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Layer 2 Switching

Introduction to Cisco Networking Technologies Study Guide: Chapter 7
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ASIC
application-specific integrated circuits; hardware based bridging
Address learning
adds each hardware address to the forward/filter table
Forward/filter decisions
the switch looks at the destination hardware address and finds the exit interface in the MAC database
Loop avoidance
Spanning Tree Protocol (STP) is used to stop network loops while still permitting redundancy
frame filtering
The switch doesn't transmit the frame out any interface except for the destination interface preseving bandwidth
show mac address-table
display which MAC addresses are associated with which port interface
broadcast storm
the switches will flood broadcasts endlessly throughout the internetwork
thrashing the MAC table
constantly updating the MAC filter table with source hardware address locations that it will fail to forward a frame
Spanning Tree Protocol (STP)
shuts down any redundant links
STP
uses the spanning-tree algorithm (STA) to first create a topology database
STP
a layer 2 protocol that is used to maintain a loop-free switched network
Root bridge
all the switches in the network to elect a root bridge that becomes the focal point in the network
Root bridge
decides which port is blocked and which port is not
Bridge Protocol Data Unit (BPDU)
shared information between bridges when electing the root bridge
Bridge ID
The bridge with the lowest bridge ID becomes the root bridge in the network. Based on bridge priority and base MAC address.
Nonroot bridge
all bridges that are not the root bridge; exchange BPDUs with all bridges and update the STP topology database on all switches
Root port
the shortest path to the root bridge based on bandwidth and lowest Bridge ID
Designated port
port with the lowest Port Cost that will act as the Forwarding Port
Port cost
determined by the bandwidth of a link
Nondesignated port
have a higher cost than the designated port and become a blocking port
Forwarding port
the port that forwards frames
Blocked port
will listen to but not forward frames
Blocking
won't forward frames; listens to BPDUs; prevent the use of looped paths
Listening
prepares to forward data frames without populating the MAC address table
Learning
populates the MAC address table but doesn't forward data frame
Forwarding
sends and receives all data frames on the bridged port; designated or root port at the end of the learning state
Disabled
does not participate in the frame forwarding or STP
Convergence
all ports on bridges and switches have transitioned to either the forwarding or blocking modes; No data is forwarded until convergence is complete
Cut-through (FastForward/Real-Time)
the switch only waits for the destination hardware address to be received before it looks up the destination address in the MAC filter table
FragmentFree (modified cut-through)
the switch checks the first 64 bytes of a frame before forwarding it for fragmentation
Store-and-Forward
the complete data frame is received on the switch's buffer, a CRC is run, and if the CRC passes, the switch looks up the destination address in the MAC filter table
What command will show you the forward/filter table
show mac address-table
If a destination MAC address is not in the forward/filter table, what will the switch do with the frame
Flood the frame out all ports except the port it was received on
What are the three switch functions at layer 2?
Address learning, forward/filter decisions, loop avoidance
If a frame is received on a switch port and the source MAC address is not in the forward/ filter table, what will the switch do?
It will add the source MAC address in the forward/filter table and associate it with the port the frame was received on
What is used at layer 2 to prevent switching loops?
Spanning Tree Protocol (STP)
Which LAN switch method receives the complete frame before beginning to forward it?
Store-and-forward
When is STP considered to be converged?
When all ports are in either the blocking or forwarding mode
Switches break up ___________________ domains
Collision
What is used to prevent switching loops in a network with redundant switched paths?
Spanning Tree Protocol (STP)
Which LAN switch method runs a CRC on every frame the switch receives?
Store-and-forward
Which of the following is a layer 2 protocol used to maintain a loop-free network?
Spanning Tree Protocol (STP)
What command will display the forward/filter table?
show mac address-table
What is the result of segmenting a network with a bridge (switch)? (Choose two options.)
It increases the number of collision domains & It makes smaller collision domains.
Which statement describes a spanning-tree network that has converged?
All switch and bridge ports are in either the forwarding or blocking state.
Your network design emphasizes efficient, error-free transport instead of fast transport. Which switching mode should be configured on the new switches to provide error-free transport to the network?
Store-and-forward
What are the three distinct functions of layer 2 switching that increase available bandwidth on the network?
address learning, forwarding and filtering of the network, and loop avoidance
What technology is used by Catalyst switches to resolve topology loops and ensure that data flows properly through a single network path?
Spanning Tree Protocol (STP)
Which of the following statements is true?
A switch creates separate collision domains but one broadcast domain. A router provides a separate broadcast domain.
Which of the following is true regarding layer 2 switches? (Choose two.)
A switch is a multiport bridge & Switches learn MAC addresses by examining the source address of each frame.
What does a switch do when a frame is received on an interface and the destination hardware address is unknown or not in the filter table?
Floods the network with the frame looking for the device
If a switch receives a frame and the source MAC address is not in the MAC address table, but the destination address is in the table, what will the switch do with the frame?
Add the source address and port to the MAC address table and forward the frame out the destination port.
Which of the following are spanning-tree switch port states?
blocking, listening, learning, forwarding, and disabled
What purpose in a switched LAN does STP perform?
Prevents switching loops in a network with redundant switched paths
Which command was used to produce the following output:
show mac address-table
Which of the following is a characteristic of having a network segment on a switch?
One device per segment can send frames to the switch at a time.
Which of the following is true in regard to bridges?
Bridges do not isolate broadcast domains by default
Layer 2 switching provides which of the following? (Choose four.)
Hardware-based bridging (ASIC), Wire speed, Low latency, Low cost
Suppose the above switch received a frame with the following MAC addresses: Source MAC: 0005.dccb.d74b Destination MAC: 000a.f467.9e8c
It will forward the frame out port Fa0/3 only
You are working on a network design and determine that a new testing application requires multiple hosts that must be capable of sharing data between each host and server running 10Mbps. Other departments use applications that require less than 3Mbps to the server. What should you recommend?
Use a switch with a 100Mbps uplink to the server and 10Mbps to the hosts
You have two switches connected together with two cross-over cables for redundancy, and STP is disabled. Which of the following will happen between the switches?
Broadcast storms will occur on the switched network.