INTERVIEW QUESTIONS FOR NETWORK ADMINISTRATORS(CISCO CERTIFIED NETWORK ASSOCIATE)

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INTERVIEW QUESTIONS FOR NETWORK ADMINISTRATORS

1. The four layers of the TCP/IP stack (also called the DoD model) are Application/Process,
Host-to-Host, Internet, and Network Access. The Host-to-Host layer is equivalent to the
Transport layer of the OSI model.

2. A client that sends out a DHCP Discover message in order to receive an IP address sends
out a broadcast at both layer 2 and layer 3. The layer 2 broadcast is all Fs in hex, or
FF:FF:FF:FF:FF:FF. The layer 3 broadcast is 255.255.255.255, which means all
networks and all hosts. DHCP is connectionless, which means it uses User Datagram
Protocol (UDP) at the Transport layer, also called the Host-to-Host layer.

3. The four layers of the DoD model are Application/Process, Host-to-Host, Internet, and
Network Access. The Internet layer is equivalent to the Network layer of the OSI model.

4. Both FTP and Telnet use TCP at the Transport layer; however, they both are Application
layer protocols, so the Application layer is the best answer.

5. turn a binary number into decimal, you just have to add the values of each bit that is a 1.
The values of 10011101 are 128, 16, 8, 4, and 1. 128 + 16 + 8 + 4 + 1 = 157.

6. Hexadecimal is a base-16 number system. The values of hexadecimal are 0, 1, 2, 3, 4, 5,
6, 7, 8, 9, A, B, C, D, E, F-16 characters total, from which to create all the numbers you’ll
ever need. So, if 1001 in binary is 9, then the hexadecimal equivalent is 9. Since we then
have 1101, which is 13 in binary, the hexadecimal answer is D and the complete
hexadecimal answer is 0x9D.

7. Internet Control Message Protocol (ICMP) is used to send error messages through the
network, but they do not work alone. Every segment or ICMP payload must be
encapsulated within an IP datagram (or packet).

8. Although Telnet does use TCP and IP (TCP/IP), the question specifically asks about layer
4, and IP works at layer 3. Telnet uses TCP at layer 4.

9. If you see that a serial interface and the protocol are both down, then you have a Physical
layer problem. If you see serial1 is up, line protocol is down, then you are not receiving
(Data Link) keepalives from the remote end.

10. The command show ip protocols will actually show you the broadcast address for each
interface – too bad it isn’t a possible answer. Your best answer is show interfaces, which
will provide the IP address and mask for each interface.

11. The erase startup-config command erases the contents of NVRAM and will put you in
setup mode if the router is restarted.

12. To copy the running-config to NVRAM so that it will be used if the router is restarted,
use the copy running-config startup-config command (copy run start for short)

13. The show controllers serial 0 command will show you whether either a DTE or DCE
cable is connected to the interface. If it is a DCE connection, you need to add clocking
with the clock rate command.

14. When a routing update is received by a router, the router first checks the administrative
distance (AD) and always chooses the route with the lowest AD. However, if two routes
are received and they both have the same AD, then the router will choose the one route
with the lowest metrics, or in RIP’s case, hop count.

15. You cannot have 16 hops on a RIP network by default. If you receive a route advertised
with a metric of 16, this means it is inaccessible.

16. Another way to avoid problems caused by inconsistent updates and to stop network loops is route poisoning. When a network goes down, the distance-vector routing protocol
initiates route poisoning by advertising the network with a metric of 16, or unreachable
(sometimes referred to as infinite).

17. RIPv2 uses the same timers and loop-avoidance schemes as RIPv1. Split horizon is used to stop an update from being sent out the same interface it was received on. Holddown timers allow time for a network to become stable in the case of a flapping link.

18. The distance-vector routing protocol sends its complete routing table out all active interfaces at periodic time intervals. Link-state routing protocols send updates containing the state of its own links to all routers in the internetwork.

19. IGRP uses bandwidth and delay of the line, by default, to determine the best path to a remote network. Delay of the line can sometimes be called the cumulative interface delay.

20. Routers operate at layer 3. LAN switches operate at layer 2. Ethernet hubs operate at layer 1. Word processing applications communicate to the Application layer interface, but do not operate at layer 7, so the answer would be none.

21. Routers provide packet switching, packet filtering, internetwork communication, and path
selection.

22. Flow control can be helps To provide a means for the receiver to govern the amount of data sent by the sender. The common types of flow control are buffering, windowing, and congestion avoidance

23. Bridges can be used to segment the network because it can break up collision domains, which allow more bandwidth for users.

24. Hubs cannot run full-duplex Ethernet. Full duplex must be used on a point-to-point connection between two devices capable of running full duplex. Switches and hosts can run full duplex between each other, but a hub can never run full duplex.

25. A reliable Transport layer connection uses acknowledgments to make sure all data is
transmitted and received reliably. A reliable connection is defined by a virtual circuit that uses acknowledgments, sequencing, and flow control, which are characteristics of the Transport layer (layer 4)

26. The IEEE ethrnet frame header has source and destination MAC addresses, an Ether-Type field to identify the Network layer protocol, the data, and the FCS field that holds the answer to the CRC.

27. To connect to a router or switch console port, you would use an RJ45 UTP rolled cable.

28. The encapsulation method is data, segment, packet, frame, bit.

USES OF Straight AND Crossover CABLES:

Straight-through UTP Cables uses:
• Switch to a router Ethernet port
• Computer to switch
• Computer to hub

Crossover UTP Cables uses:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router Ethernet port connection
• Computer to computer
• Computer to a router Ethernet port

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