Interview questions!

Hi ReneMolenaar,

I am struggling to answer these 4 questions in interview

  1. How internet works ? Tell me the Whole process while you type or on your browser.
    Need deep explanation

  2. Explain about OSI Layer

they need from scratch level. Need to explain How 2 PC/networks Communicating with example of each layer. need deep level explanation

3.How Ping and trace route works.

need deep level explanation

  1. In CISCO they asked Packet level explanation of 2 PC/Network Communication.

Need to explain deep Packet level

could you please help me on this ?

1 Like

Hello Pavithra,

You can find the explanations here:

If you still have questions after going through these lessons, let us know ok?



Thanks a lot. You are a gem :slight_smile:

Hi ReneMolenaar,
one more help

I work as a L1 engineer. and now trying for next level.
So attending interviews now.
In 2nd round Managers asking 2 LAN issues and 2 WAN issues, that you faced difficulties in troubleshooting/fixing.

Do you have any scenarios with you that i can Answer them, with my troubleshooting skills its resolved ? Something like I did this config change and issue resolved . that should be Bit tough but not that complicated.

Hello Pavithra,

Creating good interview questions takes time. Here are a couple of quick questions that come to mind:

LAN 1:

Consider the following topology:


  • SW4 is using Gi0/2 as the spanning-tree root port. What command can I use on SW4 so that Gi0/1 becomes the root port?


Consider the following topology:


In the network above, S1 is our multicast source and H1 is our only multicast receiver. SW1 is forwarding multicast packets to both R2 and R3. What command(s) do we need to add to SW1 to prevent unnecessary traffic to R3?

** LAN 3**

Consider the following topology:


There is no connectivity between H1 and H2. What commands can you use on the switches to figure out what the problem is?

WAN 1:

Consider the following topology:


We have a small LAN network where R1, R2, and R3 run OSPF. R1 is connected to an ISP. Users behind R2 and R3 complain that they are unable to reach any networks on the Internet (like The senior network engineer verified that it is not a NAT issue. What command can you use on R1 so that R2/R3 can reach the Internet?

WAN 2:

Consider the same topology as from WAN 1. The ISP is dropping all incoming traffic that exceeds 5 Mbps. What can we configure on R1 so that the ISP does not drop our outgoing traffic?

Hi Rene,
I am asked 4 questions in interview from a ISP company ?
1.If we run command sh ip bgp ROUTE in a MPBGP network . What will be the AS no. You will see ?
2. Why do we connect all area to area 0 in OSPF?
3. What is DOWN BIT in OSPF ?
4. What is OFFSET VALUR in OSPF?

How can I prepare myself for such questions

Hello Bhupesh

These are indeed somewhat difficult questions for an interview. The most important thing to realise here is that such questions are asked in order to gauge the experience of the candidate. It is true that questions like these will be able to be answered only by those that have extensively used the features involved. Although it is always good to study before an interview, if you are not at all readily able to answer at least some of these questions, then you must ask yourself if you are ready for the job in question.

The most important thing to the interviewer is not to see if you know the answer, but to determine how much real life experience you have with these features. Even if you’re able to answer the questions correctly, the interviewer will be able to determine if the answers are those of someone who has just studied and knows of the answers or someone who has used the features and understand the intimately.

I hope this has been helpful!


1 Like

Hi Laz ,
I understand that and agree what you said. I have been working as L1/L2 support and trying to get myself into L3 support. I did under go gns3vault labs. But, found some limitations to practice labs on gns3. Can you help me with iOS to practice bgp and mpls on gns3?

Hello Bhupesh

Take a look at GNS3Vault, another one of Rene’s projects. It has many premade labs for you to choose from and work with. I suggest you get started by looking through this, get a lab that is as close as possible to the scenario that you are working on and then try it out. As you do so, if you face any problems, you can come back and ask more specific questions about the topologies that you have put together and the difficulties you are facing.

I hope this was helpful!


Can you help me with iOS to practice bgp and mpls on gns3?

Hello Bhupesh

The help that we can offer here at Networklessons is in the form of responding to queries and questions in the forum. As you work on your labs in GNS3 and on any other platform you may use, you can feel free to direct all questions that result from those labs to the forum. We’ll be happy to offer any help in any way we can through the forum itself.


Hi Rene,

I need your assistance to prepare for Cisco Service Provider Interview that will be held on 11th Jan’ 2021.

I seek your suggestion to know the topic list need to cover in detail and along with it if you could suggest me any document to refer as I know you don’t have any service provider document.

If you can help me also with sub category of common topics like BGP, MPLS, MPLS-TE etc that should be appreciated.

Thank you

Hello Manami

Concerning interview topics for a service provider, the most likely topics should include:

  • MPLS
  • QoS
  • BGP
  • Metro Ethernet
  • VoIP
  • SD-WAN
  • Network Design

There is no way to get more specific than this because a service provider may have different types of goals for the specific position that they are offering. Can you tell us a little more about the specific position? Maybe then we can focus more on a particular subset of topics that may be useful to you.

You may also find it useful to go over the previous posts in this thread to see what others have been talking about. Also, the following topic may be useful to you as well:

I hope this has been helpful!


Hi Laz,

Thank you for this reply. As you said, I am trying to give you little more insight about the position I applied for ,


Minimum Qualifications

Who you are

Requires BE/BTech degree with 10+ years of related experience in IT industry.
Customer Support/Managed Services Experience (7+ years).
Excellent TCP/ IP networking skills
In depth understanding & knowledge of various switching protocols. E.g. STP, PVSTP, MSTP, LLDP etc.
In depth understanding & working knowledge on various Cisco IOS, IOS-XR & IOX-XE

Experience with MPLS technology including L2/L3 VPN and traffic engineering

Troubleshooting various MPLS & its application related issues. e.g. VPLS/MPLS-TE etc.
Experience with Configuring and troubleshooting Cisco routers and switchesExperience on Cisco ASR9k, ASR1k & Nexus 5k/7k series platform
Experience with routing protocols (OSPF, RIP, EIGRP, ISIS and BGP)
Solid Communication Skills (Written/Verbal/Presentation)
Solid standout colleague
Flexibility in working hours as some migrations will require weekend and after hours’ work.
Ability to grasp sophisticated design concepts quickly and be able to provide the right solutions to the clients.
Ability to solve implementation problems during migrations.
Good leadership skills
Experience in Change, Service Request and Problem Management functions.

Roles & Responsibilities

Analyze, configure and fix large sophisticated networks with mixed media and protocols.
Effectively build and utilize sophisticated lab setups to duplicate and solve problems, validate planned changes to software and hardware design.

Provide remote troubleshooting support to resolve UC related issues
Develop and maintain strong relationship with customer and other Cisco teams.
Build relationship with partners to understand in a better way their networks to provide quicker and more effective results to their requests.

Establish Technical Relationship to support customer network operations.

Possess detailed knowledge of customer network, critical sites, operating procedures as agreed upon with customer

Customer-specific designated support at network level to resolve and debug sophisticated networking problems

Customer concern support for critical network outages and sophisticated network issues.
Proactively monitor and review the progress of all customer cases and engage as vital.
Respond to network management system alarms according to established processes
Priority support for identified key customer functionalities and critical issues
Effectively work with multi-functional teams to resolve major customer issues.
Drive for continuous learning, results orientation and teamwork.

Desired Skills

Managed services background preferred.
CCNP or CCIE R&S/SP desired.
Python knowledge desired.

Fluency in soundness disciplines (availability, security, etc.) and operational disciplines (systems management, change management, etc.).

Consistent record in an industry or horizontal solution area.

Technically strong to solve problems with innovative ideas. Assume complete ownership with regards to the engagement with client and partners.


Hello Manami

Wow, this sounds like an interesting and exciting job, and it looks like it requires both a good training background as well as on the job experience. Based on the description it seems that most service provider topics are required such as STP, PVST, MSTP and LLDP for layer 2 and virtually all popular routing protocols for Layer 3. All of these are covered extensively in the lessons, so you should be covered there. One thing they’re asking for that’s not in the lessons is the Nexus platforms, which are similar to IOS devices but have some significant differences.

One thing I will suggest to you is that when they say “in-depth understanding and working knowledge”, this essentially means that they could ask you almost anything about these topics. Some questions will be broad, while others will be in-depth so they can see if you have specialized as well as broader knowledge of the subject. But don’t be afraid of these questions. They will rarely be obscure little known information, but will be information that anyone who has used these protocols should know.

So the best way to prepare would be to review the topics listed here as much as possible, and just keep in touch with them.

And one more thing. If you don’t know the answer to something, it’s better to simply be honest and say you don’t know. They’ll respect that much more than if you try to bungle your way through. Just some thoughts…

I hope this has been helpful!