Networking Interview Question

 OSPF

Q. How many types of area exist in OSPF and types of LSA are allowed ?
Q. Different OSPF packet types ?
Q. If you see how as DRother under show ip ospf neigbor . Whats wrong with the output ?
Q. How OSPF acts as distance vector and link state protocol and when ?. Explain how.
Q. How OSPF avoid loops in the network. Explain how.
Q. Why do we need  concept of area and why backbone area is required ?
Q. How OSPF support MPLS TE tunnel ? Explain.
Q. How many routers are recommended in OSPF area and what the limit of routers in OSPF domain?
Q. What is iSPF, BFD, Graceful restarts and BFD in OSPF.
Q. What is the SPF algorithm and how does it work .
Q. What trigger the OSPF SPF in the network and how to avoid and reduce the SPF calculations ?
Q. When OSPF routers use multicast address and unicast address ?
Q. OSPF is layer 2 or layer 3 protocol ?
Q. Best practices to implement OSPF in Data center/Enterprise/WAN ?
Q. What is an OSPF area?
Q. What are the differences between LSA structures of area ?
Q. Troubleshoot the exhange/exstart state with OSPF ?
Q. Can a non-backbone area be connected to another non-backbone area and not to backbone?
Q. We want to redistribute routes into a non-backbone Type-5. What type of area would that be?
Q. What need to be similar in the hello packet in-order to form OSPF adjacency?
Q. In what case OSPF adjacency get stuck in Attempt state??
Q. In what case OSPF adjacency get stuck in Extract state??
Q. Does OSPF form adjacency with the neighbor that are on the different subnet??
Q. OSPF load balancing scenario? There is network 172.16.1.0/24 and there are two path to reach this network. R1 would choose which path??
1. R1--100Mbps---R2----OC3(155Mbps)----R4----192.168.1.0/24
2. R1--100Mbps---R3----100Mbps---------R4----192.1681.0/24
Q. How OSPF Forwarding works  and why do we need ?
Q. Options to connect non backbone area to backbone area over another non-backbone area ?
Q. When link-state-request and link-state-update in use on OSPF ?
Q. In scenario of 4 ABR in the network, which ABR will advertise the network ?
Q. With which network type will OSPF establish router adjacencies but not perform the DR/BDR election process?
Q. What is the administrative distance of OSPF?
Q. How OSPF virtual link and Sham link work and where it used in the network ?
Q. What are the different types of router link types ?
Q. What are the different types of bits used in OSPF packet types including V B E ?

EIGRP 

Q.  EIGRP is distance vector or link state ?
Q.  How EIGRP avoid loops in the network ?
Q.  What is feasible condition in EIGRP  ?
Q . What is SIA in EIGRP and how to solve it ?
Q. How reliable mechanism work in EIGRP ?
Q. Where EIGRP use multicast and unicast packet for the neighbor relationship. ?
Q. Best practices to implement in enterprise and Data center.

ISIS

Q. How ISIS scales better then OSPF ?

Q. What is ATT bit and route -leaking and why it is required ?

Q. What is level 1 and level2 in ISIS ?

Q. What is pseudonode/DIS and how it communicates ?

Q. ISIS is distance vector or link state protocol ?

Q. How ISIS prevent loop in the network ?

Q. What is the difference between narrow and wide metrics ?

Q. Describe the ISIS route selection process ?

BGP

Q. What is the difference between EBGP and IBGP neighborship ?
Q. What transport protocol does BGP use?
Q. What is an AS_PATH and what is it used for?
Q. What is a Local Preference?
Q. How can you use BGP for load balancing traffic outbound?
Q. How can you use BGP for load balancing traffic inbound? 
Q What is the final tiebreaker in BGP path selection criteria?
Q What are the three well known mandatory attributes? What does a well known mandatory attribute imply?
Q What is BGP conditional-routing ?? 
Q Explain the BGP route selection process?
Q. How BGP multipath works?
Q. Why IBGP full mesh required ? 
Q. BGP is link state or distance vector protocol or path vector protocol ? Explain why ?
Q. When do we use BGP in network ?
Q. When we can  use BGP instead of any IGP ? Is it option ?
Q. Types of BGP routing table?
Q. Define various BGP path attributes and different types.
Q. Why weight is different path attributes ?
Q. What is confederation?
Q. What is route reflector and why it is required?
Q. When does BGP use 0.0.0.0 router id?
Q. Does route reflector come in actual path during traffic forwarding?
Q. What is Site of origin  SOO?
Q. What is the cost of external and internal BGP routes ?
Q. Can we use local preference outside the autonomous system?
Q. Does it require that BGP router-id should reachable in cloud?
Q. What is recursive lookup in BGP and how it works?
Q. If a static route is advertised in BGP without using update source what will be the next hop address in update?
Q. Define various types of communities and why they are used?
Q. Troubleshoot idle state in BGP ?
Q. How many links can be assigned for load balancing or sharing?
Q. In eBGP I am establishing my neighborship with loopback address but it’s not coming up. Please specify different reasons.
Q. Can we redistribute BGP in IGP? Please explain your answers.
Q. What is cluster id?
Q. Receiving updates from eBGP peer, will the next hop change or not?
Q. Receiving updates from iBGP peer, will the next hop change or not?
Q. How loop prevention mechanism works in BGP.
Q. What will happen if route reflector is not getting proper updates?
Q. What will happen if route reflectors does not synchronize?
Q. What is the advantage of using BGP AS Prepend?
Q. What is BGP PIC?
Q. Use BGP as Link Protection in case of Dual PoP?
Q. How to achieve Inter-AS Communication MP-eBGP?
Q. What can happen if Route Reflector(RR) is not getting proper route updates?
Q. What is route reflector synchronization?
Q. What are the common best practices to connect with ISP through BGP ?
Q. What are the latest trends for the load balancing mechanism with ISP ?
Q What are the best practices to configure BGP ?
Q. How to use BGP as PE-CE backdoor link?
Q. What address can be used for the BGP neiborship ? Interface or Loopback ?
Q. What is remotely triggered  black holing and how to triggered ?
Q. What is uRPF  ?
Q. What is Hierarchical FIB - BGP-PIC?
Q. BGP Graceful Restart, NSR and NSF ?
Q. BGP Redistribution Vs MPLS, which one you will select? 
Q. How to trigger black hole remotely ? 
Q. What is the difference/similarities between Route reflector and Route server ?

MPLS

Q. Describe the  high level MPLS packet forwarding from end to end ?
Q. Why CEF is required for MPLS and how LFIB is built in MPLS ?
Q. What is RD and RT ?
Q. How MPLS VPN works ?
Q. What is the different between LDP and TDP , RSVP ?
Q. What are the benefits/disadvantages of LDP and RSVP ?
Q. What are the different label distribution protocol ?
Q What are the VPLS / VPWS and EoMPLS, L2TPv3.
Q. What are the routing protocols used between MPLS PE and Customer Edge ?
Q. What is MPLS Fast reroute /Link protection/Node protection ?
Q. What are the benefits of using LDP over RSVP ?

MULTICAST

Q. What are the differences between PIM SM and PIM DM?

Q. What are the different types of Multicast RP ?

Q. How source and shared multicast tree is built between source and Receiver ?

Q. How PIM Bidirectional is different than PIM SM ? 
Q  Whats are the difference between IGMPv1,v2 and v3 ?
Q. What is IGMP snooping and IGMP ? Are they different or similar ?
Q. What are the different types of flags in PIM ?
Q. What are the different types of PIM packet types used in multicast ?
Q. What are the differences between PIM BSR and Auto RP.

 Layer 2 protocol

Q. What are the similarities and differences between STP/RSTP/MSTP ?

Q. How RSTP is converge faster than STP ?

Q. How TCN works in STP and RSTP and MSTP ?
Q. How to troubleshoot the STP loop ?
Q. What are the portfast, uplink fast and backbone fast ? 
Q. Best practices to implement STP/RSTP/MSTP ? 
Q.What is flexlinks, UDLD, DHCP snooping , ARP inspection.

TCP/IP

Q.  What is TCP Reno, Tahoe and Cubic,BIC,Woodside algorithm and difference among all ?
Q.  What  is the default TCP congestion algorithm used on Linux and different Windows laptop.
Q.  What is Micro burst ?
Q . What is scaling window system and how does it work?
Q.  What is Fast retransmit , Fast recovery, Duplicate Acknowledgement , Selective Acknowledgement ?
Q. How TCP handshake and TCP connection termination works ?
Q. Difference  between TCP/UDP ?
Q. What is congestion Window, slow start ,  retransmission,  TCP piggybacking , TCP Nagal Algorithm ?
Q. What is VLSM? What routing protocols support VLSM?
Q. Describe the TCP three-way handshake with flags set for each
Q. What is the directed broadcast address of the subnet 192.168.99.20/30?
Q. How many class C networks are included within a network with a subnet mask of
20 bits (/20)?
Q. Describe how ARP resolution works and does it has Layer 3 header ?
Q. Whats are the RARP, Proxy ARP and Gratuitous ARP  ?
Q. How does a switch know where to send a packet right after it powers on?
Q. What is TTL and what is it used for?
Q. How many usable host addresses are in a /30? Where would you use this mask length? Can /31 be used?
Q. Which of the following protocols operate on top of TCP ?
Q. What is a difference between Administrative Distance (AD) and a route metric or cost?
Q. Name some networking management/monitoring tools you are aware of.
Q. True or False:SNMP (Simple Network Monitoring Protocol), Syslog and Radius are protocols that can be used for monitoring systems?
Q. How many bits are used to encode TCP or UDP port number?
Q. What is the range of well known ports for TCP and UDP?
Q.What is MSS??
Q.What is default MSS size??
Q.What is TCP Half Close??
Q.What is Delayed Acknowledgement in TCP??
Q.What would be the result when running multiple traceroute from a single linux machine to same destination??
Q.What would be the result when running multiple traceroute from a single windows machine to same destination???
Q. Explain packet flow when you do ping in the following scenario
Host-1----Switch1----Router1----Router2-----Switch2------Host2
Q. How  to do the IP super netting for 192.168.0.1.0/24 and 192.168.2.0/24 ?
Q. What  will be  first packet on the wire when typing www on browse the internet ?
Q. What is the size of the IPv4, Ethernet frame, Ipv6 ?
Q. What is the G/L bit on the ethernet frame and G/I bit ?
Q. How traceroute works on Microsoft and Linux . Please explain the process and each step.
Q. How traceroute works on the links doing load balancing ?
Q. What are the different types of Ipv4 address types which includes TEST-NET in ?
Q. Different types DDOS attacks and mitigation techniques on network ?
Q. What is RACL/Tacacs/Radius ?

IPv6

Q.  What are the field in IPv6 header ?

Q.  What are the differences between Ipv6/Ipv4.

Q.  What are the different types of IPv6 address types.

Q.  How address resolution works on Ipv6.

Q.  How server boots up with Ipv6 address.?
Q. How are the Ipv6 address are divided ?

Optical -Layer 1

Q. What are the requirement for the 40gig and 100gig fiber connection ?

Q. How many fiber strand required for 40gig/100gig fiber ?. 

Q. Which one is better Multimode or Single mode fiber ? Explain Why?

Q. Explain the core size of the multimode and single mode fiber ? 
 

Fiber are two types : Single Mode and Multimode.

Multi mode Fiber :

OM1 : 62.5 Micron

OM2 : 50 Micron . 3 times more bandwidth than OM1

OM3 : Used for 10 gig, 40 gig , 100 gig.

OM4 : Used for 10 gig, 40 gig , 100 gig.

Note : OM1 and OM2 does not support 40 gig and 100 gig.

For 40 gig : 4 pairs of fiber are required in tx and 4 pairs of fiber for rx. 

For 100 gig : 10 pairs of fiber are required in tx and 10 pairs of fiber for rx.

Single Mode Fiber:

It has 8-5 to 9 Micron core and used for long distance and more than 5 times expensive compare to multi mode fiber.

 Hardware 

 Q. Describe the path of packet flow on 6500 ?

 Q. What are the different kind of ASIC used on 6500 Supervisor and Line card ?

 Q. What is TCAM and how it works ?

 Q. Describe the standard LTL indexes used on 6500 ?

 Q .What are the troubleshooting tools available on 6500 ?

 Q. How Nexus 7000 is different from 6500 ?
 Q. What are the ASIC used on Nexus 3000 ?

 Troubleshooting

Q.  Define the latest troubleshooting done by you  or good cases without any help ?

Q.  Replace the line card and supervisor on the 6500  during MW without impacting much to  all the users ?

Q.

  Design 

Q. What are the difference between  Layer 2 or Layer 3 design ?

Q. Pros and cons of layer 2 Design ?

Q. Pros and cons of layer 3 design ?

Q. Which design is preferred layer 2 or layer 3 ?
Q. What was the last design you did and on which protocol ?
Q. Design network for Data center ?
Q. Different types of topologies used in Data Center , Enterprise and WAN,Campus.
Q. Different types of architecture Model.
Q. Best practice recommendation  for data center network.
Q. How to design network with 6000 ports with 10gig capacity ?

  SCRIPTING

 Q. Difference between For and while loop ?

 Q. What is Class and object ?

 Q. What object oriented programming ?
 Q. Design a code for number vector ? 
 Q. What is Python and how to use in networking ? 
 Q. What are the different type of data structures.
 Q. What are different types of loops.
 Q .What is mutable and immutable ?
 Q. What are list, tuple, dictionaries.
 Q. How to handle exception and error in python.
 Q. What is module /library ,packages. 

   

  Management Questions

Q. What are your strength and weakness ?

Q. Where do you see yourself in next five years ?

Q. Why do you want to join this role and company ?

Q. Explain your current responsibilities and role ? 

Q. How would you handle the angry VP whose network is down ?

Q. How would you handle the conflicts between you and team member ?

 Keywords: OSPF networking question, OSPF networking, bgp networking interview questions, EIGRP networking question.