The Missing Linker

By: Scott Bradner

Virtual networking seems to be all the rage these days.

It is hard to pick up a copy of this or any of the other (but there is no reason to pick up any other) trade magazine without finding a story on virtual LANs. The way many of these stories read, all of ones problems can be solved by going virtual. I guess it does solve the parking problem.

Virtual LANs, based on frame or ATM switches, can offer great advantages, particularly for organizations which do a lot of shuffling people around. Moving Fred down the hall and being able to keep his computer on the same local area network, or keeping him in the same office but relocating his PC to another LAN when his job changes can significantly reduce the pain of changes. (According to the seemingly omni-present salesdroids.)

Some companies do seem to be rather restless, I was at one a few weeks ago where they said they did, on the average, one move per person per year. Since this was a statement of the average, I kinda wonder what its like on the wrong end of the distribution curve. Some of these cases do seem like Browninian motion being mistaken for progress.

But there is something missing from too many of the presentations about these virtual LAN paradises. Somehow the need to talk between virtual LANs seems to be forgotten. This is not the case with all of the presentations. The acerbically and accurately named "markectures" put out buy the companies that have routers in their blood do understand that isolated virtual LANs are not as useful as they might be. This seems to somehow slip past those vendors coming from other backgrounds. This problem may be solved if if the mergers continue to go the way they have been since there will be only 3 vendors of networking products left (and I'll leave you to guess which 3 I think they will be.)

For someone who spends as much time as some of the presenters do talking about how great it is to be able to remotely assign Fred to the LAN of the management's choice, one would think that they could understand that even though network architects have divided networks into LANs for many reasons, traffic separation, security and limiting broadcast domains being a few, most LANs do have to interact with other LANs. A LAN that can not interact with other LANs is like getting Friends and Family and finding out they really mean it.

Routers are not going away in the age of virtual LANs. Nor is routing going away. People who start to put in large switched networks, without real or virtual LANs will rediscover why network architects moved away from large bridged networks. By the way, it is my opinion that about half of what is now on the market as Ethernet switches started life as multi-port bridges but were transformed by the marketers. Amazing what electronic miracles one can work with a bit of paint.

The next time one of these eager, well coiffured, salespersons tells you the wonders of virtual LANs ask them how Fred on his new virtual world will talk to Bill in another new virtual world, while you are at it you might ask the salesperson how either of them talks to the Internet. A couple of years ago one of these people came to tell me the wonderful things he could do for Harvard with virtual LANs, I asked the above question and, after a bit of tooth pulling, I was told that I should get a 200 port router, but that was outside of the virtual reality he was trying to sell me.

disclaimer: Although some would claim otherwise, Harvard is better aquatinted with real reality than with virtual reality, in any case Harvard does not express an opinion about LAN realities.