Cisco CCENT/CCNA ICND1 100-101 Chapter 3

Which of the following is an accurate speed at which a leased line can operate in the United States? a. 100 Mbps b. 100 Kbps c. 256 Kbps d. 6.4 Mbps

256 Kbps

Which of the following is an accurate speed at which a leased line can operate in the United States? A. 100 Mbps B. 256 Kbps C. 100 Kbps D. 6.4 Mbps

256 Kbps Explanation: Leased lines can run at various preset speeds. These include multiples of 64 kbps, up through 24 times 64 kbps. The speeds can also be multiples of T1 speed (1.544 Mbps), up to 28 times that speed.

When PC1 on an Ethernet network sends a packet to a remote PC2 that is on another Ethernet network, and the packet is routed by exactly two routers, connected by an HDLC WAN connection, how many different Layer 2 headers will be created to encapsulate the IP packet as it travels from PC1 to PC2? A. None. HDLC doesn't use Ethernet headers. B. 3 C. 2 D. 1 E. 4

3 PC1 will use an Ethernet header, the first router will use an HDLC header, and the second router will use an Ethernet header, for a total of three. HDLC uses HDLC Layer 2 headers for any HDLC next-hop routers in the path. The HDLC would contribute to one of the headers being used in the path between PC1 and PC2.

What does the FCS do in the HDLC Header Fields?

A field used by the error detection process; it is the only trailer field in this table

What does the Address do in the HDLC Header Fields?

Identifies the destination device

What are the parts of the HDLC Header Fields?

Flag Address Type FCS

How does EoMPLS link uses Ethernet?

For both Layer 1 and Layer 2 functions.

What does the Type do in the HDLC Header Fields?

Identifies the type of Layer 3 packet encapsulated inside the frame

What is the Internet core?

Is a collection of LANs and WANs owned and operated by Internet service providers (ISP).

What are HDLC and PPP?

HDLC and PPP are Layer 2 encapsulation methods

Fred has just added DSL service at his home, with a separate DSL modem and consumer-grade router with four Ethernet ports. Fred wants to use the same old phone he was using before the installation of DSL. Which is most likely true about the phone cabling and phone used with his new DSL installation? A. The old phone must be replaced with a digital phone. B. He uses the old phone, cabled to the DSL modem's ports. C. He uses the old phone, cabled to an existing telephone port, and not to any new device. D. He uses the old phone, cabled to one of the router/switch device's Ethernet ports.

He uses the old phone, cabled to an existing telephone port, and not to any new device. Explanation: With DSL, the requirements on the phone's wiring are unchanged. The phone can connect to any working telephone jack, as if the DSL modem and router did not exist.

What are the two most popular data link layer protocols used for leased lines between two routers?

High-Level Data Link Control (HDLC) Point-to-Point Protocol (PPP)

Which of the following fields in the HDLC header used by Cisco routers does Cisco add, beyond the ISO standard HDLC? a. Flag b. Type c. Address d. FCS

Type

Which of the following fields in the HDLC header used by Cisco routers does Cisco add, beyond the ISO standard HDLC? A. Address B. Type C. Flag D. FCS

Type Explanation: The standard HDLC header does not include a Type field, which identifies the type of packet encapsulated inside the HDLC frame.

What is the purpose of the FCS field in an HDLC frame? A. Used to indicate to the receiving device that a new frame is arriving B. Used for error detection C. Identifies the destination L2 address for the frame D. Used for identifying the type of L3 payload being carried in the frame E. Specifies the destination IP address for the frame

Used for error detection The FCS field is used for error detection and is included as a trailer in the HDLC frame. The address field in the HDLC header indicates the Layer 2 destination address. The HDLC header and trailer information doesn't include the Layer 3 IP destination address (that is in the Layer 3 header information). The Type field in the HDLC header identifies the type of Layer 3 payload that is being encapsulated. A preamble is the concept of a recognizable bit pattern so that the receiving node will realize that a new frame is arriving. In HDLC, this is a field named Flag.

What does the TCP/IP network layer focuses on?

forwarding IP packets from the sending host to the destination host.

What are some of the details of Leased Lines?

The leased line service delivers bits in both directions, at a predetermined speed, using fullduplex logic.

At what layer do leased line function?

At Layer 1

Which of the following best describes the main function of OSI Layer 1 as used in WANs? a. Framing b. Delivery of bits from one device to another c. Addressing d. Error detection

Delivery of bits from one device to another

In the cabling for a leased line, which of the following typically connects to a four-wire line provided by a telco? a. Router serial interface without internal CSU/DSU b. CSU/DSU c. Router serial interface with internal transceiver d. Switch serial interface

CSU/DSU

In the cabling for a leased line, which of the following typically connects to a four-wire line provided by a telco? A. Switch serial interface B. CSU/DSU C. Router serial interface without internal CSU/DSU D. Router serial interface with internal transceiver

CSU/DSU Explanation: The four-wire circuit cable supplied by the telco connects to the device acting as the CSU/DSU. That can be an external CSU/DSU or a CSU/DSU integrated into a router serial interface card. LAN switches do not have serial interfaces, and router serial interfaces do not have transceivers.

Which of the following Internet access technologies, used to connect a site to an ISP, offers asymmetric speeds? A. Leased lines B. DSL C. BGP D. Cable Internet Select 2 answers.

DSL Cable Internet Explanation: Leased lines transmit data at the same speed in both directions, making it a symmetric service. DSL and cable Internet offer asymmetric speeds, with a faster downstream speed. BGP is a routing protocol and is not an Internet access technology.

Which of the following best describes the main function of OSI Layer 1 as used in WANs? A. Framing B. Error detection C. Delivery of bits from one device to another D. Addressing

Delivery of bits from one device to another Explanation: OSI Layer 1, the physical layer, defines how to physically transmit bits using some kind of physical medium, like a cable or radio waves. OSI Layer 2, the data link layer, defines protocols that control and manage the transmission, including the definition of data link frames, which include addresses, and fields to help perform error detection.

What does EoMPLS stand for?

Ethernet over Multi Protocol Label Switching

What are three Examples of Internet Access Links?

Leased Line DSL Cable

Which of the following are examples of common Internet access links? A. DSL B. HDLC C. Leased line D. PPP E. Cable Select 3 answers.

Leased lines, DSL, and cable are all examples of common Internet access links.

What does the Flag do in the HDLC Header Fields?

Lists a recognizable bit pattern so that the receiving nodes realize that a new frame is arriving

What does CISCO add to the HDLC Framing?

Proprietary Cisco HDLC (Adds Type Field)

Two routers, R1 and R2, connect using an Ethernet over MPLS service. The service provides point-to-point service between these two routers only, as a Layer 2 Ethernet service. Which of the following are the most likely to be true about this WAN? A. R1 will forward data link frames to R2 using an HDLC header/trailer. B. R1 will forward data link frames to R2 using an Ethernet header/trailer. C. R1 will connect to a physical Ethernet link, with the other end of the cable connected to R2. D. R1 will connect to a physical Ethernet link, with the other end of the cable connected to a device at the WAN service provider point of presence. Select 2 answers.

R1 will forward data link frames to R2 using an Ethernet header/trailer. R1 will connect to a physical Ethernet link, with the other end of the cable connected to a device at the WAN service provider point of presence. Explanation: The physical installation uses a model in which each router uses a physical Ethernet link to connect to some SP device in an SP facility called a point of presence (POP). The Ethernet link does not span from each customer device to the other. From a data link perspective, both routers use the same Ethernet standard header and trailer used on LANs; HDLC does not matter on these Ethernet WAN links.

How does the receiver of an HDLC frame know what has been encapsulated within that frame? A. HDLC only encapsulates IPv4 B. Based on the Flag field C. Based on the FCS field D. From the IP address (IPv4, IPv6, and so on) E. The Type field in the header

The Type field in the header Explanation: In the HDLC header, the Type field indicates the type of Layer 3 packet encapsulated within the HDLC Layer 2 frame. HDLC can encapsulate many different types of protocols, not just IPv4. The FCS field is used for error detection. The Flag field is similar to an Ethernet preamble, which is a specific bit pattern that allows a receiving device to realize that a new frame is arriving. The IP address is in the L3 header, not in the HDLC header.

How does the receiver of an HDLC frame know what has been encapsulated within that frame? A. Based on the Flag field B. Based on the FCS field C. HDLC only encapsulates IPv4 D. The Type field in the header E. From the IP address (IPv4, IPv6, and so on)

The Type field in the header In the HDLC header, the Type field indicates the type of Layer 3 packet encapsulated within the HDLC Layer 2 frame. HDLC can encapsulate many different types of protocols, not just IPv4. The FCS field is used for error detection. The Flag field is similar to an Ethernet preamble, which is a specific bit pattern that allows a receiving device to realize that a new frame is arriving. The IP address is in the L3 header, not in the HDLC header.

What is the purpose of the FCS field in an HDLC frame? A. Used for error detection B. Identifies the destination L2 address for the frame C. Specifies the destination IP address for the frame D. Used for identifying the type of L3 payload being carried in the frame E. Used to indicate to the receiving device that a new frame is arriving

Used for error detection Explanation: The FCS field is used for error detection and is included as a trailer in the HDLC frame. The address field in the HDLC header indicates the Layer 2 destination address. The HDLC header and trailer information doesn't include the Layer 3 IP destination address (that is in the Layer 3 header information). The Type field in the HDLC header identifies the type of Layer 3 payload that is being encapsulated. A preamble is the concept of a recognizable bit pattern so that the receiving node will realize that a new frame is arriving. In HDLC, this is a field named Flag.

Describe High-Level Data Link Control (HDLC)

When one router sends an HDLC frame, it can only go one place: to the other end of the link. So, while HDLC has an address field, the destination is implied.

What functions do data link protocols perform?

to control the correct delivery of data over a physical link of a particular type.