Interview questions for network engineer

  1. Describe the OSI model.
  2. What is the difference between a repeater, bridge, router? Relate this to the OSI model.
  3. Describe an Ethernet switch and where it fits into the OSI model.
  4. What is a VLAN? What is an ELAN? What is the difference?
  5. Relate FDDI/ATM/SONET to the OSI model.
  6. Explain how to configure a host network interface (e.g. IP address, netmask, broadcast address)?
  7. Describe Ethernet packet contents: min/max size, header.
  8. Describe TCP/IP and its protocols.
  9. Describe ATM and what are its current advantages and disadvantages.
  10. Describe SONET.
  11. What are the maximum distances for CAT5 cabling?
  12. Describe UDP and TCP and the differences between the two.
  13. What is your current IP address? Hoiw do you find that out on different OSs?
  14. Describe what a broadcast storm is.
  15. Describe what a runt, a giant, and a late collision are and what causes each of them.
  16. How do you distinguish a DNS problem from a network problem?
  17. Describe the Bandwidth Delay problem.
  18. Describe the principle of multi-layer switching.
  19. Describe the purpose and basic functionality of things like HSRP, VRRP etc.
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23 Comments on Interview questions for network engineer

  1. Anonymous
    Posted 10/14/2004 at 4:47 am | Permalink

    Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and internetworking communications.
    Communication process has been divided into 7 layers.

    In all the above layers differnt works are performed according to the work divided among these layers.

  2. Ganesh Vasudevan
    Posted 10/29/2004 at 8:19 am | Permalink

    #9 ATM is the short form for Asynchonous Transfer Mode.

    Currently ATM is used in places where we require high speed data transfer. The ATM is a technology of sending and recieving the packets and so it requires carriers such as SONET/SDH etc. The packet size of the ATM packet is fixed and is 53 bytes.


    1. As the packet size is fixed switching can be implemented in Hardware and so it is very fast.
    2. The packet size small and constant so the latency is too small so that it can support real time data transfer.
    3. The ATM supports Quality of Service (QOS).


    1. The packet size is too small and if u take the additional header that is attached then it will be huge. So the header size to the actual data send is less and so overhead is too much.
    2. End to end is not ATM and so we still require ATM adapters and other equipments.

    Ganesh Vasudevan

  3. Hala Widaa Salim
    Posted 6/29/2005 at 4:55 am | Permalink

    Repeaters, bridges, and routers are devices used to link individual LANs together to form larger internetworks. each one operates within a specific layer of the OSI model.
    Repeaters operate at the Physical Layer of the OSI model. They simply listen to all network traffic on one port and send it back out through one or more ports, extending smaller networks into a larger, single network. A repeater simply receives frames, regenerates them, and passes them along. It performs no processing of the frames or the data they contain.
    Relation to OSI Layer Functions

    Because repeaters operate at the Physical Layer, they do not need any addressing data from the frame. Repeaters do not even look at the frames they are forwarding, passing along even damaged frames. This can be especially problematic if one segment malfunctions and begins a broadcast storm. All those erroneous broadcasts are forwarded faithfully by the repeater!

    Bridges operate at the Data Link Layer. They use the Data Link Layer and its physical addressing to join several networks into a single network efficiently.
    Bridges join two or more network segments together, forming a larger individual network. They function similarly to a repeater, except a bridge looks to see whether data it receives is destined for the same segment or another connected segment. If the data is destined for a computer on the same segment, the bridge does not pass it along. If that data is going to a computer on another segment, the bridge sends it along.

    Bridges use a routing table to determine whether data is destined for the local network or not. On a bridge, the routing table contains MAC addresses. Each time the bridge receives data, it looks in its routing table to see whether or not the data is destined for a node on the local network. If it belongs to the local network, it does not forward the data. If it is not destined for the local network, it looks in the routing table to determine which physical network the destination address resides on, and sends the data out onto that network.

    Bridges can not join dissimilar networks. If you have an Ethernet network and a Token Ring network, you cannot use a bridge; you must use a router. However, a bridge can join networks that use the same frame type but different media, just like a repeater.
    Relation to OSI Layer Functions

    Bridges work with the MAC sublayer of the Data Link Layer. Remember that the Data Link Layer is concerned with communicating on the local network only. Bridges use information from the MAC sublayer to make decisions on whether a packet is destined for the same network or another network. The MAC address is used by bridges to determine first if the destination is local or not, then to choose which connected network it must go to.
    The Network Layer is concerned with network addressing for larger networks that consist of many physical networks, often with multiple paths between them. Routers operate at the Network Layer. They use the addressing information provided at the network level to join the many networks together to form an internetwork.

    Routers divide larger networks into logically designed networks. Routers may seem a lot like bridges, but they are much smarter. Bridges cannot evaluate possible paths to the destination to determine the best route. This can result in inefficient use of network resources. Bridges also cannot use redundant paths. While two bridges can connect two networks, they risk sending packets in an endless loop between the two networks. This behavior eventually saturates the network, rendering it unusable.

    The drawback to a router’s inherent intelligence is their speed. Because they process so much information, routers tend to be slower than bridges.
    Relation to OSI Layer Functions

    Routers operate at the Network Layer of the OSI model. The Network Layer provides addressing for internetworks, and routers use this addressing information to determine how to pass along packets of data. Because routers operate at the Network Layer, they can link different physical network topologies.

  4. Karan
    Posted 7/22/2005 at 3:25 am | Permalink

    Qustions on Tecnologies like SDH,DWDM,CDMA,PCM & equipments based on these technology will be helpfull for telelcom people.

  5. Jay
    Posted 5/23/2006 at 12:00 am | Permalink


    Difference between UDP and TCP. UDP is much faster, used for streaming video and audio files on the net. TCP is slower, because it contains the main factor UDP does not have, which is flow/error control.

    TCP is used by most users on the net because data transferred needs to be verified. Error correction allows data to be effectively received

    Posted 1/9/2007 at 6:28 am | Permalink

    Vlan is virtual lan it used to put some interface in one broadcast domain and some interfaces in another,it used for security purpose and group departments, based on the mac address the vlan is configured in the switch ports

  7. Raja
    Posted 1/20/2007 at 5:27 am | Permalink

    TCP/IP is a set of Protocol, which is use to communicate data(packet)between to host and destination PCs.
    TCP(Transmission control protocol)
    IP (Internet Protocol)
    Tcp/IP work on OSI Model. and Its port is 80.

  8. Raja
    Posted 1/20/2007 at 5:39 am | Permalink

    Repeater is a network device which is use to regenerate packet(data) out of 100m distance of server.

    Bridge: it is also a network device which is use to connect multiple Pc in the network. it is use in small or LANs Network. It work on Layer 2 or 3(some times)of OSI is connect pc through HUB.

    Router: Router is electronic machine and network device which is work as gateway.Router connect multiple Network or wireless network between two base on Layer 3 of OSI Model.

  9. pankaj
    Posted 1/24/2007 at 12:05 am | Permalink

    VLAN — Virtual Local Area Network

    ELAN — Emulated Local Area Network
    Difference between these two are as follows:-
    An ELAN is a type of VLAN over an ATM network. However, it is defined at the MAC layer while VLANs may be defined by a MAC layer or by a IP address, including by protocols.


  10. Ashish
    Posted 2/6/2007 at 2:37 am | Permalink

    state in which a message that has been broadcast across a network results in even more responses, and each response results in still more responses in a snowball effect. A severe broadcast storm can block all other network traffic, resulting in a network meltdown. Broadcast storms can usually be prevented by carefully configuring a network to block illegal broadcast messages.

  11. Ashish
    Posted 2/6/2007 at 2:41 am | Permalink

    Hot Standby Routing Protocol, a proprietary protocol from Cisco. HSRP is a routing protocol that provides backup to a router in the event of failure. Using HSRP, several routers are connected to the same segment of an Ethernet, FDDI or token-ring network and work together to present the appearance of a single virtual router on the LAN. The routers share the same IP and MAC addresses, therefore in the event of failure of one router, the hosts on the LAN are able to continue forwarding packets to a consistent IP and MAC address. The process of transferring the routing responsibilities from one device to another is transparent to the user.

    VRRP :
    Virtual Router Redundancy Protocol, an election protocol that dynamically assigns responsibility for one or more virtual router(s) to the VRRP router(s) on a LAN, allowing several routers on a multiaccess link to utilize the same virtual IP address. A VRRP router is configured to run the VRRP protocol in conjunction with one or more other routers attached to a LAN. In a VRRP setup, one router is elected as the master router with the other routers acting as backups in case of the failure of the master router.

  12. Ashish
    Posted 2/6/2007 at 2:47 am | Permalink

    Multilayer switching

    Multilayer switching is simply the combination of traditional Layer 2 switching with Layer 3 routing in a single product. Multilayer switching is new, and there is no industry standard yet on nomenclature. Vendors, analysts, and editors don’t agree about the specific meaning of terms such as multilayer switch, Layer 2 router, Layer 3 switch, IP switch, routing switch, switching router, and wirespeed router. The term multilayer switch seems to be the best and most widely used description of this class of product that performs both Layer 3 routing and Layer 2 switching functions.

    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. Following packets 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 learn the MAC/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.

  13. Babuji P
    Posted 7/11/2007 at 1:04 pm | Permalink

    Q#12 - TCP is a connection oriented protocol which works on ACK based communication. It provides error recovery & detection under Layer 4 of OSI model. Also, the TCP works in reliable network which offers secured communication and no loss of data.

    UDP is a User Datagram Protocol, used in a faster network. No ACK is required for the data sent to the network. Also, the application like TFTP prefers using UDP for its transport layer communication. Its a connectionless protocol.

  14. sayied anwer 007
    Posted 8/19/2008 at 6:00 am | Permalink

    Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984,

    Communication process has been divided into 7 layers.

  15. Posted 9/17/2008 at 10:40 am | Permalink

    2.Hub= anything that comes in one port is sent out to the others.
    Switch= it can “learn” where particular addresses are,forward the frame to a specific destination port

  16. sayiede anwer 007
    Posted 10/13/2008 at 10:23 am | Permalink

    TCP/IP, the Transmission Control Protocol / Internet Protocol, is one of the fundamental technologies that power the Internet. As computer networking continues to grow in popularity, a basic understanding of TCP/IP becomes crucial. Accomplished author and editor Pete Loshin provides this up-to-date text for computer professionals as well as those with merely a casual interest in the subject.
    Learning about TCP/IP and similar technical topics can seem intimidating at first. The author offers this sensible caution in his introduction: “If you are entirely new to networking, don’t expect to ‘get it’ in a single reading.” Clear, thorough explanations insure that all but the most advanced networkers will find this book a useful reference.

  17. Emad Zaki
    Posted 12/1/2008 at 2:38 pm | Permalink

    Each A-Net component in a system can have up to 500 feet (150 meters) of Category 5e cable (UTP, Unshielded Twisted Pair) between it and the next A-Net component (for example, from a Input Module to a Personal Mixer, or from one Personal Mixer to another in series). Cat-5e cable comes in two varieties, stranded and solid. Stranded wire is more flexible, but may not perform as well as solid wire at extreme distances. The number of components in the system is unlimited.

  18. jitendera sinha
    Posted 2/4/2009 at 2:10 am | Permalink

    osi-model-when the computer system has been devloped then each vendor use difreent layyer.the problem is that inthe past when ever we connect same vender copmuter on network they satrt comunicate where as we use diffrent vender machine they donot so to saolve the paroble a satnderd is devloped and thats is called osi madel

  19. jitendera sinha
    Posted 2/4/2009 at 2:32 am | Permalink adrees mask and broad cast
    router#config t
    router(config)#interface ethernet0/0
    router(config-if)#ip adreess
    router(config)#no shut
    router(config)#interface serial0
    router(config-if)#ip adreess
    router(config-if)no shut
    router(config-if)#clock rate 6400
    by this comand we can assign n/w adreess and ip mask.
    cisco says invalid to broad cast adreess but rule can be broken by applyong comand
    #ip-subnet zero

  20. jitendera sinha
    Posted 2/4/2009 at 2:37 am | Permalink

    switch is a single broad cast domain and due to that it consume more resources thus by creating v-lan(virtual lan)we braek the braod cast domain to increase the performance

  21. jitendera sinha
    Posted 2/4/2009 at 2:40 am | Permalink

    ELAN — Emulated Local Area Network
    Difference between these two are as follows:-
    An ELAN is a type of VLAN over an ATM network. However, it is defined at the MAC layer while VLANs may be defined by a MAC layer or by a IP address, including by protocols.

  22. jitendera sinha
    Posted 2/4/2009 at 2:59 am | Permalink

    atm-ansynchorans tranfer mode-it is a conection oriented data transfre mode and it is applyed when high sped of data transfer take place.a atm is used 53 bit in which 5 bit for hedare bita nd 48 bit for user bit
    u can read maore bat that compter n/w(by tennon bom)
    so atm wa going to solve the problem of world telecomunication and n/wrking by adding voice data telegaraph etc

  23. jitendera sinha
    Posted 2/4/2009 at 3:04 am | Permalink

    diffrence b/w udp and tcp,
    (1)tcp is a conection less protocal where as udp is conection orenetd protocal
    (2)data can tarvel in tcp by any path of the n/w where as in udp it follow a stritly one path,
    (3) in the tcp ack get after reciving the each farne on the distanyion so it support fane tagging
    whaer as in udp ack get when ever there is all farme of data ahs transfred

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