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