Get Familiar With Interconnecting Cisco Networking Devices Part 1
BackBy Certification Magazine — October 2, 2008
These questions are based on 640-822: Interconnecting Cisco Networking Devices Part 1.A self test software practice test for Cisco CCENT and CCNA certifications.
Objective: Implement a small switched network.
Sub-objective: Explain the technology and media access control method for Ethernet technologies.
Single answer, multiple-choice
Which media access control method is used by Ethernet technology to minimize collisions in the network?
A. CSMA/CD.
B. Token passing.
C. Back-on algorithm.
D. Full-duplex.
Answer:
A. CSMA/CD.
Tutorial:
Carrier Sense Multiple Access - Collision Detection (CSMA/CD) is used by Ethernet technology to minimize collisions in the network. The CSMA/CD method uses a back-off algorithm to calculate random time for retransmission after a collision. When two stations start transmitting at the same time, their signals will collide. The CSMA/CD method detects the collision, and both stations hold the retransmission for a certain amount of time, determined by the back-off algorithm. This is an effort to help ensure that the retransmitted frames do not collide.
Token passing is used by the token-ring network topology to control communication on the network.
Full-duplex is the Ethernet communication mode that allows workstation to send and receive simultaneously. With the use of full-duplex, the bandwidth of the station can effectively be doubled. Hubs are not capable of handling full-duplex communication. You need dedicated switch ports to allow full-duplex communication.
The back-on algorithm is an invalid option. There is no such contention method.
Reference:
Cisco Documentation > Internetworking Technology Handbook > Ethernet Technologies
Objective: Implement an IP addressing scheme and IP services to meet network requirements for a small branch office.
Sub-objective: Identify and correct IP addressing issues.
Multiple answer, multiple-choice
Which two addresses are in the same subnet? (Choose two.)
A. 192.168.1.55/26
B. 192.168.1.85/26
C. 192.168.1.45/26
D. 192.168.1.203/26
Answer:
A. 192.168.1.55/26
C. 192.168.1.45/26
Tutorial:
When a /26 mask is used with a class C address such as 192.168.1.0, the interval between the resulting network IDs is 64. That means that resulting subnets are as follows:
192.168.1.0
192.168.1.64
192.168.1.128
192.168.1.192
Therefore, the only two options in the same subnet are 192.168.1.55 and 192.168.1.45, which are both in the 192.168.1.0 subnet.
192.168.185 is the only address given that is in the 192.168.1.64 subnet.
192.168.1.203 is the only option given that is in the 192.168.1.192 subnet.
Reference:
Cisco > Support > IP Routing > Design TechNotes > Document ID: 13788 > IP Addressing and Subnetting for New Users
Objective: Implement a small routed network.
Sub-objective: Select the appropriate media, cables, ports and connectors to connect routers to other network devices and hosts.
Single answer, multiple-choice
How many serial ports are on a Cisco 2501 router?
A. 3
B. 1
C. 2
D. 4
Answer:
C. 2
Tutorial:
There are two serial and one Ethernet interface on a Cisco 2501 router. The Serial interfaces are synchronous DB-60 serial ports that are used for the purpose of providing Wide Area Network (WAN) connections. High-speed lines (E1 or T1) can be configured using serial interfaces. In synchronous communication, the communication takes place using synchronization. The communication depends on the timing for controlling the transmission. This includes agreement on parameters such as the time interval between the sending of data bits.
All other options are incorrect.
References:
Cisco Documentation > Cisco IOS Release 12.0 Dial Solutions Configuration Guide > Configuring Synchronous Serial Ports
2000 Trainers: Serial Ports on Cisco Routers
Objective: Explain and select the appropriate administrative tasks required for a WLAN.
Sub-objective: Identify and describe the purpose of the components in a small wireless network (including: SSID, BSS, ESS).
Single answer, multiple-choice
Which wireless authentication standard uses a pre-shared key (PSK) in the personal authentication mode?
A. WPA.
B. WPA2.
C. WEP.
D. LEAP.
Answer:
B. WPA2.
Tutorial:
WPA2 uses a PSK for authentication in personal mode.
Enterprise and Personal are the two operational modes of WPA and WPA2. In Personal mode, WPA uses a PSK for authentication and the temporal key integrity protocol (TKIP) and message integrity check (MIC) for encryption. WPA2 uses a PSK for authentication, but uses AES and cipher block chaining message authentication code protocol (CCMP) for encryption. In enterprise mode, WPA and WPA2 use 802.1x or EAP for authentication.
WPA2 is the next generation of WPA. In addition to TKIP, the use of the advance encryption standard (AES)-based algorithm and CCMP make WPA2 virtually impossible to break.
Wi-Fi protected access (WPA) is a security solution from the Wi-Fi Alliance based on the IEEE 802.11i standard. WPA was developed to overcome weaknesses in the wired equivalent privacy (WEP). WPA uses an RC4 stream cipher, with a 128-bit key and a 48-bit initialization vector (IV) for data encryption. Use of a larger IV helps counter the key recovery attacks possible on WEP. WPA also employs Temporal Key Integrity Protocol (TKIP), which changes the encryption keys dynamically after a specified interval of time.
TKIP eliminates any chance of encryption key compromise. TKIP includes other important features such as per-packet key mixing that ensures every data packet is secured with a unique encryption key. In addition, TKIP also includes a message integrity check and a re-keying mechanism to ensure full protection.
WEP is an encryption technique that uses 40-bit and 128-bit static keys that provide secure transaction between an AP and a wireless client by encrypting the transmitted data. WEP keys must be configured and matched on both the AP and the wireless client.
Lightweight EAP (LEAP) uses the TCP handshake process similar to EAP-TLS but employs a user name and password for authentication using a RADIUS server. EAP-TLS requires the use of certificates.
LEAP authentication provides two-way security:
• Using dynamic session WEP keys: The dynamic session-based WEP keys are generated by the RADIUS authentication server and encrypt the data sent over wireless media between the access points and the client adapters. This reduces administration since the keys then do not require static configuration on both ends as with standard WEP.
• User authentication: The user database can be defined either on the RADIUS server or on a Windows server.
References:
Cisco > Solutions > Enterprise > Networking Solutions for Enterprise > Wireless/Mobility Solutions For Enterprise > Wireless Network Security > White Papers > “Five Steps to Securing Your Wireless LAN and Preventing Wireless Threats”
Cisco > Support > Product Support > Wireless > Cisco 4400 Series Wireless LAN Controllers > Configure > Configuration Examples and Technotes > Wi-Fi Protected Access (WPA) in a Cisco Unified Wireless Network Configuration Example
Objective: Implement and verify WAN links.
Sub-objective: Describe different methods for connecting to a WAN.
Single answer, multiple-choice
Which wide area network (WAN) switching technology is used by asynchronous transfer mode (ATM)?
A. Packet switching.
B. Virtual switching.
C. Cell switching.
D. Circuit switching.
Answer:
C. Cell switching.
Tutorial:
Cell switching is a WAN switching technology that is used by ATM. ATM is an International Telecommunication Union-Telecommunications (ITU-T) standard for transmission of data, voice or video traffic using a fixed size frame of 53 bytes, known as cells. Out of these 53 bytes, the initial 5 bytes are header information and the rest 48 bytes is the payload.
Packet switching is incorrect because packet switching is popularly used for data transfer, as data is not delay sensitive, and it does not require real-time transfer from a sender to a receiver. With packet switching, the data is broken into labeled packets and transmitted using packet-switching networks.
Virtual switching is incorrect because no such WAN switching technology exists.
Circuit switching is incorrect because circuit switching dynamically establishes a virtual connection between a source and destination. The virtual connection cannot be used by other callers unless the circuit is released. Circuit switching is the most common technique used by the public switched telephone network (PSTN) to make phone calls.
A dedicated circuit is temporarily established for the duration of call between caller and receiver. Once the caller or receiver hangs up the phone, the circuit is released and is available for other users.
Reference:
Cisco Documentation > Internetworking Technology Handbook > Introduction to WAN Technologies > Circuit Switching
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