Cisco II Semester 2 Module 3 Guided Reading

Cisco II Semester 2 Module 3 Guided Reading

Section 3.1.2

1. Name two advantages of using time-division multiplexing (TDM) for transmitting data.

a.       1^st Paragraph - Time-division multiplexing (TDM) is the transmission of several sources of information using one common channel, or signal, and then the reconstruction of the original streams at the remote end

Section 3.1.5

2. Give three statements that describe the High-Level Data Link Control protocol.
1. 2^nd Paragraph, 2^nd sentence - allows for flow control and error control
2. 3rd Paragraph, last sentence - HDLC is the default Layer 2 protocol for Cisco router serial interfaces
3. 2^nd Paragraph, 2^nd sentence - using acknowledgments (and sequencing)

3. How did Cisco alter the HDLC encapsulation to allow a single link to carry multiple protocols?
1. 3^rd Paragraph, 2^nd sentence - The Cisco HDLC frame uses a proprietary 'type' field that acts as a protocol field (Cisco added this to basic HDLC)

Section 3.1.7

4. A technician is testing the functionality of a recently installed router. The technician is unable to ping the serial interface of a remote router. The technician executes the show interface serial 0/0 command on the local router and receives the following output:

Serial0/0 is up, line protocol is down(disabled)

What are two possible causes for this command output?

a.       Look at Graphic #3 - it lists 3 possible conditions. I'm not telling you which two you have to know!

A high error rate has occurred due to a WAN service provider problem

A CSU or DSU hardware problem has occurred

Router hardware (interface) is bad

5. A technician has used Telnet to gain remote access to a router that has no connectivity on its serial interface. What command should be issued to determine if the serial cable is connected properly?
1. 2^nd Paragraph, 2^nd sentence - The show controllers output indicates the state of the interface channels and whether a cable is attached to the interface
6. When troubleshooting the Serial 0/0 interface of a router, a technician issues the show controllers command. The following was the output of the command:

Interface is Serial0/0, electrical interface is UNKNOWN

Give three conclusions that can be drawn about the Serial 0/0 interface.

a. Final Paragraph - If the electrical interface output is shown as UNKNOWN, instead of V.35, EIA/TIA-449, or some other electrical interface type,(1) an improperly connected cable is the likely problem. (2) A problem with the internal wiring of the card is also possible. If the electrical interface is unknown, the corresponding display for the show interfaces serial <X> command will show that (3) the interface and line protocol are down (Serial0/0 is up, line protocol is down).

Section 3.2.1

7. Give three statements that describe the functions of the Point-to-Point protocol with regards to the OSI model.
1. 1^st Paragraph, 3^rd Sentence - uses the data link layer for testing the connection (error detection and compression)
2. 3rd Paragraph, 3rd Sentence - encapsulate and negotiate options for multiple network layer protocols (multiplexing several network layer protocols)

c. 2^nd Paragraph, 1^st Sentence (first 2 bullets) - PPP can be configured on the following types of physical interfaces:

Asynchronous serial

Synchronous serial

8. PPP uses several protocols for communication. Name two options that the LCP protocol in the PPP architecture can provide.
1. 3^rd Paragraph, last sentence - used to establish, configure, and test the data-link connection.

b. 4^th Paragraph, 1^st bullet - (Provides) Authentication options

9. What advantage does the multilink option provide when using PPP?
1. 4^th Paragraph, 5^th bullet - This alternative provides load balancing over the router interfaces that PPP uses.

Section 3.2.2

10. Several tasks must occur before a link between two routers can pass data using PPP. What is required to establish and maintain a PPP session between two routers?
1. Wow.what a vague question! This entire section is about the whole process of establishing, maintaining and terminating PPP sessions between 2 routers. So, what has to happen? Well, in general, LCP and NCP have to send frames to negotiated configuration parameters. That's about as vague as the question itself!

Section 3.2.3

11. Give one reason for using such protocols as PAP and CHAP.
1. First, you have to recognize that PAP and CHAP are authentication protocols. What does the curriculum say about authentication protocols? In the 2^nd Paragraph, it says ".helps to ensure that the user has the permission of the network administrator to make the call" (in other words, be on the network). What's another way to say this? Restricting access to networks connected by serial and ISDN links.

Section 3.2.4

12. Which authentication protocol can be spoofed to allow playback attacks?
1. 2^nd Paragraph, 1^st and 2^nd Sentences - PAP is not a strong authentication protocol. Passwords are sent across the link in clear text and there is no protection from playback or repeated trial-and-error attacks.

Section 3.2.5

13. How is the MD5 function valuable in authentication?
1. 2^nd Paragraph, 2^nd Sentence - using a one-way hash function, which is typically Message Digest 5 (MD5)
2. 3^rd Paragaph, 1^st Sentence - challenge value that is unique
14. What are three features of the CHAP protocol?
1. Lots to read here. Here's what you should pick up about CHAP

i. Exchanges a random challenge number during the session to verify identity

ii. Prevents transmission of login information in plain text

iii. Disconnects the PPP session if authentication fails

Section 3.3.2

15. ISDN BRI service uses two B channels to send data, voice, and video. If the first channel becomes saturated, the second channel can be configured to forward packets. What command will allow ISDN to load balance across both links?
1. The last paragraph gives you three commands that can be used to load balance across multiple links. I'm not telling you which one you have to know!

Router(config)#interface serial 0/0

Router(config-if)#encapsulation ppp

Router(config-if)#ppp multilink

16. What command specifies a link quality over a PPP link.
1. 4^th Paragraph - Router(config-if)#ppp quality percentage (percentage is a number that you have to supply when you actually key in this command)

Section 3.3.3

17. A two router network is running PPP over the serial interfaces that connect them. The enable password on the Denim router is "gateway." The Denim router also has a locally configured authentication password for the Plaid router which is "fortress." Which command must be executed on the Plaid router to allow Denim to authenticate to the Plaid router using CHAP?
1. Look at the Graphic, step 1. It says: "On each router, define the username and password to expect from the remote router:" then gives you a command. Since we are talking about 2 routers working together and being "remote" from each other, so we need to use that command, with the information given in this question. So the final answer would be:

Plaid(config)# username Denim password fortress

Section 3.3.4

18.

Refer to the output of the show interface Serial0/0 command in the graphic shown above. How many NCPs have been established?

a. The answer is 2. I cannot find a good explanation for why, though.

Section 3.3.5

19.

What command was used to display the partial output shown in the graphic shown above?

1. Well, the curriculum gives an example the command, but in no way shows what its output looks like, so..the answer is:

Debug ppp negotiotion

What can be concluded from the output shown in the graphic above (regarding authentication)

1. Again, an unclear answer. So here goes (yep, there are three answers):

The LCPs were already negotiated

The router can begin NCP negotiations.

The debug ppp authentication command was executed