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23 Cards in this Set
- Front
- Back
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What does BPDU stand for? What does it do?
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Bridge protocol data unit. All switches configured with STP send these packets out every 2 seconds using a multicast frame. Essentially a keep alive.
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What does BID stand for? What is it's function?
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Bridge ID. The BID is unique to its switch or bridge. It is comprised of a priority value(2 bytes) and the bridge MAC address(6bytes). The default priority, in accordance with IEEE 802.1D is 32,768.
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What are the 5 STP port states?
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Blocking
Listening Learning Forwarding Disabled(this isn't strictly part of STP, this can be manually shut by administrator) |
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What modes does an STP port go through when its first coming up?
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1.Blocking
2. Listening 3. Learning If everything is properly configured the port will stabilize to either forwarding or blocking state. |
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What is maximum age(max_age), and what is its default value?
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It is the period of time the port listens for BPDU's in blocking state before the port goes to listening state. The default value is 20 seconds.
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What three steps are preformed when a bridge is in the STP listening state?
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- Selects a root bridge
- Selects the root ports on the nonroot bridges - Selects the designated ports on each segment |
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What is the time it takes for a port to transition from the listening state to the learning state in STP called? What is that default value?
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Forward Delay
Default value = 15seconds |
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How long does it typically take for a port to transition from blocking state to forwarding state in STP?
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30-50 seconds
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What is Spanning-tree PortFast?
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Causes an interface that is configured as a layer 2 access port to transition immediately from the blocking state to the forwarding state, bypassing the listening and learning states.
This would be used on ports directly connected to workstations/servers where a loop can't happen. |
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What command is used to configure portfast?
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SwitchX(config-if)# spanning-tree portfast
OR SwitchX(config)# spanning-tree portfast default This command is as you see globally configured to it enables portfast on all *access* interfaces |
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What are the Spanning-tree path costs for the following:
1. 10Mb/s 2. 100Mb/s 3. 1 Gb/s 4. 100Gb/s |
1. 100
2. 19 3. 4 4. 2 |
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What is STP Convergence?
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It is a state in which all the switch and bridge ports have transitioned to either the forwarding or the blocking state. This can take anywhere from 30-50 seconds with a default configuration.
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What does PVST+ stand for?
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Per VLAN spanning Tree Plus protocol
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What statements are true about Common Spanning Tree(CST)?
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-No load sharing is possible; one uplink must block for all VLANs.
- The CPU is spared; only one instance of spanning tree must be computed. |
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What is true about Per VLAN spanning Tree Plus(PVST+)?
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- Optimum load sharing can result.
- One spanning-tree isntance of each VLAN maintained can mean a considerable waste of CPU cycles for all the switches in the network(in addition to the bandwidth used for each instance to send its own BPDUs). |
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What does a standard Bridge ID(BID) consist of? What does a PVST+ extended BID consist of?
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Standard = {[2bytes bridge Priority] [6 bytes MAC Address]}
Extended = {[4bits - Bridge Priority] [12 bits - VLAN] [48bits - Mac Address]} |
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What does RSTP stand for? What is its benefit?
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Rapid Spanning Tree Protocol
It significantly reduces the time to re converge the active topology of the network when changes to the physical topology or its configuration parameters occur. |
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What new port roles and states does RSTP introduce? What are there definitions?
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Roles:
Alternate -An alternate path to the root bridge that is different from the path that the root takes. Backup - A backup path that provides a redundant(but less desirable) connection to a segment to which another switch port already connects. Backup ports can exist only where two ports are connected together in a loopback by a point-to-point link or bridge with two or more connections to a shared LAN segment. States: Discarding - Is the same as Blocking, listening and Disabled in STP. Learning - Same as STP Forwarding - Same as STP |
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What standard is each of the below based on?
1. PVST+ 2. PVRST+ 3. MSTP |
1. 802.1D
2. 802.1W 3. 802.1S |
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What are the steps to configure PVRST+?
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1. Enable PVRST+
2. Designate and configure a switch to be the root bridge. 3. designate and configure a switch to be the secondary(backup) root bridge. 4. Verify the configuration |
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What commands are used to "implement" PVRST+?
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SwitchX(config)# spanning-tree mode rapid-pvst
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What commands are used to "verify" PVRST+?
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Verifies the spanning-tree configuration:
SwitchX# show spanning-tree vlan 'vlan#' [detail] Displays PVST+ event debug messages: SwitchX# debug spanning-tree pvst+ |
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What commands are used to "configure" Root and Secondary Bridges?
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Configuring Primary:
SwitchA(config)# spanning-tree vlan 1 root primary Configuring Secondary: SwitchA(config)#spanning-tree vlan 2 root secondary OR This command statically sets the priority(increments of 4096) SwitchA(config)# spanning-tree vlan # priority PRIORITY |
