CCNP SWITCH 642-813 - Advanced Spanning Tree & Security Flashcards

bpdu guard
Terms Definitions
What are the 5 states a port can have after convergence in STP?
Root port, Designated port, Blocking port, Alternate port, and Forwarding port.
When should STP Root Guard be used?
On switchports where you never expect to find the root bridge for any VLAN.
What happens when a BPDU is received on a port with Root Guard configured?
It is placed in the blocking state, with a root-inconsistent state.
If a port is placed in the errDisabled state, what is the only way it can be re-enabled?
By being manually re-enabled, or waiting for the errDisabled timeout function.
What does BPDU guard do to a switchport?
If a BPDU is received on a port with BPDU guard, it is immediately placed into the errDisabled state.
What is the relationship between PortFast and BPDU guard?
All ports with PortFast have BPDU guard enabled by default.
What ports should BPDU guard never be enabled on?
Switch uplinks where the root bridge is located.
What two STP features help detect or prevent the unexpected loss of BPDUs?
Loop Guard, and Unidirectional Link Detection (UDLD).
What does Loop Guard do to switch ports?
It monitors BPDU activity on non-designated ports. When BPDUs go missing, Loop Guard moved the port into a loop-inconsistent state. When BPDUs are received again, the port progresses automatically through the STP states and becomes active.
Even though loop-guard is configured on switch ports, it action is taken on a per-_____ basis.
per VLAN!
What is a Cisco proprietary method to detect or prevent the unexpected loss of BPDUs?
Unidirectional Link Detection (UDLD).
How does UDLD work to protect STP?
It sends a special UDLD frame to the other end of a link, and that link replies to it to ensure that a link is truly bi-directional.
Where must you configure UDLD for it to work?
on both ends of the link.
What is the default message interval for UDLD?
15 seconds.
What are the 2 modes of UDLD operation?
Normal and Aggressive.-Normal: When a unidirectional link is detected, it is still allowed to continue its operation, it marks the port as having an undetermined state, and generates a syslog message. -Aggressive: The port is placed in the errDisabled state after 8 UDLD messages sent one second apart.
When enabled globally, what ports does UDLD effect? How do you enable it?
Only Fiber-Optic ports. (config)udld [enable, aggressive, message time ###]
How does UDLD work on EtherChannel ports?
It exchanges and echos messages on each link independently.
What does BPDU filtering do?
It effectively disables STP on a switchport.
How can you globally enable BDPU filtering on all PortFast ports?
(config)spanning-tree portfast bpdufilter default
How do you enable/disable BPDU filtering on a per-port basis?
(if)spanning-tree bpdufilter [enable, disable]
Give a quick explanation of where the following STP configurations should be used: Root guard, BPDU guard, Loop guard, UDLD.
-Root guard, Apply to ports where root is never expected.-BPDU guard, apply to all ports that have PortFast enabled.-Loop guard, Apply to non-designated ports, but ok to apply to all ports.-UDLD, Apply to both sides of all fiber links.
Are the following configuration combinations permissible on a switch port?Loop Guard and UDLD
Permissible!
Are the following configuration combinations permissible on a switch port?Root guard and UDLD
Permissible!
Are the following configuration combinations permissible on a switch port?Root guard and Loop guard
NOT-Permissible!
Are the following configuration combinations permissible on a switch port?Root guard and BPDU guard
NOT-Permissible!
What is the IEEE standard for RSTP?
802.1w
What is the IEEE standard for MST?
802.1s
What is the IEEE standard for STP?
802.1D
According to RSTP, any port role can have what three possible states?
-Discarding, incoming frames are dropped, no MACs are learned.-Learning, only MACs are learned.-Forwarding, frames are forwarded according to learned frames.
RSTP uses what BPDU version?
version 2.
In RSTP how often are BPDUs exchanged?
The default hello timer in RSTP is 2 seconds.
Can RSTP coexist on a network with CST?
Yes, each versions BPDUs are compatible.
What are the three types of RSTP ports?
-Edge port, where only a single host connects.-Root port, has the best cost to the root.-Point-to-point, any port that connects to another switch and becomes a designated port.
In RSTP, non-edge ports begin in what RSTP state?
The RSTP discarding state.
What type of message does RSTP send when negotiating convergence?
It sends a proposal!
When does RSTP detect a topology change?
When a non-edge port transitions to the forwarding state.
What does RSTP assume with regard to duplex settings?
That full-duplex links are Point-to-Point and half-duplex links fall back to CST.
What does the 'spanning-tree link-type point-to-point' command accomplish?
It forces a RSTP port to be point-to-point regardless of duplex settings.
How do you globally enable Rapid Per-VLAN Spanning Tree (RPVST+)
(config)spanning-tree mode rapid-pvst
When running MST, all switches must have what three identical attributes to be considered in the same region?
The same MST configuration name, revision number, and instance-to-VLAN mapping table.
How does CST work out a loop-free technology with MST?
It considers each MST region as a single 'bridge'
Within MST what is an IST?
Internal Spanning Tree, it is a locally significant CST bounded by the edges of the MST region.
How many MSTIs can exist in a single MST region?
16. The IST is always MSTI 0, and that leaves MSTI 1-15 open for use.
In MST, what MSTI is allowed to send BPDUs?
Only the IST, on MSTI 0, us allowed to send BPDUs.
How to other MSTIs receive BPDU information in MST?
The MST BPDU is sent on the IST (MSTI 0) with a special M-Record appended to the BPDU.
In MST, by default, what VLANs are mapped to the IST (MSTI 0)?
All of the VLANs are mapped to the IST by default. You must explicitly map them to another MSTI if needed.
Can a switch run both MST and PVST+ at the same time?
No! MST relies on the RSTP configuration to operate, and therefor, cannot use PVST+.
What are the 5-steps to configuring MST on a single switch?
1. spanning-tree mode mst2. spanning-tree mst configuration3. name NAME4. revision #####5. instance #ID# vlan #LIST#
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