Hi Amit,

Think about what happens when a switch receives a broadcast, unknown-unicast
(that is a frame destined for a unicast receiver that the switch doesn't
know how to reach yet) or a multicast frame sometimes referred to as BUM
frames.

The switch will send it out all ports except the one it received the frame
from.

This isn't a problem except if you start to introduce physical loops into
your network to provide resiliency against a link failure, you can get a BUM
frame spinning around the network.  Unlike IP there is no TTL that decreases
and eventually hits zero and gets dropped, that guy is there until something
breaks the path.

Spanning Tree protocol is a mechanism to detect and deterministically break
the loop by blocking a link.

Cheers,
Adam



On Thu, Apr 14, 2011 at 4:39 PM, Amit Jp <[email protected]> wrote:

> I,need to know what is switching loop how a frame is moved across I have
> read bcmsn but some parts aren't clearly
> explained
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