LAN Switch Types
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has been determined to have the designated port, switch 1900C will put port 1
in blocking state to stop any network loop from occurring.
LAN Switch Types
L
AN switching is used to forward or filter frames based on their hard-
ware destination. However, there are three different methods in which
frames can be forwarded or filtered. Each method has its advantages and dis-
advantages, and by understanding the different LAN switch methods avail-
able, you can make smart switching decisions.
There are three switching modes:
Store-and-forward With the store-and-forward mode, the complete
data frame is received on the switch's buffer, a cyclic redundancy check
(CRC) is run, and then the destination address is looked up in the MAC
filter table.
Cut-through With the cut-through mode, the switch waits for only the
destination hardware address to be received and then looks up the desti-
nation address in the MAC filter table.
FragmentFree FragmentFree is the default mode for the Catalyst 1900
switch; it is sometimes referred to as modified cut-through. Checks the
first 64 bytes of a frame for fragmentation (because of possible collisions)
before forwarding the frame.
Figure 4.7 shows the different points where the switching mode takes
place in the frame. The different switching modes are discussed in detail in
the following sections.
F I G U R E 4 . 7
Different switching modes within a frame
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