Modules 1 - 4: Switching Concepts, VLANs, and InterVLAN Routing
What is the minimum Ethernet frame size that will not be discarded by the receiver as a runt frame?
64 bytes Explanation: The minimum Ethernet frame size is 64 bytes. Frames smaller than 64 bytes are considered collision fragments or runt frames and are discarded.
Refer to the exhibit. How many broadcast domains are displayed?
8 Explanation: A router defines a broadcast boundary, so every link between two routers is a broadcast domain. In the exhibit, 4 links between routers make 4 broadcast domains. Also, each LAN that is connected to a router is a broadcast domain. The 4 LANs in the exhibit result in 4 more broadcast domains, so there are 8 broadcast domains in all.
Which tasks can be accomplished by using the command history feature? (Choose two.)
=Set the command history buffer size. =Recall previously entered commands. Explanation: The history command allows you to view and reuse previously entered commands stored in the buffer. It is also used to manage the of the buffer.
What is the significant difference between a hub and a Layer 2 LAN switch?
A hub extends a collision domain, and a switch divides collision domains. Explanation: Hubs operate only at the physical layer, forwarding bits as wire signals out all ports, and extend the collision domain of a network. Switches forward frames at the data link layer and each switch port is a separate collision domain which creates more, but smaller, collision domains. Switches do not manage broadcast domains because broadcast frames are always forwarded out all active ports.
Which switch component reduces the amount of packet handling time inside the switch?
ASIC Explanation: Application-specific integrated circuits (ASICs) are used in Cisco switches to speed up switch operations so that the switch can have an increased number of ports without degrading switch performance.
What is a characteristic of an IPv4 loopback interface on a Cisco IOS router?
It is a logical interface internal to the router. Explanation: The loopback interface is a logical interface internal to the router and is automatically placed in an UP state, as long as the router is functioning. It is not assigned to a physical port and can therefore never be connected to any other device. Multiple loopback interfaces can be enabled on a router.
Canonical Format Identifier (CFI)
an identifier that enable Token Ring frames to be carried across Ethernet links
Because destination is not known, switch forwards frame out all ports except port through which frame arrived.
occurs second
What must an administrator have in order to reset a lost password on a router?
physical access to the router Explanation: Console access to the device through a terminal or terminal emulator software on a PC is required for password recovery.
When configuring a switch for SSH access, what other command that is associated with the login local command is required to be entered on the switch?
username username secret secret Explanation: The login local command designates that the local username database is used to authenticate interfaces such as console or vty.
Under which two occasions should an administrator disable DTP while managing a local area network? (Choose two.)
when connecting a Cisco switch to a non-Cisco switch on links that should not be trunking Explanation: Cisco best practice recommends disabling DTP on links where trunking is not intended and when a Cisco switch is connected to a non-Cisco switch. DTP is required for dynamic trunk negotiation.
Which protocol adds security to remote connections?
SSH Explanation: SSH allows a technician to securely connect to a remote network device for monitoring and troubleshooting. HTTP establishes web page requests. FTP manages file transfer. NetBEUI is not routed on the Internet. POP downloads email messages from email servers.
What does a switch use to locate and load the IOS image?
BOOT environment variable Explanation: The BOOT environment variable contains the information about where to find the IOS image file.
Which statement is correct about Ethernet switch frame forwarding decisions?
Frame forwarding decisions are based on MAC address and port mappings in the CAM table. Explanation: Cut-through frame forwarding reads up to only the first 22 bytes of a frame, which excludes the frame check sequence and thus invalid frames may be forwarded. In addition to broadcast frames, frames with a destination MAC address that is not in the CAM are also flooded out all active ports. Unicast frames are not always forwarded. Received frames with a destination MAC address that is associated with the switch port on which it is received are not forwarded because the destination exists on the network segment connected to that port.
Which characteristic describes cut-through switching?
Frames are forwarded without any error checking. Explanation: Cut-through switching reduces latency by forwarding frames as soon as the destination MAC address and the corresponding switch port are read from the MAC address table. This switching method does not perform any error checking and does not use buffers to support different Ethernet speeds. Error checking and buffers are characteristics of store-and-forward switching.
A network contains multiple VLANs spanning multiple switches. What happens when a device in VLAN 20 sends a broadcast Ethernet frame?
Only devices in VLAN 20 see the frame. Explanation: VLANs create logical broadcast domains that can span multiple VLAN segments. Ethernet frames that are sent by a device on a specific VLAN can only be seen by other devices in the same VLAN.
On a switch that is configured with multiple VLANs, which command will remove only VLAN 100 from the switch?
Switch(config)# no vlan 100 Explanation: To remove all VLANs from a switch, the delete flash:vlan.dat command would be used. To change the assigned VLAN for an interface, the no switchport access vlan 100 interface configuration command would be used. To remove VLAN 100 as an allowed VLAN on a trunk, the no switchport trunk allowed vlan 100 would be used, but this would not remove the VLAN from the switch. To delete a single VLAN, such as VLAN 100, the no vlan 100 global configuration command would be used.
explanation
The first step a switch does when processing a frame is to see if the source MAC address is in the MAC address table. If the address is not there, the switch adds it. The switch then examines the destination MAC address and compares it to the MAC address table. If the address is in the table, the switch forwards the frame out the corresponding port. If the address is missing from the table, the switch will forward the frame to all ports except the port through which the frame arrived.
How do switch buffers affect network performance?
They store frames received, thus preventing premature frame discarding when network congestion occurs. Explanation: Switches have large frame buffers that allow data waiting to be transmitted to be stored so the data will not be dropped. This feature is beneficial especially if the incoming traffic is from a faster port than the egress port used for transmitting.
Explanation: The IEEE 802.1Q standard header includes a 4-byte VLAN tag:
Type - A 2-byte value called the tag protocol ID (TPID) value. User priority - A 3-bit value that supports level or service implementation. Canonical Format Identifier (CFI) - A 1-bit identifier that enables Token Ring frames to be carried across Ethernet links. VLAN ID (VID) - A 12-bit VLAN identification number that supports up to 4096 VLAN IDs.
type
a value for the tag protocol ID value
User Priority
a value that supports level or service implementation
After which step of the switch bootup sequence is the boot loader executed?
after POST execution Explanation: The correct bootup sequence order is as follows:1.- The switch loads and executes the POST.2.- The switch loads the boot loader software.3.- The boot loader performs low-level CPU initialization.4.- The boot loader initializes the flash memory.5.- The boot loader locates and loads the default IOS image.
Which impact does adding a Layer 2 switch have on a network?
an increase in the size of the broadcast domain Explanation: Adding a Layer 2 switch to a network increases the number of collision domains and increases the size of the broadcast domain. Layer 2 switches do not decrease the amount of broadcast traffic, do not increase the amount of network collisions and do not increase the number of dropped frames.
Which command is used to set the BOOT environment variable that defines where to find the IOS image file on a switch?
boot system Explanation: The boot system command is used to set the BOOT environment variable. The config-register and confreg commands are used to set the configuration register. The boot loader command supports commands to format the flash file system, reinstall the operating system software, and recover from a lost or forgotten password.
Which switch characteristic helps keep traffic local and alleviates network congestion?
high port density Explanation: Switches that have a lot of ports (high port density) reduce the number of switches required and keep some of the traffic locally on the switch, thus removing the need to send it between switches.
What is the first action in the boot sequence when a switch is powered on?
load a power-on self-test program Explanation: The first action to take place when a switch is powered on is the POST or power-on self-test. POST performs tests on the CPU, memory, and flash in preparation for loading the boot loader.
The switch adds the source MAC address to the MAC address table
occurs first
If one end of an Ethernet connection is configured for full duplex and the other end of the connection is configured for half duplex, where would late collisions be observed?
on the half-duplex end of the connection Explanation: Full-duplex communications do not produce collisions. However, collisions often occur in half-duplex operations. When a connection has two different duplex configurations, the half-duplex end will experience late collisions. Collisions are found on Ethernet networks. Serial interfaces use technologies other than Ethernet.
Which command displays information about the auto-MDIX setting for a specific interface?
show controllers Explanation: To examine the auto-MDIX setting for a specific interface, the show controllers ethernet-controller command with the phy keyword should be used.
What information is added to the switch table from incoming frames?
source MAC address and incoming port number Explanation: A switch "learns" or builds the MAC address table based on the source MAC address as a frame comes into the switch. A switch forwards the frame onward based on the destination MAC address.
Which switching method ensures that the incoming frame is error-free before forwarding?
store-and-forward Explanation: Two methods used by switches to transmit frames are store-and-forward and cut-through switching. The store-and-forward method performs error checking on the frame using the frame check sequence (FCS) value before sending the frame. In contrast, cut-through switching sends the frame as soon as the destination MAC address part of the header has been read and processed.
Refer to the exhibit. In what switch mode should port G0/1 be assigned if Cisco best practices are being used?
trunk Explanation: The router is used to route between the two VLANs, thus switch port G0/1 needs to be configured in trunk mode.
Which two characteristics describe the native VLAN? (Choose two.)
The native VLAN traffic will be untagged across the trunk link. The native VLAN provides a common identifier to both ends of a trunk. Explanation: The native VLAN is assigned to 802.1Q trunks to provide a common identifier to both ends of the trunk link. Whatever VLAN native number is assigned to a port, or if the port is the default VLAN of 1, the port does not tag any frame in that VLAN as the traffic travels across the trunk. At the other end of the link, the receiving device that sees no tag knows the specific VLAN number because the receiving device must have the exact native VLAN number. The native VLAN should be an unused VLAN that is distinct from VLAN1, the default VLAN, as well as other VLANs. Data VLANs, also known as user VLANs, are configured to carry user-generated traffic, with the exception of high priority traffic, such as VoIP. Voice VLANs are configured for VoIP traffic. The management VLAN is configured to provide access to the management capabilities of a switch.
What happens to switch ports after the VLAN to which they are assigned is deleted?
The ports stop communicating with the attached devices. Explanation: The affected ports must be reconfigured for an active VLAN.
Refer to the exhibit. A network administrator is reviewing port and VLAN assignments on switch S2 and notices that interfaces Gi0/1 and Gi0/2 are not included in the output. Why would the interfaces be missing from the output?
They are configured as trunk interfaces. Explanation: Interfaces that are configured as trunks do not belong to a VLAN and therefore will not show in the output of the show vlan brief commands.
VLAN ID
VLAN number
