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CCNA 640-802 Ch.8
CCNA Ch. 8 Layer 2 Switching and STP
45
Computer Networking
Professional
03/11/2013

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Term
What are the advantages of Layer 2 switching?
Definition
Each user has dedicated bandwidth.
Quicker than routing, as it does not manipulate the packet, it either forwards, floods or drops a packet.
Break up collision domains
Term
What are the three functions of a switch at layer 2?
Definition
Address learning
Forward/filter decisions
Loop Avoidance
Term
What does address learning mean pertaining to layer 2 switches?
Definition
When a frame is passed through a frame for the first time, the source MAC Address is stored in the filter table. The frame is then forwarded out all ports except the source port until it is ack'd. The Physical Address is then placed in the database for future use.
Term
What does Forward/Filter mean pertaining to Layer 2 switching
Definition
If a frame's destination MAC Address is in the database table it is only forwarded out that interface. If it is not known, it is forwarded out all ports.
Term
What series of commands would be issues to shutdown a port if more than one host connects to it?
Definition
switch(config)#int fa0/1
switch(config-if)#switchport port-security maximum 1
switch(config-if)#switchport port-security violation shutdown
Term
What is a Root Bridge?
Definition
A bridge with the lowest ID. All switches elect a root bridge.
Term
What is BPDU?
Definition
Bridge Protocol Data Unit - This is used to compare configurations with neighboring switches. This helps in the election of a root switch.
Term
What is Bridge ID?
Definition
This value is how all switches are tracked on the network. It is a combination of the bridge priority and the base MAC Address. The bridge with the lowest ID becomes the root bridge.
Term
What is the default bridge priority?
Definition
32,768
Term
What are Nonroot Bridges?
Definition
Bridges that are not elected as the root. They exchange BPDU's and STP Topology database to prevent loops and failures.
Term
How is Port Cost
Definition
Determines the best rout to a switch with multiple paths.
Term
How is port cost determined?
Definition
Determined by the bandwidth on the line.
Term
What is a Root Port?
Definition
Is always the link directly connected to the root bridge, or the shortest path to the root bridge.
Term
How is the root port determined?
Definition
Directly connected link.
If more than one link, port cost used
Same cost? then lower advertising ID is used
Term
What is a designated port?
Definition
One that has the lowest cost. This port is marked as a forwarding port.
Term
What is a Nondesignated port?
Definition
One with a higher cost. These ports are in blocking mode.
Term
What does a blocked port do?
Definition
It will only listen to frames, it will not forward them.
Term
What is the STP Process
Definition
Root Bridge Elected
Every switch determines one root port
All other ports are placed in blocking state
Term
By default, how often are BPDU's sent
Definition
Every 2 seconds out all active ports.
Term
What is the command to change the bridge priority?
Definition
router(config)#spanning-tree vlan 1 priority 4096
(Multiples of 4096) This switch will have 4096 for all of VLAN 1.
Term
What does a priority of 0 mean on a switch
Definition
The switch will always be the root.
Term
What is the highest priority that can be set on a switch?
Definition
61440
Term
What does the blocking port state do?
Definition
Does not forward frames. This is default on all ports when the switch powers up.
Term
What does the listening port state do?
Definition
Prepares to forward data frames without populating the Mac Address table. This state is to ensure no routing loops are occurring.
Term
What does the learning port state do?
Definition
Listens to BPDU and learns all the paths in the network. Only populates MAC Address table and does not forward any frames.
Term
What is forward delay? and what is the default value?
Definition
The time it takes a port to transition from listening to learning and the default is 15 seconds.
Term
What is the command to display the forward delay time?
Definition
show spanning-tree
Term
What does the forwarding port state do?
Definition
Port sends and receives all data frames on the bridged port.
Term
When does convergence occur on a switch
Definition
When all ports are either in a forward or blocking mode.
Term
What is spanning-tree portfast used for?
Definition
Used when a port is connected to a server or a pc device. It will bypass the 50 second forwarding mode with STP and
Term
What is the command to enable portfast?
Definition
switch(config)#spanning-tree portfast
Term
What is spanning-tree uplink fast?
Definition
Cisco convergence that improves convergence time on a link failure. Allows a switch to find an alternate path to the root bridge before the primary link fails.
Term
Where does Cisco reccomend using uplinkfast?
Definition
On Access layer devices.
Term
What is spanning-tree BackboneFast?
Definition
Used when a link not directly connected to a switch fails. This is to be enabled on all catalyst switches to allow for detection on indirect failures.
Term
What is Rapid Spanning-Tree Protocol?
Definition
Combines all the features of portfast, uplinkfast, backbone fast, into one protocol. All switches must run the same STP.
Term
What is EtherChannel?
Definition
Allows multiple links to appear as one link on a switch.
Term
What is BPDUGuard?
Definition
Configured on Access layer switches that have portfast configured. This prevents the switch going into errdisabled state if it receives a BPDU
Term
What is BPDUFilter?
Definition
This prevents BPDU's from filtering to the switch all together.
Term
What is the command to enable BPDUGuard?
Definition
switch(config-if)#spanning-tree bpduguard enable
Term
What is the command to enable BPDUFilter?
Definition
switch(config-if)#spanning-tree bpdufilter enable
Term
What is the command to enable RSTP?
Definition
switch(config)#spanning-tree mode rapid-pvst
Term
What is the series of commands to enable and configure etherchannel?
Definition
switch(config-if)#int port-channel 1
switch(config-if)#switchport mode trunk nonegotiate
switch(config-if)#channel-group 1 mode desirable
Term
What is the command to add a static mac address?
Definition
switch(config)mac-address-table static aaaa.bbbb.cccc vlan 1 int fa0/5
Term
What is the command to set a switch as the root without having to adjust priorties?
Definition
switch(config)#spanning-tree vlan 1 root primary
Term
what command would you issue to disable stp on a port connect to a server
Definition
switch(config)# spanning-tree portfast
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