Answering my own question:
Unicast flooding is fundamental. Unicast flooding in response to a null
switching table is the only way for a frame to reach the intended host,
say, if the switching table had an entry which expired before it could
be re-populated with the host's arp reply.
On 8/16/2016 2:19 PM, Karl Fife wrote:
Hey all. I'm trying to get to the bottom of an Ethernet concept:
If an Ethernet switch has no switching/forwarding table entry for a
given MAC, does it flood/broadcast BY DESIGN (e.g. to behave like a
good old-fashioned Ethenet HUB) or is unicast flooding an accidental
characteristic of the way Ethernet switches work (i.e. down on the
metal)?
For example, I could imagine an Ethernet switch design which the
switch always returns null in the switching table for
FF:FF:FF:FF:FF:FF, triggering a broadcast/flood, thus other bona-fide
null (expired) lookups also happen to flood, BUT that this behavior is
not strictly required to function.
Clarification on this detail would be much appreciated.
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