Tuesday, June 23, 2009

Networking Interview Questions

Network engineer interview questions
Describe OSPF in your own words.
OSPF areas, the purpose of having each of them
Types of OSPF LSA, the purpose of each LSA type
What exact LSA type you can see in different areas
How OSPF establishes neighboor relation, what the stages are
If OSPF router is stucked in each stage what the problem is and how to troubleshoot it
OSPF hierarchy in the single or multi areas. Cool OSPF behavior in broadcast and nonbroadcast
Draw the diagram of typical OSPF network and explain generally how it works, DR, BDR, election, ASBR, ABR, route redistribution and summarization
How it works and the purpose
Diff types (SSTP, MSTP, RSTP) Cisco - PVST/PVST+
root election
Diff. port stages and timing for convergence
Draw the typical diagram and explain how diff types of STP work
What ports are blocking or forwarding
How it works if there are topology changes
What are they
Diff types
Write an example if you want to allow and to deny…
Well-known port numbers (DNS - 53 and etc…)
What is that
What is the diff b/w L2 and L3 QoS
How it works
Draw the typical network diagram you have to deal with
explain how it works
What part of it you are responsible
firewall, what is that, how it works, how it is diff from ACLs
What problems with the network you had had and how you solved it.
What are the ways to troubleshoot the network, techniques, commands
network security, ways to achieve it
How a L2 switch works with broadcast, unicast, multicast, known/unknown traffic
port monitoring and mirroring
L3 switch, how it works
PIM sparse and dense modes

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Windows admin interview questions
Describe how the DHCP lease is obtained. It’s a four-step process consisting of (a) IP request, (b) IP offer, © IP selection and (d) acknowledgement.
I can’t seem to access the Internet, don’t have any access to the corporate network and on ipconfig my address is 169.254.*.*. What happened? The 169.254.*.* netmask is assigned to Windows machines running 98/2000/XP if the DHCP server is not available. The name for the technology is APIPA (Automatic Private Internet Protocol Addressing).
We’ve installed a new Windows-based DHCP server, however, the users do not seem to be getting DHCP leases off of it. The server must be authorized first with the Active Directory.
How can you force the client to give up the dhcp lease if you have access to the client PC? ipconfig /release
What authentication options do Windows 2000 Servers have for remote clients? PAP, SPAP, CHAP, MS-CHAP and EAP.
What are the networking protocol options for the Windows clients if for some reason you do not want to use TCP/IP? NWLink (Novell), NetBEUI, AppleTalk (Apple).
What is data link layer in the OSI reference model responsible for? Data link layer is located above the physical layer, but below the network layer. Taking raw data bits and packaging them into frames. The network layer will be responsible for addressing the frames, while the physical layer is reponsible for retrieving and sending raw data bits.
What is binding order? The order by which the network protocols are used for client-server communications. The most frequently used protocols should be at the top.
How do cryptography-based keys ensure the validity of data transferred across the network? Each IP packet is assigned a checksum, so if the checksums do not match on both receiving and transmitting ends, the data was modified or corrupted.
Should we deploy IPSEC-based security or certificate-based security? They are really two different technologies. IPSec secures the TCP/IP communication and protects the integrity of the packets. Certificate-based security ensures the validity of authenticated clients and servers.
What is LMHOSTS file? It’s a file stored on a host machine that is used to resolve NetBIOS to specific IP addresses.
What’s the difference between forward lookup and reverse lookup in DNS? Forward lookup is name-to-address, the reverse lookup is address-to-name.
How can you recover a file encrypted using EFS? Use the domain recovery agent.

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Network engineer/architect interview questions
Explain how traceroute, ping, and tcpdump work and what they are used for?
Describe a case where you have used these tools to troubleshoot.
What is the last major networking problem you troubleshot and solved on your own in the last year?
What LAN analyzer tools are you familiar with and describe how you use them to troubleshoot and on what media and network types.
Explain the contents of a routing table (default route, next hop, etc.)
What routing protocols have you configured?
Describe the commands to set up a route.
What routing problems have you troubleshot?
How do you display a routing table on a Cisco? On a host?
How do you use a routing table and for what?
What is a route flap?
What is a metric?
When do you use BGP, IGRP, OSPF, Static Routes?
What do you see as current networking security issues (e.g. NFS mounting, spoofing, one time passwords, etc.)?
Describe a routing filter and what it does.
Describe an access list and what it does.
What is a network management system?
Describe how SNMP works.
Describe the working environment you are currently in, e.g. frequent interruptions, frequent priority shifting, team or individual.
What do you use to write documentation? Editor? Mail reader?
What platform (s) do you currently work on at your desk?
How do you manage multiple concurrent high level projects?
Describe a recent short term stressful situation and how you managed it.
How do you manage a long term demanding stressful work environment?
Have you worked in an assignment based environment, e.g. work request/trouble ticket system, and if so, describe that environment.
Describe what network statistics or measurement tools you are familiar with and how you have used them.
Describe what a VPN is and how it works.
Describe how VoIP works.
Describe methods of QoS.
How does ToS bit work?

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CCNA/Cisco admin interview questions
You need to retrieve a file from the file server for your word processing application, which layer of the OSI model is responsible for this function?
Presentation layer
Application layer
Session layer
Transport layer
Datalink layer
You are working in a word processing program, which is run from the file server. Your data comes back to you in an unintelligible manner. Which layer of the OSI model would you investigate?
Application layer
Presentation layer
Session layer
Network layer
Datalink layer
The IEEE subdivided the datalink layer to provide for environments that need connectionless or connection-oriented services. What are the two layers called?
You are working with graphic translations. Which layer of the OSI model is responsible for code formatting and conversion and graphic standards.
Network layer
Session layer
Transport layer
Presentation layer
Which is the best definition of encapsulation?
Each layer of the OSI model uses encryption to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
Data always needs to be tunneled to its destination so encapsulation must be used.
Each layer of the OSI model uses compression to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
Each layer of the OSI model uses encapsulation to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
Routers can be configured using several sources. Select which of the following sources can be used.
Console Port
Virtual Terminals
TFTP Server
Floppy disk
Removable media
Which memory component on a Cisco router contains the dynamic system configuration?
Which combination of keys will allow you to view the previous commands that you typed at the router?
Which commands will display the active configuration parameters?
show running-config
write term
show version
display term
You are configuring a router, which prompt tells you that you are in the privileged EXEC mode?
What does the command “IP name-server accomplish?
It disables domain name lookup.
It sets the domain name lookup to be a local broadcast.
This is an illegal command.
The command is now defunct and has been replaced by “IP server-name ip any”
The following selections show the command prompt and the configuration of the IP network mask. Which two are correct?
Router(config-if)#netmask-format { bitcount | decimal | hexadecimal }
Router#term IP netmask-format { bitcount | decimal | hexadecimal }
Router(config-if)#IP netmask-format { bitcount | decimal | hexadecimal }
Router#ip netmask-format { bitcount | decimal | hexadecimal }
Which layer is responsible for flow control with sliding windows and reliability with sequence numbers and acknowledgments?
Network Interface
Which processes does TCP, but not UDP, use?
Source Port
Destination Port
Select which protocols use distance vector routing?

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Networking and Unix interview questions
What is UTP?

UTP — Unshielded twisted pair 10BASE-T is the preferred Ethernet medium of the 90s. It is based on a star topology and provides a number of advantages over coaxial media:

It uses inexpensive, readily available copper phone wire. UTP wire is much easier to install and debug than coax. UTP uses RG-45 connectors, which are cheap and reliable.

What is a router? What is a gateway?

Routers are machines that direct a packet through the maze of networks that stand between its source and destination. Normally a router is used for internal networks while a gateway acts a door for the packet to reach the ‘outside’ of the internal network

What is Semaphore? What is deadlock?

Semaphore is a synchronization tool to solve critical-section problem, can be used to control access to the critical section for a process or thread. The main disadvantage (same of mutual-exclusion) is require busy waiting. It will create problems in a multiprogramming system, where a single CPU is shared among many processes.

Busy waiting wastes CPU cycles.

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.

What is Virtual Memory?

Virtual memory is a technique that allows the execution of processes that may not be completely in memory. A separation of user logical memory from physical memory allows an extremely large virtual memory to be provided for programmers when only a smaller physical memory is available. It is commonly implemented by demand paging. A demand paging system is similar to a paging system with swapping. Processes reside on secondary memory (which is usually a disk). When we want to execute a process, we swap it into memory.

Explain the layered aspect of a UNIX system. What are the layers? What does it mean to say they are layers?

A UNIX system has essentially three main layers:

. The hardware

. The operating system kernel

. The user-level programs

The kernel hides the system’s hardware underneath an abstract, high-level programming interface. It is responsible for implementing many of the facilities that users and user-level programs take for granted.

The kernel assembles all of the following UNIX concepts from lower-level hardware features:

. Processes (time-sharing, protected address space)

. Signals and semaphores

. Virtual Memory (swapping, paging, and mapping)

. The filesystem (files, directories, namespace)

. Pipes and network connections (inter-process communication)