Sunday, June 8, 2008

Interview Question and Answers




Hello friend

Here one more try for you to get job in network field wish it will be helpful to you. on that answers I passed several hours for you only so you can get answer just directly....... wish ya luck


Interview question for network

1. What are 10Base2, 10Base5 and 10BaseT Ethernet LANs?


  Media Type Max. Segment Length Max. # Nodes/Segment
10Base5 Thick coaxial 500 meters 100
10Base2 RG58 (thin) coaxial 185 meters 30
10BaseT UTP 100 meters 1024
10BaseF (FOIRL) Fiber-optic 2,000 meters 1024k


2. What is the difference between an unspecified passive open and a fully specified passive open

An unspecified passive open has the server waiting for a connection request from a client. A fully specified passive open has the server waiting for a connection from a specific client.


3. Explain the function of Transmission Control Block

A TCB is a complex data structure that contains a considerable amount of information about each connection.


4. What is a Management Information Base (MIB)

Formal description of a set of network objects that can be managed using the Simple Network Management Protocol (SNMP).


4. What is anonymous FTP and why would you use it?

No authentication needed.


5. What is a pseudo tty?

A pseudo tty or false terminal enables external machines to connect through Telnet or rlogin. Without a pseudo tty, no connection can take place


6. What does the Mount protocol do?

The Mount protocol returns a file handle and the name of the file system in which a requested file resides. The message is sent to the client from the server after reception of a client's request.


7. What is External Data Representation?


8. What is the Network Time Protocol?

Synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP as its transport layer. It is designed particularly to resist the effects of variable latency.


9. What is a DNS resource record?

Entry in a name server's database.


10. What protocol is used by DNS name servers?

Tcp/udp port 53


11. What is the difference between interior and exterior neighbor gateways?

Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside world.


12. What is the HELLO protocol used for?

To establishing maintain and negotiation of neighbor ship


13. What are the advantages and disadvantages of the three types of routing tables?

The three types of routing tables are fixed, dynamic, and fixed central

The fixed table  must be manually modified every time there is a change

A dynamic table changes its information based on network traffic, reducing the amount of manual maintenance


A fixed central table lets a manager modify only one table, which is then read by other devices. The fixed central table reduces the need to update each machine's table, as with the fixed table.


14. What is source route?


15. What is RIP (Routing Information Protocol)?

It is a simple protocol used to exchange information between the routers.


16. What is SLIP (Serial Line Interface Protocol)?

It is a very simple protocol used for transmission of IP datagrams across a serial line.


17. What is Proxy ARP?

It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.


18. What is OSPF?

It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.

It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet’s topology to make accurate routing decisions


19. What is Kerberos?

It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.


20. What is a Multi-homed Host?

It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host


21. What is NVT (Network Virtual Terminal)?

It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session


22. What is Gateway-to-Gateway protocol?

It is a protocol formerly used to exchange routing information between Internet core routers.


23. What is BGP (Border Gateway Protocol)?

It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).


24. What is autonomous system?

It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.


25. What is EGP (Exterior Gateway Protocol)?

It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.

26. What is IGP (Interior Gateway Protocol)?

It is any routing protocol used within an autonomous system.


27. What is Mail Gateway?

It is a system that performs a protocol translation between different electronic mail delivery protocols.


28. What is wide-mouth frog?

Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.


29. What are Digrams and Trigrams?

The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.


30. What is silly window syndrome?

It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.


31. What is region?

When hierarchical routing is used, the routers are divided into what we call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.


32. What is multicast routing?

Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.


33. What is traffic shaping?

One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping


34. What is packet filter?

Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.

Example : IDS/IPS


35. What is virtual path/ virtual channel?

Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.


36. What is logical link control?

One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection


37. Why should you care about the OSI Reference Model?

It provides a framework for discussing network operations and design.


38. What is the difference between routable and non- routable protocols?

Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router

39. What is MAU?

In token Ring , hub is called Multistation Access Unit(MAU).


40. Explain 5-4-3 rule.

In a Ethernet network, between any two points on the network, there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.


41. What is the difference between TFTP and FTP application layer protocols?

The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.

The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information


42. What is the range of addresses in the classes of internet addresses?

Class A -

Class B -

Class C -

Class D -

Class E -

43. What is the minimum and maximum length of the header in the TCP segment and IP datagram?

The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.

44. What is difference between ARP and RARP?

ARP: map ip Network addresses to the hardware

RARP: Map MAC address to IP address


45. What is ICMP?

ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages. Example: PING, traceroute


46. What are the data units at different layers of the TCP / IP protocol suite?

The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.


47. What is Project 802?

It is a project started by IEEE to set standards that enable intercommunication between equipment from a variety of manufacturers

802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.


48. What is Bandwidth?

Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.


49. Difference between bit rate and baud rate?

bits transmitted during one second

baud rate refers to the number of signal units per second

bits.baud rate = bit rate / no-of-bits represented by each signal shift


50. What is MAC address?

Address for a device


51. What is attenuation?

The degeneration of a signal over distance


52. What is cladding?

A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.


53. What is RAID?

A method for providing fault tolerance by using multiple hard disk drives.


54. What is NETBIOS and NETBEUI?

NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.

NETBEUI is NetBIOS extended user interface. A transport protocol designed by Microsoft and IBM for the use on small subnets.


55. What is redirector?

Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer


56. What is Beaconing?

The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.


57. What is terminal emulation, in which layer it comes?

Telnet is also called as terminal emulation. It belongs to application layer.


58. What is frame relay, in which layer it comes?

Frame relay is a packet switching technology. It will operate in the data link layer.


59. What do you meant by “triple X” in Networks?

triple X this term use in packet assembler/disassembler.

X.3, X.28, X.29


60. What is SAP?

system applications products and databases


61. What is subnet?

A generic term for section of a large networks usually separated by a bridge or router.


62. What is Brouter?

Short for bridge router and pronounced BROW-ter, a device that functions as both a router and a bridge. A brouter understands how to route specific types of packets, such as TCP/IP packets. Any other packets it receives are simply forwarded to other network(s) connected to the device (this is the bridge function).


63. How Gateway is different from Routers?

A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats.


64. What are the different type of networking / internetworking devices?

1) Hub

2) Switch, Bridge

3) Router, layer-3 switch Gateways

4) Hosts, printers...etc.


65. What is mesh network?

A network in which there are multiple network links between computers to provide multiple paths for data to travel.


66. What is passive topology?

When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.

67. What are the important topologies for networks?

BUS topology:

In this each computer is directly connected to primary network cable in a single line.


Inexpensive, easy to install, simple to understand, easy to extend.

STAR topology:

In this all computers are connected using a central hub.


Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.

RING topology:

In this all computers are connected in loop.


All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.


68. What are major types of networks and explain?

Server-based network

Peer-to-peer network

Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.

Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration


69. What is Protocol Data Unit?

The data unit in the LLC level is called the protocol data unit (PDU)


70. What is difference between baseband and broadband transmission?

In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

71. What are the possible ways of data exchange?

(i) Simplex   (ii) Half-duplex   (iii) Full-duplex.


72. What are the types of Transmission media?

Guided Media:

These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.

Unguided Media:

This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.


73. What is point-to-point protocol?

A communications protocol used to connect computers to remote networking services including Internet service providers.


74. What are the two types of transmission technology available?

(i) Broadcast and (ii) point-to-point


75. Difference between the communication and transmission?

Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.Communication means the meaning full exchange of information between two communication media.

76. What is a different between switch and Hub?

Hub work at layer 1 where switch work at layer 2, hub is known as dumb device where switch are smart device


77. What are the Advantages and Disadvantages of DHCP?

Your IP address remains the same
so that you can run Internet services that require your IP address to remain the same in order for them to work properly (ie. Web Server, FTP Server).
If, for some reason, the RPI DHCP server is having difficulties handing out IP address, you will still be able to access the web, since your IP is predetermined.
You will only be able to effectively use your static IP address from your place of residence. You will be unable to use the web from other places on campus.
Configuring the network settings on your computer is more difficult for static IP than for DHCP, since DHCP is automatic and static IP is manual.


78. What is ERD(Emergency Repair Disk)?

ERD is a diskette that creates backups of important system files and settings and is used to help troubleshoot fix issues for Microsoft WINNT and WIN 2000.


79. What is the difference between POP3 and IMAP Mail Server?

POP3 is Email clients download your emails onto your computer. Using a specialized email program such as Outlook Express or Apple Mail has the advantage of giving you complete control over your email; every email you receive is placed on your computer and you can keep as many large file attachments as you want.

IMAP is protocol that is being used in webmail. Checking your email through our webmail is similar to using Hotmail or YAHOO! Mail. You never actually copy your messages to your computer; in fact, you are looking at them through your web browser on somebody else's computer. When you are not online, you are not able to see your email.


80. What is .ost file?

An OST file (.ost) is an offline folder file in Microsoft Outlook. Offline folders make it possible for the user to work offline and then to synchronize changes with the Exchange server the next time they connect. The ability to work offline is useful in environments with limited or unreliable connectivity.


81. What’s the difference between DNS and WINS 'Windows Internet Name Service'?

DNS maps TCP/IP host names to IP addresses and WINS maps NetBIOS host names to IP addresses


82. How can we create VPN to connect to branch office of the same office.what would be the preliminary requirement?

Best way to connect branch offices via VPN is to have VPN concentrator (Cisco, Nortel or a SOHO VPN enabled routers) installed and create LAN-to-LAN VPN tunnels between the offices


83. Why should we care about the OSI Reference Model? What is the main purpose for creating this osi model? Why it is a layered model?


84. What is layer-3 switch?

A switch who can handle routing also known as layer 3 switch


85. What is an email client? What is difference between email client and web mail?

Email clients download your emails onto your computer

Checking your email through our webmail is similar to using Hotmail or YAHOO! Mail


86. What is the vlan? How it is work?

Vlan= virtual LAN

It’s separated LAN in to logical sub LAN, it can help by limiting broadcast in LAN and improve network security


87. Name three network tools used to determine where network connectivity is lost between two sites A&B.





88. Which protocol is used for retrieving mails?



89. What is piggy backing?

Occurs when an authorized person allows (intentionally or unintentionally) others to pass through a secure door


90. What is the default subnet mask for an ipv6 address?

/32 OR

91. What is fragmentation of a packet?

Every packet-based network has an MTU (Maximum Transmission Unit) size. The MTU is the size of the largest packet which that network can transmit.

Packets larger than the allowable MTU must be divided into multiple smaller packets, or fragments, to enable them to traverse the network.


92. What is MTU of a link?

MTU (Maximum Transmission Unit), The MTU is the size of the largest packet which that network can transmit.

Ethernet: 1500, token ring 4096


93. Name any field of IP header that can prevent a packet to loop infinitely?

TTL field of ip header.


94. Under what situations a packet can go into infinite loop in a network?

if there are more than one way for reaching a particular router from the same source router


95. Describe a 3-way TCP/IP Handshake.

The active open is performed by sending a SYN to the server.
In response, the server replies with a SYN-ACK.
Finally the client sends an ACK back to the server.


96. What is a default gateway?

The exit-point from one network and entry-way into another network, often the router of the network.


97. How do you set a default route on an IOS Cisco router?

ip route destination address


98. What is the difference between a domain local group and a global group?

Domain local groups grant permissions to objects within the domain in which the reside. Global groups contain grant permissions tree or forest wide for any objects within the Active Directory.


99. What is LDAP used for?

LDAP is a set of protocol used for providing access to information directories.


100. What tool have you used to create and analyze packet captures?

Network Monitor in Win2K / Win2K3, Ethereal in Linux, OptiView Series II (by Fluke Networks).


101. How does HSRP work?

If one router goes down, a backup router takes over the routing functions of the primary one.


102. What is the significance of the IP address

The limited broadcast address is utilized when an IP node must perform a one-to-everyone delivery on the local network but the network ID is unknown.


Security interview questions for network admin

1. What is a firewall?

Firewalls are of two types:
-Hardware Firewall
-Software Firewall.
Firewall in simple manner is bascially the utility to provide the security over the network.


2. Describe, generally, how to manage a firewall


3. What is a Denial of Service attack?

Attempt to make a computer resource unavailable to its intended users


4. What is a “spoofed” packet?

Creation of IP packets with a forged (spoofed) source IP address


5. What is a SYN Flood?

The attacker (Mallet) sends several packets but does not send the "ACK" back to the server


6. What do you do if you are a victim of DoS?

Having a separate emergency block of IP addresses for critical servers with a separate route can be invaluable and change IP.


7. What is GPG/PGP?


8. What is SSH?

Secure shell


9. What is SSL? How do you create certificates?

Secure Sockets Layer

10. What would you do if you discovered a Windows system on your network has been compromised?

Update antivirus and system patch that is update of window


11. What is DNS Hijacking?

Hijacking the resolution of DNS names to IP addresses by the use of rogue DNS servers, particularly for the practice of phishing


12. What is a log host?

A designated device for receiving and storing a record of events from another device or program


13. What is IDS or IPS, and can you give me an example of one?

Intrusion-detection systems (IDS), intrusion-prevention systems (IPS)

FIREWALL, Microsoft ISA 2000/2003, Cisco IOS, checkpoint


14. Why are proxy servers useful?

To hide real IP of sever


15. What is web-caching?

By retrieving content saved from a previous request, made by the same client or even other clients


Cisco-specific network engineer questions


1. What is a wildcard mask, and how is it different from a netmask?

wildcard mask A 32-bit quantity used in conjunction with an IP address to determine which bits in an IP address should be ignored when comparing that address with another IP address. A wildcard mask is specified when setting up access lists.

The difference is wildcard mask is used in ACL, OSPF etc.,where has net mask is the mask use to define ip addressing


2. How do you configure a Cisco switch or router? What are the steps needed?


3. How would I place an interface into trunking mode?

Catalyst_4000(config)# int fa0/1

Catalyst_4000(config-if)# switchport mode trunk

Catalyst_4000(config-if)# exit


4. How do you shutdown an interface on a router or switch?

Router(config) # int s 0/0



5. What is VTP?

VLAN Trunking Protocol (VTP) is a Cisco Layer 2 messaging protocol that manages the addition, deletion, and renaming of VLANs


6. What is VMPS?

VLAN Membership Policy Server


7. What is SPAN/RSPAN?

Switched Port Analyzer (SPAN) and Remote SPAN (RSPAN)

SPAN/RSPAN allows you to duplicate traffic from a VLAN or a range of ports on a Catalyst switch to another port, where you can plug a network analyzer and tools like Netflow Simulator. RSPAN stands for Remote SPAN and allows to duplicate traffic from a switch and to send it to another switch in your network.

What is flow/netflow?

NetFlow is an open but proprietary network protocol developed by Cisco Systems to run on Cisco IOS-enabled equipment for collecting IP traffic information.


8. What is TACACS? Radius?

TACACS and Radius are AAA server

RADIUS uses UDP while TACACS+ uses TCP, Radius is open standard where TACACS is cisco proprietary


Network engineer interview questions




1. Describe OSPF in your own words.

o Ospf stand for open shortest path first

o OSPF use a link-state in the individual areas that make up the hierarchy. A computation based on Dijkstra's algorithm is used to calculate the shortest path tree inside

2. OSPF areas, the purpose of having each of them

o logical groupings of routers whose information may be summarized towards the rest of the network

o Backbone area

The backbone area (also known as area zero or area forms the core of an OSPF network. All other areas are connected to it, and inter-area routing happens via routers connected to the backbone area and to their own non-backbone areas. It is the logical and physical structure for the 'OSPF domain' and is attached to all nonzero areas in the OSPF domain. Note that in OSPF the term Autonomous System Border Router (ASBR) is historic, in the sense that many OSPF domains can coexist in the same Internet-visible autonomous system

The backone area is resposible for distributing routing information beetween non backbone areas. The backbone must be contiguous,but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links

o Stub area

· A stub area is an area which does not receive external routes except the default route, but does receive inter-area routes. This kind of area is useful when, for example, all Internet access goes through autonomous system border routers (ASBRs) [Note: ASBR is an ancient term as written in the "Backbone area" section!] in Area, but there are multiple paths to other nonzero areas in the OSPF domain.

· All routers in the area need to agree they are stub, so that they do not generate types of LSA not appropriate to a stub area. The Type 3 LSA for the default route is the only external that should enter the area, and none of its routers may generate externals.

· Stub areas do receive inter-area (IA) routes, advertised with Type 3 and Type 4 LSAs. If the stub area has more than one area border router (ABR), the information on other non-backbone areas allows the routers in the stub area to pick the best route to another area.

· Stub areas do not have the transit attribute and thus cannot be traversed by a virtual link.

· Stub areas receive default routes as type 3 network summary LSAs

Totally stubby area

· A totally stubby area (TSA), which is a nonstandard but useful extension by Cisco , is similar to a stub area, however this area does not allow summary routes in addition to the external routes, that is, inter-area (IA) routes are not summarized into totally stubby areas. The only way for traffic to get routed outside of the area is a default route which is the only Type-3 LSA advertised into the area. When there is only one route out of the area, fewer routing decisions have to be made by the route processor, which lowers system resource utilization.

· Occasionally, it is said that a TSA can have only one ABR. This is not true. If there are multiple ABRs, as might be required for high availability, routers interior to the TSA will send non-intra-area traffic to the ABR with the lowest intra-area metric (the "closest" ABR).

· An area can simultaneously be not-so-stubby and totally stubby. This is done when the practical place to put an ASBR, as, for example, with a newly acquired subsidiary, is on the edge of a totally stubby area. In such a case, the ASBR does send externals into the totally stubby area, and they are available to OSPF speakers within that area. In Cisco's implementation, the external routes can be summarized before injecting them into the totally stubby area. In general, the ASBR should not advertise default into the TSA-NSSA, although this can work with extremely careful design and operation, for the limited special cases in which such an advertisement makes sense.

· By declaring the totally stubby area as NSSA, no external routes from the backbone, except the default route, enter the area being discussed. The externals do reach area via the TSA-NSSA, but no routes other than the default route enter the TSA-NSSA. Routers in the TSA-NSSA send all traffic to the ABR, except to routes advertised by the ASBR.

Not-so-stubby area

· Not-so-stubby area (NSSA) is a type of stub area that can import autonomous system (AS) external routes and send them to the backbone, but cannot receive AS external routes from the backbone or other areas. The NSSA is a non-proprietary extension of the existing stub area feature that allows the injection of external routes in a limited fashion into the stub area.

· Cisco also implements a proprietary version of a NSSA called a NSSA totally stubby area. It takes on the attributes of a TSA, meaning that type 3 and type 4 summary routes are not flooded into this type of area. It is also possible to declare an area both totally stubby and not-so-stubby, which means that the area will receive only the default route from area, but can also contain an autonomous system border router (ASBR) that accepts external routing information and injects it into the local area, and from the local area into area

· Redistribution into an NSSA area creates special type of LSA known as TYPE 7, which can exist only in an NSSA area. An NSSA ASBR generates this LSA, and an NSSA ABR router translates it into type 5 LSA which gets propagated into the OSPF domain.

Transit Areas

Transit areas are used to pass traffic from one adjacent area to the backbone (or to another area if the backbone is more than two hops away from an area). The traffic does not originate in, nor is it destined for, the transit area.

3. Types of OSPF LSA, the purpose of each LSA type

1. Router LSA

2. Network LSA

3. Summary LSA (IP Network)

4. Summary LSA (Autonomous System Boundary Router)

5. Autonomous System External LSA

Type 1: Router link advertisements generated by each router for each area it belongs to. Flooded to a single area only.

Type 2: Network link advertisements generated by designated routers describing the set of routers attached to a particular network. Flooded to the area that contains the network.

Type 3/4: Summary link advertisements generated by ABRs

describing inter-area routes. Type 3 describes routes to networks and is used for summarization. Type 4 describes routes to the ASBR.

Type 5: Generated by the ASBR and describes links external

to the Autonomous System (AS). Flooded to all areas except stub areas.

Type 6: Group membership link entry generated by multicast OSPF routers.

Type 7: NSSA external routes generated by ASBR. Only flooded to the NSSA. The ABR converts LSA type 7 into LSA type 5 before flooding them into the backbone (area 0).


2. What exact LSA type you can see in different areas


3. How OSPF establishes neighbor relation, what the stages are

INIT, Ex-start, Ex-change, Loading, Full


4. If OSPF router is stacked in each stage what the problem is and how to troubleshoot it


5. OSPF hierarchy in the single or multi areas. Cool OSPF behavior in broadcast and no broadcast

Multi area

6. Draw the diagram of typical OSPF network and explain generally how it works, DR, BDR, election, ASBR, ABR, route redistribution and summarization



1. How it works and the purpose

o prevent switching loops in the LAN

o Spanning Tree works by first using an algorithm to find redundant links in the LAN and selecting the best paths. Its initial goal is to put all links in either Forwarding or Blocking.


2. Diff types (SSTP, MSTP, RSTP) Cisco - PVST/PVST+


3. root election


4. Diff. port stages and timing for convergence


5. Draw the typical diagram and explain how diff types of STP work


6. What ports are blocking or forwarding


7. How it works if there are topology changes




1. What are they?

Filter defined by administrator


2. Diff types of acl

Standard, extended, Named acl


3. Write an example if you want to allow and to deny…

Access-list 101 Permit tcp any eq 21

Access-list 101 deny tcp any eq 80


4. Well-known port numbers (DNS - 53 and etc…)



Pop3 110 TCP





QoS quality of service


1. What is QoS

In the field of computer networking and other packet-switched telecommunication networks, the traffic engineering term quality of service (QoS) refers to resource reservation control mechanisms rather than the achieved service quality

Guarantee a certain level of performance to a data flow


2. What is the diff b/w L2 and L3 QoS

o pure L2 QoS mechanisms, e.g., VP/VC based for ATM networks, DLCI based for FR networks, or VLAN tag for Ethernet

o intermediate L2/L3 QoS mechanisms, e.g., MPLS

o pure L3 QoS mechanisms, e.g., DiffServ

o L3 over L2 QoS mechanisms, e.g., DiffServ over ATM or FR

o L3 over intermediate L2/L3, e.g., DiffServ and MPLS seamless integration


How it works



1. VLANs

2. STP

3. How a L2 switch works with broadcast, unicast, multicast, known/unknown traffic


5. port monitoring and mirroring

6. L3 switch, how it works

7. PIM sparse and dense modes


Wireless engineer interview questions


A recruiter from Atlanta submitted this set of questions for interviewing at a wireless equipment company.

1. Describe your home WLAN setup.

(Pay attention to candidate’s confidence. Plus if the candidate built it himself. Plus if the network is secured additionally, regardless of the protocols used. Plus if the candidate fought poor coverage.)

2. Ad-hoc vs. infrastructure topology. Advantages and disadvantages.

Ad-hoc networks are easy to set up. By definition ad-hoc WLANs do not require access point, so they are cheaper. With infrastructure WLANs one can connect to wired LAN, enable wireless roaming for office workers, centralize WLAN management, and boost the range.

3. Your preferred brand for wireless cards and access points.

(An experienced candidate will be able to come up with strong argument to defend his preferences. He will point to the past projects as well.)

4. Range and throughput of 802.11a, 802.11b and 802.11g networks.

The official spec for 802.11a is 54 Mbps and 25-75 feet indoors.

The official spec for 802.11b is 11 Mbps and 100-150 feet indoors.

The official spec for 802.11g is 54 Mbps and 100-150 feet indoors.

An experienced candidate will provide his own observations.

5. How do you secure a wireless network?

Forbid SSID broadcasting,

Enable MAC-level access where appropriate,

Enable WEP, OR enable WPA

Enable 802.11i where available,

Enable firewalls,


6. What does Wi-Fi stand for?

Wireless Fidelity.

7. What is 802.11i?

It’s a new IEEE standard defining wireless network security.

8. What are the recommended channels if you’re setting up three WLANs and want minimum interference?

1, 6 and 11 for the US, 1, 7 and 13 for Europe and 1, 7 and 14 for Japan.

9. What are your preferred tools for war-driving?

Somewhere the names Kismet, *stumbler or others should come up. Ask the

candidate to describe his preferred configuration for war-driving.


Network engineer/architect interview questions


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



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 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.




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.


2. Describe a case where you have used these tools to troubleshoot.

Explain your experience


3. What is the last major networking problem you troubleshot and solved on your own in the last year?

Explain your practical life problem u had which you consider was important achievement


4. What LAN analyzer tools are you familiar with and describe how you use them to troubleshoot and on what media and network types.

MGRT, PGRT, WIRE SHARK (formally ethereal) for bandwidth monitoring and server monitoring


5. Explain the contents of a routing table (default route, next hop, etc.)


6. What routing protocols have you configured?

Most of time static route we use in our wireless network, but I m very familiar with OSPF


7. Describe the commands to set up a route.

Ip route (source network) (destination network) interface


8. What routing problems have you troubleshot?


9. How do you display a routing table on a Cisco? On a host?

Sh cdp neighbor detail

Sh ip route (local)


10. How do you use a routing table and for what?

For troubleshooting and searching for route to destination


11. What is a route flap?

o Route flapping occurs when a router alternately advertises a destination network via one route then another (or as unavailable, and then available again) in quick sequence.

o Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors, unreliable connections, etc.) within the network which cause certain reachability information to be repeatedly advertised and withdrawn. The most common causes of route flapping are configuration errors and intermittent errors in communications links. Route flapping often forces a router to recalculate a new or preferred route to a particular network, while traffic destined for that network is in transit through the router.


12. What is a metric?

Metric is a measure used in calculating the next host to route a packet to.


13. When do you use BGP, IGRP, OSPF, and Static Routes?

· BGP - Boarder Gateway protocol

Use for communicating different Ad number, and use in very large network like internet for route maintaining

· IGRP - Interior Gateway Routing Protocol

IGRP is dynamic routing protocol and use for routing in large flat network. (All Cisco Device only)

· OSPF - Open Shortest Path First

OSPF is dynamic routing protocol and use for routing in large hierarchical network. And it is open standard.

· Static Route use for maintaining manual routes and point-to-point communication


14. What do you see as current networking security issues (e.g. NFS mounting, spoofing, one time passwords, etc.)?

One time password, wireless security


15. Describe a routing filter and what it does.


16. Describe an access list and what it does.


17. What is a network management system?

Network Management System - A comprehensive system of equipment used in monitoring, controlling, and managing a data communications network. Usually consists of testing devices, CRT displays and printers, patch panels, and circuitry for diagnostics and reconfiguration of channels, generally housed together in an operator console unit.


18. Describe how SNMP works.

The simple network management protocol (SNMP) use for monitoring of network-attached devices for any conditions that warrant administrative attention. It is use to manage IP network devices such as servers, routers, switches etc. Administrator can find or manage network performance, solve problem or even optimize it further. It works at TCP/IP Application layer 5 (L5).


19. Describe the working environment you are currently in, e.g. frequent interruptions, frequent priority shifting, team or individual.


20. What do you use to write documentation? Editor? Mail reader?


21. What platform (s) do you currently work on at your desk?

Window XP


22. How do you manage multiple concurrent high level projects?

Time and team management


23. Describe a recent short term stressful situation and how you managed it.

When I was working for base station and same time shifting of NOC


24. How do you manage a long term demanding stressful work environment?

By time management, I always keep my work at work place and home at home I m able to manage both place


25. Have you worked in an assignment based environment, e.g. work request/trouble ticket system, and if so, describe that environment.


26. Describe what network statistics or measurement tools you are familiar with and how you have used them.



27. Describe what a VPN is and how it works.

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


28. Describe how VoIP works.

Voice over IP, or VoIP, means that your voice is carried over the IP network, otherwise known as the Internet. Your voice, which is an analogue signal, is converted to digital data, which is then disassembled and transmitted through the Internet only to be re-converted back to an analogue signal on the other end.

Protocols used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols.


29. Describe methods of QoS.

clip_image002First-in, first-out (FIFO) queuing

clip_image002[1]Priority queuing (PQ)

clip_image002[2]Custom queuing (CQ)

clip_image002[3]Flow-based weighted fair queuing (WFQ)

clip_image002[4]Class-based weighted fair queuing (CBWFQ)


30. How does ToS bit work?

The Type of Service (ToS) field in the IP header constitutes the bits used for IP precedence. These bits are used to provide a priority from 0 to 7


RF and radio engineering interview questions


1. What’s a PCB?

Printed Circuit Board.


2. Name some band definitions.

L-Band - 1-2 GHz, S-Band - 2-4 GHz, C-Band - 4-8 GHz, X-Band - 8-12 GHz, Ku-Band - 12-18 GHz.


3. What’s the definition of gain?

The signal going into the device is smaller than the signal going out.


4. What’s a definition of an amplifier?

It’s a device that exhibits gain.


5. Insertion loss?

The signal going in is greater than the signal that’s coming out.


6. Thermal impedance?

A measure of how hot the device gets with varying electrical input.


7. What’s the relation between dB and change of signal?

+3 dB is 2 times bigger, +10 dB is 10 times bigger.


8. What’s an octave?

The bandwidth characterized by higher band being twice as much as lower band (100-200 MHz).


9. What’s a decade?

A bandwidth, where the higher band is 10x the lower band (100 MHz - 1 GHz).


10. Skin effect?

The signal is reported on the surface of the object, but not inside, e.g. a solid brick wall.


11. VSWR?

Voltage Standing Wave Ratio. The numeric representation of the device leak, written like X: 1 where X is greater when the leak is greater and 1:1 is the absolute no-leakage VSWR.


12. Describe an impedance matching circuit.

A circuit capable of changing the impedance with different values for incoming and outgoing impedance.


13. Describe circular polarization.

The signal travels both vertically and horizontally.


14. What’s the job of the amplifier?

To increase the incoming signal.


15. What is noise figure?

The level of noise that a low-noise amplifier (LNA) is capable of discriminating.


16. What’s a transfer curve?

It is a graph of the output power versus the input power of an amplifier.


17. What’s the 911 point?

The point where the input power results in flames on the other end.


18. What’s saturation point?

The point where the amplifier loses its linearity of the transfer curve.


19. What does balanced amplifier consist of?

Two amplifiers stuck together.


20. What is the filters function?

To filter out all the unwanted radio signals.


21. What filter types are there?

Low-pass (all frequencies below are allowed to pass in), high-pass, bandpass (all frequencies of a given bandwidth are allowed) and band-reject.


22. What are saw filters used for?

Very low frequency filtering.


23. What are mixers used for?

To change the frequency of the signal.


24. What’s a superheterodyne receiver?

It’s a receiver that uses two mixers in a row.


25. Describe VCO.

Voltage-controlled oscillators change the frequency of the produced sine wave depending on the voltage they receive.


26. Who is responsible for PLLs?

Phase-locked loops are done by synthesizer that samples the sine wave and if it’s not good enough, changes it.

1 comment:

Cisco firewall said...

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