STP Flashcards
BPDU guard should be implemented on what kind of port?:
access port
Root guard should be implemented on what kind of port?:
Designated port
Loop guard should be implemented on what kind of port?:
root and alternate ports
Unidirectional link detection should be implemented on what kind of port?:
all ports!
Portfast configured ports can receive BPDUs
False
What happens when a portfast-enabled interface receives a BPDU?:
interface shuts down and goes into “err-disable” state.
How to you bring up a shutdown, err-disabled interface?:
Shut then no shut the interface to bring it back up
Enabling BPDU guard on an interface has the same effect as disabling STP
True
What happens if an interface is configured to automatically recover an err-disabled port, but the invalid configuration that disabled the port is still present on the network?
The interface will go back to “err-disable” mode and must be manually recovered
BPDU’s are sent on all ports, even with portfast enabled
True
what effect does BPDU filtering have?:
prevents a switch from sending BPDU’s to portfast-enabled interfaces. it will ignore any BPDU’s it sees
What happens when a root guard-enabled interface receives BPDU’s that are superior to what the current root bridge is sending?:
the interface is put in a “root-inconsistent” state
interfaces in the “root-inconsistent” state will recover automatically once the offending BPDU packets stop
True
What happens when BPDU’s are not received on a non-designated port (root or blocked port) when Loopguard is enabled?
interface is put into “loop-inconsistent” state and logs the messages- it will recover automatically
What effect does loop guard have on non-designated (root or blocked) ports?:
prevents a non-designated port from becoming designated
Portfast should be enabled on what kinds of interfaces?:
edge interfaces – interfaces that connect to a user
What is the main purpose of Multiple Spanning Tree (MST)?:
reduce total number of spanning tree instances, which reduces the CPU cycles of the switch
MST uses the same convergence mechanism as RSTP
True
How many RSTP instances can you have?:
16
MST instances run RSTP for fast convergence
True
How does MST operate?:
MST enables you to build multiple spanning trees over trunks by grouping VLANs and associating them with spanning-tree instances.
Each instance can have a topology independent of other spanning-tree instances
The default MST instance, MST 0, can be deleted
False
what does the following command do?:
spanning-tree mst 1 root primary
assigns a root bridge and makes the local switch the primary switch for MST instance 1
for proper MST functionality, what must be the same across an MST instance?:
- revision number
- name
- VLAN to MST instance mapping
What is the IEEE name for the STP protocol?:
802.1D
What is the IEEE name for the MST protocol?:
802.1s
What is the IEEE name for the RSTP protocol?:
802.1w
What are the STP port states?:
- blocked
- disabled
- listening
- learning
- forwarding
What are the STP port types?:
- root port – there should only be one per vlan on a switch
- designated port – there should only be one on a segment/link
- blocking port
What types of BPDU’s (bridge protocol data unit) are there?:
- configuration BPDU
- topology change notification BPDU
What state are all ports in on a root switch?
designated forwarding
What is the STP bridge priority default value?
32,768
What is the STP system ID extension?
a 12-bit value that indicates the VLAN that the BPDU correlates to
What is the STP default Hello time?
2 seconds
What is the STP default Listening and Learning time?
15 seconds
What is the STP Bridge ID?
a combination of the root bridge MAC address, system ID, and bridge extension
