Networking Basics Questions and Answers

Q: What protocol does PPP use to identify the Network layer protocol?

Correct answer: NCPPPP has two sublayers above the physical link. LCP establishes, configures and tests the connection itself, handling authentication, compression, multilink and error detection. NCP then negotiates one control protocol per network layer protocol carried - IPCP for IP, IPXCP for IPX - which is how PPP supports several protocols over one link. HDLC is a different encapsulation altogether, and ISDN is a physical service.

Q: Which of the following commands will allow you to set your Telnet password on a Cisco router?

Correct answer: line vty 0 4Telnet and SSH sessions arrive on the virtual terminal lines, so the password is set under line vty 0 4 - five simultaneous sessions on most routers - followed by password and login. Without a vty password configured the router refuses the connection outright, reporting that a password is required. line con 0 is the console port, line aux 0 the auxiliary port, and line telnet is not a command.

Q: Which protocol does DHCP use at the Transport layer?

Correct answer: UDPDHCP runs over UDP, on port 67 for the server and 68 for the client. It must, because the client has no IP address when it begins: the initial DHCPDISCOVER is a broadcast from 0.0.0.0, and TCP cannot establish a connection without addresses at both ends. IP is a network layer protocol rather than a transport one, and ARP is a layer 2 resolution protocol.

Q: Which command is used to determine if an IP access list is enabled on a particular interface?

Correct answer: show ip interfaceshow ip interface reports the IP configuration of each interface, including the lines showing which access list, if any, is applied inbound and outbound. show access-lists displays the contents of every list and their match counters but says nothing about where they are applied - the two questions are separate, and a list can perfectly well exist without being applied anywhere.

Q: Where is a hub specified in the OSI model?

Correct answer: Physical layerA hub simply regenerates and repeats the electrical signal out of every other port. It reads no addresses, makes no forwarding decisions and does not examine frames at all, so it belongs to the physical layer - it is a multiport repeater. A switch, which reads MAC addresses and forwards selectively, is a data link layer device, and a router, which reads IP addresses, is a network layer device.

Q: Which protocol is used to send a destination network unknown message back to originating hosts?

Correct answer: ICMPICMP carries the error and diagnostic messages of the IP suite, including destination unreachable - of which "network unreachable" is one code - time exceeded, and the echo request and reply that ping uses. A router that has no route to a destination discards the packet and returns an ICMP message to the source. ARP resolves IP addresses to MAC addresses, and TCP handles reliability for its own connections only.

Q: How often are BPDUs sent from a layer 2 device?

Correct answer: Every 2 secondsBridge protocol data units are sent every two seconds by default, which is the spanning tree hello time. They carry the bridge ID and path cost information from which every switch determines the root bridge, its own root port and any blocking ports. The interval matters because convergence times are derived from it: max age is twenty seconds, ten missed hellos, and forward delay fifteen.

Q: How many broadcast domains are created when you segment a network with a 12-port switch?

Correct answer: 1A switch breaks up collision domains, not broadcast domains: a broadcast frame arriving on one port is flooded out of all the others, so all twelve ports remain in a single broadcast domain by default. Splitting that domain requires either a router or VLANs configured on the switch, each VLAN forming a broadcast domain of its own. The complementary question - how many collision domains - gives twelve.

Q: What does the command routerA(config)#line cons 0 allow you to perform next?

Correct answer: Set your console password.line cons 0 enters line configuration mode for the console port, where password and login then set and enforce the password for anyone connecting through the physical console cable. The Telnet password belongs to line vty 0 4, a different set of lines. Entering line configuration mode neither shuts the router down nor disables the console.

131.

What protocol does PPP use to identify the Network layer protocol?

A.NCP
B.ISDN
C.HDLC
D.LCP

Answer: A

Correct answer: NCP

PPP has two sublayers above the physical link. LCP establishes, configures and tests the connection itself, handling authentication, compression, multilink and error detection. NCP then negotiates one control protocol per network layer protocol carried - IPCP for IP, IPXCP for IPX - which is how PPP supports several protocols over one link. HDLC is a different encapsulation altogether, and ISDN is a physical service.

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132.

Which of the following commands will allow you to set your Telnet password on a Cisco router?

A.line telnet 0 4
B.line aux 0 4
C.line vty 0 4
D.line con 0

Answer: C

Correct answer: line vty 0 4

Telnet and SSH sessions arrive on the virtual terminal lines, so the password is set under line vty 0 4 - five simultaneous sessions on most routers - followed by password and login. Without a vty password configured the router refuses the connection outright, reporting that a password is required. line con 0 is the console port, line aux 0 the auxiliary port, and line telnet is not a command.

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133.

Which protocol does DHCP use at the Transport layer?

A.IP
B.TCP
C.UDP
D.ARP

Answer: C

Correct answer: UDP

DHCP runs over UDP, on port 67 for the server and 68 for the client. It must, because the client has no IP address when it begins: the initial DHCPDISCOVER is a broadcast from 0.0.0.0, and TCP cannot establish a connection without addresses at both ends. IP is a network layer protocol rather than a transport one, and ARP is a layer 2 resolution protocol.

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134.

Which command is used to determine if an IP access list is enabled on a particular interface?

A.show access-lists
B.show interface
C.show ip interface
D.show interface access-lists

Answer: C

Correct answer: show ip interface

show ip interface reports the IP configuration of each interface, including the lines showing which access list, if any, is applied inbound and outbound. show access-lists displays the contents of every list and their match counters but says nothing about where they are applied - the two questions are separate, and a list can perfectly well exist without being applied anywhere.

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135.

Where is a hub specified in the OSI model?

A.Session layer
B.Physical layer
C.Data Link layer
D.Application layer

Answer: B

Correct answer: Physical layer

A hub simply regenerates and repeats the electrical signal out of every other port. It reads no addresses, makes no forwarding decisions and does not examine frames at all, so it belongs to the physical layer - it is a multiport repeater. A switch, which reads MAC addresses and forwards selectively, is a data link layer device, and a router, which reads IP addresses, is a network layer device.

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136.

What does the passive command provide to dynamic routing protocols?

A.Stops an interface from sending or receiving periodic dynamic updates.
B.Stops an interface from sending periodic dynamic updates but not from receiving updates.
C.Stops the router from receiving any dynamic updates.
D.Stops the router from sending any dynamic updates.

Answer: B

Correct answer: Stops an interface from sending periodic dynamic updates but not from receiving updates.

The passive-interface command suppresses outgoing routing advertisements on that interface while leaving the router willing to receive them, and the network remains advertised to the rest of the topology. It is used on interfaces facing hosts or stub segments, where advertising routes wastes bandwidth and exposes the routing domain unnecessarily. Note that in EIGRP and OSPF the effect is stronger, since suppressing hellos prevents adjacencies forming at all.

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137.

Which protocol is used to send a destination network unknown message back to originating hosts?

A.TCP
B.ARP
C.ICMP
D.BootP

Answer: C

Correct answer: ICMP

ICMP carries the error and diagnostic messages of the IP suite, including destination unreachable - of which "network unreachable" is one code - time exceeded, and the echo request and reply that ping uses. A router that has no route to a destination discards the packet and returns an ICMP message to the source. ARP resolves IP addresses to MAC addresses, and TCP handles reliability for its own connections only.

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138.

How often are BPDUs sent from a layer 2 device?

A.Never
B.Every 2 seconds
C.Every 10 minutes
D.Every 30 seconds

Answer: B

Correct answer: Every 2 seconds

Bridge protocol data units are sent every two seconds by default, which is the spanning tree hello time. They carry the bridge ID and path cost information from which every switch determines the root bridge, its own root port and any blocking ports. The interval matters because convergence times are derived from it: max age is twenty seconds, ten missed hellos, and forward delay fifteen.

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139.

How many broadcast domains are created when you segment a network with a 12-port switch?

A.1
B.2
C.5
D.12

Answer: A

Correct answer: 1

A switch breaks up collision domains, not broadcast domains: a broadcast frame arriving on one port is flooded out of all the others, so all twelve ports remain in a single broadcast domain by default. Splitting that domain requires either a router or VLANs configured on the switch, each VLAN forming a broadcast domain of its own. The complementary question - how many collision domains - gives twelve.

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140.

What does the command routerA(config)#line cons 0 allow you to perform next?

A.Set the Telnet password.
B.Shut down the router.
C.Set your console password.
D.Disable console connections.

Answer: C

Correct answer: Set your console password.

line cons 0 enters line configuration mode for the console port, where password and login then set and enforce the password for anyone connecting through the physical console cable. The Telnet password belongs to line vty 0 4, a different set of lines. Entering line configuration mode neither shuts the router down nor disables the console.

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