CISCO Switching Basics : Switching Modes

3- Switching Modes :

   Cisco switches has offered 3 ways to switch the traffic, this depends on how the frame is checked before it is forwarded, so the more checking performed, the more latency will be introduced by the switch.
the three switching modes to choose from are :

• Cut-through
• Store-and-forward 
• Fragment-Free

however the default mode en modern switches is the Store-and-forward mode.

3-1- Cut-through :

   this methode is fast, so it introduces the lowest latency. the idea here is the the incoming frame is read up until the destination MAC address. when it reaches the destination MAC address, the switch then will check its CAM table (Content Addressable Memory) to retrieve the correct port to forward the frame out of and sends it. there is no error checking, so this methode has the lowest latency as advantage, but on the other hand the biggest drawback is that the switch will forward any frames containing errors.

3-2- Store-and-forward :

   in this mode here, the switch read the entire frame and then makes a copy of it into its buffers, however the frame is checked for any errors by the Cyclic redundancy check (CRC), if ever any errors are found th frame is dropped, as a result of this error checking the store-and-forward methode is considered as the one with the highest latency of all the switching modes. on the other hand, the switching table is examined and then the frame is transmitted.
there is important thing must be mentioned, the store-and-forward methode checks the length of the frame, if it's smaller than 64 bytes or larger than 1518 bytes, the switch will discard the frame.

3-3- Fragment-free :

   as we have seen earlier in this corse, the cut-through switching doesn't check for errors and the store--and-forward methode takes too long, we need a methode that is quick and reliable at the same time
we can say that fragment-free switching is a modified version of cut-through switching. only the first 64 bytes are examined for any errors, if there is no errors detected, the frame will be passed on.

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so this is it Guys, hope i covered it up as clear as possible.
Next we will talk about VLANs (virtual local area networks)

please comment for any notes or questions, propositions...

Thank you All!