On 4/12/2022 9:49 AM, Paul Koning via cctalk wrote:
On Apr 12, 2022, at 12:42 AM, Grant Taylor<cct...@gtaylor.tnetconsulting.net>
wrote:
On 4/11/22 6:16 PM, Paul Koning wrote:
[..SNIP..]
I think there is a large, > 80%, overlap between switch and bridge, but they
aren't perfect. Bridging some traffic between otherwise incompatible networks
comes to mind; e.g. SNAP between Token Ring and Ethernet or Ethernet to xDSL (RFC
1483).
That's not where the term "switch" was introduced. And devices like that were called
"bridge" by market leaders like DEC -- the two generations of FDDI to Ethernet bridges I mentioned
were both called "bridge".
Also, the general operation of the device is the same whether it does MAC frame tweaking
or not, 802.1d applies unchanged. Ethernet to non-Ethernet bridges have to do some
tinkering with Ethernet protocol type frames (which is where SNAP comes in, all nicely
standardized in the FDDI days). For 802.5 they also have to deal with the misnamed
"functional" addresses, but that's not hard.
There also was such a thing as a "source routing bridge", an 802.5 only bad
idea invented by IBM and sold for a while until the whole idea faded away.
The big difference in my mind between bridge and switch is:
* Switches learn what port given MACs are on and only sends unicast
traffic destined for that MAC address on that port and not all
* Bridges send unicast traffic to all ports
Of course it's important for bridges to follow the standard and switches
to make sure they don't cause packet storms by forwarding on ports they
shouldn't
[..SNIP..]
My $.02
Todd
