Network engineer interview questions

Network engineer interview questions and answers

Network interviews start with the OSI model and subnetting and quickly move to routing, switching and troubleshooting. These are the questions asked most, with what each one checks.

What to revise before the interview

  • OSI and TCP/IP models
  • TCP vs UDP, common ports
  • IP addressing and subnetting
  • Switching: VLANs, trunking, STP
  • Routing: static, OSPF, BGP basics
  • DNS, DHCP and NAT
  • ACLs and firewalls
  • Troubleshooting with ping, traceroute and show commands

  1. 1.Explain the OSI model.

    What they're checking
    The most common networking question.
    How to answer
    Seven layers: physical, data link, network, transport, session, presentation, application. Give an example device or protocol at key layers - switch (2), router and IP (3), TCP and UDP (4), HTTP (7).

  2. 2.TCP vs UDP?

    What they're checking
    Transport basics.
    How to answer
    TCP is connection-oriented and reliable (handshake, acknowledgements, ordering) - used for web and email. UDP is connectionless and faster - used for DNS queries, voice and video.

  3. 3.How many usable hosts are in a /26 network?

    What they're checking
    Subnetting is tested in almost every round.
    How to answer
    A /26 leaves 6 host bits: 2^6 = 64 addresses, minus network and broadcast = 62 usable hosts. Practise until you can do these in your head.

  4. 4.What is a VLAN, and why use one?

    What they're checking
    Switching knowledge.
    How to answer
    A VLAN splits one physical switch into separate broadcast domains - for example, separating finance and guest traffic. Trunk ports carry several VLANs between switches using 802.1Q tags.

  5. 5.What does Spanning Tree Protocol prevent?

    What they're checking
    Layer 2 stability.
    How to answer
    Loops in switched networks with redundant links. It blocks some ports so there is only one active path, and unblocks them if a link fails.

  6. 6.OSPF vs BGP?

    What they're checking
    Routing protocol understanding.
    How to answer
    OSPF is a link-state interior protocol that finds the shortest paths inside one organisation. BGP is the path-vector protocol that routes between organisations on the internet, based on policies.

  7. 7.How does DHCP assign an IP address?

    What they're checking
    Everyday services.
    How to answer
    DORA: Discover, Offer, Request, Acknowledge. Mention DHCP relay when the server is on another subnet.

  8. 8.What is NAT?

    What they're checking
    Addressing and the internet.
    How to answer
    Network Address Translation maps private IP addresses to a public one, so many devices can share it. PAT does this using different ports.

  9. 9.A user can't open a website. How do you troubleshoot?

    What they're checking
    Methodical problem solving - the job itself.
    How to answer
    Work up the layers: link and IP configuration, ping the gateway, ping an external IP, test DNS with nslookup, traceroute to find where it stops, then check firewall rules and proxies.

  10. 10.What is the difference between a router and a switch?

    What they're checking
    A basics check for freshers.
    How to answer
    A switch forwards frames within a network using MAC addresses (layer 2); a router forwards packets between networks using IP addresses (layer 3).

Frequently asked questions

Is CCNA enough to get a network engineer job?

CCNA is the most common entry certification in India and helps a lot with shortlisting, especially combined with lab practice in Packet Tracer or GNS3.

What do network engineer interviews include?

Networking theory, subnetting, routing and switching scenarios, and troubleshooting questions - sometimes on a lab or simulator.

Is network engineering still a good career?

Yes, and it increasingly overlaps with cloud networking and security, so learning those adds a lot of value.

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