Data Link Networking Concepts

This chapter is from the book

CCNA Exam Prep 2 (Exam 640-801)

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This chapter is from the book

This chapter is from the book 

CCNA Exam Prep 2 (Exam 640-801)

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Apply Your Knowledge

Exercises

3.1 IEEE 802.3 Ethernet Standards

You may be asked to identify the standards associated with IEEE Ethernet on the CCNA exam. In this exercise, I am listing the ethernet specification and want you to complete the table to include the IEEE-defined standard, the associated speed, and the cable or media type used for each specification. You may refer back to Tables 3.4, 3.5, 3.6, and 3.7 to check your answers.

Estimated Time: 10 minutes

Review Questions

1. Define token-passing.
2. List the characteristics of a token ring network.
3. List the characteristics of an FDDI network.
4. Define unicast, multicast, and broadcast.
5. Describe CSMA/CD.
6. What are the primary tasks performed by both bridges and switches?
7. Describe half- and full-duplex.
8. Define microsegmentation.

Exam Questions

1. Which of the following is the IEEE standard for token ring?
1. 802.2
2. 802.3a
3. 802.3u
4. 802.5
2. ANSI X3T9.5 is the specification for which LAN technology?
1. Token ring
2. Fast Ethernet
3. FDDI
4. LLC
3. What Data Link layer technology inserts a three-byte token (or special bit pattern) into a frame and passes it in a single direction from one node to another until it forms a complete loop?
1. Token-passing
2. Unicast
3. Multicast
4. Broadcast
4. Which of the following LAN protocols use token-passing for frame transmission? (Choose the 2 best answers.)
1. Fast Ethernet
2. Token ring
3. Gigabit Ethernet
4. FDDI
5. This MAC sublayer address type identifies the MAC address of an individual LAN or NIC card.
1. Unicast
2. Multicast
3. Broadcast
4. Token
6. Which of the following addresses is an example of a unicast address? (Choose all that apply.)
1. 0000.0C12.3456
2. 0100.5E12.3456
3. FFFF.FFFF.FFFF
4. 0200.1111.1111
7. This MAC sublayer address type sends a frame to a subset of devices on the LAN.
1. Unicast
2. Multicast
3. Broadcast
4. Token
8. Which of the following addresses is an example of a multicast address?
1. 0000.0C12.3456
2. 0100.5E12.3456
3. FFFF.FFFF.FFFF
4. 0200.1111.1111
9. This MAC sublayer address type sends a frame to all the devices on the LAN.
1. Unicast
2. Multicast
3. Broadcast
4. Token
10. Which of the following addresses is an example of a broadcast address?
1. 0000.0C12.3456
2. 0100.5E12.3456
3. FFFF.FFFF.FFFF
4. 0200.1111.1111
11. The OSI model Data Link layer uses __________ to transport data between layers.
1. Bits
2. Frames
3. Packets
4. Segments
12. Which field of a frame is used for error detection?
1. SAP
2. DSAP
3. SSAP
4. FCS
13. Which IEEE Ethernet standards define Gigabit Ethernet? (Choose all that apply.)
1. 802.3u
2. 802.3ab
3. 802.3z
4. 802.3ae
14. Bridges and switches segment a network and create an additional _______________ domain for each segment.
1. Collision
2. Broadcast
3. Unicast
4. Multicast
15. Bridges and switches examine the __________________ of each inbound frame to learn MAC addresses.
1. Multicast MAC address
2. Broadcast MAC address
3. Source MAC address
4. Destination MAC address
16. Which device uses ASIC hardware chips for frame forwarding?
1. Hub
2. Repeater
3. Bridge
4. Switch
17. With a 10Mbps ethernet LAN, dedicated bandwidth enables a switch port to guarantee what data transmission speed?
1. 10Mbps
2. 100Mbps
3. 1000Mbps
4. 10,000Mbps
18. This Data Link protocol eliminates loops that are caused by redundant connections.
1. CRC
2. FCS
3. CSMA/CD
4. STP
19. This communication mode allows for only one-way data transmissions at any time.
1. 10Mbps
2. 100Mbps
3. Half-duplex
4. Full-duplex
20. This communication mode allows for simultaneous two-way data transmissions.
1. 10Mbps
2. 100Mbps
3. Half-duplex
4. Full-duplex

Answers to Review Questions

1. Token-passing is a Data Link protocol that inserts a three-byte token (or special bit pattern) into a frame and passes it around the network in a single direction from one node to another until it forms a complete loop. The node that has possession of the token is the only one that can send data at any given time on that LAN. Because only one node can send data at a time, collisions are avoided.
2. Standardized by the IEEE 802.5 specification

A token-passing media access technology

Set up as a physical ring or physical star topology

Creates a logical ring topology

Speeds are assigned as either 4Mbps or 16Mbps

Utilizes an MSAU rather than a switch or hub

Provides collision-free data transfer

High overhead

3. Developed by ANSI with the ANSI X3T9.5 specification

A token-passing media access technology

Set up as a dual ring topology

Redundant, fault-tolerant network

Speed is 100Mbps

Runs over fiber-optic cable

Not susceptible to EMI

Provides collision-free data transfer

Fault-detection provided by beaconing

High overhead

4. A unicast address identifies the MAC address of an individual LAN or NIC card.

A multicast address forwards a frame to a subset of devices in the same LAN. IEEE ethernet multicast addresses always begin with 0100.5E in hexadecimal format. The last three bytes can be any combination.

A broadcast address sends a frame to all devices in the same LAN. Broadcast addresses are always the same value, which is FFFF.FFFF.FFFF.

5. CSMA/CD or Carrier Sense Multiple Access Collision Detection is an algorithm that sends a jam signal to notify the devices that there has been a collision. The devices then halt transmission for a random back-off time.
6. The primary tasks performed by both bridges and switches are as follows:

The source MAC address of every inbound frame is examined to learn its MAC address.

You can decide whether to forward or filter a frame based on the destination MAC address.

Eliminate loops that are caused by redundant connections by configuring Spanning Tree Protocol (STP).

7. Half-duplex allows for one-way communication, which means that a device can only send or receive a data transmission at any given time. As a part of a shared collision domain, hubs must use half-duplex.

Full-duplex allows for two-way communication, which means that a device can simultaneously send and receive data transmissions. Full-duplex is available with dedicated switch port connections to a single device. If a switch port connection is configured for full-duplex, the CSMA/CD algorithm must be disabled. Also, an ethernet connection set for full-duplex allows for 100% transmission speeds in both directions.

8. Microsegmentation occurs when a switch creates a dedicated path for sending and receiving transmissions with each connected host. Each host then has a separate collision domain and a dedicated bandwidth.

Answers to Exam Questions

1. D. IEEE 802.5 defines token ring. Answers A, B, and C are incorrect because IEEE 802.2 defines LLC, 802.3a defines ethernet, and 802.3u defines Fast Ethernet.
2. C. ANSI X3T9.5 defines FDDI. Answers A, B, and D are incorrect because they are all IEEE standards. IEEE 802.5 defines token ring, 802.3u defines Fast Ethernet, and 802.2 defines LLC.
3. A. Token-passing inserts a three-byte token (or special bit pattern) into a frame and passes it in a single direction from one node to another until it forms a complete loop. Answers B, C, and D are all incorrect because unicast, multicast, and broadcast are all types of ethernet addresses.
4. B, D. Token ring and FDDI use token-passing to send frames. Answers A and C are incorrect because Fast Ethernet and Gigabit Ethernet both use 802.3 MAC and 802.2 LLC headers and trailers for framing.
5. A. Unicast addresses identify the MAC address of an individual LAN or NIC card. Answer B is incorrect because multicast addresses send a frame to a group of devices in the same LAN. Answer C is incorrect because broadcast addresses send a frame to all the devices in the same LAN. Answer D is incorrect because a token is a special bit pattern used with token-passing networks.
6. A, D. Both 0000.0C12.3456 and 0200.1111.1111 are unicast addresses. 0000.0C is Cisco’s OUI. Answers B and C are incorrect because 0100.5E12.3456 is a multicast address and FFFF.FFFF.FFFF is a broadcast address.
7. B. Multicast addresses send a frame to a subset of devices in the same LAN. Answer A is incorrect because unicast addresses identify the MAC address of an individual LAN or NIC card. Answer C is incorrect because broadcast addresses send a frame to all the devices in the same LAN. Answer D is incorrect because a token is a special bit pattern used with token-passing networks.
8. B. 0100.5E12.3456 is a multicast address. Multicast addresses always start with 0100.5E. Answers A and D are incorrect because both 0000.0C12.3456 and 0200.1111.1111 are unicast addresses. Answer C is incorrect because FFFF.FFFF.FFFF is a broadcast address.
9. C. Broadcast addresses send a frame to all the devices in the same LAN. Answer A is incorrect because unicast addresses identify the MAC address of an individual LAN or NIC card. Answer B is incorrect because multicast addresses send a frame to a subset of devices in the same LAN. Answer D is incorrect because a token is a special bit pattern used with token-passing networks.
10. C. Broadcast addresses are always represented as FFFF.FFFF.FFFF. Answers A and D are incorrect because both 0000.0C12.3456 and 0200.1111.1111 are unicast addresses. Answer B is incorrect because 0100.5E12.3456 is a multicast address.
11. B. Frames are used by the Data Link layer to transport data between the Network and Physical layer. Framing is the process of interpreting data that is either received or sent out across the network. Answers A, C, and D are incorrect because bits are used at the Physical layer, packets are used at the Network layer, and segments are used at the Transport layer of the OSI model.
12. D. The frame check sequence (FCS) field of a frame uses a mathematical formula to determine whether any bit errors occurred during data transmission. Answer A is incorrect because Service Access Point (SAP) identifies the upper-layer protocol such as IP. Answer B is incorrect because DSAP is the destination SAP or destination upper-layer protocol. Answer C is incorrect because SSAP is the source SAP or the source upper-layer protocol.
13. B, C. IEEE 802.3ab and 802.3z define Gigabit Ethernet standards. Answers A and D are incorrect because 802.3u defines the Fast Ethernet standard, and 802.3ae defines the 10 Gigabit Ethernet standard.
14. A. Collision domains are increased with the addition of bridges or switches on a network. Answer B is incorrect because routers create additional broadcast domains. Answers C and D are incorrect because unicast and multicast are both addresses used by ethernet.
15. C. The source MAC address of an incoming frame is examined by a bridge or switch to learn the MAC address for the bridge table. Answers A and B are incorrect because multicast and broadcast addresses can never be the source MAC address. Answer D is incorrect because the destination MAC address is not used by a bridge or switch to create the bridge table.
16. D. Switches use ASIC hardware chips for frame forwarding. Answers A and B are incorrect because hubs and repeaters do not forward frames because they are Physical layer or Layer 1 devices. Answer C is incorrect because bridges use software for frame forwarding.
17. A. 10Mbps is guaranteed with dedicated bandwidth on a 10Mbps ethernet LAN. Answers B, C, and D are incorrect because other speeds of 100, 1000, and 10,000Mbps are all faster speeds that require a different ethernet LAN standard.
18. D. Spanning Tree Protocol (STP) is a Data Link protocol that eliminates loops caused by redundant connections on a LAN. Answers A and B are incorrect because cyclical redundancy check (CRC) and frame check sequence (FCS) both provide error detection. Answer C is incorrect because CSMA/CD is an algorithm that is used for arbitration on an ethernet network.
19. C. Half-duplex allows for only one-way data transmissions at any time. Answers A and B are incorrect because 10Mbps and 100Mbps are speed classifications primarily associated with ethernet LANs. Answer D is incorrect because full-duplex allows for two-way data transmissions.
20. D. Full-duplex allows for simultaneous two-way data transmissions. Answers A and B are incorrect because 10Mbps and 100Mbps are speed classifications primarily associated with ethernet LANs. Answer C is incorrect because half-duplex allows for only one-way data transmissions at any time.

Suggested Readings and Resources

The following are some recommended readings for LAN networking and related terminology:

1. "TechEncyclopedia," http://www.techweb.com/encyclopedia.
2. "RFC 1700," http://www.isi.edu/in-notes/rfc1700.txt.
3. "Layer 1 & 2," http://www.hojmark.net/layer1-2.html#lan.
4. "Cisco Long-Reach Ethernet," http://www.cisco.com/warp/public/779/servpro/solutions/long_ethernet/.
5. Barnes, David and Sakandar, Basir. Cisco LAN Switching Fundamentals. Cisco Press, 2004.