CCNA 2 - Modules 5-6 - Redundant Networks Flashcards
(55 cards)
What additional information is contained in the 12-bit extended system ID of a BPDU?
- MAC address
- VLAN ID
- IP address
- port ID
- VLAN ID
During the implementation of Spanning Tree Protocol, all switches are rebooted by the network administrator. What is the first step of the spanning-tree election process?
- Each switch with a lower root ID than its neighbor will not send BPDUs.
- All the switches send out BPDUs advertising themselves as the root bridge.
- Each switch determines the best path to forward traffic.
- Each switch determines what port to block to prevent a loop from occurring.
- All the switches send out BPDUs advertising themselves as the root bridge.
Which STP port role is adopted by a switch port if there is no other port with a lower cost to the root bridge?
- designated port
- root port
- alternate
- disabled port
- root port
Explanation:
The root port is the port with the lowest cost to reach the root bridge.
Which two concepts relate to a switch port that is intended to have only end devices attached and intended never to be used to connect to another switch? (Choose two.)
- bridge ID
- edge port
- extended system ID
- PortFast
- PVST+
- edge port
- PortFast
Which three components are combined to form a bridge ID?
- extended system ID
- cost
- IP address
- bridge priority
- MAC address
- port ID
- extended system ID
- bridge priority
- MAC address
Explanation:
The three components that are combined to form a bridge ID are bridge priority, extended system ID, and MAC address.
Match the STP protocol with the correct description. (Not all options are used.)
In which two port states does a switch learn MAC addresses and process BPDUs in a PVST network? (Choose two.)
- disabled
- forwarding
- listening
- blocking
- Forwarding
- Learning
Explanation:
Switches learn MAC addresses at the learning and forwarding port states. They receive and process BPDUs at the blocking, listening, learning, and forwarding port states.
If no bridge priority is configured in PVST, which criteria is considered when electing the root bridge?
- lowest MAC address
- lowest IP address
- highest IP address
- highest MAC address
- lowest MAC address
Explanation:
Only one switch can be the root bridge for a VLAN. The root bridge is the switch with the lowest BID. The BID is determined by priority and the MAC address. If no priority is configured then all switches use the default priority and the election of the root bridge will be based on the lowest MAC address.
Match the spanning-tree feature with the protocol type. (Not all options are used.)
Place the options in the following order:
- PVST - Cisco implementation of IEEE 802.1D
- RSTP - Fast converging enhancement of IEEE 802.1D
- MSTP - IEEE standard that reduces the number of STP instances
- MST - Proprietary per VLAN implementation of IEEE 802.1w
- Rapid PVST+ - an evolution of STP that provides faster convergence
When the show spanning-tree vlan 33 command is issued on a switch, three ports are shown in the forwarding state. In which two port roles could these interfaces function while in the forwarding state? (Choose two.)
- alternate
- designated
- disabled
- blocked
- root
- designated
- root
Explanation:
The role of each of the three ports will be either designated port or root port. Ports in the disabled state are administratively disabled. Ports in the blocking state are alternate ports.
What is the function of STP in a scalable network?
- It decreases the size of the failure domain to contain the impact of failures.
- It protects the edge of the enterprise network from malicious activity.
- It combines multiple switch trunk links to act as one logical link for increased bandwidth.
- It disables redundant paths to eliminate Layer 2 loops.
- It disables redundant paths to eliminate Layer 2 loops.
Explanation:
STP is an important component in a scalable network because it allows redundant physical connections between Layer 2 devices to be implemented without creating Layer 2 loops. STP prevents Layer 2 loops from forming by disabling interfaces on Layer 2 devices when they would create a loop.
What is a characteristic of spanning tree?
- It is enabled by default on Cisco switches.
- It is used to discover information about an adjacent Cisco device.
- It has a TTL mechanism that works at Layer 2.
- It prevents propagation of Layer 2 broadcast frames.
- It is enabled by default on Cisco switches.
Explanation: Spanning tree does work at Layer 2 on Ethernet-based networks and is enabled by default, but it does not have a TTL mechanism. Spanning tree exists because Layer 2 frames do not have a TTL mechanism.
Layer 2 frames are still broadcast when spanning tree is enabled, but the frames can only be transmitted through a single path through the Layer 2 network that was created by spanning tree. Cisco Discovery Protocol (CDP) is used to discover information about an adjacent Cisco device.
Which spanning tree standard supports only one root bridge so that traffic from all VLANs flows over the same path?
- PVST+
- 802.1D
- MST
- Rapid PVST
- 802.1D
Explanation:
MST is the Cisco implementation of MSTP, an IEEE standard protocol that provides up to 16 instances of RSTP. PVST+ provides a separate 802.1D spanning-tree instance for each VLAN that is configured in the network.
802.1D is the original STP standard defined by the IEEE and allows for only one root bridge for all VLANs. 802.1w, or RSTP, provides faster convergence but still uses only one STP instance for all VLANs.
What is the purpose of the Spanning Tree Protocol (STP)?
- creates smaller collision domains
- prevents routing loops on a router
- prevents Layer 2 loops
- allows Cisco devices to exchange routing table updates
- creates smaller broadcast domains
- prevents Layer 2 loops
Explanation:
The Spanning-Tree Protocol (STP) creates one path through a switch network in order to prevent Layer 2 loops.
What is the value used to determine which port on a non-root bridge will become a root port in a STP network?
- the path cost
- the highest MAC address of all the ports in the switch
- the lowest MAC address of all the ports in the switch
- the VTP revision number
- the path cost
Explanation:
STP establishes one root port on each non-root bridge. The root port is the lowest-cost path from the non-root bridge to the root bridge, indicating the direction of the best path to the root bridge. This is primarily based on the path cost to the root bridge.
Refer to the exhibit. Which switch will be the root bridge after the election process is complete?
- S1
- S2
- S3
- S4
- S2
Explanation:
The root bridge is determined by the lowest bridge ID, which consists of the priority value and the MAC address. Because the priority values of all of the switches are identical, the MAC address is used to determine the root bridge. Because S2 has the lowest MAC address, S2 becomes the root bridge.
What are two drawbacks to turning spanning tree off and having multiple paths through the Layer 2 switch network? (Choose two.)
- The MAC address table becomes unstable.
- The switch acts like a hub.
- Port security becomes unstable.
- Broadcast frames are transmitted indefinitely.
- Port security shuts down all of the ports that have attached devices.
- The MAC address table becomes unstable.
- Broadcast frames are transmitted indefinitely.
Explanation:
Spanning tree should never be disabled. Without it, the MAC address table becomes unstable, broadcast storms can render network clients and the switches unusable, and multiple copies of unicast frames can be delivered to the end devices.
A small company network has six interconnected Layer 2 switches. Currently all switches are using the default bridge priority value. Which value can be used to configure the bridge priority of one of the switches to ensure that it becomes the root bridge in this design?
- 1
- 28672
- 32768
- 34816
- 61440
- 28672
Explanation:
The default bridge priority value for all Cisco switches is 32768. The range is 0 to 61440 in increments of 4096. Thus, the values 1 and 34816 are invalid. Configuring one switch with the lower value of 28672 (and leaving the bridge priority value of all other switches unchanged) will make the switch become the root bridge.
Refer to the exhibit. The administrator tried to create an EtherChannel between S1 and the other two switches via the commands that are shown, but was unsuccessful. What is the problem?
- Traffic cannot be sent to two different switches through the same EtherChannel link.
- Traffic cannot be sent to two different switches, but only to two different devices like an EtherChannel-enabled server and a switch.
- Traffic can only be sent to two different switches if EtherChannel is implemented on Gigabit Ethernet interfaces.
- Traffic can only be sent to two different switches if EtherChannel is implemented on Layer 3 switches.
- Traffic cannot be sent to two different switches through the same EtherChannel link.
Explanation:
An EtherChannel link can only be created between two switches or between an EtherChannel-enabled server and a switch. Traffic cannot be sent to two different switches through the same EtherChannel link.
Which statement is true regarding the use of PAgP to create EtherChannels?
- It requires full duplex.
- I t increases the number of ports that are participating in spanning tree.
- It requires more physical links than LACP does.
- It mandates that an even number of ports (2, 4, 6, etc.) be used for aggregation.
- It is Cisco proprietary.
- It is Cisco proprietary.
Explanation:
PAgP is used to automatically aggregate multiple ports into an EtherChannel bundle, but it only works between Cisco devices. LACP can be used for the same purpose between Cisco and non-Cisco devices.
PAgP must have the same duplex mode at both ends and can use two ports or more. The number of ports depends on the switch platform or module. An EtherChannel aggregated link is seen as one port by the spanning-tree algorithm.
What are two requirements to be able to configure an EtherChannel between two switches? (Choose two.)
- All the interfaces need to work at the same speed.
- All interfaces need to be assigned to different VLANs.
- Different allowed ranges of VLANs must exist on each end.
- All the interfaces need to be working in the same duplex mode.
- The interfaces that are involved need to be contiguous on the switch.
- All the interfaces need to work at the same speed.
- All the interfaces need to be working in the same duplex mode.
Explanation:
All interfaces in the EtherChannel bundle must be assigned to the same VLAN or be configured as a trunk. If the allowed range of VLANs is not the same, the interfaces do not form an EtherChannel even when set to auto or desirable mode.
Refer to the exhibit. On the basis of the output that is shown, what can be determined about the EtherChannel bundle?
- The EtherChannel bundle is down.
- Two Gigabit Ethernet ports are used to form the EtherChannel.
- A Cisco proprietary protocol was used to negotiate the EtherChannel link.
- The EtherChannel bundle is operating at both Layer 2 and Layer 3.
- A Cisco proprietary protocol was used to negotiate the EtherChannel link.
Explanation: Two protocols can be used to send negotiation frames that are used to try to establish an EtherChannel link: PAgP and LACP. PAgP is Cisco proprietary, and LACP adheres to the industry standard.
Which two parameters must match on the ports of two switches to create a PAgP EtherChannel between the switches? (Choose two.)
- port ID
- PAgP mode
- MAC address
- speed
- VLAN information
- speed
- VLAN information
Explanation:
For an EtherChannel to be created, the ports that are concerned on the two switches must match in terms of the speed, duplex, and VLAN information. The PAgP mode must be compatible but not necessarily equal. The port ID and the MAC addresses do not have to match.
Refer to the exhibit. A network administrator is configuring an EtherChannel link between two switches, SW1 and SW2. Which statement describes the effect after the commands are issued on SW1 and SW2?
- The EtherChannel is established after SW2 initiates the link request.
- The EtherChannel is established after SW1 initiates the link request.
- The EtherChannel is established without negotiation.
- The EtherChannel fails to establish.
- The EtherChannel fails to establish.
Explanation:
The interfaces GigabitEthernet 0/1 and GigabitEthernet 0/2 are configured “on” for the EtherChannel link. This mode forces the interface to channel without PAgP or LACP. The EtherChannel will be established only if the other side is also set to “on”. However, the mode on SW2 side is set to PAgP desirable. Thus the EtherChannel link will not be established.
