04 - Building Redundancy Switched Topology Flashcards
This instance of spanning tree is a Cisco enhancement of STP that provides separate 802.1D spanning-tree for each VLAN.
PVST+
This instance of spanning tree is the legacy standard, one spanning instance for entire network.
IEEE 802.1D STP
This instance of spanning tree maps multiple VLANs into same spanning-tree instance
802.1s (MSTP)
This instance of spanning tree improves convergence by adding roles to ports and enhancing BPDU exchanges.
802.1w (RSTP)
This instance of spanning tree is a Cisco enhancement of RSTP using PVST+
Rapid PVST+
What are the 3 types of BPDUs?
- Configuration BPDUS
- TCN BPDUs (topology change notification)
- TCA BPDUs (topology change ack)
How is a root bridge elected?
Based on lowest BID (combination of priority and MAC).
What are the fields in a BPDU frame?
- Protocol ID
- Version
- Message type
- Flags
- Root bridge ID
- Root path cost
- Send bridge ID
- Port ID
- Message age
- Maximum age
- Hello time
- Forward delay
What are the port roles?
- Root port
- Designated port
- Nondesignated port
- Disabled port
A _____ port will find the best path to the root bridge.
root
A ___ port will receive and forward frames toward the root bridge as needed.
designated
A ___ port does not forward (blocking)
nondesignated
A ____ port is a shutdown port
Disabled
What are the classic STP port states?
- Disabled
- Blocking
- Listening
- Learning
- Forwarding
A classic STP port state of ____ is administratively shut down.
Disabled
A classic STP port state of ____ receives BPDUs but cannot receive or transmit data.
Blocking
A classic STP port state of ____ is listening to see if there is a possibility that it will be selected as root or designated.
Listening
A classic STP port state of ____ after a time, forward delay in the listening state, the port is moved to ____.
Learning
A classic STP port state of ____ after another time. Forward delay in the learning state, the port is moved to ____.
Forwarding
What are the RSTP port states?
- Discarding
- Learning
- Forwarding
A RSTP port state of ____ prevents the forwarding of data frames, thus “breaking” the continuity of a Layer 2 loop.
Discarding
A RSTP port state of ____ accepts data frames to populate the MAC table to limit flooding of unknown unicast frames.
Learning
Spanning tree can be set in increments of …
4096
Default priority is ____ + VLAN number
32768
How do you change the switch priority?
- spanning-tree vlan vlan-id priority bridge-priority
* spanning-tree vlan vlan-id root primary
How do you debug spanning-tree?
debug spanning-tree events
What are the link types?
point to point & shared
MST information is conveyed with ___ BPDU regardless of the number of internal instances. Individual instances do not send individual BPDUs
one
What type of port should be configured between switches when using MST?
Trunk with no pruning
What is pruning?
Getting rid of unwanted VLANs
This is a Cisco enhancement of STP that allows a switchport to be in forwarding much faster than a switchport in normal STP mode.
• Immediate transition to forwarding state
• Configured only on access ports
PortFast
- If BPDU is received, it shuts down the port
* Usually used in combination of PortFast
BPDU guard
How do you configure BPDUguard and portfast on an interface?
SwitchX(config)# interface FastEthernet0/1
SwitchX(config-if)# spanning-tree portfast
SwitchX(config-if)# spanning-tree bpduguard enable
How do you enable PortFast on all nontrunking interfaces and enable BPDU guard globally for all PortFast-enabled ports?
SwitchX(config)# spanning-tree portfast bpduguard default
SwitchX(config)# spanning-tree portfast default
How long does it take standard STP without portfast configured to progress from blocked to forwarding?
50 seconds
