Check Your Understanding Questions
Complete all the review questions listed here to test your understanding of the topics and concepts in this chapter. The appendix, “Answers to the ‘Check Your Understanding’ Questions,” lists the answers.
Match each PPP establishment step with its appropriate sequence number:
- Test link quality (optional).
- Negotiate Layer 3 protocol options.
- Send link-establishment frames to negotiate options such as MTU size, compression, and authentication.
- Send configuration-acknowledgment frames.
- NCP reaches Open state.
Which output from the show interfaces s0/0/0 command indicates that the far end of a point-to-point link has a different encapsulation set than the local router?
- Serial 0/0/0 is down, line protocol is down.
- Serial 0/0/0 is up, line protocol is down.
- Serial 0/0/0 is up, line protocol is up (looped).
- Serial 0/0/0 is up, line protocol is down (disabled).
- Serial 0/0/0 is administratively down, line protocol is down.
What is the default encapsulation for serial interfaces on a Cisco router?
- Frame Relay
What is the function of the Protocol field in a PPP frame?
- It identifies the application layer protocol that will process the frame.
- It identifies the transport layer protocol that will process the frame.
- It identifies the data link layer protocol encapsulation in the frame’s Data field.
- It identifies the network layer protocol encapsulated in the frame’s Data field.
Match each description with its corresponding term:
Allows load balancing:
- Magic number
- Call in
Which of the following statements describe the function of statistical time-division multiplexing (STDM)? (Choose three.)
- Multiple data streams share one common channel.
- Bit interleaving controls the timing mechanism that places data on the channel.
- Time slots are used on a first-come, first-served basis.
- STDM was developed to overcome the inefficiency caused by time slots still being allocated even when the channel has no data to transmit.
- Sources of data alternate during transmission and are reconstructed at the receiving end.
- Priority can be dedicated to one data source.
Which of the following describes the serial connection between two routers using the High-level Data Link Control (HDLC) protocol?
- Synchronous or asynchronous bit-oriented transmissions using a universal frame format
- Synchronous bit-oriented transmissions using a frame format that allows flow control and error detection
- Asynchronous bit-oriented transmissions using a frame format derived from the Synchronous Data Link Control (SDLC) protocol
- Asynchronous bit-oriented transmissions using a V.35 DTE/DCE interface
If an authentication protocol is configured for PPP operation, when is the client or user workstation authenticated?
- Before link establishment
- During the link establishment phase
- Before the network layer protocol configuration begins
- After the network layer protocol configuration has ended
Why are Network Control Protocols used in PPP?
- To establish and terminate data links
- To provide authentication capabilities to PPP
- To manage network congestion and to allow quality testing of the link
- To allow multiple Layer 3 protocols to operate over the same physical link
Which statement describes the PAP authentication protocol?
- It sends encrypted passwords by default.
- It uses a two-way handshake to establish identity.
- It protects against repeated trial-and-error attacks.
- It requires the same username to be configured on every router.
A technician testing the functionality of a recently installed router is unable to ping the serial interface of a remote router. The technician executes the show interfaces serial 0/0/0 command on the local router and sees the following line in the router:
Serial0/0/0 is down, line protocol is down
What are two possible causes of this command output?
- The clock rate command is missing.
- The carrier detect signal is not sensed.
- Keepalives are not being sent.
- The interface is disabled due to a high error rate.
- The interface is shut down.
- The cabling is faulty or incorrect.
The network administrator is configuring Router1 to connect to Router2 using three-way handshake authentication. Match each description with the command necessary to configure Router1:
Configure the username and password:
Enter interface configuration mode:
Specify the encapsulation type:
- username Router2 password cisco
- username Router1 password cisco
- interface serial 0/1/0
- encapsulation ppp
- encapsulation hdlc
- ppp authentication pap
- ppp authentication chap
What is required to successfully establish a connection between two routers using CHAP authentication?
- The hostnames of both routers must be the same.
- The usernames of both routers must be the same.
- The enable secret passwords configured on both routers must be the same.
- The password configured with the router’s username must be the same on both routers.
- The ppp chap sent-username command must be configured the same on both routers.
For each characteristic, indicate whether it is associated with PAP or CHAP:
Open to trial-and-error attacks:
Password sent in cleartext:
Uses a one-way hash function:
For each description, indicate whether it is associated with LCP or NCP:
Negotiates link establishment parameters:
Negotiates Layer 3 protocol parameters:
Maintains/debugs a link:
Can negotiate multiple Layer 3 protocols:
Terminates a link:
- Describe the functions of LCP and NCP.
- Describe the five configurable LCP encapsulation options.
Refer to the following configurations for Router R1 and Router R3:
hostname R1, username R1 password cisco123 ! int serial 0/0 ip address 220.127.116.11 255.255.255.0 encapsulation ppp ppp authentication pap ----------------------------- hostname R3 username R1 password cisco ! int serial 0/0 ip address 18.104.22.168 255.255.255.0 encapsulation ppp ppp authentication CHAP
Router R1 is unable to connect with Router R3. On the basis of the information presented, which configuration changes on Router R1 would correct the problem?