Interview Questions on Linux Networking with Answers

1. How do you perform NIC teaming?

Ans: Follow the below link
NIC Bonding in Red Hat Linux

2. What is the difference between TCP and UDP protocol?

Ans: 

• TCP is a connection oriented protocol and contain the information of sender as well as receiver.
• Eg: HTTP.FTP, Telnet
• TCP is slower than UDP due to its error checking mechanism

• UDP protocols are connection less packets have no information to where they are going. These type of ports are generally used for broadcasting. 
• For eg: DNS, DHCP
• UDP are faster

3. What are the benefits of NIC Teaming?

Ans: Load balancing
Fault Tolerance
Failover

4. Mention all the network configuration files you would check to configure your ethernet card

Ans: /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network
/etc/resolv.conf
/etc/nsswitch.conf

5. What is the the use of /etc/resolv.conf?

Ans: It contains the details of nameserver i.e details of your DNS server which helps us connect to Internet

6. What is the use of /etc/hosts file?

Ans: To map any hostname to its relevant IP

7. What is the command to check all the open ports of your machine?

Ans: 
nmap localhost
Follow the below link for more details
How to get a list of open ports in Linux?

8. What is the command to check all the listening ports and services of your machine?

Ans: netstat -ntlp

9. How can you make a service run automatically after boot?

Ans: using chkconfig command

10. What are the 6 run levels of linux? And how can you configure your script to run only when the system boots into GUI and not to any other runlevel

Ans: 0 power off
1 single user
2 multi user without network
3 multiuser with network
4 development purpose
5 GUI
6 Restart

chkconfig --level 5 service_name on
chkconfig --level 1234 service_name off

11. What is a 3 way handshake protocol? Give an example of it

Ans: SYN - system 1 sends SYN signal to rmote system
SYN-ACK - remote sysstem receives the syn signal and sends ack signal
ACK - system again receives ack signal from remote system and connection is established

For Example: When you ping to a machine you are sending a SYN signal which is ACK by the remote machine then it sends a SYN ACK signal back to the host machine. Then the host machine receives SYN ACK and sends the ACK signal back to confirm the same.

12. What are the possible ways to check if your system is listening to port 67

Ans: # nmap localhost | grep 67
# netstat -ntlp | grep 67