit that provides desktop, network, and ISP support for K-12 schools, libraries, and other local agencies.

Perhaps the job candidate is using a wireless server for the family or maybe just trying out cutting-edge technology to see how it goes. Maybe she’s turned an

old laptop into a picture frame. Any of those technologies are okay. It’s not necessarily one specific technology that you should look for. It’s more the mindset,

says Sherrill.

Of course, this is not to negate a person who has a healthy balance of home life and work; you also want people who don’t invest too much time into their home

operation.

However, the answers you get to this question can provide more character insight than the candidate realizes.

“We had a candidate who went on and on about all the pirated software that he had, so right away we had the opportunity to ask: Is this the type of character

we want in our organization? He was trying to score points by describing how big his network was and that sort of thing. That this person admitted to something

like this in an interview means he is probably not going to be good for us,” says Sherrill.

Honesty Check: What was the Worst Mistake You’ve Made as a Network Administrator?


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All thieving aside, a good check of a person’s honesty is finding how easily he will lie to make himself look good.

“I look for a willingness to admit your own faults. Everybody makes mistakes. The key aspect of a mistake is to learn from that mistake. If you’re not willing to

say, ‘Here’s what went wrong, here’s what I did,’ then you are never going to learn from what you did,” says David Nolan, a senior network engineer for a

midsized global company in the Pittsburgh area. “It’s not about who’s to blame. It’s about how do we avoid this in the future, how do we improve the process,

how do we make this better.”

Nolan also presents a list of technologies that his company uses asks the candidate which ones she knows. “If I list 20 technologies and you claim to beexperienced with all of them, I’m going to be worried,” says Nolan.

Weeding out the hands-off managers is also key. While the above question is a good indicator, so is asking a candidate to give a detailed description of a project

she worked on, from high level to ground work. If the candidate can’t articulate a coherent project vision, you’ve found a superficial show dog whose resume is a

waste of ink.

Discretion Check: What was the Worst/Strangest Network You’ve Managed?

In addition to checking whether your candidate can bark out a clear narrative that tells the story behind a beyond-bizarre network and how its oddities were

resolved, by asking this question helps you find out if the job candidate will blurt out the secrets of his previous employer.

For example, the job candidate might explain a problem encountered on a network she managed – “how the guys at AT&T had exposed all this iPad stuff” and

add, “I told them and told them and they didn’t listen to me.” At one level the candidate is explaining a technical issue. However, “You just told me who your

client was, and you just told me what their problem was,” points out Terry Hamilton, president of IASSIST in Toronto. That’s a breach of trust, if not a security

issue — and it does not bode well for the candidate’s trustworthiness.

“If someone had relayed that type of information who had worked in a financial institution, or somewhere similar, I would not want them to tell me the

organization had (or even perhaps still has) a hole in their network, or had security problems, or had issues with data loss,” he says.

Ethics Check: Do You Belong to LOPSA, SAGE, or USENIX?

People with a code of ethics have given time and thought about the kind of person they want to be. They live according to a set of standards they have given

themselves, and no one has asked them to do it. A code of ethics is often something you have to search for and adopt. The League of Professional System

Administrators (LOPSA), USENIX (The Advanced Computing Systems Association), and the USENIX special interest group for system administrators known as

SAGE all share a code of ethics.

“I always ask if people belong to [these organizations], and people rarely say Yes. It has been my experience that only a small percentage of the people have

given any consideration to the ethics of what they are doing,” says Brockway.


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“Consider how we use the Internet these days and everything we use it for. The network administrator can spy on your traffic and can do so without anyone

knowing, because the network administrator has that privilege and has that knowledge. I’ve come to the conclusion that ethics is extremely important. And

that’s one of the reasons why I’m a supporter of these organizations,” he says.

Community Check: Do You Belong to Any User Groups?

If your network administrator doesn’t know that answer to a problem, especially a time-sensitive one, how does he solve it? Does the candidate have a network

of peers to turn to, either online or offline? How plugged in is he to technologies that are gaining speed or losing momentum? Who or what is his sources ofresearch and information?

Belonging to a user group, says Brockway, shows that the candidate is interested in technology. “The people who are passionate about something are the best at

the subject,” says Brockway.

Sanity Check: If You were a Kitchen Appliance, What Would You Be?

Wisdom, character, honor, integrity, your candidate can have it all. But if they are a whack-a-doodle all that becomes moot. A nut-bar hunt requires drastic

measures—even shock and awe tactics. Granted, asking this may backfire and you can lose a good candidate, but you might just be better off without her if she

can’t fetch an answer to this question.

There are clear warnings in people’s responses. Electric knives, garbage disposals, bread makers are all cause for alarm. But an interviewee may say he is an oven

because he likes to be where the action (and heat) is, or the microwave because he is quick and convenient. Better yet, he might say he is the coffee maker, and

as we all know, no office should be without one of those.

However, there is a method to this madness, says Damion Alexander, a system administrator for Bard College in Annandale-on-Hudson, NY.

In addition to checking whether the candidate has a sense of humor, he says, “I want to know if they can think on their feet. Since this question is rarely heard of

(so far), it catches people off guard. This gives some measure of how they respond to a situation they’ve never seen or heard before.”

“I rarely measure time [in answering the question], but if they give up easily that doesn’t fare well. If they give the name of an appliance and can’t come up with

at least a basic reason why, then I would worry if they would just spew answers to customers and coworkers with no comprehension of why they were giving

that answer,” Alexander says.

“I’ve actually had a CIO candidate refuse to answer the question. Since he had pondered for a while before that, everyone came to the conclusion that he would

not do well when things hit the fan.”

The question also shows how a candidate views himself and how he operates, says Alexander.

“For example, we had two candidates for the same position give an answer of dish washer. The first ‘liked to throw everything in and make it clean.’ The second

‘liked to line everything up nice and neat, so that the water reaches every surface, etc.,’” says Alexander.


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