Question 1

What happens when you type a URL into the browser and press Enter?

Accepted Answer

The browser first finds the IP address using DNS: browser cache, OS cache, then a DNS resolver that asks the root, TLD and domain name servers. It opens a TCP connection to that IP on port 443 and does a TLS handshake to set up encryption and check the certificate. Then it sends an HTTP request, the server or load balancer returns a response, and the browser renders the HTML and loads the CSS, JS and images.

Question 2

What is the difference between TCP and UDP?

Accepted Answer

TCP is connection-based and reliable. It does a handshake, keeps packets in order and resends lost ones, so it is used for web, SSH and databases. UDP just sends packets with no connection or guarantee, which makes it faster and lighter. It is used for DNS, video calls, streaming and gaming, where speed matters more than a few lost packets.

Question 3

What is DNS and what are the common record types?

Accepted Answer

DNS turns names like akopslabs.com into IP addresses. Common records: A maps a name to an IPv4 address, AAAA to IPv6, CNAME points one name to another name, MX is for mail servers, TXT holds text used for verification like SPF, and NS lists the name servers for the domain. TTL sets how long the answer can be cached, which matters when you change records.

Question 4

What do the HTTP status codes 200, 301, 403, 404, 500 and 502 mean?

Accepted Answer

200 means OK. 301 is a permanent redirect. 403 means forbidden: the server knows who you are but you are not allowed. 404 means not found. 500 is an internal server error in the app. 502 Bad Gateway means a proxy or load balancer could not get a valid response from the backend, often because the app is down or crashed. 503 means the service is unavailable or overloaded, and 504 means the backend timed out.

Question 5

What is the difference between a Layer 4 and a Layer 7 load balancer?

Accepted Answer

A Layer 4 load balancer works with TCP or UDP. It sends connections to backends based on IP and port without reading the content, so it is very fast. AWS NLB is an example. A Layer 7 load balancer understands HTTP, so it can route by host name, path or headers, handle TLS, add sticky sessions and do HTTP health checks. AWS ALB and NGINX are examples.

Networking interview questions