Network Interview Questions

Network Interview Questions


Network Beginner

Question
What is Ethernet?
                    

Question
What is a MAC address? What is it used for?
                    

Question
When is this MAC address used?: ff:ff:ff:ff:ff:ff
                    

Question
What is an IP address?
                    

Question
Explain subnet mask and given an example
                    

Question
What is a private IP address? What do we need it for?
                    

Question
Explain the OSI model. What layers there are? What each layer is responsible for?
Application: user end (HTTP is here)
Presentation: establishes context between application-layer entities (Encryption is here)
Session: establishes, manages and terminates the connections
Transport: transfers variable-length data sequences from a source to a destination host (TCP & UDP are here)
Network: transfers datagrams from one network to another (IP is here)
Data link: provides a link between two directly connected nodes (MAC is here)
Physical: the electrical and physical spec the data connection (Bits are here)
                    

Question
For each of the following determine to which OSI layer it belongs: * Error correction * Packets routing * Cables and electrical signals * MAC address * IP address * Sessions between applications * 3 way handshake
                    

Question
What delivery schemes are you familiar with?
Unitcast: One to one communication where there is one sender and one receiver.

Broadcast: Sending a message to everyone in the network. The address ff:ff:ff:ff:ff:ff is used for broadcasting.
           Two common protocols which use broadcast are ARP and DHCP.

Multicast: Sending a message to a group of subscribers. It can be one-to-many or many-to-many.
                    

Question
What is CSMA/CD? Is it used in modern ethernet networks?

CSMA/CD stands for Carrier Sense Multiple Access / Collision Detection.
Its primarily focus it to manage access to shared medium/bus where only one host can transmit at a given point of time.

CSMA/CD algorithm:

1. Before sending a frame, it checks whether another host already transmitting a frame.
2. If no one transmitting, it starts transmitting the frame.
3. If two hosts transmitted at the same time, we have a collision.
4. Both hosts stop sending the frame and they send to everyone a 'jam signal' notifying everyone that a collision occurred
5. They are waiting for a random time before sending again
6. Once each host waited for a random time, they try to send the frame again and so the
                    

Question
Describe the following network devices and the difference between them: * router * switch * hub
                    

Question
What is NAT?
                    

Question
What is a proxy? How it works? What do we need it for?
                    

Question
What is the difference between TCP and UDP?
TCP establishes a connection between the client and the server to guarantee the order of the packages, on the other hand, UDP does not establish a connection between client and server and doesn't handle package order. This makes UDP more lightweight than TCP and a perfect candidate for streaming services.
                    

Question
Explain "default gateway"
                    

Question
How TCP works? What is the 3 way handshake?
                    

Question
What is ARP? How it works?
                    

Question
What is TTL?
                    

Question
What is DHCP? How it works?
                    

Question
What is SSL tunneling? How it works?
                    

Question
What is a socket? Where can you see the list of sockets in your system?
                    

Question
What is IPv6? Why should we consider using it if we have IPv4?
                    

Question
What is VLAN?
                    

Question
What is MTU?
                    

Question
True or False?. Ping is using UDP because it doesn't care about reliable connection
                    

Question
What is SDN?
                    

Question
What is ICMP? What is it used for?
                    

Question
What is NAT? How it works?
                    
Advanced Network

Question
Explain Spanning Tree Protocol (STP)
                    

Question
What is link aggregation? Why is it used?
                    

Question
What is Asymmetric Routing? How do deal with it?
                    

Question
What overlay (tunnel) protocols are you familiar with?
                    

Question
What is GRE? How it works?
                    

Question
What is VXLAN? How it works?
                    

Question
What is SNAT?
                    

Question
Explain OSPF
                    

Question
Explain Spine & Leaf
                    

Question
Using Hamming code, what would be the code word for the following data word 100111010001101?
00110011110100011101