Spanning Tree Protocol Flashcards
What command is used to prevent a new unconfigured switch from being elected root
spanning-tree guard root
When STP is used, what is used to prevent newly introduced switches from being elected as the new root switch?
root guard
When STP is used, which device will be elected root?
the device with the lowest switch priority
What can you enable to ensure that a port immediately transitions to the STP forwarding state?
PortFast
What two STP states are bypassed when using PortFast?
listening and learning
What feature prevents nondesignated ports from inadvertently forming bridging loops if the steady flow of BPDUs is interrupted?
loop guard
When a switchport stops receiving BPDUs, what state will loop guard put the port into?
loop inconsistent state which keep the port in a blocking state
What command will enable loop guard for the entire switch?
spanning-tree loopguard default
What command will enable loop guard for specific ports?
spanning-tree guard loop
What is used to disable ports that erroneously receive BPDUs?
BPDU guard
When BPDU guard is applied, the reciept of a BPDU on a port will result in the port being placed into what state?
error-disabled state
What command can be used to automatically recover from a BPDU guard induced error-disable state?
errdisable recovery cause bpdugaurd and
errdisable recovery interval {interval value]
In STP, what is the switch with the lowest bridge ID called?
root bridge
What is the Bridge ID composed of?
Two byte bridge priority and a 6 byte MAC address
If two or more switches have the lowest priority then what is used to determine the root bridge?
lowest MAC address
What is the Port ID composed of?
port priority and port number
What are ports on a root bridge always considered to be?
designated ports
How many port states does Spanning Tree Protocol (STP) have?
5
What are the STP port states?
disabled, blocking, listening, learning, forwarding
How many port states does Rapid Spanning Tree Protocol have?
3
What are the RSTP port states?
discarding, learning, forwarding
What is VTP used for?
to synchronize VTP and Vlan configuration information between switches.
What must match on all switches in for switches to synchronize information over VTP?
VTP domain name, VTP password, VTP version
what is the command to manually set the bridge priority?
spanning-tree priority [value]
What is the default bridge priority?
32768
The time period between Hellos created by the STP root.
Hello timer
How long any switch should wait, after ceasing to hear Hellos, before trying to change the STP topology.
MaxAge timer
Delay that affects the process that occurs when an interface changes from blocking state to forwarding state. A port stays in an interim listening state, and then an interim learning state, for the number of seconds defined by the forward delay timer.
Forward delay timer
Default Hello timer
2 seconds
Default MaxAge
10 times Hello
Default Forward Delay timer
15 seconds
Feature that allows a switch to immediately transition from blocking to forwarding, bypassing
listening and learning states.
PortFast
feature helps defeat these kinds of problems by disabling a port if any BPDUs are received on the port.
BPDU Guard
Two components of the Bridge ID that affect whether a switch will be elected root
Lowest priority and if that ties, the lowest MAC address
messages which switches use to
exchange information with each other.
bridge protocol data units (BPDU),
Global configuration command to set the STP
mode.
spanning-tree mode {pvst |
rapid-pvst | mst}
Global configuration command that changes this
switch to the root switch. The switch’s priority is
changed to the lower of either 24,576 or 4096 less
than the priority of the current root bridge when
the command was issued.
spanning-tree vlan [vlan-number] root primary
Global configuration command that changes the
bridge priority of this switch for the specified
VLAN.
spanning-tree vlan [vlan-id] priority [priority value}
Interface subcommand that changes the STP cost to
the configured value.
spanning-tree vlan [vlan-number] cost [cost value]
Interface subcommand that changes the STP port
priority in that VLAN (0 to 240, in increments of
16).
spanning-tree vlan [vlan-number] port-priority [priority]
Interface subcommand that enables EtherChannel
on the interface.
channel-group [channel-group number] mode {auto | desirable | active | passive | on}
Interface subcommand that enables PortFast on the
interface.
spanning-tree portfast
Interface subcommand that enables BPDU Guard on
an interface.
spanning-tree bpduguard enable
Global command that changes the switch default for PortFast on access interfaces from disabled to enabled.
spanning-tree portfast default
Global command that changes the switch default for
BPDU Guard on access interfaces from disabled to
enabled.
spanning-tree portfast bpduguard default
Global command that changes the global setting for
PortFast to disabled.
no spanning-tree portfast default
Global command that changes the global setting for
BPDU Guard to disabled.
no spanning-tree portfast bpduguard default
Interface subcommand that disables PortFast on the
interface.
spanning-tree portfast disable
Interface subcommand that disables BPDU Guard
on an interface.
spanning-tree bpduguard disable
Lists details about the state of STP on the
switch, including the state of each port.
show spanning-tree
Lists STP information only for the specified
port.
show spanning-tree interface [interface id]
Lists STP information for the specified VLAN
show spanning-tree vlan vlan-id
Lists information about each VLAN’s root or for
just the specified VLAN.
show spanning-tree [vlan vlan-id] root
Lists STP information about the local switch for
each VLAN or for just the specified VLAN
show spanning-tree [vlan vlan-id]
bridge
Lists global STP settings for a switch, including
the default PortFast and BPDU Guard settings,
and the VLANs for which this switch is the root
switch
show spanning-tree summary
Causes the switch to provide informational
messages about changes in the STP topology
debug spanning-tree events
Lists a one-line status message about PortFast on
the listed interface.
show spanning-tree interface [type/number ] portfast
Lists information about the state of
EtherChannels on this switch.
show etherchannel [channel-group number]
{brief | detail | port | portchannel | summary}
