Chapter 3 - STP

Rapid PVST+

A Cisco enchancement of RSTP that uses PVST+

Denial of Service (DoS)

A _______ ____ _________ issue is when no bandwidth is available for legitimate traffic and the network becomes unavailable for data communication

Bridge priority

A customizable value that can be used to influence which switch becomes the root bridge

BPDU ( Bridge protocol data unit)

A messaging frame exchanged by switches for STP election process

Learning or Forwarding

A port must be in either of these two states in order to learn MAC addresses

Disabled port

A switch port that is shut down as opposed to blocked

One

A switch that is not the root bridge will have _____ root port(s) defined

instance

A switched LAN or broadcast domain is known as a spanning tree _____________

MSTP - Multiple Spanning Tree Protocol (MST is the Cisco implementation)

A type of STP that maps multiple VLANs to the same STP instance by combining the logical and physical topology

Unknown unicast frame

A type of frame when the switch does not have a destination MAC in its table and must forward the frame out all ports but the ingress

Every two seconds

After a switch boots, how often does it send BPDUs?

Designated port

Any non-root port that is permitted to forward traffic on a network is assigned this role

Port role

Describes a switchport's relation to the root bridge and whether it is allowed to forward traffic.

Per-segment

Designated ports are selected on a _____-___________ basis

2 seconds

Hello Time is the time between root bridge config messages. By deafult, how often are these sent?

Up to 16

How many instances of RSTP does MSTP provide?

4

How may bits is the bridge priority field?

Designated port

If one end of a segment is a root port, then the other end always a _________________ _____________

BID - Remember, BID is a combination of priority and MAC. (Technically, MAC could also be the correct answer here as well. The lowest MAC would also produce the lowest BID of all its neighbors.)

If two switches have the same priority value at the start of STP election, the switch with the lowest _______ will become root

Root ID

In a BPDU frame, this field indicates the root bridge

Unicast

MAC table instabilities prevent the proper forwarding of these kinds of frames to their hosts

802.1D - STP and PVST+ 802.1w - RSTP and Rapid PVST+ 802.1s - MSTP

Match the standard to the type(s) of STP that uses them 802.1D 802.1w 802.1s

0 and 7 1 and 6 2 to 5 4 and 5

Name the bits used for the flag byte field in an RSTP BPDU: Topology change and acknowledgment Proposal Agreement for rapid convergence Encoding the role and state of a port Encode the port role using a 2 bit code

The port speed for each switch port along a given path (2,4,19,100)

Port cost is determined using what?

logical

STP ensures that there is only one ___________ path between all destinations on the network

The default priority value had VLAN 1's ID added to it, using extended ID, it to make a total of 32796. If you have vlan 2, it would be 32770 and so on.

Scenario: I have all my switches set at the default priority value. Why would I see a priority of 32769 rather than the default 32768?

blocking-state ports

Strategically placed ports created by STP in order to create a loop-free path through the network by stopping user data from traversing that port

lowest

Switches use the ____________ BID to designate the root bridge

internal root path

The ______ ________ ________ cost is equal to the sum of all the port costs along the path to the root bridge

32768

The default priority number

Root bridge

The name given to a single switch that STA dedicates as a reference point for all path calculations

Priority value MAC of sending switch extended system ID (optional)

The three things contained in a BID that determine the total BID value are? (one is optional)

learning and forwarding

The two processes of a switch that are the most negatively affected by layer 2 looping

Physically disconnect the looping connections Power down one of the switches in the loop

The two ways to stop a layer 2 loop without protocols

Type 2, Version 2 Type 0, Version 0

The type and version of BPDUs used in RSTP. What is the type and version used in original STP?

logical redundancy

The type of redundancy provided when using protocols

MAC database instability Broadcast storms Multiple frame transmission

There are three primary issues that can arise when using multiple paths without STP. What are they?

PVST+ and Rapid PVST+

These 2 protocols support PortFast, BPDU guard, BPUD filter, root guard and loop guard.

PVST +

This protocol supports UplinkFast and BackboneFast in addition to BPUD guards and filters AND loop and root guards.

RSTP

This type of STP protocol does not use blocked port status but instead uses discarding status

True

True or False: All switches initially assume that they are the root bridge in an STP instance

True

True or False: Multiple frame transmission can cause unrecoverable errors

False - requires protocols too

True or False: Redundancy can be successfully implemented by simply using multiple links and devices

no spanning-tree cost

What command can be used to restore the port cost to its default value?

Spanning Tree Algorithm (STA)

What does STP use to determine which switch will be the root bridge and which mode the ports will be placed in?

STA calculates the shortest path to the root for all non-root bridge switches

What happens right after the root bridge is determined?

802.1w (RSTP)

What is included in 802.1D-2004 that allows faster network convergence?

Switch location in the LAN design in regard to traffic flow for VLANs Switch processing power Access to the switch is easier physically and remotely

What three things could make an administrator set a PVST+ root bridge manually?

4 and 12 16

When a BPDU contains an extended system ID, ______ bits are used for the bridge priority ID and _____ bits are used for the extended system ID. If the extended system ID is not used, how many bits make up the bridge priority ID?

Broadcast storm

When a switches flood broadcasts endlessly

After - root ports are always decided first

When does PVST+ select designated ports for VLANs; before or after selecting the root port on non-root bridges?

When user data is prevented from entering or leaving the port

When is a port considered blocked?

Multiple frame transmission

When multiple copies of unicast frames are delivered to a destination.

RSTP, Rapid PVST+ and MSTP

Which 3 STP protocols have fast convergence rates?

PVST+ and Rapid PVST+

Which STP protocols separate instances per VLAN?

Rapid PVST+

Which protocol is the most resource intensive in the STP family?

Radia Perlman

Who invented STP?

RSTP - Rapid spanning tree protocol

According to the IEEE, STP has been superseded by this protocol

Designated port

All ports on the root bridge are given this role

0 to 65,535

Bridge priority values range from ___ to ____________

CPU

Broadcast storms and MAC table instability issues are rough on the __________ of a switch and can cause the switch to slow its performance when legitimate traffic arrives

PVST+

Cisco switches running 15.0 IOS or higher run this STP by default

4096

The range of priority values in Cisco switches is 0 - 61440 in increments of ________________

PVST+ and Rapid PVST +

These two STP protocols are Cisco proprietary

Extended system ID

This BPDU field, which is part of a BID, is now often included to support VLAN technology in some STP versions such as PVST+

RSTP

This STP version is the preferred protocol for preventing layer 2 loops

show spanning-tree

This comman will allow you to view and verify port and internal root path cost to the root bridge

spanning-tree cost [value]

This command is used for configuring port cost manually

show spanning-tree summary

This command will display the STP status of ports on a switch

debug spanning-tree events

This command will give verbose output regarding spanning tree events on a switch

PVST+

This enhancement of STP provides separate 802.1D STP instances for each VLAN

Path redundancy

This ensures availability of network services by eliminating the possibility of single point failure

network redundancy

This is the key to maintaining network reliability

BPUD (Bridge protocol data unit)

This kind of frame is not prevented from traversing blocked ports

Neither end can be a root port

This must be true in order for a port to be selected as an alternate port

Layer 2 loop

This occurs when multiple paths exist between two or more layer 2 network devices and there is no STP on the switches

PVST+

This protocol can be used to implement layer 2 load balancing, meaning there can be a root bridge for each VLAN STP instance

Root ports

This role is given to ports closest to the root bridge in terms of overall cost to the root bridge.

False - Ethernet frames have no TTL attribute

True or False: Although looping is an annoyance, looped frames that are maxing switch resources are not a big deal as they will eventually be discarded due to their TTL

True

True or False: Blocking ports comes into play when two ports on the same switch provide redundant links through the network

False - every port but the original ingress port

True or False: Broadcast frames are forwarded out EVERY switch port

True

True or False: Broadcasts storms can use all of a network's available bandwidth

False

True or False: Due to its old, clunky nature, original 802.1D STP is high in resource usage

False - could be any other switch in the broadcast domain (STP instance)

True or False: For a switch to update its root ID and/or identify another switch as the root bridge, that other switch must be adjacent.

False

True or False: Hosts caught in a network loop are still accessible to others hosts in the network

True - different sets of VLANs may have their own depending on the STP standard in use

True or False: It is possible to have more than one root bridge

False - Recommendation is to have the admin select the desired root bridge by manually configuring it to have lower priority than all other swtiches in the STP instance

True or False: It is recommended to allow STP to dynamically configure the root bridge in an STP instance

False

True or False: Network traffic is still forwarded while STP negotiations are taking place

False - they are inevitable

True or False: Not all networks containing layer 2 loops suffer from broadcast storms

True

True or False: PVST+ allows a port to be blocked for forwarding for one VLAN while allowing forwarding for another VLAN. Example: A port is blocked for VLAN 20 traffic and a designated port for VLAN 10.

True HOWEVER, disabled ports cannot do diddly squat with BPDUs or any other data for that matter

True or False: Ports can always receive and process BPDUs, no matter the port role or state

True

True or False: RSTP can change a port status from discarding to designated when it senses a network change and can do this in milliseconds

True

True or False: RSTP can communicate with switches using type 0, ver 0 BPDUs

True

True or False: STP is enabled by default on Cisco switches

False

True or False: The bridge priority value can not be modified

True

True or False: The root bridge will configure ALL of its switch ports in the designated role once it takes the root bridge role

False

True or False: UplinkFast and BackboneFast are supported with RSTP

10GB/s = 2 1 Gb/s = 4 100 Mb/s = 19 10 Mb/s = 100

What are the default port costs for 1 and 10 Gb/s and 100 and 10 Mb/s ports?

200,000,000

What is the highest value that can be set for port cost?

MAC database instability

When copies of the same frame are received on different ports on a switch, causing data forwarding issues due to addressing problems