consistent policy != consistent announcements

John Hawkinson jhawk at
Sat Mar 15 16:14:32 UTC 1997

> Yes.  Suppose that I am "M", and I have two providers "A" and "B".  The
> links M/A and M/B are expensive international links, much lower bandwidth
> than I would like, and prone to congestion.  Further suppose that A is a
> customer of R, and B is a peer of R.  For load balancing reasons, I would
> like R to send some of my traffic via A and some via B.  Since I pay A and
> B for transit, and A pays R for transit, and A and B both agree to play
> along with my desire to load balance, it's reasonable for us to ask R to
> do this.

> From R's point of view, their customer A and their indirect customer
> M have asked them to treat peer routes (via B) and customer routes
> (via A) to destinations in M as being equivalent.

This is just plain difficult to orchestrate, if one asks R to treat
some subset of peer routes as transit routes.

Far better to adopt the reverse solution of having R de-preference
the routes received from A to be an equivalent localperf to those
received from B. That is, give special treatment to a subset of
customer roues, and continue to treat all peer routes the same.

RFC1998 provides a very nice example of this, as implemented by
one provider (MCI).

Nevertheless, this is not a panacea.

Peers of R may still receive routes with different as-paths, but
as-path lengths and origin codes (which matter for selection) should
at least be the same, which should be sufficient.


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