Mod7 v1
What is the auto-MDIX feature on a switch?
What is the automatic configuration of an interface for a straight-through or a crossover Ethernet cable connection
The auto-MDIX enables a switch to use a crossover or a straight-through Ethernet cable to connect to a device regardless of the device on the other end of the connection.
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7.4 Switch Speeds and Forwarding Methods
What is the purpose of the FCS field in a frame?
What is to compute the CRC header for the data field
The FCS field in a frame is used to detect any errors in the transmission and receipt of a frame. This is done by comparing the CRC value within the frame against a computed CRC value of the frame. If the two values do not match, then the frame is discarded.
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1.7.1 Ethernet Frames
Go to Module 7 Dynamic 26 picture.
Refer to the exhibit. What is the destination MAC address of the Ethernet frame as it leaves the web server if the final destination is PC1?
The destination MAC address is used for local delivery of Ethernet frames. The MAC (Layer 2) address changes at each network segment along the path. As the frame leaves the web server, it will be delivered by using the MAC address of the default gateway.
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1.7.3 The MAC Address Table
Which switching method has the lowest level of latency?
what is fragment free
Fast-forward switching begins to forward a frame after reading the destination MAC address, resulting in the lowest latency. Fragment-free reads the first 64 bytes before forwarding. Store-and-forward has the highest latency because it reads the entire frame before beginning to forward it. Both fragment-free and fast-forward are types of cut-through switching.
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1.7.4 Switch Speeds and Forwarding Methods
A Layer 2 switch is used to switch incoming frames from a 1000BASE-T port to a port connected to a 100Base-T network. Which method of memory buffering would work best for this task?
What is shared memory buffering
With shared memory buffering, the number of frames stored in the buffer is restricted only by the of the entire memory buffer and not limited to a single port buffer. This permits larger frames to be transmitted with fewer dropped frames. This is important to asymmetric switching, which applies to this scenario, where frames are being exchanged between ports of different rates. With port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports making it possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. Level 1 cache is memory used in a CPU. Fixed configuration refers to the port arrangement in switch hardware.
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1.7.4 Switch Speeds and Forwarding Methods
Which advantage does the store-and-forward switching method have compared with the cut-through switching method?
What is frame error checking
A switch using the store-and-forward switching method performs an error check on an incoming frame by comparing the FCS value against its own FCS calculations after the entire frame is received. In comparison, a switch using the cut-through switching method makes quick forwarding decisions and starts the forwarding process without waiting for the entire frame to be received. Thus a switch using cut-through switching may send invalid frames to the network. The performance of store-and-forward switching is slower compared to cut-through switching performance. Collision detection is monitored by the sending device. Store-and-forward switching does not use IPv4 Layer 3 and 4 information for its forwarding decisions.
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1.7.4 Switch Speeds and Forwarding Methods
What are two examples of the cut-through switching method? (Choose two.)
What is fast-forward switching & fragment-free switching
Store-and forward switching accepts the entire frame and performs error checking using CRC before forwarding the frame. Store-and-forward is often required for QOS analysis. Fast-forward and fragment-free are both variations of the cut-through switching method where only part of the frame is received before the switch begins to forward it.
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1.7.4 Switch Speeds and Forwarding Methods
When the store-and-forward method of switching is in use, what part of the Ethernet frame is used to perform an error check?
What is cyclic redundancy (CRC) in the trailer
The cyclic redundancy check (CRC) part of the trailer is used to determine if the frame has been modified during transit. If the integrity of the frame is verified, the frame is forwarded. If the integrity of the frame cannot be verified, then the frame is dropped.
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1.7.4 Switch Speeds and Forwarding Methods
Which frame forwarding method receives the entire frame and performs a CRC check to detect errors before forwarding the frame?
What is store-and-forward switching
Fast-forward and fragment-free switching are variations of cut-through switching, which begins to forward the frame before the entire frame is received.
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7.4 Switch Speeds and Forwarding Methods
Which switching method uses the CRC value in a frame?
What is fragment-free
When the store-and-forward switching method is used, the switch receives the complete frame before forwarding it on to the destination. The cyclic redundancy check (CRC) part of the trailer is used to determine if the frame has been modified during transit. In contrast, a cut-through switch forwards the frame once the destination Layer 2 address is read. Two types of cut-through switching methods are fast-forward and fragment-free.
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1.7.4 Switch Speeds and Forwarding Methods