Explanation:
The full duplex mode of transmission is not provided by flow control. Full duplex transmission is an Ethernet concept where hosts are able to send and receive at the same time. There are no collisions in a full-duplex Ethernet network. A dedicated switch port is required for each node in a full-duplex Ethernet network. Both the host’s NIC and the switch port must be capable of operating in full-duplex mode. When full duplex is implemented, no collisions will occur on the link between the switch and the device. That will be one error condition that can be removed from consideration when troubleshooting a full duplex link.

Flow control is a function that prevents network congestion. It does so by ensuring that the transmitting device does not flood the receiving device with data. The following statements are true regarding flow control:

– Controls the amount of data which the sender can send to the receiver.
– Uses buffering, transmitting source-quench messages, and windowing to handle network congestion.
– Determines the rate at which the data is transmitted between the sender and receiver.
– Types of flow control include windowing, buffering, and congestion avoidance.

Flow control generally operates at the Transport layer in the OSI model. The Transport layer is responsible for error-free and sequential delivery of data. This layer is used to manage data transmission between devices.

Buffering is a method by which network devices use to save temporary overflows of excess data into the memory. The data is stored in the memory until it is processed.

Source-quench messages are used by the devices that receive the data to avoid buffer overflow.
Windowing is a scheme in which an acknowledgement is required by the source device from the destination after the transmission of a fixed number of packets.

Explanation:
A router allows communication across separate broadcast domains. A broadcast domain is group of hosts and network devices in which a broadcast frame sent by one host can be received by all of the other hosts in the broadcast domain. A router determines the path to other destination networks, and forwards data packets to the next hop along this path. A router operates at Layer 3 of the Open System Interconnect (OSI) layered communication model and uses an Internet Protocol (IP) address hierarchy to identify and route data through source and destination devices.

A switch does not allow communication across separate broadcast domains. A switch creates collision domains and enables communications across different collision domains. A collision domain is a logical group of hosts and network devices where packets can potentially collide with one another, causing a communications disruption. Switches forward broadcasts so they do not form a separate broadcast domain unless Virtual LANs (VLANs) are created.

A hub does not allow communication across separate broadcast domains. A hub transmits frames, which means that they neither form separate collision or broadcast domains nor allow communication across these domains. Hubs are multiport devices that allow consolidation of various LAN segments and amplify signals that pass through them. Hubs operate at OSI Layer 1.

An access point does not allow communication across separate broadcast domains. Access points (APs) are OSI Layer 2 wireless hubs that allow client hosts to connect to the backbone network wirelessly.

Explanation:
Network Control Protocol (NCP) is responsible for negotiating upper-layer protocols that will be carried across the PPP connection. NCP defines how the two PPP peers negotiate with the network layer protocols, such as IP and IPX, which will be used across the PPP connection.

Link Control protocol (LCP) is not responsible for negotiating upper-layer protocols that will be carried across a PPP connection. Link Control protocol (LCP) has the primary responsibility of negotiating and maintaining the PPP connection. LCP, defined in Request for Comments (RFCs) 1548 and 1570, has the primary responsibility to establish, configure, authenticate, and test a PPP connection. LCP negotiates the following when setting up a PPP connection:

– Authentication method used (PAP or CHAP), if any
– Compression algorithm used (Stacker or Predictor), if any
– Callback phone number to use, if defined
– Multilink; other physical connections to use, if configured

Local Management Interface (LMI) is not responsible for negotiating upper-layer protocols that will be carried across the PPP connection. LMI is a characteristic of a frame relay connection. There are three types of LMIs supported by Cisco routers:
– Cisco
– ANSI Annex D
– Q933-A Annex A

LMI has nothing to do with PPP connections.

Integrated Services Digital Network (ISDN) is a type of WAN connection and has nothing to do with PPP connections.

Explanation:
The Serial 0 is up, line protocol is down statement in the output signifies the following:

– There are no problems with the physical connectivity.
– There is a configuration problem in the local or remote router.
– The remote router might not be sending the keep-alives.
– There may be a problem with the leased lines such as line noise and a malfunctioning switch.
– There is an incorrect configuration of the CSU/DSU, which can cause timing issues on the cable.
– The local or remote CSU/DSU might have failed.

The option stating that the shutdown interface command is present in the router configuration is incorrect because if the shutdown interface command is present in the router configuration, the message displayed would be Serial 0 is administratively down, line protocol is down.

The option stating that a cable is unplugged is incorrect because that would be indicated by Serial 0 is down, line protocol is down. Physical problems such as a bad cable or cable unplugged are addressed in the first part of the output (serial0 is up/down).

The option stating that the message refers to normal operation of the interface is incorrect because the line protocol is shown as down, which indicates a problem. Objective:

Explanation:
The show interfaces trunk command displays a list of interfaces currently operating as trunks, and their configuration (such as supported VLANs or frame tagging method).

Switch# show interfaces trunk
Port Mode Encapsulation Status Native vlan Gi0/1 desirable 802.1q trunking 1
Gi0/2 desirable 802.1q trunking 1

Port Vlans allowed on trunk Gi0/1 1-4094
Gi0/2 1-4094
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>

This output indicates that switch ports Gi0/1 and Gi0/2 are both currently operating as trunks (Status), and that 802.1q frame tagging is being used on the trunk links.

The remaining options are incorrect because they are not valid Cisco IOS commands.

Explanation:
The show ip ospf command is used to view information about the OSPF routing processes. It does so by displaying the collection of link states present in the database.

The show ip ospf database command is incorrect because this command is used to view the OSPF database for a specific router.

The show ip ospf statistics command is incorrect because this command is no longer valid in IOS version 12.4.

The show ip ospf traffic command is incorrect because this command is no longer valid in IOS version 12.4.

Explanation:
Full-duplex communication occurs when workstations can send and receive data simultaneously. To support full-duplex communication, both communicating hosts should be configured to transmit in full-duplex mode. With the use of full-duplex communication, the bandwidth can effectively be doubled. Hubs are not capable of handling full-duplex communication, and you need a dedicated switch port to allow full-duplex communication.

Half-duplex is the term used for the Ethernet communication mechanism when hosts can send or receive data, but not simultaneously.

Explanation:
Default routes are to route packets that are destined for networks not listed in the routing table. Also, default routes are ideal for use in stub networks. Stub networks are those that have only one adjacent router interface and therefore only one interface to send any packet, regardless of destination. When used in this fashion the default route will be the only route in the routing table.

The following statements are also true of default routes:
A default route is also known as the gateway of last resort.
The default route in Internet Protocol Version 4 (IPv4) is represented as 0.0.0.0/0.

The option stating that default routes are used to route packets destined only for networks that are listed in the routing table is incorrect. Default routes are used for routing packets that are destined for networks not listed in the routing table.

The option stating that default routes should not be used in a stub network is incorrect. Default routes are helpful in topologies where it is not necessary to learn specific networks, making them ideal for use in a stub network.
The option stating that network security is increased by using default routes is incorrect. Default routes are not concerned with enhancing network security.

Explanation:
The “r” in the output of the show cdp neighbors command is a capability code that represents a repeater. The capability codes from the output of the show cdp neighbors command along with their descriptions are:

Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge S – Switch, H – Host, I – IGMP, r – Repeater