Bring whiteboard to the interview. Ask candidate to draw a network topology and explain design decisions.

Additionally, break your interviews into L2/L3/L7 and platform. For L2, ask candidate to draw a switch with 2 hosts, and explain how mac learning and arp work.

Draw a box architecture with 4 switches, ask candidate to run STP (ie: explain how it'll converge).

Explain IP, fields in the header, ICMP, IPv6, ICMPv6, OSPF.

Ask candidate to pick any L7 protocol and explain how it operates (think: FTP or HTTP. FTP is a good one to throw them off with NAT, active and passive)

Ask candidate to pick their preferred platform (switch/router) and describe it's architecture. Ask them to contrast it against another platform and explain what are positive/negative aspects about this platform.

How does STP works?

How does OSPF and BG works?

What is the difference between a VLAN and subnet?

Describe how the traceroute command works.

What are the three IPv4 software configuration components you need for basic network connectivity (bonus if they mention extras)?

What is VLSM and how does it allow you to manage IP space?

A user says "The network is down". Describe the steps you would take to troubleshoot and isolate the problem.

Name your favourite network protocol - can be anything from BGP to MPLS to STP to Ethernet.

Tell me something cool about it, something you find interesting and enjoyed playing with.

Tell me something you don't like doing in networking. What makes you sad/angry/annoyed about that networking thing? (adding occasionally if they're hesitant: It's ok that we might do it, I dislike firewalls but I end up configuring quite a few, and it's ok to say something other than a technology.)

Explain why proxy ARP is a bad idea to have on by default.

Describe how to discover a network topology with nothing but an account on the WAN router.

what is the difference between a routing and routed protocol? give an example of each.

Layer 1 (Copper, Fiber, Basic Binary) basics.

Layer 2 (VLAN, PVLAN, STP, BCast vs Unicast flooding, CAM Tshooting, Port Security)

Layer 3 (IP Subnets, Routing Vs. Forwarding, Basic OSPF, BGP)

Layer 4 (UDP, TCP, TCP's Finite State Machine, Tshooting, More TCP, Did I say TCP?)

Layer 7 (Tracert, Ping, Paris, MTR, What is IPAM, Basic Tshooting)

Layer 8 (Soft Skills, Ambition, Energy, Problem Solving)

What is a VLAN?

What’s the difference between VLAN and PVLAN?

What is STP?

What is the difference between Broadcast and Unicast flooding?

What is port security?

How many IP addresses are in a /26, /23, /18?

What’s the difference between routing and forwarding?

List some routing protocols and why you would use it over another.

What is BGP used for?

What is the difference between TCP and UDP and when would you use one over the other?

What is the Finite state machine?

What does a tracert do? What does a ping do?

What is a MTR?

What is IPAM?

Walk me through a layer 1 to 7 packet. Walk me through a layer 7 to 1.

What is a CAM table?

What does a broadcast domain really mean?

Why shouldn't I disable spanning tree? Or conversely, why should I disable it?

Also, does anyone care about RIPv1 anymore?

What if any difference is there between the operation of a layer 3 switch versus a router on a stick configuration?

You have RSTP enabled and you are seeing port flapping, what do you do?

Is it better practice in ACL's to use implicit deny all, or implicit allow all, and why?

Why should you / should you not enable portfast in a core switch.

You get a ticket and all it says is, "Help, the network is down!" What to do to resolve it?

BGP between two of your routers is down. Tell me what you would do to troubleshoot.

Can you explain what the 3-way handshake is?

What port does ping use?

What should the last line of a firewall rule set be?

How to configure a VPN, why it might fail at phase 1 or phase 2?

What is an IPsec?

What is the difference between RAID5 and RAID2?

How do DNS and DHCP relate?

What are some products AWS has and what do they do?

Windows PC has an IP address 169.254.X.X. What does it typically mean and whit the cause? How would you troubleshoot it? What would you look for on the DHCP server? Is there any log you can look at?

In class C space, how many host can you have in that space? Is there a special IP address that cannot be used?

What EXACTLY is TCP/IP?

Tell me about different DNS record types.

Is it possible to overwrite the DNS record at the PC?

How to find out if web server listens on the port?
* port DNS - 53
* port POP3 - 110
* port HTTP - 80

What is the UDP timeout value?

What is reverse DNS good for?

What are some HTTP errors and their meaning?

How many VPN tunnels can you have without NAT

What are the classes of private IPV6?

Interior/exterior gateway routing protocols difference?

What exactly happens when you type www.amazon.com into the browser?"

What exactly is the cloud?

What is an IPsec tunnel and transport mode?

What’s the difference between main and aggressive mode?

Name some OSPF neighbor states.

TCP/IP window size and packet header?

What is the “grep” command?

“My personal favorite is taking out my wallet and my cell phone. I put them across the table from one another. Find a random piece of paper and place is in the middle.
This piece of paper, is a switch. He's already turned on.

These "nodes" are my computers. Off.

Tell me what hap

What if any difference is there between the operation of a layer 3 switch versus a router on a stick configuration?

You have RSTP enabled and you are seeing port flapping, what do you do?

Is it better practice in ACL's to use implicit deny all, or implicit allow all, and why?

BGP between two of your routers is down. Tell me what you would do to troubleshoot.

What do you think is the best way to combat social engineering?

Are you familiar with the CIA triangle? (Confidentiality of data, data Integrity, Accessibility Availability of data) What order of importance would you place these in?

Can you explain what the 3-way handshake is?

What port does ping use?

What should the last line of a firewall rule set be?

Why do you want to be a net. engineer? (I always want to hear an answer about either passion for learning or problem-solving)

Tell me your 5 year plan and how this company fits into that plan?

How does traceroute work?

If Machine A is unable to communicate Machine B, how would you troubleshoot this scenario ?


What is virtualization? Explain the types of virtualization.


Explain VPN. Why do you need VPN?

What are the differences between LAN, WAN, & VLAN.

Could a network across offices throughout the city be a WAN?

Briefly touched on trunking & having a node in multiple VLANs.

Vendor specific questions about Cisco CLI,