CCNA Cisco Certified Network Associate Study Guide - FTP Server

86 Chapter 2 � Switching Technologies
Some switches can be configured to perform cut-through switching on a
per-port basis until a user-defined error threshold is reached. At that point,
they automatically change over to store-and-forward mode so they will stop
forwarding the errors. When the error rate on the port falls below the threshold,
the port automatically changes back to cut-through mode.
FragmentFree (Modified Cut-Through)
Summary
FragmentFree is a modified form of cut-through switching, in which the
switch waits for the collision window (64 bytes) to pass before forwarding.
If a packet has an error, it almost always occurs within the first 64 bytes.
FragmentFree mode provides better error checking than the cut-through
mode with practically no increase in latency. This is the default switching
method for the 1900 switches.
The information presented in this chapter was designed to give you the
background in layer-2 switching that you need before continuing with the
rest of this book. Specifically, we covered the following information:
� Layer-2 switching and how switches differ from bridges
� Address learning and how the MAC address filter table was built
� Forward/filtering decisions that layer-2 switches make and how they
make them
� Loop avoidance and the problems caused when loop avoidance
schemes are not used in the network
� Spanning-Tree Protocol and how it prevents loops
� LAN switch types used on Cisco routers and how they differ