CCNA 4 v6.0 (Connecting Networks v6) Chapter 2: Point-to-Point Connections: Check Your Understanding Questions Answers
1. Which command can be used to view the cable type that is attached to a serial interface?
- Router(config)# show interfaces
- Router(config)# show controllers
- Router(config)# show ip interface
- Router(config)# show ip interface brief
Explanation: The show controllers command enables an administrator to view the type of cable attached to a serial interface such as a V.35 DCE.
2. Which serial 0/0/0 interface state will be shown if no serial cable is attached to the router, but everything else has been correctly configured and turned on?
- Serial 0/0/0 is administratively down, line protocol is down
- Serial 0/0/0 is down, line protocol is down
- Serial 0/0/0 is up (disabled)
- Serial 0/0/0 is up (looped)
- Serial 0/0/0 is up, line protocol is down
- Serial 0/0/0 is up, line protocol is up
Explanation: The show interfaces privileged EXEC mode command shows the state of the interfaces, along with other information that related to them. “Serial 0/0/0 is down, line protocol is down” is displayed if there is no cable connected because there is no Layer 1 or Layer 2 activity going on. The interface has been turned on by the use of the no shutdown command; otherwise, the “Serial 0/0/0 is administratively down, line protocol is down” message would be displayed, whether or not a cable has been connected.
3. Which is an advantage of using PPP on a serial link instead of HDLC?
- Fixed-size frames
- Higher speed transmission
- Option for authentication
- Option for session establishment
Explanation: Authentication, multilink, and compression are options on PPP that are advantages over HDLC.
4. How does PPP interface with different network layer protocols?
- By encoding the information field in the PPP frame
- By negotiating with the network layer handler
- By specifying the protocol during link establishment through LCP
- By using separate NCPs
Explanation: PPP can support multiple network layer protocols, such as IPv4, IPv6, IPX, and AppleTalk. It handles the interface with various network layer protocols via separate NCPs. There is a protocol field in a PPP frame to specify the network layer protocol that is being used. The information field in a PPP frame is the data payload. LCP sets up and terminates a link. It does not check which network layer protocol is used for the data.
5. Which three are types of LCP frames used with PPP? (Choose three.)
- Link-acknowledgment frames
- Link-control frames
- Link-establishment frames
- Link-maintenance frames
- Link-negotiation frames
- Link-termination frames
Explanation: Link-establishment frames establish and configure a link. Link-maintenance frames manage and debug a link. Link-termination frames terminate a link.
6. Which protocol will terminate the PPP link after the exchange of data is complete?
- CDPCP
- IPCP
- IPV6CP
- LCP
- NCP
Explanation: LCP terminates a link after exchange of data is complete by exchanging link-termination packets. The link may terminate for various reasons before the data exchange is complete. NCP will only terminate the network layer and NCP link. IPCP and IPXCP are specific network control protocols.
7. Which three statements are true about PPP? (Choose three.)
- PPP can be used only between two Cisco devices.
- PPP can use synchronous and asynchronous circuits.
- PPP carries packets from several network layer protocols in LCPs.
- PPP is a default encapsulation of serial interfaces on Cisco routers.
- PPP uses LCPs to agree on format options such as authentication, compression, and error detection.
- PPP uses LCPs to establish, configure, and test the data link connection.
Explanation: PPP can be used on slower legacy asynchronous serial lines and faster synchronous serial interfaces. PPP LCP is responsible for negotiating PPP options and for the link establishment and link quality monitoring. PPP is an open standard and is not Cisco specific. Network protocols are carried in NCPs, and the default encapsulation of serial interfaces on Cisco routers is HDLC.
8. What PPP information will be displayed if a network engineer issues the show ppp multilink command on a Cisco router?
- The IP addresses of the link interfaces
- The link LCP and NCP status
- The queuing type on the link
- The serial interfaces participating in the multilink
Explanation: The show ppp multilink command displays the multilink interface, the hostnames for the endpoints, and the serial interfaces assigned to the multilink bundle. The show interfaces command will display the IP address, the LCP and NCP (IPCP) status, and the queuing type.
9. A network engineer is monitoring an essential but poor-quality PPP WAN link that periodically shuts down. An examination of the interface configurations shows that the ppp quality 90 command has been issued. What action could the engineer take to reduce the frequency with which the link shuts down?
- Issue the command ppp quality 70.
- Issue the command ppp quality 100.
- Set the DCE interface to a lower clock rate.
- Use the bandwidth command to increase the bandwidth of the link.
Explanation: Issuing the ppp quality 70 command will reduce the link quality threshold before it shuts down from 90 percent of packets received that were sent, to a drop rate of 70 percent before shutting down. Setting the threshold to 100 percent will shut down the link if 100 percent of packets are not received. Lowering the clock rate will not help a link that is going down. The bandwidth command is used for routing protocol calculations, not link quality.
10. In which situation would the use of PAP be preferable to the use of CHAP?
- When a network administrator prefers it because of ease of configuration
- When multilink PPP is used
- When plaintext passwords are needed to simulate login at the remote host
- When router resources are limited
Explanation: Sometimes PAP should be used instead of CHAP. When a plaintext password is needed to simulate login at a remote host, PAP is preferable because passwords are not sent in clear text with CHAP.