1) What is unicast and how does it work?
A) Unicast is a one-to-one transmission method. A
single frame is sent from the source to a destination on a network. When this
frame is received by the switch, the frame is sent on to the network, and the
network passes the frame to its destination from the source to a specific
destination on a network.
2) What is multicast and how does it work? A) Multicast is a one-to-many transmission method. A single frame is sent from the source to multiple destinations on a network using a multicast address. When this frame is received by the switch, the frame is sent on to the network and the network passes the frame to its intended destination group.
3) What is broadcast and how does it work? A) Broadcast is a one-to-all transmission method. A single frame is sent from the source to a destination on a network using a multicast address. When this frame is received by the switch, the frame is sent on to the network. The network passes the frame to all nodes in the destination network from the source to an unknown destination on a network using a broadcast address. When the switch receives this frame, the frame is sent on to all the networks, and the networks pass the frame on to all the nodes. If it reaches a router, the broadcast frame is dropped.
4) What is fragmentation? A) Fragmentation in a network is the breaking down of a data packet into smaller pieces to accommodate the maximum transmission unit (MTU) of the network.
5) What is MTU? What's the MTU for traditional Ethernet? A) MTU is the acronym for maximum transmission unit and is the largest frame size that can be transmitted over a network. Messages longer than the MTU must be divided into smaller frames. The network layer (Layer 3) protocol determines the MTU from the data link layer (Layer 2) protocol and fragments the messages into the appropriate frame size, making the frames available to the lower layer for transmission without further fragmentation. The MTU for Ethernet is 1518 bytes.
6) What is a MAC address?
A) A MAC address is the physical address of a network device and is 48 bits (6 bytes) long. MAC addresses are also known as physical addresses or hardware addresses.
7) What is the difference between a runt and a giant, specific to traditional Ethernet? A) In Ethernet a runt is a frame that is less than 64 bytes in length, and a giant is a frame that is greater than 1518 bytes in length. Giants are frames that are greater than the MTU used, which might not always be 1518 bytes.
8) What is the difference between store-and-forward and cut-through switching?
A) Cut-through switching examines just the frame header, determining the output switch port through which the frame will be forwarded. Store-and-forward examines the entire frame, header and data payload, for errors. If the frame is error free, it is forwarded out its destination switch port interface. If the frame has errors, the switch drops the frame from its buffers. This is also known as discarding the frame to the bit bucket.
9) What is the difference between Layer 2 switching and Layer 3 switching? A) Layer 2 switches make their forwarding decisions based on the Layer 2 (data link) address, such as the MAC address. Layer 3 switches make their forwarding decisions based on the Layer 3 (network) address.
10) What is the difference between Layer 3 switching and routing?
A) The difference between Layer 3 switching and routing is that Layer 3 switches have hardware to pass data traffic as fast as Layer 2 switches. However, Layer 3 switches make decisions regarding how to transmit traffic at Layer 3 in the same way as a router. A Layer 3 switch cannot use WAN circuits or use routing protocols; a router is still required for these functions.
2) What is multicast and how does it work? A) Multicast is a one-to-many transmission method. A single frame is sent from the source to multiple destinations on a network using a multicast address. When this frame is received by the switch, the frame is sent on to the network and the network passes the frame to its intended destination group.
3) What is broadcast and how does it work? A) Broadcast is a one-to-all transmission method. A single frame is sent from the source to a destination on a network using a multicast address. When this frame is received by the switch, the frame is sent on to the network. The network passes the frame to all nodes in the destination network from the source to an unknown destination on a network using a broadcast address. When the switch receives this frame, the frame is sent on to all the networks, and the networks pass the frame on to all the nodes. If it reaches a router, the broadcast frame is dropped.
4) What is fragmentation? A) Fragmentation in a network is the breaking down of a data packet into smaller pieces to accommodate the maximum transmission unit (MTU) of the network.
5) What is MTU? What's the MTU for traditional Ethernet? A) MTU is the acronym for maximum transmission unit and is the largest frame size that can be transmitted over a network. Messages longer than the MTU must be divided into smaller frames. The network layer (Layer 3) protocol determines the MTU from the data link layer (Layer 2) protocol and fragments the messages into the appropriate frame size, making the frames available to the lower layer for transmission without further fragmentation. The MTU for Ethernet is 1518 bytes.
6) What is a MAC address?
A) A MAC address is the physical address of a network device and is 48 bits (6 bytes) long. MAC addresses are also known as physical addresses or hardware addresses.
7) What is the difference between a runt and a giant, specific to traditional Ethernet? A) In Ethernet a runt is a frame that is less than 64 bytes in length, and a giant is a frame that is greater than 1518 bytes in length. Giants are frames that are greater than the MTU used, which might not always be 1518 bytes.
8) What is the difference between store-and-forward and cut-through switching?
A) Cut-through switching examines just the frame header, determining the output switch port through which the frame will be forwarded. Store-and-forward examines the entire frame, header and data payload, for errors. If the frame is error free, it is forwarded out its destination switch port interface. If the frame has errors, the switch drops the frame from its buffers. This is also known as discarding the frame to the bit bucket.
9) What is the difference between Layer 2 switching and Layer 3 switching? A) Layer 2 switches make their forwarding decisions based on the Layer 2 (data link) address, such as the MAC address. Layer 3 switches make their forwarding decisions based on the Layer 3 (network) address.
10) What is the difference between Layer 3 switching and routing?
A) The difference between Layer 3 switching and routing is that Layer 3 switches have hardware to pass data traffic as fast as Layer 2 switches. However, Layer 3 switches make decisions regarding how to transmit traffic at Layer 3 in the same way as a router. A Layer 3 switch cannot use WAN circuits or use routing protocols; a router is still required for these functions.
V-LAN:
What is a VLAN? When is it used?
Answer: A VLAN is a group of devices on the same broadcast domain,
such as a logical subnet or segment. VLANs can span switch ports, switches
within a switch block, or closets and buildings. VLANs group users and devices
into common workgroups across geographical areas. VLANs help provide
segmentation, security, and problem isolation.
2. When a VLAN is configured on a Catalyst switch port, in how much of the campus network will the VLAN number be unique and significant?
The VLAN number will be significant in the local switch. If trunking is enabled, the VLAN number will be significant across the entire trunking domain. In other words, the VLAN will be transported to every switch that has a trunk link supporting that VLAN.
3. Name two types of VLANs in terms of spanning areas of the campus network.
Local VLAN
End-to-end VLAN
4. What switch commands configure Fast Ethernet port 4/11 for VLAN 2?
interface fastethernet 4/11
switchport mode access
switchport access vlan 2
5. Generally, what must be configured (both switch and end-user device) for a port-based VLAN?
The switch port
6. What is the default VLAN on all ports of a Catalyst switch?
VLAN 1
7. What is a trunk link?
A trunk link is a connection between two switches that transports traffic from multiple VLANs. Each frame is identified with its source VLAN during its trip across the trunk link.
8. What methods of Ethernet VLAN frame identification can be used on a Catalyst switch trunk?
802.1Q
ISL
9. What is the difference between the two trunking methods? How many bytes are added to trunked frames for VLAN identification in each method?
Answer: ISL uses encapsulation and adds a 26-byte header and a 4-byte trailer. 802.1Q adds a 4-byte tag field within existing frames, without encapsulation.
10. What is the purpose of the Dynamic Trunking Protocol (DTP)?
Answer: DTP allows negotiation of a common trunking method between endpoints of a trunk link.
11. What commands are needed to configure a Catalyst switch trunk port Gigabit 3/1 to transport only VLANs 100, 200 through 205, and 300 using IEEE 802.1Q? (Assume that trunking is enabled and active on the port already. Also assume that the interface gigabit 3/1 command already has been entered.)
Answer: switchport trunk allowed vlan 100, 200-205, 300
12. Two neighboring switch trunk ports are set to the auto mode with ISL trunking encapsulation mode. What will the resulting trunk mode become?
Answer: Trunking will not be established. Both switches are in the passive auto state and are waiting to be asked to start the trunking mode. The link will remain an access link on both switches.
13. Complete the following command to configure the switch port to use DTP to actively ask the other end to become a trunk: switchport mode ____ ?
Answer: switchport mode dynamic desirable
14. Which command can set the native VLAN of a trunk port to VLAN 100 after the interface has been selected?
Answer: switchport trunk native vlan 100
15. What command can configure a trunk port to stop sending and receiving DTP packets completely?
switchport nonegotiate
16. What command can be used on a Catalyst switch to verify exactly what VLANs will be transported over trunk link gigabitethernet 0/0?
show interface gigabitethernet 0/0 switchport
or
show interface gigabitethernet 0/0 switchport trunk
17. Suppose that a switch port is configured with the following commands. A PC with a nontrunking NIC card then is connected to that port. What, if any, traffic will the PC successfully send and receive?
Interface fastethernet 0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport trunk allowed vlan 1-1005
switchport mode trunk
Answer: The PC expects only a single network connection, using a single VLAN. In other words, the PC can't participate in any form of trunking. Only untagged or unencapsulated frames will be understood. Recall that an 802.1Q trunk's native VLAN is the only VLAN that has untagged frames. Therefore, the PC will be capable of exchanging frames only on VLAN 10, the native VLAN.
2. When a VLAN is configured on a Catalyst switch port, in how much of the campus network will the VLAN number be unique and significant?
The VLAN number will be significant in the local switch. If trunking is enabled, the VLAN number will be significant across the entire trunking domain. In other words, the VLAN will be transported to every switch that has a trunk link supporting that VLAN.
3. Name two types of VLANs in terms of spanning areas of the campus network.
Local VLAN
End-to-end VLAN
4. What switch commands configure Fast Ethernet port 4/11 for VLAN 2?
interface fastethernet 4/11
switchport mode access
switchport access vlan 2
5. Generally, what must be configured (both switch and end-user device) for a port-based VLAN?
The switch port
6. What is the default VLAN on all ports of a Catalyst switch?
VLAN 1
7. What is a trunk link?
A trunk link is a connection between two switches that transports traffic from multiple VLANs. Each frame is identified with its source VLAN during its trip across the trunk link.
8. What methods of Ethernet VLAN frame identification can be used on a Catalyst switch trunk?
802.1Q
ISL
9. What is the difference between the two trunking methods? How many bytes are added to trunked frames for VLAN identification in each method?
Answer: ISL uses encapsulation and adds a 26-byte header and a 4-byte trailer. 802.1Q adds a 4-byte tag field within existing frames, without encapsulation.
10. What is the purpose of the Dynamic Trunking Protocol (DTP)?
Answer: DTP allows negotiation of a common trunking method between endpoints of a trunk link.
11. What commands are needed to configure a Catalyst switch trunk port Gigabit 3/1 to transport only VLANs 100, 200 through 205, and 300 using IEEE 802.1Q? (Assume that trunking is enabled and active on the port already. Also assume that the interface gigabit 3/1 command already has been entered.)
Answer: switchport trunk allowed vlan 100, 200-205, 300
12. Two neighboring switch trunk ports are set to the auto mode with ISL trunking encapsulation mode. What will the resulting trunk mode become?
Answer: Trunking will not be established. Both switches are in the passive auto state and are waiting to be asked to start the trunking mode. The link will remain an access link on both switches.
13. Complete the following command to configure the switch port to use DTP to actively ask the other end to become a trunk: switchport mode ____ ?
Answer: switchport mode dynamic desirable
14. Which command can set the native VLAN of a trunk port to VLAN 100 after the interface has been selected?
Answer: switchport trunk native vlan 100
15. What command can configure a trunk port to stop sending and receiving DTP packets completely?
switchport nonegotiate
16. What command can be used on a Catalyst switch to verify exactly what VLANs will be transported over trunk link gigabitethernet 0/0?
show interface gigabitethernet 0/0 switchport
or
show interface gigabitethernet 0/0 switchport trunk
17. Suppose that a switch port is configured with the following commands. A PC with a nontrunking NIC card then is connected to that port. What, if any, traffic will the PC successfully send and receive?
Interface fastethernet 0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport trunk allowed vlan 1-1005
switchport mode trunk
Answer: The PC expects only a single network connection, using a single VLAN. In other words, the PC can't participate in any form of trunking. Only untagged or unencapsulated frames will be understood. Recall that an 802.1Q trunk's native VLAN is the only VLAN that has untagged frames. Therefore, the PC will be capable of exchanging frames only on VLAN 10, the native VLAN.
Layer 3 Switching:
1. What might you need to implement interVLAN routing?
** One or more Layer 3 interfaces
One or more SVIs
Static routes
A dynamic routing protocol
2. Can interVLAN routing be performed over a single trunk link?
** Yes. Packets can be forwarded between the VLANs carried over the trunk.
3. To configure an SVI, what commands are needed?
** First, make sure the VLAN is defined on the switch.
interface vlan vlan-id
ip address ip-address mask
no shutdown
4. What command can verify the VLAN assignments on a Layer 2 port?
** show interface type mod/num switchport
or
show interface status
5. A switch has the following interface configurations in its running configuration:
interface fastethernet 0/1
switchport access vlan 5
!
interface vlan 5
ip address 192.168.10.1 255.255.255.0
no shutdown
what is necessary for packets to get from the FastEthernet interface to the VLAN 5 SVI?
Answer: Nothing. Both are assigned to VLAN 5, so normal Layer 2 transparent bridging will take care of all forwarding between the two.
6. What is the source of FIB information?
** The routing table, as computed by the Layer 3 engine portion of a switch.
7. How often is the FIB updated?
** As needed. It is downloaded or updated dynamically by the Layer 3 engine whenever the routing topology changes or an ARP entry changes.
8. What is meant by the term "CEF punt"?
** A packet can't be forwarded or switched by CEF directly because it needs further processing. The packet is "punted" to the Layer 3 engine, effectively bypassing CEF for a more involved resolution.
9. What happens to the FIB when distributed CEF (dCEF) is used?
** It is simply replicated to each of the independent CEF engines. The FIB itself remains intact so that each engine receives a duplicate copy.
10. What happens during a "CEF glean" process?
** The MAC address (ARP reply) for a next-hop FIB entry is not yet known. The Layer 3 engine must generate an ARP request and wait for a reply before CEF forwarding can continue to that destination.
11. What does a multilayer switch do to the IP TTL value just before a packet is forwarded?
** The TTL is decremented by one, as if a router had forwarded the packet.
12. What is fallback bridging?
** On switch platforms that cannot multilayer-switch (route) all routable protocols, those protocols can be bridged transparently between VLANs instead.
13. Is it possible for an SVI to go down? If so, for what reasons?
** Yes. The SVI can be shut down administratively with the shutdown command, as with any other interface. Also, if the VLAN associated with the SVI is not defined or active; the SVI will appear to be down.
** One or more Layer 3 interfaces
One or more SVIs
Static routes
A dynamic routing protocol
2. Can interVLAN routing be performed over a single trunk link?
** Yes. Packets can be forwarded between the VLANs carried over the trunk.
3. To configure an SVI, what commands are needed?
** First, make sure the VLAN is defined on the switch.
interface vlan vlan-id
ip address ip-address mask
no shutdown
4. What command can verify the VLAN assignments on a Layer 2 port?
** show interface type mod/num switchport
or
show interface status
5. A switch has the following interface configurations in its running configuration:
interface fastethernet 0/1
switchport access vlan 5
!
interface vlan 5
ip address 192.168.10.1 255.255.255.0
no shutdown
what is necessary for packets to get from the FastEthernet interface to the VLAN 5 SVI?
Answer: Nothing. Both are assigned to VLAN 5, so normal Layer 2 transparent bridging will take care of all forwarding between the two.
6. What is the source of FIB information?
** The routing table, as computed by the Layer 3 engine portion of a switch.
7. How often is the FIB updated?
** As needed. It is downloaded or updated dynamically by the Layer 3 engine whenever the routing topology changes or an ARP entry changes.
8. What is meant by the term "CEF punt"?
** A packet can't be forwarded or switched by CEF directly because it needs further processing. The packet is "punted" to the Layer 3 engine, effectively bypassing CEF for a more involved resolution.
9. What happens to the FIB when distributed CEF (dCEF) is used?
** It is simply replicated to each of the independent CEF engines. The FIB itself remains intact so that each engine receives a duplicate copy.
10. What happens during a "CEF glean" process?
** The MAC address (ARP reply) for a next-hop FIB entry is not yet known. The Layer 3 engine must generate an ARP request and wait for a reply before CEF forwarding can continue to that destination.
11. What does a multilayer switch do to the IP TTL value just before a packet is forwarded?
** The TTL is decremented by one, as if a router had forwarded the packet.
12. What is fallback bridging?
** On switch platforms that cannot multilayer-switch (route) all routable protocols, those protocols can be bridged transparently between VLANs instead.
13. Is it possible for an SVI to go down? If so, for what reasons?
** Yes. The SVI can be shut down administratively with the shutdown command, as with any other interface. Also, if the VLAN associated with the SVI is not defined or active; the SVI will appear to be down.
Spanning Tree Protocol:
1. What three link types have been defined for Rapid Spanning-Tree
Protocol? (Choose three.)
shared
edge-type
point-to-point
2. What Rapid Spanning Tree Protocol (RSTP) role is assigned to the forwarding port elected for every switched Ethernet LAN segment?
Designated
3. How can a network administrator influence which STP switch become the root bridge?
Set the switch priority to a smaller value than that of the other switches in the network.
4. Refer to the exhibit. What can be determined from the output shown?
The priority was statically configured to identify the root.
5. Which three statements are accurate regarding RSTP and STP? (Choose three.)
Both RSTP and STP use the portfast command to allow ports to immediately transition to forwarding state.
Configuration commands to establish primary and secondary root bridges are identical for STP and RSTP.
Because of the format of the BPDU packet, RSTP is backward compatible with STP.
6. What is the first step in the process of convergence in a spanning tree topology?
Election of the root bridge
7. Which two statements are true about the default operation of STP in a Layer 2 switched environment that has redundant connections between switches? (Choose two.)
Decisions on which port to block when two ports have equal cost depend on the port priority and identity.
Non-root switches each have only one root port.
8. What two elements will exist in a converged network with one spanning tree? (Choose two.)
One root bridge per network
one root port per non-root bridge
9. Which statement or set of paired statements correctly compares STP with RSTP?
STP waits for the network to converge before placing ports into forwarding state. RSTP places alternate ports into forwarding state immediately.
10. Refer to the exhibit. Server sends an ARP request for the MAC address of its default gateway. If STP is not enabled, what will be the result of this ARP request?
Switch A and Switch B will continuously flood the message onto the network.
11. In which two ways is the information that is contained in BPDUs used by switches? (Choose two.)
To identify the shortest path to the root bridge
to determine which ports will forward frames as part of the spanning tree
12. Which two statements describe the BIDs used in a spanning tree topology? (Choose two.)
They consist of a bridge priority and MAC address.
They are used by the switches in a spanning tree topology to elect the root bridge.
13. Which two actions does an RSTP edge port take if it receives a BPDU? (Choose two.)
Immediately loses its edge status
becomes a normal spanning-tree port
14. Which two items are true regarding the spanning-tree portfast command? (Choose two.)
PortFast is Cisco proprietary.
If an access port is configured with PortFast, it immediately transitions from a blocking to a forwarding state.
15. Refer to the exhibit. The spanning-tree port priority of each interface is at the default setting. The network administrator enters the spanning-tree vlan 1 root primary command on S4. What is the effect of the command?
Gi0/2 on S3 transitions to a root port.
16. What two features of the Spanning-Tree Protocol contribute to the time it takes for a switched network to converge after a topology change occurs? (Choose two.)
the max-age timer
the forward delay
17. In which STP state does a port record MAC addresses but not forward user data?
Learning
18. When PVST+ was developed, the Bridge ID was modified to include which information?
VLAN ID
19. Refer to the exhibit. All switches in the network have empty MAC tables. STP has been disabled on the switches in the network. How will a broadcast frame that is sent by host PC1 be handled on the network?
Switch SW1 will forward the broadcast out all switch ports, except the originating port. This will generate an endless loop in the network.
20. Which two criteria does a switch use to select the root bridge? (Choose two.)
Bridge priority
base MAC address
shared
edge-type
point-to-point
2. What Rapid Spanning Tree Protocol (RSTP) role is assigned to the forwarding port elected for every switched Ethernet LAN segment?
Designated
3. How can a network administrator influence which STP switch become the root bridge?
Set the switch priority to a smaller value than that of the other switches in the network.
4. Refer to the exhibit. What can be determined from the output shown?
The priority was statically configured to identify the root.
5. Which three statements are accurate regarding RSTP and STP? (Choose three.)
Both RSTP and STP use the portfast command to allow ports to immediately transition to forwarding state.
Configuration commands to establish primary and secondary root bridges are identical for STP and RSTP.
Because of the format of the BPDU packet, RSTP is backward compatible with STP.
6. What is the first step in the process of convergence in a spanning tree topology?
Election of the root bridge
7. Which two statements are true about the default operation of STP in a Layer 2 switched environment that has redundant connections between switches? (Choose two.)
Decisions on which port to block when two ports have equal cost depend on the port priority and identity.
Non-root switches each have only one root port.
8. What two elements will exist in a converged network with one spanning tree? (Choose two.)
One root bridge per network
one root port per non-root bridge
9. Which statement or set of paired statements correctly compares STP with RSTP?
STP waits for the network to converge before placing ports into forwarding state. RSTP places alternate ports into forwarding state immediately.
10. Refer to the exhibit. Server sends an ARP request for the MAC address of its default gateway. If STP is not enabled, what will be the result of this ARP request?
Switch A and Switch B will continuously flood the message onto the network.
11. In which two ways is the information that is contained in BPDUs used by switches? (Choose two.)
To identify the shortest path to the root bridge
to determine which ports will forward frames as part of the spanning tree
12. Which two statements describe the BIDs used in a spanning tree topology? (Choose two.)
They consist of a bridge priority and MAC address.
They are used by the switches in a spanning tree topology to elect the root bridge.
13. Which two actions does an RSTP edge port take if it receives a BPDU? (Choose two.)
Immediately loses its edge status
becomes a normal spanning-tree port
14. Which two items are true regarding the spanning-tree portfast command? (Choose two.)
PortFast is Cisco proprietary.
If an access port is configured with PortFast, it immediately transitions from a blocking to a forwarding state.
15. Refer to the exhibit. The spanning-tree port priority of each interface is at the default setting. The network administrator enters the spanning-tree vlan 1 root primary command on S4. What is the effect of the command?
Gi0/2 on S3 transitions to a root port.
16. What two features of the Spanning-Tree Protocol contribute to the time it takes for a switched network to converge after a topology change occurs? (Choose two.)
the max-age timer
the forward delay
17. In which STP state does a port record MAC addresses but not forward user data?
Learning
18. When PVST+ was developed, the Bridge ID was modified to include which information?
VLAN ID
19. Refer to the exhibit. All switches in the network have empty MAC tables. STP has been disabled on the switches in the network. How will a broadcast frame that is sent by host PC1 be handled on the network?
Switch SW1 will forward the broadcast out all switch ports, except the originating port. This will generate an endless loop in the network.
20. Which two criteria does a switch use to select the root bridge? (Choose two.)
Bridge priority
base MAC address
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