ICND1 Test #2: LAN Switching Fundamentals

Which three options are switchport configurations that can always avoid duplex mismatch error between the switches?

Set both sides to auto negotiation. Set both sides to half-duplex. Set one side to auto negotiation and the other side to half duplex. Explanation: On an Ethernet connection, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex. The effect of a duplex mismatch is a link that operates inefficiently. Duplex mismatch may be caused by manually setting two connected network interfaces at different duplex modes or by connecting a device that performs auto-negotiation to one that is manually set to a full duplex mode. When a device set to auto-negotiation is connected to a device that is not using auto-negotiation, the auto negotiation process fails. The auto-negotiation end of the connection is still able to correctly detect the speed of the other end, but cannot correctly detect the duplex mode. For backwards compatibility with Ethernet hubs, the standard requires that the auto-negotiating interface fall back to half-duplex mode when it is not successful in auto-negotiation

Which MTU size can cause a baby giant error?

Standard Ethernet frame MTU (payload/actual data) is 1500 bytes. This does not include the Ethernet header and Cyclic Redundancy Check (CRC) trailer, which id 18 bytes in length, to make the total Ethernet frame size of 1518. Here MTU size refers only to Ethernet payload. Ethernet frame size refers to the whole Ethernet frame, including the header and the trailer. Standard Ethernet frame= MTU+ Header & CRC trailer= 1500+18= 1518 bytes Now baby giant frames refer to Ethernet frame size up to 1600 bytes, and jumbo frame refers to Ethernet frame size up to 9216 bytes.

Which command can you enter to view the ports that are assigned to VLAN 20?

Switch#show lan id 20 Explanation: The show vlan [vlan-id] command displays information about a particular VLAN that is identified by a VLAN ID number; valid values are from 1 to 4094

Which command sequence can you enter to create VLAN 20 and assign it to an interface on a switch?

Switch(config)#vlan 20 Switch (config)#Interface gig x/y Switch(config-if)#switchport access vlan 20

What command can you enter to assign an interface to the default VLAN?

Switch(config-if)#switchport access vlan 1 Explanation: In interface configuration mode, we can use the switchport access vlan command followed by the vlan number to set the VLAN that the interface belongs to. SW(config-if)#switchport access vlan number On Cisco switches, VLAN 1 is the default VLAN. To assign an interface, say fa0/2 to the default VLAN, use the following commands: Sw(config)#intfa0/2 SW(config-if)#switchport access vlan1

What is a valid hostname for a switch?

SwitchCisc0 Explanation: A Cisco device hostname must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphens. Names must be 63 characters or fewer. Creating an all numeric hostname is not recommended but the name will be accepted after an error is returned

VLAN 3 is not yet a configured on your switch. What happens if you set the switchport access vlan 3 command in interface configuration mode?

The command is accepted and the respective VLAN is added to vlan.dat. Explanation: In interface configuration mode, we can use the switchport access vlan command followed by the vlan number to set the VLAN that the interface belongs to. SW(config-if)#switchport access vlan number For example, int fa0/2 is configured for VLAN 10:

Configuration of which option is required on a Cisco switch for the Cisco IP phone to work?

The interface as an access port to allow the voice VLAN ID

What are two reasons that duplex mismatches can be difficult to diagnose?

The interface displays a connected (up/up) state even when the duplex settings are mismatched. The symptoms of a duplex mismatch may be intermittent Explanation: A duplex mismatch is a situation in which they switch operates at full-duplex and the connected devices operates at half-duplex, or vice versa. The result of a duplex mismatch is extremely slow performance, intermittent connectivity, and loss of connection. This intermittent impaired performance condition is the most difficult to detect since a connection is established, but with errors which can disturb normal traffic

Two hosts are attached to a switch with the default configuration. Which statement about the configuration is true?

The two hosts are in the same broadcast domain. Explanation: With default configuration all switch ports are in the same broadcast domain. So the two hosts connected to a switch are in the same broadcast domains

Which three statements are true about the operation of a full-duplex Ethernet network?

There are no collisions in full-duplex mode. A dedicated switch port is required for each full-duplex node. The host network card and the switch port must be capable of operating in full-duplex. Explanation: Full duplex connections require a point to point connection between two devices. For full-duplex operation the host needed a full-duplex Network Interface Card, a dedicated switch port operating in full-duplex mode and a medium supporting full-duplex communication, e.g., UTP/STP Cat 5 cable. With this type of connection, both devices can simultaneously send and receive without any collisions occurring. Ethernet switches support full duplex communication at 100 Mbps because a dedicated circuit is established between communicating ports and there is no chance of collision Full-duplex uses one pair of cables for sending and the other pair for receiving data

Which of the following are benefits of VLANs

They allow logical grouping if users by function. They can enhance network security. They increase the number of broadcast domains while decreasing the size of the broadcast domains Explanation: A VLAN makes up a switched network that is logically segmented by functions, project teams, or applications, without regard to the physical location of users. The introduction of VLANS into a network has a number of benefits. The benefits include Security, Segmentation and Flexibility. VLANS allow you to group users into a common broadcast domain, adding new broadcast domains, and reducing the size of individual broadcast domains. The greater flexibility of VLANS allows users to be moved easily. Changes to the network can be a simple as configuring a port and security can be increased.

What are three advantages of VLANs?

They establish broadcast domains in switched networks They can simplify adding, moving, or changing hosts on the network They allow access to network services based on department, not physical location Explanation: A VLAN makes up a switched network that is logically segmented by functions, project teams, or applications, without regard to the physical location of users. Each switch port can be assigned to a VLAN. Ports assigned to the same VLAN share broadcasts. Ports that do not belong to that VLAN do not share these broadcasts. This improves the overall performance of the network. So a VLAN adds broadcast domains, reducing broadcasts on any singe segment. VLANs have nothing to do with collisions. Using switches and routers that have embedded VLAN intelligence obviates the need for expensive, time-consuming recabling to extend connectivity in switched LAN environments. We just need to assign the switch port to the desired VLAN for moving a host from one VLAN to the other.

Which two statements about late collisions are true?

They may indicate a duplex mismatch. By definition, they occur after the 512th bit of the frame has been transmitted. Explanation: The subset of all collisions that happen after the 64th byte (512th bit) of the frame has been transmitted, are called late collisions. In a properly working Ethernet LAN, collisions should occur within the first 64 bytes; late collisions today often point to a duplex mismatch. In normal half-duplex operations late collisions do not occur. However, in a duplex mismatch the collisions seen on the half-duplex side of the link are often Late Collisions. The full-duplex side usually will register FCS(frame check sequence) errors, or Runts

A network interface port has collision detection and carrier sensing enabled on a shared twisted pair network. From this statement, what is known about the network interface port?

This is an Ethernet port operating at half-duplex Explanation: The keywords "shared twisted pair network," and "collision detection and carrier sensing," indicate an ethernet port operating at half duplex. This will be a port connected to a hub. Ethernet cards on shared medium use CSMA/CD technique to detect collisions and resume transmission after a random wait time. Only one device can transmit the signals at once. This results in half-duplex communication.

Which device is used to allow multiple VLANs between switches without using L3 devices?

Trunk

On which type of port can switches interconnect for multi-VLAN communication?

Trunk port Explanation: The Trunk Port on a switch carriers traffic from multiple VLANs to another directly connected switch

Which statement about VLAN operation on Cisco catalyst switches is true?

Unknown unicast frames are retransmitted only to the ports that belong to the same VLAN Explanation: When the switch receives a frame with the destination as a unicast, and the destination address is not in the address table, it forwards the frame on all ports in the same VLAN, expect the port on which the frame was received.

Which protocol allows VLANs to be dynamically configured between multiple switches?

VLAN Trunk Protocol reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributes through all switches in the domain

In an Ethernet network, under what two scenarios can devices transit?

When they detect no other devices are sending. When the medium is idle.

If a switch received a frame while forwarding others, how the frame would be handled?

Will be forwarded at the same time with the current frame Explanation: All Catalyst use store-and-forward switching method, expect the Nexus switches which use cut-through switching method for reduced latency. Therefore, the switch will put new frame in the buffer (queue) indwell transmit it after the current frame is transferred.

Which two options will help to solve the problem of a network that is suffering a broadcast storm?

a router a Layer 3 switch Explanation: A Layer 3 device can eliminate broadcast storms. A router and a Layer 3 switch both operate at Layer 3.

Which command would you configure globally on a Cisco router that would allow you to view directly connected Cisco devices?

cdp run Explanation: to enable to the CDP globally, use the cdp run command in global configuration mode. To disable CDP, use the no form of this command. CDP is enabled by default at the global level and on each supported interface to send or receive CDP information, on Cisco devices.

Which type of MAC address is aged out automatically by the switch?

dynamic

Which command can you enter to determine whether a switch is operating in trunking mode?

show interface switchport Explanation: You can use show interface trunk to show interface switchport command to determine if a switch is operating in trunking mode.

Which two commands can be used to verify a trunk link configuration status on a given cisco switch?

show interfaces interface trunk show interfaces interface switchport Explanation: The show interfaces trunk command will list all the interfaces that are currently trunking. The show interfaces switchport command will show you the operational and administrative mode of each interface. If you are investigating the mode of a particular interface the show interfaces interface switchport command or the show interfaces interface trunk command (where interface is the type/number of the particular interface) is the faster way to go.

If host Z needs to send data through router R1 to a strong server, which destination MAC address does not host Z use to transmit packets?

the MAC address of the interface on R1 that connects to host Z Explanation: In Ethernet transmission, Layer 2 source and destination addresses keep on changing as the frame moves from one device to the other. Layer 2 source address is the MAC address of the last sending device and Layer 2 destination address is the MAC address of receiving device. For packets destined to a host on another IP network, the destination MAC address will be the LAN interface of the router (default gateway). Therefore, the destination Layer 2 address is the MAC address of the interface on R1 that connects to host Z.

For what two purposes does the Ethernet protocol use physical addresses?

to uniquely identify devices at Layer 2 to allow communication between different devices on the same network.

Which two VLANs are reserved for system use only?

0 4095 Explanation: VLANs 3968 to 4095 are reserved for internal use in each VDC by default. VLAN 0 is reserved for 802.1p traffic

What is the maximum size of an Ethernet frame that uses 802.1Q tagging?

1522 bytes Explanation: Standard Ethernet frame=MTU+ Header & CRC trailer =1500 +18 =1518 bytes The 802.1Q tag is 4 bytes. Therefore, the resulting Ethernet frame can be as large as 1522 bytes. The minimum size of the Ethernet frame with 802.1Q tagging is 68 bytes.

If three devices are plugged into one port on a switch and two devices are plugged into a different port, how many collision domains are on the switch?

2 Explanation: Each switch port is a separate collision domain. Two switch ports = Two collision domains

If a router has 3 hosts connected in one port and two other hosts connected in another port, how may broadcast domains are present on the router?

2 Explanation: With default settings, each router port makes a separate broadcast domain. Therefore, 2 router ports create 2 broadcast domains.

Assuming the default switch configuration, which VLAN range can be added, modified and removed on a Cisco switch?

2 through 1001 Explanation: Normal-range VLANs are VLANs with VLAN IDs to 1 to 1005. If the switch is in VTP server or VTP transparent mode, you can add, modify or remove configurations for VLANs 2 to 1001 in the VLAN database. (VLAN IDs 1 and 1002 to 1005 are automatically created and cannot be removed.)

If a router has four interfaces and each interface is connected to four switched, how many broadcast domains are present on the router?

4 Explanation: Each router interface makes a separate broadcast domain. Therefore, 4 router interfaces create 4 broadcast domains.

A switch has 48 ports and 4 VLANs. How many collisions and broadcast domains exist on the switch (collision, broadcast)?

48,4 Explanation: Each switchport is a separate collision domain and each VLAN is a separate broadcast domain. Therefore, the switch contains 48 collision domains and 4 broadcast domains.

Which three of these statements regarding 802.1Q trunking are correct?

802.1Q native VLAN frames are untagged by default. 802.1Q trunks can use 10 Mb/s Ethernet interfaces. 802.1Q trunks should have native VLANS that are the same at both ends. Explanation: Yes, it is true that 802.1Q trunks can use 10 Mbps Ethernet but is it is not common practice and not recommended. 802.1Q trunk does not require full-duplex connectivity; it works on half-duplex as well but full-duplex connectivity is recommended for desired performance, because the trunk carries traffic for all the VLANs.

What is true about Ethernet?

802.3 protocol CSMA/CD stops transmitting when congestion occurs Explanation: The algorithm, known as the carrier sense multiple access with collision detection algorithm, defines hoe to act when a collision does occur. IEEE 802.3 is a standard specification for Ethernet, a method of physical communication in local area network

Why will a switch never learn a broadcast address?

A broadcast address will never be the source address of a frame

What are three benefits of implementing VLANs?

A higher level of network security can be reached by separating sensitive data traffic from other network traffic. A more efficient use of bandwidth can be achieved allowing many logical networks to use the same network infrastructure. Broadcast storms can be mitigated by increasing the number of broadcast domains, thus reducing their size. Explanation: VLAN provide numerous networking benefits and have become popular in the market. For instance, it helps reduce administrative costs when users are geographically dispersed.

On which type of device is every port in the same collision domain?

A hub Explanation: The definition of a collision is a set of LAN devices whose frames could collide with one another. This happens with hubs, bridges, repeaters and wireless access points as only one device can send and receive. If more than one device tries sending or receiving, the information is lost and irrecoverable it will need to be resent. This can slow down network performance along with making it a security threat

How does a Layer 2 switch differ from a hub?

A switch tracks MAC addresses of directly-connected devices: -Learning: They learn the source (MAC) address of each device connected to a port -Forwarding: They intelligently switch frames to the port or ports where the destination is located -Rewarding layer-2 loops: They remove loops with the Spanning Tree Protocol (STP), so that frames do not continually circle around the network.

A workstation has just resolved a browser URL to the IP address of a server. Which protocol will the workstation now use to determine the destination MAC address to be placed into frames directed toward the server?

ARP Explanation: On Ethernet devices use Address Resolution Protocol (ARP) to find IP address to MAC addresses mapping

If a host experiences intermittent issues that relate to congestion within a network while remaining connected, what could cause congestion on this LAN?

Broadcast storms Explanation: Too many hosts in a broadcast domain would cause may broadcasts, resulting in network congestion. Broadcast storms will reduce the available bandwidth. A network with a low bandwidth capacity is more likely to be congested. Half-duplex operation also causes congestion but it creates intermittent connectivity problem as well, that is not the case here (notice the phrase while remaining connected.)

Which table displays the MAC addresses that are learned on a switch?

CAM Explanation: Content Addressable Memory (CAM) table is a MAC address table that maps switch ports to the MAC addresses found on those ports. TCAM(ternary content-addressable memory) is a specialized type of high speed memory that searches its entire contents in a single clock cycle. The term ternary refers to the ability to store and query data using three different inputs: 0,1 and X. TCAM is found on layer 3 switches and routers

Which two protocols can detect Native VLAN mismatch errors?

CDP STP

On a Cisco switch, which protocol determines if an attached VoIP phone is from Cisco or from another vendor?

CDP Explanation: Cisco Discovery Protocol is Cisco's proprietary protocol that provides information about connected Cisco devices only. So if you can see the VoIP phone via the show cdp neighbors command on a Cisco switch then that phone is from Cisco

What feature allows a device to use a switch port that is configured for half-duplex to access the network?

CSMA/CD

Which MAC protocol sets a random timer to reattempt communication?

CSMA/CD Explanation: Carrier sense multiple access with collision detection (CSMA/CD) is a media access control method used most notably in early Ethernet technology for local area networking. It uses a carrier sensing scheme in which a transmitting station detects collisions by sensing transmissions from other stations while transmitting a frame. When this collision condition is detected, the station stops transmitting that frame, transmits a jam signal, and then waits for a random time interval before trying to resend the frame.

When troubleshooting Ethernet connectivity issues, how can you verify that an IP address is known to a router?

Check whether the IP address is in the ARP table. Explanation: ARP table is the table that holds binding between a certain IP address and corresponding MAC address. It is a layer 3 to Layer 2 mapping table on IP-enabeld devices. MAC address table, also known as Content Addressable Memory (CAM) table is a table that switches use to forward packets at layer 2. It is a binding between a MAC address, VLAN and a port number in the switch.

Which statement about native VLAN traffic is true?

Cisco Discovery Protocol traffic travels on the native VLAN by default Explanation: By default, all management traffic (VTP, CDP, DTP, LACP etc) is always sent using Native VLAN over trunk. It does not mean the Native VLAN should he VLAN 1, we can define any VLAN as Native VLAN on per trunk port basis

Which feature builds a FIB and an adjacency table to expedite packet forwarding

Cisco Express Forwarding Explanation: Cisco Express Forwarding (CEF) is a packet-switching technique that is the default for many of Cisco routers. It provides the ability to switch packets through a device in a very quick efficient way while also keeping low load on the processor of the router

Which symptom most commonly indicates that two connecting interfaces are configured with a duplex mismatch?

Collisions on the interface Explanation: A duplex mismatch occurs when one device is operating at full duplex and the connected device is operating at half duplex or the other way around. Duplex mismatches can cause extremely slow performance, intermittent connectivity and loss of connection. Duplex mismatches on Ethernet segments in the same VLAN (same subnet) results in half-duplex operation that leads to collisions.

Which network configuration can you use to segregate broadcast traffic for two different departments in your organization?

Configure a separate VLAN for each department Explanation: A VLAN is a separate broadcast domain. You can segregate the broadcast traffic of two departments by configuring a separate VLAN for each department

What switching method duplicates the first six bytes of a frame before making a switching decision?

Cut-through switching

At which layer of the OSI model does the protocol that provides the information that is displayed by the show cdp neighbors command operate?

Data link Explanation: The show cdp neighbors command uses CDP to provide information about neighboring connected Cisco devices. CDP operates at the Data Link layer (layer 2)

Which address type does a switch use to make selective forwarding decisions?

Destination MAC address Explanation: Layer 2 switches maintain a table of destination MAC addresses and associated ports. When a unicast frame is received, its destination MAC address is searched in the MAC address table. If a match is found the frame is forwarded through the port associated with that destination MAC address. IF no entry matches, the frame is flooded out all ports expect the receiving port. In brief, the switches forward frames based on the destination MAC address.

Which two pieces of information can be shared with LLDP TLVS?

Device management address Device type

Which feature facilitates the tagging of frames on a specific VLAN?

Encapsulation Explanation: The Trunk Port on a switch carries traffic from all VLANS to another directly connected switch. To identify the traffic of one VLAN from that of others, Frame tagging (encapsulation) is used to insert VLAN membership into Ethernet frames, before sending them through the shared turns link. Two types of frame encapsulations are: ISL- Cisco proprietary, and 802. 1Q - an IEEE standard.

Which two statements about Ethernet standards are true?

Ethernet is defined by IEEE standard 802.3. When an Ethernet network uses CSMA/CD, it terminates transmission as soon as a collision occurs

Which three options are fields in a basic Ethernet data frame?

Frame check sequence Type/length Preamble

Which method does a connected trunk port use to tag VLAN traffic?

IEEE 802.1Q Explanation: IEEE 802.1Q (sometimes referred to as 1Q or DOT1Q) is the networking standard that supports virtual LANs (VLANs) on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in the handling such frames.

Which statement about unicast frame forwarding on a switch is true?

If the destination MAC address is unknown, the frame is flooded to every port that is configured in the same VLAN expect on the port that it was received on. Explanation: Layer 2 switches maintain a table of destination MAC addresses and associated ports. When a unicast frame is received, its destination MAC address is searched in the MAC address Table. If a match is found the frame is forwarded through the port associated with that destination MAC address. If no entry matches, the frame is flooded out all ports in the same VLAN expect the receiving port.

Which two statements describe the operation of the CSMA/CD access method?

In a CSMA/CD collision domain, stations must wait until the media is not in use before transmitting. After a collision, all stations run a random backoff algorithm. When the backoff delay period has expired, all stations have equal priority to transmit data. Explanation: The algorithm, known as the carrier sense multiple access with collision detection CSMA/CD algorithm, defines how to act when a collision does occur The CSMA/CD algorithm works like this: 1. A device with a frame to send listens until the Ethernet is not busy 2. When the Ethernet is not busy, the sender begins sending the frame 3. The sender listens to make sure that no collision occurred 4. Once the senders hear the collision, each of them sends a jamming signal, to ensure that all stations recognize the collision and stop sending frames 5. After the jamming is complete, each sender randomizes a timer and waits that long 6. When each timer expires, the process starts over with Step 1 So, all devices on the Ethernet need to use CSMA/Cd to avoid collisions and to recover when inadvertent collisions occur

What is the function of the command "switchport trunk naive VLAN 999" on a Cisco Catalyst switch?

It designates VLAN 999 for untagged traffic. Explanation: The switchport trunk native command specifies the native VLAN number for the trunk. By default, this is VLAN 1. When a tagged frame is received by a port, the tag is respected. All untagged frames will be assigned to the native VLAN. Therefore, "switch port trunk native VLAN 999 designates VLAN 999 for untagged traffic, is the correct answer.

Which statement about LLDP is true?

It is configured in global configuration mode. Explanation: The Link Layer Discovery Protocol is a vendor-neutral link layer protocol in the Internet Protocol Suite used by network devices for advertising their identify, capabilities, and neighbors on an IEEE 802 local area network, principally wired Ethernet. LLDP performs functions similar to other proprietary protocols, such as Cisco Discovery Protocol. The Cisco implementation of LLDP is based on the IEEE 802.1ab standard. Use of LLDP is limited to 802.2 media types such as Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) networks

Which of the following is a characteristic of full-duplex communication?

It is point-to-point only. Explanation: Full-duplex connections require a point-to point connection between two devices. With this type of connection, both devices can simultaneously send and receive without any collisions occurring

Which two of these are characteristics of the 802.1Q protocol?

It modifies the 802.3 frame header and thus requires that the FCS be recomputed. It is a trunking protocol capable of carrying untagged frames. Explanation: There are two trunking protocols, ISL and 802.3 1Q. ISL is Cisco proprietary and 802.1Q is the open standard protocol defined by IEEE.

Which interface counter can you use to diagnose a duplex mismatch problem?

Late collisions Explanation: A duplex mismatch is a situation on which the switch operates at full-duplex and the connected device operates at half-duplex, or vice-versa. The result of a duplex mismatch is extremely slow performance, intermittent connectivity, and loss of connection. Use the show interfaces command to verify the duplex settings

What adverse situation can occur if an Ethernet cable is too long?

Late collisions Explanation: Late collisions should never occur in a properly designed Ethernet network. They usually occur when Ethernet cables are too long or when there are too many repeaters in the network

On which OSI layer does a VLAN operate?

Layer 2 Explanation: VLANs operate at Layer 2 (the data link layer) of the OSI model. Administrators often configure a VLAN to map directly to an IP network, or subnet, which gives the appearance of involving Layer 3 (the network layer).

Which two types of information are held in the MAC address table?

MAC address Port numbers

Which three statements accurately describe layer 2 Ethernet switches?

Micro-segmentation decreases the number of collisions on the network. In a properly functioning network with redundant switched paths, each switched segment will contain one root bridge with all its ports in the forwarding state. All other switches in that broadcast will have only one root port. Establishing vlans increases the number of broadcast domains Explanation: Micro-segmentation is a method for dividing your network using switches. Each switch port is a separate collision domain. Only two nodes are coexisting on each collision domain: one node is the host and the other one is the switch. Micro-segmentation increases the number of collision domains by dividing a large collision domain into smaller collision domains. As a result, micro-segmentation decreases the number of collisions on the network.

What is the first 24 bits in a MAC address called?

OUI Explanation: A MAC adress is 48 bin in binary (12 hexadecimal digits). The first half of the address identifies the manufacture of the card, called the Organizationally Unique Identifier (OUI). This code is assigned to each manufacturer by the IEEE.

Which fields are contained in a Layer 2 Ethernet frame?

Preamble Type/length Frame Check Sequence

Which command can you enter to re-enable Cisco Discovery Protocol on a local router after it has been disabled?

Router (config)#cdp run Explanation: To enable Cisco Discovery Protocol on an interface, use the cdp enable command in the interface configuration mode. To disable CDP on an interface, use the no form of this command. If CDP is disabled globally, you cannot enable it on each interface using the cdp enable interface configuration mode command.

After you configure the Loopback0 interface, which command can you enter to verify the status of the interface and determine whether fast switching is enabled?

Router#show ip interface loopback 0

Which six-byte field in a basic Ethernet frame must be an individual address?

SA Explanation: Source Adress (6-byte) must be unique in a basic Ethernet frame. The Destination Address can be a unique address or a broadcast or multicast address.