Interview questions on networking basics

1. Can a Window based operating system communicate with a Linux operating system. Provide supporting statements

This is possible, since both Windows and Linux support TCP/IP

2. A Cisco router and a Window operating system wish to use TCP/IP to achieve network communication. Is this possible

TCP/IP is a vendor neutral protocol. Any vendor can deploy TCP/IP. Cisco and Microsoft can have TCP/IP installed as part of their respective operating systems and communicate.

3. Is the OSI model installed on an operating system

The OSI model is a set of guidelines which is developed by ISO organization. It is not installed on any operating system. Protocols are developed by using OSI model as a reference

4. Is TCP/IP software, hardware or a theoretical model

TCP/IP is a software which is installed on a device. For example, operating systems like Windows, Linux has TCP/IP installed as part of the operating system.

5. A PC is configured with a DNS server address but not the default gateway. Can the PC access internet.

A default gateway is always required for packets to be send to the internet. This is because packets which are bound for the internet are always on different network addresses and not known beforehand.

6. What is the destination mac-address of a frame whose destination IP address is 192.168.1.255

The destination IP address, 192.168.1.255 is a directed broadcast. This is a broadcast packet and the corresponding destination mac-address in the frame would be FF-FF-FF-FF-FF-FF

7. What is the destination mac-address of a frame whose destination IP address is 255.255.255.255

The IP address 255.255.255.255 is a All subnet directed broadcast. The corresponding destination mac-address in the frame would be FF-FF-FF-FF-FF-FF.

8. Give an example of a packet which uses the destination IP address of 255.255.255.255

DHCP Discover packets use 255.255.255.255 as the destination IP address. DHCP Discover packets are initiated by DHCP clients to find DHCP servers on the network.

9. What is the common security issue with telnet and FTP

Both telnet and FTP, sends data in clear text. So confidential information like Username, passwords, data etc can be sniffed easily using a protocol analyzer.

10. Is a 3 way handshake initiated when a TFTP client communicates with a TFTP server

The TFTP protocol uses UDP protocol at the transport layer. The 3 way handshake is a functionality of the TCP protocol. It is initiated only by applications which use TCP at the transport layer.

11. Why isn’t a response received for a ping request when a Proxy is configured

Ping uses ICMP at layer 3. A proxy understands only protocols for which it is configured for. Examples of proxies are HTTP, FTP based proxy. So when a ping packet reaches the proxy, it would drop the packet, since a proxy is not a routing device and cannot route IP packets.

12. How much data can be accommodated in a TCP 3 way handshake

The TCP 3 way handshake is used only for synchronization and not used for carrying data. Data transfer happens only after the TCP 3 way handshake is successful

13. How does a PC differentiate traffic between two different instances of the same website on multiple browsers

Assume that the user opens the website on IE and types www.tcpipguru.com. The user then opens another browser (Mozilla) and types www.tcpipguru.com. When the user opens the browser and initiates the connection to the websites, different pairs of TCP sockets are created on the PC for both the instances. Within the TCP sockets, the TCP source port numbers would be used for differentiating the connections

14. How does a PC route internet traffic when two connections are available

Assume that a PC has two network interface cards, out of which both has internet connection. The routing table of the PC would consist of two default route entries for networks associated with both the cards. The route entry which has a lower metric would be chosen for the internet connection.

15. Can a computer be connected to two internet connections simultaneously

This is possible. A typical scenario would a computer connected to the internet through LAN interface and another internet connection through a wireless USB device.

16. Which organization is responsible for managing Public IP addresses on the Internet.

ICANN

17. Can two organizations have networks belonging to the same private IP address range

Private IP addresses are used by organizations for devices which reside within their network. It is not used for public communication (Internet). So this is possible.

18. Which protocol is used to find out the mac-address of a gateway in an ethernet-based network

The ARP protocol is used to find out the mac-address of devices on an Ethernet segment

19. Can two computers use the same dynamic ports for communication to a remote server simultaneously?

This is possible since communication is based on socket pairs. Each socket pair consists of a unique port number and an IP address. So the socket pair on the respective PC’s would be different as the IP addresses of the computers would be different