Retro networking / WAN communities

[Todd Goodman]

On 4/12/2022 9:49 AM, Paul Koning via cctalk wrote:
>
>> On Apr 12, 2022, at 12:42 AM, Grant Taylor<cctalk at 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