[ih] The story of BGP?

Noel Chiappa jnc at mercury.lcs.mit.edu
Fri Feb 8 08:09:11 PST 2013

    > From: Justine Sherry <justine at eecs.berkeley.edu>

Just looking back at your original message, a few comments, better answering
your original questions (which didn't really get answered, I think).

    > Pre-1994: EGP, hierarchical Internet to NSFNet
    > Some point in 1994: "Flag Day" and everyone switches to BGP
    > Since 1994: Minimal evolution in BGP

I'm not sure where 1994 comes from (that's the date on BGP-4, is that it?),
but it's wrong.

The conversion to BGP happened considerably before that. By the time of the
BGP-1 spec in mid-1989, BGP was already in use; (from RFC-1105):

  At the time of this writing, the Border Gateway Protocol implementations
  exist for cisco routers as well as for the NSFNET Nodal Switching Systems

I don't recall how long EGP2 remained in use after mid-1989, but it wasn't
long, IIRC. And there was no 'flag day' - the Internet was already too big,
and used too heavily, for that kind of thing.

And of course BGP has continued to evolve since 1994 (communities, route
reflectors, dampening, iBGP, yadda-yadda) although it's as much in
operational practises as in the basic protocol.

    > why was it settled on as what we all switched to in 1994? Were there
    > alternatives in mind?

There weren't any real alternatives, in the early stages (around 1989). EGP3
never happened (I think because most of the 'routing' people wanted to build
something with more capabilities), and anything more sophisticted would have
taken, and did take, too long. A few other things were bruited (FGP, DGP, Guy
Almes' thing, whose name escapes me at the moment - maybe MIRA?) but none
were more than paper - whereas BGP had implementations available. Moving off
EGP2 was absolutely necessary (as Louie notes, the single-IP-packet routing
updates were terminally limiting), and BGP-1 was the only thing available.

Later on, IDPR made it into code (and Nimrod got half-way done), but I think
the thing that sunk them was completely different: they arrived while the
Internet was in a phase of extremely explosive growth, and people were
running flat out just trying to keep up with the growth in traffic. Switching
to a whole new routing architecture just didn't have a snowball's chance of
happening. CIDR only happened because it was absolutely critical, and it
involved only minimal changes. Not being involved deeply in IDPR, I can't
speak for them, but I know with Nimrod a lot of people thought it was really
neat, and very powerful, but it was pretty clear that people just didn't have
enough spare time/energy/resources to make it happen. And then we'd missed
the window - the Internet was too big to make that kind of change, and its
evolution had become _completely_ driven by relatively short-term
cost/benefit considerations. So unless there was an absolute necessity for
something different - and there wasn't - there was no way to replace BGP.

    > How is the BGP we switched to in 1994 different from the BGP we used
    > today, and who drove those changes?

BGP-1 to today, or BGP-4 circa 1994 to today? (Which was just after CIDR was
taken up, which was in September 1993.) There's a big difference between
those two. But someone else can answer that better.


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