Interview Questions on Linux Networking

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 benifits 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
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

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