network engineer interview questions

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OSPF 1 Describe OSPF in your own words 2 OSPF areas, the purpose of having each of them 3 Types of OSPF LSA, the purpose of each LSA type 4 What exact LSA type you can see in different areas 5 How OSPF establishes neighboor relation, what the stages are 6 If OSPF router is stucked in each stage what the problem is and how to troubleshoot it 7 OSPF hierarchy in the single or multi areas Cool OSPF behavior in broadcast and nonbroadcast 8 Draw the diagram of typical OSPF network and explain generally how it works, DR, BDR, election, ASBR, ABR, route redistribution and summarization STP 1 How it works and the purpose 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 ACLs 1 What are they 2 Diff types 3 Write an example if you want to allow and to deny… 4 Well-known port numbers (DNS - 53 and etc…) QOS 1 What is that 2 What is the diff b/w L2 and L3 QoS 3 How it works Network: 1 Draw the typical network diagram you have to deal with 2 explain how it works

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Network Engineer Interview

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Page 1: Network Engineer Interview Questions

OSPF 1 Describe OSPF in your own words 2 OSPF areas, the purpose of having each of them 3 Types of OSPF LSA, the purpose of each LSA type 4 What exact LSA type you can see in different areas 5 How OSPF establishes neighboor relation, what the stages are 6 If OSPF router is stucked in each stage what the problem is and how to

troubleshoot it 7 OSPF hierarchy in the single or multi areas Cool OSPF behavior in broadcast and

nonbroadcast 8 Draw the diagram of typical OSPF network and explain generally how it works,

DR, BDR, election, ASBR, ABR, route redistribution and summarization

STP 1 How it works and the purpose 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

ACLs 1 What are they 2 Diff types 3 Write an example if you want to allow and to deny… 4 Well-known port numbers (DNS - 53 and etc…)

QOS 1 What is that 2 What is the diff b/w L2 and L3 QoS 3 How it works

Network: 1 Draw the typical network diagram you have to deal with 2 explain how it works 3 What part of it you are responsible 4 firewall, what is that, how it works, how it is diff from ACLs 5 What problems with the network you had had and how you solved it 6 What are the ways to troubleshoot the network, techniques, commands 7 network security, ways to achieve it

Switching: 1 VLANs 2 STP

Page 2: Network Engineer Interview Questions

3 How a L2 switch works with broadcast, unicast, multicast, known/unknown traffic 4 VRRP, GLBP 5 port monitoring and mirroring 6 L3 switch, how it works 6 PIM sparse and dense modes

Networking Basics1 Can you define protocol?2 Can you explain the concept of OSI layer?3 Can you explain the different layers in OSI model?4 Can you explain Application layer in OSI model?5 Can you explain Presentation layer in OSI model?6 Is it compulsory that compression, encryption and translation7 functions will be used during communication?8 Can you explain Session layer in OSI model?9 What's the concept of Simplex, Half Duplex and Full Duplex dialogs?10 What are the different types of dialogs in Session layer?11 Can you explain Transport layer in OSI model?12 Can you explain the concept of Congestion?13 Can you explain Network Layer?14 Can you explain Data link Layer?15 Can you explain the Physical layer?16 Can you explain what an IP address is?17 How to convert Decimal to Binary?18 How many IP addresses can come in IPV4?19 Can you explain the concept of Unicast IP address?20 Can you explain the concept of IP multicasting or multicast IPaddress?21 How many different types of subnet classful networks are present?22 What are the IP address ranges for public and private IP address?23 Why do we need class and how many different types of class exists?24 How are the IP addresses distributed between different classes?25 Can you explain what is classful IP addressing?26 Can you explain the concept of subnetting?27 What are the advantages of using subneting?28 If the host has the subnet ID why do we need a subnet mask?29 How is network address calculated from the subnet?30 What is the advantage of using classless addressing over classfuladdressing scheme?31 Can you explain the concept of CIDR?32 Twist :- Can you explain superneting ?33 Can you explain concept of custom subneting?34 What is the implication of increasing and decreasing subnet Bits?35 Why do we need to subtract two from number of hosts?36 Can you explain the concept of VLSM?

Page 3: Network Engineer Interview Questions

Can you explain IP protocol?

Routers1 Can you explain the concept of DPU, Segments, Datagram, Frame and packet?2 What is IP datagram fragmentation and MTU?3 Can you explain in detail with example how data fragmentation works?4 Larger the IP datagram less the overhead, is it true or false?5 What is the minimum size of MTU bytes?6 Can you explain how optimal MTU size is calculated?7 How does the IP message finally reassemble?8 Can you explain the concept of Repeaters, Hubs, Bridges, Switches and Routers?9 On what layers do router , switched , bridges and hubs operate ?10 Can you explain the concept of Layer 3 switches?11 what are CSU, DSU and TSU?12 what are the basic components of the router?13 Can you explain the WAN and LAN Interface in Routers?14 What are DB-15, DB-60 and RJ-45 in CISCO routers?15 Can you explain the concept of TTL?16 What is the concept of ICMP packets?17 Which operating system does CISCO have?18 Can you explain the concept of NAT?19 How is NAT implemented?20 Can you explain how actually NAT works?21 why does collision occur in HUBS and repeaters?22 Can you explain the concept of Collision domain?23 What is the concept of routing tables?24 what is the use of route print?25 Can you explain how in detail how routing table looks like?26 How can you see route tables on the router?27 Can you explain the concept of static and dynamic routing?28 When to use Static routes and dynamic routes?29 How do you configure static routes on a router?30 Can you explain static default routes?31 What is the advantage of using Static default routes?32 Why do workstations have route tables?33 What is the concept of gateway of last resort?34 Can you explain the concept of routing protocol?35 What activities does routing protocol perform?36 What metrics are used by routing protocols to determine the best path?37 Can you explain what is interior and exterior routing protocols?38 Can you explain the concept of intradomain and interdomain routing protocols?39 Can you explain the concept of internetwork and intranetwork routing

Page 4: Network Engineer Interview Questions

protocols?40 Which method does routing protocol use to determine shortest path?41 What is distance vector routing protocol?42 How do router share information in Distance Vector routing?43 What is the main issue with routing by rumor?44 Can you explain the count-to-infinity problem in distance vector?45 How is metric or the cost calculated for Distance Vector routing protocol?46 What is the main issue with hop count metric issue?47 Can you explain how Link-State routing protocols work?48 Can you explain the concept of broad cast and multi-cast?49 Can you tell which protocols lie in Distance vector and which in Link- State?50 What's the difference between distance vector and link-state protocol?51 Can you explain difference between Single path and Multipath?52 Can you explain route summarization?53 How are the series of IP combined in to one route path in route summarization?54 Can you explain RIP protocol?55 How is route table populated by RIP protocol?56 Can you explain convergence in networks?57 Can you explain RIP timers in detail?58 Can you explain routing loop issue in RIP protocol?59 How do we avoid routing loop issue in RIP?60 In RIP why do we have HOP count of 15?61 How do we disable auto-summarization in RIP?62 Can you explain IGRP?63 How does IGRP work?64 How many timers does IGRP have?65 How does IGRP calculate metric?66 Can multiple instance of IGRP run on one physical router?67 How is load balancing done in IGRP?68 What's the command to configure IGRP?69 Can you explain EIGRP?70 What does neighbor terminology mean in EIGRP?71 What are different types of packets in EIGRP?72 How does EIGRP protocol update route information to its neighbors?73 What is the concept of successor in EIGRP?74 What is DUAL in EIGRP?75 Can you explain reported distance (RD), feasibility distance (FD) and76 Feasibility condition (FC)?77 Can you explain the concept of successor and feasible successor?78 Can you explain passive and active route states?79 What is SIA or stuck in active?80 How do packets and timers in EIGRP work?

Page 5: Network Engineer Interview Questions

81 What are the different tables used in EIGRP?82 Can you explain EIGRP metrics?83 Can you explain how EIGRP finds its successor and feasible successor?84 Can you explain Active and Passive route?85 Can you explain OSPF?86 How does OSPF populate route table?87 What are the different tables in OSPF?88 Can you explain different areas in OSPF?89 Can you explain different router types in OSPF?90 Can you explain Designated Router and Backup designated router?91 Can you explain different router states in OSPF?92 Can you explain different OSPF packet types?93 What are the different types of OSPF timers?94 How SPF algorithm does the route determination?95 Can you explain autonomous system?96 What are different types of dynamic protocols?97 Can you explain autonomous numbers in EGP?98 What is BGP?99 What is the concept of BGP speakers and Peers?100 What is EBGP and IBGP?101 What is RIB?102 Can you explain the concept of BGP confederations?103 What are BGP path attributes?104 What is the concept of NLRI?105 How are routing neighbors discovered in BGP?106 Can you explain how BGP does the decision process?107 What is the concept of redistribution?108 Can you explain the concept of one way redistribution and mutual109 distribution?110 How does metric translation takes place in redistributing routes?

Firewall1 Can you define what a FIREWALL is?2 What are the different types of firewalls?3 Can you explain packet filtering firewall?4 Can you explain circuit level gateway?5 Can you explain stateful inspection?6 What is Application Gateway?7 Is NAT a firewall?8 Are personal firewall actually firewalls?9 Can you explain the concept of demilitarized zone?10 What is the meaning of bastion host?11 What are the different types of firewall architectures?12 Can you explain dual home architecture?13 Can you explain screened host architecture?14 Can you explain screened subnet architecture?

Page 6: Network Engineer Interview Questions

15 What is the use of perimeter area?16 What is IP spoofing and how can it be prevented?

VPN1 Can you explain the difference between trusted and untrusted networks?2 Can you define in short what VPN is?3 What are the different types of VPN?4 What requirements should a VPN fulfill?5 How many ways are there to implement VPN architecture?6 What are the different ways authentication mechanism in VPN?7 Can you explain the basic of encryption in VPN?8 what's the difference between Symmetric and Asymmetric cryptosystem?9 what are the different symmetric algorithms?10 What are the disadvantages of symmetric algorithms?11 what are the different asymmetric algorithms?12 Can you explain different components in PKI?13 What is a digital certificate?14 Can you explain tunneling?15 what is the concept of HA and FA in VPN tunneling?16 Can you explain VPN tunneled packet in detail?17 Can you explain voluntary and compulsory tunnels?18 Can you explain static and dynamic tunnels?19 Can you explain encapsulating, carrier and passenger protocol?20 On which layer does L2F, PPTP and L2TP operate?21 Can you explain PPP protocol?22 Can you explain PPP link process step by step?23 Can you explain PPP packet format?24 How does PPP use LCP for link control?25 Can you explain PPTP (Point-to-Point Tunneling Protocol)?26 What is GRE in PPTP?27 How does PPTP encapsulate data?28 Can you explain CHAP?29 Can you explain PAP?30 what does PPTP use for encryption and authentication?31 What is a L2F protocol?32 Can you explain the broader steps of how L2F establishes the tunnel?33 Can you explain how L2F data tunneling process works?34 How do we do encryption and authentication in L2F?35 Can you explain L2TP?36 Can you define LAC and LNS?37 How does L2TP process?38 How do we do encryption and authentication in L2TP?39 Can you explain what IPSec is?40 Can you give an overview of various components in IPSec?41 In IPSec what is SAD, SPD and SA's?

Page 7: Network Engineer Interview Questions

42 Can you explain in a generic manner the packet of IPSec?43 Can you describe the Authentication Header (AH) Protocol?44 what is ESP (Encapsulating Security Payload)?45 What is Transport and Tunnel mode?46 Can you explain IKE (Internet Key Exchange)?47 Can you explain IKE phases?48 Can you explain IKE modes?49 Can you explain transport and tunnel mode in detail with datagram packets?50 What is DTE and DCE in terms of Router Configuration and what is the purpose of DTE and DCE differentiate?

Networking

1 Explain how traceroute, ping, and tcpdump work and what they are used for? 2 Describe a case where you have used these tools to troubleshoot 3 What is the last major networking problem you troubleshot and solved on your own in the last year? 4 What LAN analyzer tools are you familiar with and describe how you use them to troubleshoot and on what media and network types 5 Explain the contents of a routing table (default route, next hop, etc) 6 What routing protocols have you configured? 7 Describe the commands to set up a route 8 What routing problems have you troubleshot? 9 How do you display a routing table on a Cisco? On a host? 10 How do you use a routing table and for what? 11 What is a route flap? 12 What is a metric? 13 When do you use BGP, IGRP, OSPF, Static Routes? 14 What do you see as current networking security issues (eg NFS mounting, spoofing, one time passwords, etc)? 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? 18 Describe how SNMP works 19 Describe the working environment you are currently in, eg 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? 22 Describe a recent short term stressful situation and how you managed it 23 How do you manage a long term demanding stressful work environment? 24 Have you worked in an assignment based environment, eg work request/trouble ticket system, and if so, describe that environment 25 Describe what network statistics or measurement tools you are familiar with and how you have used them

Page 8: Network Engineer Interview Questions

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 (eg 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 20 Describe the OSI model

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