Leading the way in IT testing and certification tools, You want your Catalyst switch to implement a switching method that holds a packet in its memory

Leading the way in IT testing and certification tools, You want your Catalyst switch to implement a switching method that holds a packet in its memory until the data portion of the respected packet reaches the switch. Which method should you employ on your Catalyst switch?


A. Fast Forward
B. Store and forward
C. Frag-free
D. None of the above

Answer: C

Explanation:
Fragment Free switching filters out the majority of packet errors before forwarding begins. In a properly functioning network, most packet "errors" are due to collisions which are resolved within the first 64 bytes of the packet. These collisions cause packet fragments. After a packet has successfully passed this fragment threshold, it will continue to be received without error with near-certainty. (The next biggest cause of failure arises from "late" collisions which can occur when the network is physically interrupted.) This is how the Fragment Free option works. Fragment Free switching waits until the received packet passes the 64-byte fragment threshold and then forwards the packet.


Incorrect Answers:

A. Fast Forward switching is optimized for performance. It offers the lowest level of latency by immediately forwarding a packet upon receipt of only the destination address (after the first 6 bytes are received). Because Fast Forward does not wait until the entire packet is received before forwarding, this form of switching may sometimes relay a packet that has an error. Although this will be an infrequent occurrence and the destination network adapter will discard the faulty packet upon receipt, this superfluous traffic may be deemed unacceptable in certain environments. Such cut-through overhead can be reduced by using the Fragment Free option.
B. Another switching mode supported by Catalystswitches is the traditional
Store-and-Forward bridging mode. Complete packets are stored and checked for errors prior to transmission. Latency varies by packet size since the entire packet needs to be received prior to transmission.