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Re: Open Source BGP Route Optimization?

  • From: Bruce Pinsky
  • Date: Fri May 28 15:37:16 2004

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Per Gregers Bilse wrote:

| On May 28, 10:37am, "Sam Stickland" <sam_ml@spacething.org> wrote:
|
|>Are there any BGP extensions that would cause a BGP speaker to foward all of
|>it's paths, not just it best? I believe quagga had made some recent attempts
|
|
| It has been discussed and been on wish lists, but:
|

And as I said in my other post, there were two drafts submitted that never
went anywhere.

|
|>in this direction. IIRC the problem isn't to do with the route annoucements,
|>it's the route withdrawals. I believe BGP only specifies the prefix being
|>withdrawn and not the path, so if it's advertised multiple paths to a prefix
|>it's impossible to know which has been withdrawn.
|
|

But the "optimizing" device is in need of receiving all potential paths
from the border routers.  Essentially, it needs a complete picture of all
viable paths, not just the best that each border has.  It would not be
advertising multiple paths.

| That is 100% correct, yes.  Selective withdrawal is not supported.
|

But the "optimizing" device wouldn't be advertising multiple paths.  It
would be advertising its selected path from all viable paths based on the
selection criteria/policy implemented by the user.  The optimizing device
can then keep track of what it has advertised and withdraw as
appropriate/necessary.


| Another issue is that there isn't much point, as far as regular BGP
| and routing considerations go.  Whichever is the best path for a border
| router is the best path; telling other routers about paths it will not
| use serves no (or at best very little) point in this context.
|

The point is not to tell other borders about paths it will not use, but for
the "optimizing" device to select the desired path from all available paths
and cause that path to become "best path" for all border routers.  And
"best" in this case is a user influenced choice based on any number of
factors including path performance, cost, load, or other policies that the
device can use as a selection criteria.

| Funny coincidence, just earlier today I was talking to somebody about
| BGP and its general applicability, and while there can be no question
| that BGP has stood the test of time and achieved all its objectives,
| there are things one would do differently if one were to start over.
| But that's always the case.
|

Does a great job at what it was designed for as appropriate for the time it
was conceived.  As always, times change.

- --
=========
bep

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