On 12/19/2015 12:17, William Herrin wrote:
[snip]
I recommend you stop using the word "bridge." I think see where you're
heading with it, but I think you're chasing a blind alley which
encourages a false mental model of how layer 2 networks function. You
came here for answers. This is one of them.
"Bridge" describes a device which existed in layer 2 networks a
quarter century ago. You had a 10-base2 ethernet with every station
connected to a shared coax wire. Or you had a token ring where each
station was wired to the next station in a loop. Or if you were
sophisticated you had 10-baseT with a hub that repeated bits from any
port to all ports with no concept of packets.
And then you had a bridge which could connect these networks together,
buffering complete packets and smartly repeating only the packets
which belong on the other side. The bridge let you expand past the
distance limitations imposed by the ethernet collision domain, and it
let you move between two different speed networks.
These networks are now largely a historical curiousity. There are no
hubs, no 10-base2, no token passing rings. Not any more. Individual
stations now connect directly to a bridge device, which these days we
often call a "switch." Even where the stations have a shared media
(e.g. 802.11), the stations talk to the bridge, not to each other.
Bridge specifies a condition that, today, is close enough to always
true as makes no difference.
Super explanation.
But I still have one question (which might be based on errors)--
I think I have used WiFi terminals ("air ports", "WiFi routers" [spit])
that offer a "bridge" mode, apparently to build a dedicated radio link
between two such terminals.
Are they operating as a Radia Perlman "bridge", or is this yet another
example if the Wiffy World high-jacking words and terms that used to
have actual meanings?
Nice write-up, even though it is sort of sad to be confronted with the
fact that my experience and knowledge with hose-connected (10base5.
10base2) or token-ring networks, and hubs, and stuff is now without
value. That is the very worst part of getting old.
Next objective: Somebody to 'splain at what happened to the
wonderfulness of the OSI model where layer X did not know, could not
know, did not care what layer X-1 was, did, or how it did it.
--
sed quis custodiet ipsos custodes? (Juvenal)
