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Routing > Module 5 > Flashcards

Module 5 Flashcards

1
Q

What is the purpose of STP?

A

STP is a loop-prevention network protocol that allows for redundancy while creating a loop-free Layer 2 topology.

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2
Q

Who invented the Spanning Tree Algorithm?

A

Radia Perlman.

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3
Q

What does the Spanning Tree Algorithm (STA) do?

A

Creates a loop-free topology by selecting a single root bridge where all other switches determine a single least-cost path.

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4
Q

What is the function of BPDU guard in Cisco switches?

A

Puts the switch port in an error-disabled state upon receipt of any BPDU to protect against potential loops.

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5
Q

What are the three timers required for STP convergence?

A
  • Hello timer
  • Forward delay timer
  • Max age timer
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6
Q

What are the port states in STP?

A
  • Blocking
  • Listening
  • Learning
  • Forwarding
  • Disabled
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7
Q

What is the difference between RSTP and STP?

A

RSTP provides faster convergence than STP.

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8
Q

What does PVST+ stand for?

A

Per-VLAN Spanning Tree Plus.

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9
Q

When is PortFast used?

A

On access ports to allow immediate network access.

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10
Q

What is a broadcast storm?

A

An abnormally high number of broadcasts overwhelming the network.

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11
Q

What happens when a Layer 2 loop occurs?

A

It causes MAC address table instability, link saturation, and high CPU utilization.

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12
Q

What is the purpose of the Spanning Tree Protocol?

A

To prevent endlessly circulating frames in a Layer 2 network.

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13
Q

What does RSTP stand for?

A

Rapid Spanning Tree Protocol.

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14
Q

What are the three port states in RSTP?

A
  • Learning
  • Forwarding
  • Discarding
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15
Q

What is an unknown unicast frame?

A

A frame for which the switch does not have the destination MAC address in its MAC address table.

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16
Q

What is the role of the root bridge in STP?

A

It is the central point of the spanning tree topology from which all paths are calculated.

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17
Q

Fill in the blank: STP prevents loops by configuring a loop-free path through the network using strategically placed _______.

A

[blocking-state ports]

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18
Q

What is the internal root path cost?

A

The sum of all the individual port costs along the path from the switch to the root bridge.

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19
Q

How does STP handle network failures?

A

By dynamically unblocking previously blocked ports.

20
Q

True or False: RSTP is backward compatible with STP.

A

True.

21
Q

What is the main benefit of using Layer 3 routing over Layer 2?

A

It allows for redundant paths and loops in the topology without blocking ports.

22
Q

What is the function of a designated port in STP?

A

It is the port on a segment that has the internal root path cost to the root bridge.

23
Q

What does the acronym BPDU stand for?

A

Bridge Protocol Data Unit.

24
Q

What is the role of the alternate port in STP?

A

It serves as a backup path to the root bridge.

25
Q

What does the acronym MSTP stand for?

A

Multiple Spanning Tree Protocol.

26
Q

What is Rapid PVST+?

A

Cisco’s enhancement of RSTP that provides a separate instance of RSTP per VLAN.

27
Q

What is the purpose of the hello timer in STP?

A

To determine the frequency of sending BPDUs.

28
Q

Fill in the blank: Without STP enabled, ________ loops can form, causing broadcast, multicast and unknown unicast frames to loop endlessly.

A

[Layer 2]

29
Q

What is the main purpose of the Spanning Tree Algorithm (STA)?

A

To create a loop-free topology in a network

The STA achieves this by selecting a root bridge, blocking redundant paths, and recalculating paths in case of link failure.

30
Q

What does PVST+ stand for?

A

Per-VLAN Spanning Tree Plus

PVST+ is a Cisco enhancement of STP that provides a separate 802.1D spanning tree instance for each VLAN in the network.

31
Q

What is RSTP?

A

Rapid Spanning Tree Protocol

RSTP is an evolution of STP that provides faster convergence.

32
Q

What does MSTP stand for?

A

Multiple Spanning Tree Protocol

MSTP is an IEEE standard that maps multiple VLANs into the same spanning tree instance.

33
Q

What is the default bridge priority for Cisco switches?

A

32768

The bridge priority can be configured in increments of 4096, with a lower value being preferable.

34
Q

What happens if two or more switches have the same priority in STP?

A

The switch with the lowest MAC address becomes the root bridge

This is because the MAC address is used as a tie-breaker when priorities are the same.

35
Q

What is the role of designated ports in STP?

A

Designated ports are the ports that have the best path to the root bridge for each segment

All ports on the root bridge are designated ports.

36
Q

Fill in the blank: The internal root path cost is equal to the sum of all the _______ along the path to the root bridge.

A

port costs

This cost determines the preferred path to the root bridge.

37
Q

What are BPDUs used for in STP?

A

To share information about switches and their connections

BPDUs are used to elect the root bridge, root ports, designated ports, and alternate ports.

38
Q

What is the purpose of the Hello Timer in STP?

A

It defines the interval between BPDUs

The default Hello Timer is 2 seconds but can be modified.

39
Q

What does the Forward Delay Timer control in STP?

A

The time spent in the listening and learning states

The default is 15 seconds but can be adjusted.

40
Q

True or False: All ports attached to end devices are designated ports.

A

True

This is part of the STP port role assignments.

41
Q

What is the significance of the Max Age Timer in STP?

A

It is the maximum time a switch waits before attempting to change the STP topology

The default is 20 seconds but can be modified.

42
Q

What occurs during the first step of STP operations?

A

Elect the root bridge

The root bridge serves as a reference point for all path calculations.

43
Q

Fill in the blank: If a port is not a root port or a designated port, it becomes an _______ port.

A

alternate

Alternate ports are in a blocking state to prevent loops.

44
Q

What is the primary focus of the latest IEEE documentation on spanning tree?

A

RSTP has superseded STP

The IEEE uses ‘STP’ to refer to the original implementation and ‘RSTP’ for the updated version.

45
Q

How does STP handle multiple equal-cost paths to the root bridge?

A

It uses a tie-breaking process based on sender BID, port priority, and port ID

This ensures a consistent selection of root ports in complex topologies.

46
Q

What is the significance of the extended system ID in STP?

A

It is added to the bridge priority to identify the VLAN

This helps in distinguishing between multiple VLANs in BPDU frames.

47
Q

What does MST provide in terms of RSTP instances?

A

Up to 16 instances of RSTP

MST allows combining many VLANs into a common RSTP instance.

Routing (19 decks)

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