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23 Cards in this Set

  • Front
  • Back
What does BPDU stand for? What does it do?
Bridge protocol data unit. All switches configured with STP send these packets out every 2 seconds using a multicast frame. Essentially a keep alive.
What does BID stand for? What is it's function?
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.
What are the 5 STP port states?
Disabled(this isn't strictly part of STP, this can be manually shut by administrator)
What modes does an STP port go through when its first coming up?
2. Listening
3. Learning
If everything is properly configured the port will stabilize to either forwarding or blocking state.
What is maximum age(max_age), and what is its default value?
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.
What three steps are preformed when a bridge is in the STP listening state?
- Selects a root bridge
- Selects the root ports on the nonroot bridges
- Selects the designated ports on each segment
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?
Forward Delay
Default value = 15seconds
How long does it typically take for a port to transition from blocking state to forwarding state in STP?
30-50 seconds
What is Spanning-tree PortFast?
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.
What command is used to configure portfast?
SwitchX(config-if)# spanning-tree portfast


SwitchX(config)# spanning-tree portfast default
This command is as you see globally configured to it enables portfast on all *access* interfaces
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
What is STP Convergence?
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.
What does PVST+ stand for?
Per VLAN spanning Tree Plus protocol
What statements are true about Common Spanning Tree(CST)?
-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.
What is true about Per VLAN spanning Tree Plus(PVST+)?
- 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).
What does a standard Bridge ID(BID) consist of? What does a PVST+ extended BID consist of?
Standard = {[2bytes bridge Priority] [6 bytes MAC Address]}

Extended = {[4bits - Bridge Priority] [12 bits - VLAN] [48bits - Mac Address]}
What does RSTP stand for? What is its benefit?
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.
What new port roles and states does RSTP introduce? What are there definitions?
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.
Discarding - Is the same as Blocking, listening and Disabled in STP.
Learning - Same as STP
Forwarding - Same as STP
What standard is each of the below based on?
1. PVST+
1. 802.1D
2. 802.1W
3. 802.1S
What are the steps to configure PVRST+?
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
What commands are used to "implement" PVRST+?
SwitchX(config)# spanning-tree mode rapid-pvst
What commands are used to "verify" PVRST+?
Verifies the spanning-tree configuration:
SwitchX# show spanning-tree vlan 'vlan#' [detail]

Displays PVST+ event debug messages:
SwitchX# debug spanning-tree pvst+
What commands are used to "configure" Root and Secondary Bridges?
Configuring Primary:
SwitchA(config)# spanning-tree vlan 1 root primary
Configuring Secondary:
SwitchA(config)#spanning-tree vlan 2 root secondary

This command statically sets the priority(increments of 4096)
SwitchA(config)# spanning-tree vlan # priority PRIORITY