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ICND2 - STP
CCNA Spanning Tree Protocols
| Question | Answer |
|---|---|
| Spanning Tree Protocols prevent ? | Switching loops |
| Broadcast storms, MAC table instabilities, and multiple frame transmissions are all symptoms of _______________ and are prevented by ____________________ ? | Switching loops Spanning Tree Protocol |
| 5 States of STP | Disabled, Blocking, Listening, Learning, Forwarding |
| If the port shows that the interface is disabled in STP it is most likely? | shut down administratively or the interface has a failure |
| Ports that are in a blocking STP state are? | not forwarding frames and not learning mac addresses |
| Interface that does not forward frames and removes addresses from the MAC table if it doesn't hear from them during the period are in what STP state | Listening |
| When an interface is not forwarding frames, but is learning MAC addresses it is in what STP state? | Learning |
| The forwarding STP state causes an interface to do what with frames and what with MAC addresses? | Forward frames and learn MAC addresses |
| What is the correct 4 step sequence when an interface goes from blocking STP frames to forwarding them? | 1) Blocking 2)Listening 3)Learning 4)Forwarding |
| What does BPDU stand for? | Bridge Protocol Data Unit |
| BPDU BIDs are ____ bytes | 8 (2 byte priority field + 6 byte Burned in MAC address) |
| The priority field in a BPDU BID is made up of | 4 bit priority number + 12 bit system extension ID (VLAN ID) |
| How is the Root Bridge Election decided? | Lowest Priority field in BID wins, tie breaker is lowest System Extension ID, tie breaker is the lowest MAC address |
| A switch believes it is the Root Bridge until it receives a ? | Superior Hello BPDU |
| Hello BPDUs contain? | the Root Bridge ID, sender's BID, Sender's Root Cost, Timer Values |
| The Root Bridge ID in the Hello BPDU is ? | what the sender believes is the Root Switch |
| Hello BPDU root cost is calculated by | STP cost between sending switch and the current root. |
| Default Timer Values | Hello 2 seconds, Max Age 20 seconds, Forward Delay 15 seconds |
| What is the first value considered in STP Root Port Selection | Lowest Root Cost |
| If the root cost are the same in STP Root Port Selection process what are the tie breakers? | 2) lowest neighbor BID 3) lowest neighbor port priority (first 4 bits of port ID) 4) lowest neighbor port number (last 12 bits of port ID) |
| Root cost is determined by ? | Port cost of every outbound interface in the path for root bridge, 1 root port per non-root switch. (root is in forwarding state) |
| Designated ports are in _____________ state, while all other ports are put into ____________ state | forwarding, blocking |
| STP Designated Port Selection process | 1) Lowest interface root cost 2) Lowest local BID 3)lowest neighbor port priority 4)lowest neighbor port number |
| There should only be one designated port per LAN segment | True, but there may be more than one LAN segment per switch. |
| Default Port Cost for a 10 Mbps Ethernet | 100 |
| Default Port Cost for a 100 Mbps Ethernet | 19 |
| Default Port Cost for a 1 Gbps Ethernet | 4 |
| Default Port Cost for a 10 Gbps Ethernet | 2 |
| If there are no STP-speaking devices on the LAN segment what will happen? | Port becomes a Designated Port |
| Hello timer | time period between Hellos created by the root (default: 2 seconds) |
| Forward delay timer | how long the port stays in listening and learning state (default: 15 seconds [total: 30 seconds from blocking to forwarding]) |
| When MaxAge timer expires | switch makes all it's choices again |
| STP default convergence time | 50 seconds |
| RSTP convergence time | less than 10 seconds |
| RSTP Alternate port | replaces the root port when the root port fails |
| RSTP Backup port | replaces a designated port when a designated port fails |
| When RSTP root port fails first thing that happens is ? | Both switches confirm that the other switch will use its alternate port as the root port |
| When RSTP root port fails second thing that happens is ? | The switch flushes the required MAC table entries (faster than STP waiting for time out) |
| When RSTP root port fails third thing that happens is ? | Switch transitions the root port to the disabled state and alternate port to root port |
| When RTSP root port fails last thing that happens is ? | Switch transitions the new root port to a forwarding state immediately |
| RSTP is short for ? | Rapid Spanning Tree Protocol |
| RSTP does not have a listening state and combines STP disabled and blocking state to ? | RSTP discarding state |
| ports that connect two switches and are not at the edge of the network | Point-to-point |
| Point-to-point edge are ports that connect to ? | a single endpoint device at the edge |
| In RSTP shared ports connect to a hub and share ? | a single collision domain |
| The Root Switch does not have any root ports | True it has Designated Ports |
| The show spanning-tree command lists ____________________________ if the local switch is the root bridge | "This switch is the root" |
| This command lists an empty RP column if local switch is the root | show spanning-tree root |
| Commands to use to find the root switch or root cost | show spanning-tree, show spanning-tree root |
| Cisco default, makes PVST+ the STP mode | spanning-tree mode pvst |
| This command makes RPVST+ the STP mode | spanning-tree mode rapid-pvst |
| This command makes MST the STP mode | spanning-tree mode mst |
| PVST+ allows different instances of STP for | each VLAN (STP load balancing) |
| Command that lists "Spanning tree enabled protocol ieee OR rstp OR mst" and shows the RSTP port roles | show spanning-tree vlan #### |
| show spanning-tree vlan #### lists alternate and backup ports and RSTP port types in the output even when using STP and not RSTP | True |
| show spanning-tree vlan #### bridge - lists in _______________ Protocol field | "ieee", "rstp" or "mst" |
| The show spanning-tree vlan #### interface#### state command shows ? | the port's state |
| To configure the priority field of the BID what command can you use? | spanning-tree vlan #### priority #### (has to be a multiple of 4096; base priority) |
| spanning-tree vlan #### root primary configures | the local switch to attempt to be the root switch |
| The spanning-tree vlan #### root primary command sets the local switch base priority to 24576 if ? | the current root has a base priority higher than 24576 |
| Using the command spanning-tree vlan #### root primary and the current root's base priority is 24576 or lower, the local switch sets the base priority to the? | highest number that still results in the local switch becoming root |
| spanning-tree vlan #### root secondary is the command that is used to configure ? | the local switch to attempt to be the switch that will take over when the root switch fails |
| What happens when spanning-tree vlan #### root secondary command is issued on a switch | Set the local switch's base priority to 28672 regardless of the root switch's current priority value |
| What command configures the STP port cost | spanning-tree [vlan ####] cost # (needs VLAN keyword for per-VLAN config on trunk linterfaces) |
| command that sets the port priority for the interface | spanning-tree vlan #### port-priority # |
| 3 show spanning-tree commands used to verify STP root bridge selections | show spanning-tree vlan ####, vlan #### root, vlan #### bridge |
| The command show spanning-tree interface int-id detail lists ? | PortFast and BPDU Guard status if they are enabled |
| shows the global settings for PortFast and BDPU Guard, as well as the STP mode | show spanning-tree summary |
| Allows port to immediately transition from blocking to forwarding state (especially at connections to end-user devices where there is no risk of creating loops) | PortFast |
| RSTP point-to-point edge ports are trunking ports that have PortFast enabled | False, they can not be trunking ports |
| spanning-tree portfast enables PortFast on an interface, what command enables PortFast globally? | spanning-tree portfast default |
| Command that shows the PortFast enabled status | show spanning-tree interface #### portfast |
| prevents attackers becoming the root switch and harming the network, disables a port (err-disabled state) if any BPDUs are received on them, and is used with PortFast to prevent loops when a switch is connected. | BPDU guard |
| BPDU guard should ___________ be enabled on a port that connects to another switch | NEVER |
| spanning-tree bpduguard {enable | disable} enables/disables the BPDU guard on an | interface |
| command to globally enable BPDU guard | spanning-tree portfast bpduguard default |
Created by:
Jjwtwo
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