Facebook/Meta Network Production Engineer

Meta Interview Experience

Network Round Screening:

1. What happens when you type facebook.com in a browser? Answer: Concepts to discuss include DHCP for local IP, how DHCP provides the default gateway, IP/subnet for the laptop and local DNS, DNS query generation, ARP concepts in the local LAN, DNS caching, and routing.
2. Switching concepts - what happens if a layer 2 destination MAC address is not found in the switch? Answer: It will broadcast to all ports except the incoming one.
3. DHCP 4-way handshake (follow-up questions were asked).
4. TCP handshake, TCP connection closing. Follow-up: What if the server does not acknowledge your closing request? How is reliable transfer maintained? Answer: Using sequence and acknowledgement numbers (detailed follow-ups).
5. Routing: How does a routing table look? How does a router prefer certain routes over others? Answer: Considerations include IP specificity, administrative distance, and path metric.

Round Result: Pass

Coding Screen:

1. Invalid Parentheses Given a string such as (ap[), determine if the string has valid parentheses. Example 1: ()ap[] - Answer: Valid Example 2: Pa([]) - Answer: Invalid Example 3: (([])} - Answer: Invalid Answer: Use a stack.

2. Dinosaur Question Given two CSV files, each with two properties as columns and one column as the dinosaur name, print the five fastest dinosaurs. Speed is calculated using a formula that incorporates all four properties.

Round Result: Pass

Final Stage:

1. Behavioral Current work experience, past work experience, and various situational questions were asked. It is important to prepare answers that align with Meta's values. For example, when asked about a time you had a conflict with someone, you could discuss a situation where you proactively improved code speed but learned the importance of creating separate tickets for each task.

Round Result: Pass

2. Network (a) What are the physical components of a router? (I struggled here but should have mentioned buffers and NIC cards.) (b) In-depth discussion of TCP components and follow-up questions. (Pass) (c) When a packet is sent from A to B, describe all headers at each layer. The interviewer even asked about HTTP headers, which I was not prepared for. Follow-up: Which header values would change when host B receives the packet? Answer: The IP checksum in layer 4 and the destination MAC address in layer 2 would change. (d) BGP: How does BGP internal peering prevent loops? (Fail) (e) How would you troubleshoot a slow network and what tools would you use when sending data from host A to B over the internet? (Fail) Overall Round Result: Fail

3. Coding (a) Determine if a string is a palindrome. (b) Given a file containing messages with multiple lines, each ending with a newline character and '%', print a random message ensuring equal probability among different messages. You can use built-in random functions. Follow-up questions focused on space complexity (O(1)) and handling the case where you can only read a certain number of characters at a time. The final follow-up question involved using a hashmap with the index as the key and the seek byte stream as the value.

Round Result: Pass

4. Network Design This was the toughest interview. I informed the interviewer of my limited experience in network design. The question involved arranging 100 servers across four racks. I discussed the access, distribution, and core layers of a network topology. Follow-up questions explored bandwidth utilization and load balancing. I made the mistake of mentioning NAT, which led to further questioning that I did not answer well. In hindsight, NAT was not necessary.

Round Result: Fail

Overall Result: Fail