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Re: Cut-through vs Store & Forward [7:48316] posted 07/09/2002
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Hello again,
  Priscilla, you have said that an ethernet frame must be at least 64 bytes,
right?. I have just placed an sniffer on my LAN and I found over 3000 out of
15.000 packets. Does this mean that 20% of those packets are illegal?

Thanks

Alejandro Acosta

----- Original Message -----
From: "Priscilla Oppenheimer" 
To: 
Sent: Monday, July 08, 2002 1:08 PM
Subject: RE: Cut-through vs Store & Forward [7:48316]


> Alejandro Acosta Alamo wrote:
> >
> > Hello,
> >   I understand the differences between Cut-through and Store &
> > Forward. My
> > question is: How do you decide with method to use?, in whch
> > situation have
> > you change the switching method?.
> >
> > Thanks
> >
> > Alejandro Acosta
> >
> >
> A lot of switches support only one method, so you don't have a choice. If
> you do have a choice, the decision is based on the number of errors on
your
> network. Cut-through doesn't do any error checking and in fact forwards
> frames that have a bad CRC or are too short. Ethernet says that frames
must
> be at least 64 bytes. Anything less is considered a fragment and is
illegal.
> Cut-through forwards fragments that have an entire destination address
that
> can be looked up to get a port number.
>
> If your switch connects many shared networks, then CRC errors and
fragments
> due to collisions are normal. But why waste bandwidth forwarding these to
> other ports on the LAN? In this case, you might want to go with
> store-and-forward which does not forward errored frames or fragments.
>
> If your switch connects single devices all using full-duplex, then it's
> unlikely that you are experiencing many CRC or fragments. So, cut-through
> makes the most sense.
>
>
> Priscilla Oppenheimer
> http://www.priscilla.com




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