consistent policy != consistent announcements

Alan Barrett apb at
Fri Mar 14 07:51:27 UTC 1997

The topology we are discussing:

                  /   \
                 A     B      * Peer link
                 |     *      | Customer link
          Point1 *     * Point2

  Vince Fuller said:
> > What we are seeing, though, is "R A M" at Point1 and nothing at
> > Point2, likely because Randy doesn't consider "R B M", received from
> > one of his peers, to be a customer route.

I suppose that R should change their policy, so that all routes to M get
treated as customer routes, even if non-customers appear in the path
between R and M.  Then R would announce "R A M" to V at Point1, and
would announce "R B M" to V at Point2, and V would be happy.

But if A and B have other providers (P, Q), or if B peers with V, then
V is likely to see some non-zero number of paths like "P A M", "P B M",
"Q A M", "Q B M" or "B M" at or near Point2, and so V will not actually
have to carry M's traffic all the way from Point2 to Point1.  In this
case, V should be happy despite R's failure to announce "R B M" at

David Schwartz said:
>       It is not consistent policy to route to a customer through both
> another customer and a non-customer. That's what you can't do.

M might very well have requested R to consider the paths "R A M" and "R
B M" to be equally good, and M doesn't care that A is a customer of R
but B is not a customer of R.  It's perfectly reasonable for R to accede
to M's wishes in this regard.

> Alternatively, if you do decide you must accept routes to a customer
> from a non-customer, you must consider those routes to be customer
> routes.


--apb (Alan Barrett)

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