ISRO interview experience and takeaways

Jan 29, 2022

Note: This post was originally written on Jan 29, 2022 but I never posted it. Posting it now keeping the original authoring date, but with commit date of Aug 05, 2022.

This post was on my bucket list for almost one year, but I kept ignoring it for one or another reason. Anyway, I wanted to write this post to add my experience to several other interview experiences to help others. Another intention was to document this experience for my own consumption in the future to relive one of the greatest moments in my life and career without worrying about diminishing memory.

I had decided to take the ISRO exam as part of my GATE preparation strategy. The paper was apparently very lengthy and came with time-consuming calculations. With some difficulty, I could solve a fair number of questions. Then, I forgot about this and started focusing on my GATE preparation again. The GATE journey is also memorable, which I may describe in a future post. While I was waiting for results for both ISRO and GATE, the pandemic hit the country, and I made a quick jump back to my hometown. The pandemic also delayed the ISRO results. But when it was announced, it was a surprise for me. I was selected for further interview rounds. Then, a long wait ensued. I had to wait till February 2021 to get an interview call. I attended the interview for the post of 'Scientist' in ISRO on March 4, 2021, in New Delhi.

I had been part of very few interviews in my life until ISRO's interview. I could count them on fingers -

  1. SSL admin interview at NITC (which I rocked :P)
  2. The Directi interview (where I reached till last round), and
  3. The Cisco interview (I rocked this one too).

I haven't been part of any other interview in my life, so far. So, I am notably less experienced in giving interviews. But, unlike other fields in my life, I have never felt nervous while giving interviews. I am not yet sure of the exact reasons behind this confidence. Perhaps, I am not an introvert as I think I am.

Anyway, the decision to attend or not attend the interview was tough. There were many reasons -

  1. What if I get selected for the interviews! The pressure to join ISRO will be enormous.
  2. What if I get COVID during the journey or stay in New Delhi!
  3. If I am not interested in joining ISRO, why should I waste money on travel and accommodation!

My parents didn't know that I had taken the ISRO exam. So, it was a pleasant surprise for them. I decided to attend the interviews because my parents looked ecstatic about this opportunity. My brother accompanied me to Delhi; we stayed in a nice hotel, ate good food, and visited some excellent locations in Delhi together.

Coming to the primary purpose of this post, how was my interview experience? Well, it was a mixed bag. I wasn't satisfied with some of my answers, but I could feel that the interview panel liked my answers. Like all other interviews I have given, this interview revolved mostly around Linux, Networking, OS, and Security. One good thing about ISRO interviews is that ask your preferred subjects before starting the discussion. I said that my favorite subjects are OS, Security, and Networking. They did ask me why I don't like DBMS. I told them that I had never worked with DBs until now, so I am not very familiar with its practical aspects. After that, they asked me questions from my preferred domains only. As expected, I had absolutely no issues answering most of the questions accurately. There were some tricky questions where they tried to stress-test me, but I was able to deflect them.

Although I had to be physically present at the ISRO center, the actual interview happened virtually on Cisco WebEx (!).

Below is an inaccurate version of the converstaion -

Interview Panel (IP): Please introduce yourself.

Me: Introduced myself. The panel specifically asked about my graduation details and final project details.

IP: So, you work in Cisco. What are you doing there?

Me: Explained my work in Snort and FTD team

IP: What purpose does FTD serve?

Me: Explained in brief, as I had just joined the FTD team at that time.

IP: We are using FTDs in ISRO. It is giving us too many issues. How do we fix it?

Me: Suggested some solutions, including Hardware and Software ones. They tried to stress-test me on this. Thankfully I didn't lose my patience and kept giving them some answers.

IP: What happens behind the scenes when you type a web address in the browser?

Me: Explained

IP: How does the router know where to forward the packet?

Me: I fumbled a bit on this one because I did make a mistake in the previous question. Anyway answered it correctly in the end.

IP: What is page fault and context switch? Does a page fault require a context switch?

Me: Answered. Don't remember the answer now. It is very clearly explained in OSTEP.

IP: How is kernel mode switched?

Me: Explained

IP: What is a trap? What does the trap handler do? How is it invoked?

Me: Explained

IP: Explain Linux File Permissions? How to interpret directory 555 and file 777 permissions?

Me: Explained

IP: Do you know about the security of OS?

Me: Explained some concepts. I mentioned Linux Hardening, then they asked many questions on the overall idea of hardening of the OS.

IP: How to modify a Kernel to work with resource-constrained devices?

Me: I explained some modifications, like removing unnecessary drivers and blobs used for generic purposes, etc.

IP: What is a TCP wrapper? Do you know about Netstat?

Me: I didn't know about TCP wrappers, so I said I don't know. Explained Netstat briefly.

IP: How can we improve the security of an OS?

Me: I explained some ways to secure OS connected to a network by installing some tools and firewalls, like Fail2Ban, FTDs, UFW, etc. They were expecting IPTables, so they asked about it next.

IP: What are IPTables? Do you know about chains in IPTables?

Me: I explained IPTables, but couldn't answer the concept of chains.

IP: Explain some common web attacks?

Me: I explained OWASP Top 10 and a few attacks like SQL Injection, XSS, etc.

IP: Which attacks are possible in an OS?

Me: Explained buffer overflow, heap overflow, stack smashing, etc.

In the end, they asked some general questions about Linux Kernel, which I don't remember now. Then they concluded the interview and asked me to leave. The interview took around 30-45 minutes. The discussion entirely revolved around the systems side of things, which worked in my favor.

I analyzed my performance after the interview. There were some things that I would like to fix in the future.

  1. While preparing for GATE, I didn't focus on making notes. Having short notes helps at the last moment. I suffered because I had to go through the entire syllabus again, even for a quick revision.
  2. I have improved my communication skills significantly, but they are still not up to the mark. My inherently introverted nature keeps pulling me back. During this interview, I fumbled quite a bit. It may be that seeing myself on camera on screen made me self-conscious. Still, I need to work on this aspect of my soft skills because I am sure that I will need to use communication skills a lot in the coming future.
  3. My knowledge of Linux, Networking, and OS is invaluable. I need to make sure that I don't neglect them in the future and keep myself up to date with the latest trends in the field.
  4. I severely lack focus and motivation. Even during the interview, I faced issues with focusing on the questions. My mind keeps on having distracting thoughts. I need to find some ways to improve my focus significantly. Otherwise, my mind will lose its capabilities even faster with growing age.
  5. My understanding of Cisco products is severely limited. I spent three years in Cisco. Still, I don't know much about any Cisco product lines completely. I don't even know about all Cisco's Security unit's products, even after spending my entire 3 years there. This is a difficult situation. Unfortunately, now that I have left Cisco, there is no way/reason to get that understanding.

The results came in September 2021, and to my surprise, I was selected for the post with AIR 30. My final marks in the written exam were 110/216 (some questions were canceled), and I scored 83.18/100 in interviews. However, I decided not to join ISRO because the center assigned to me didn't align with my interests and other reasons that I mentioned in a separate post. My parents were delighted with my achievement; however, they supported my decision not to join ISRO.

August 2018 to February 2020 was a very frustrating yet fruitful phase of my life. The knowledge I acquired during this time helped me overcome my self-doubt due to my failures in academics in NITC. Getting selected for ISRO made the entire process memorable in the end. I will always cherish this achievement of mine.