nanog mailing list archives
Re: reliably detecting the presence of a bridge?
From: Larry Sheldon <larrysheldon () cox net>
Date: Sat, 19 Dec 2015 15:53:26 -0600
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)
Current thread:
- Re: reliably detecting the presence of a bridge?, (continued)
- Re: reliably detecting the presence of a bridge? Jared Mauch (Dec 15)
- Re: reliably detecting the presence of a bridge? Matthew Kaufman (Dec 15)
- Re: reliably detecting the presence of a bridge? William Herrin (Dec 15)
- Re: reliably detecting the presence of a bridge? Dave Taht (Dec 16)
- Re: reliably detecting the presence of a bridge? Masataka Ohta (Dec 16)
- Message not available
- Re: reliably detecting the presence of a bridge? Carsten Bormann (Dec 16)
- RE: reliably detecting the presence of a bridge? Chuck Church (Dec 16)
- Re: reliably detecting the presence of a bridge? Anoop Ghanwani (Dec 16)
- Re: reliably detecting the presence of a bridge? Dave Taht (Dec 19)
- Re: reliably detecting the presence of a bridge? Dave Taht (Dec 16)
- Re: reliably detecting the presence of a bridge? William Herrin (Dec 19)
- Re: reliably detecting the presence of a bridge? Larry Sheldon (Dec 19)
- Re: reliably detecting the presence of a bridge? John Levine (Dec 19)
- Re: reliably detecting the presence of a bridge? James R Cutler (Dec 19)
- Re: reliably detecting the presence of a bridge? Larry Sheldon (Dec 19)
- Re: reliably detecting the presence of a bridge? Larry Sheldon (Dec 19)