Radia Perlman and TRILL
Bob Brown interviewed Radia Perlman (famous for inventing the spanning tree algorithm, among other things) for Network World. Dr. Perlman works as a Distinguished Engineer at Sun Labs.
When asked, “What else is on your plate?” Radia said:
[tease]
I’ll tell you, but there’s a story behind it. A couple of years back there was this Boston Globe article about a hospital network melting down and in the middle of it was mentioned the spanning tree algorithm. I’m thinking: those are words that don’t belong in a Boston Globe article even if spanning tree was involved. Eventually we tracked down the company providing the switches and indeed it was a giant bridged network.
Now, bridging was never intended to do that: it was kind of a hack because people at the time were all confused about what Layer 3 was and they thought Ethernet was a competitor to DECnet. With bridges we did such a good job and it was so plug-and-play that you didn’t have to think about them, so people are still taking large networks and doing bridges. As it turns out people kind of believed IP must have been the best protocol ever because it just took over the world (just like English must be the best language ever because it’s going to take over the world, but no, it has nothing to do with how good a language it is).
DECnet would have been a much better protocol for the world to have adopted. It had a lot of advantages, like a larger address space (We’re still talking about will IPv6 ever happen and if it does, there’s nothing better about it than what we could have had 15 years ago). One of the advantages DECnet had was the ability to have a whole campus that was zero-configuration, that all had the same prefix , and you didn’t have to divvy up your address space for every link like IP does. But given that companies didn’t go in that direction they’re using bridging, which is inherently more fragile, especially when you take that notion and try to make it more responsive by doing all these things that involve lots of configuration. If you get the configuration wrong things can melt down. You shouldn’t be stressing it really hard.
One of the things I’m trying to do now, given that we’re stuck with IP, is come up with something that gives you the advantages of bridging so it can be all zero-configuration within a campus and all look like one big prefix and not be confined to just transmitting data along the spanning tree. You’d be able to use shortest paths and will be safer if you have temporary loops, so it shouldn’t melt down. About a year ago we finally got through the politics and got an IETF working group started called TRILL, which stands for “transparent interconnection of lots of links.” I’d written a paper about this five years ago and have been trying to sell it to the various standards bodies. I’m pretty sure it will get implemented. There are a lot of companies asking the sort of questions that only would be asked if they were planning to.