Implementation of RIPE-181++

 * I think this question and the one I asked a week back are both due to
 * the ambiguity on the relation between as-in and interas-in. I think
 * the relation between as-in and interas-in needs to be made clear and
 * explicit.

Seeing the different interpretations of the text, we indeed need to
make this clear.

 * >From the perspective of someone who read ripe181 Sep 16 version, all
 * solutions proposed do not solve Laurant's problem. I.e. solutions are
 * not consistent with ripe181 document.
 * 
 * Marten Terpstra (Marten.Terpstra at ripe.net) on September 20:
 * > aut-num:    AS1
> as-in:      AS2 100 AS100 OR {10.0.0.0/8}
 * > interas-in: AS2 as1nap1 as2nap1 AS100
 * > interas-in: AS2 as1nap2 as2nap2 AS100
 * > interas-in: AS2 as1nap3 as2nap3 AS100 OR {10.0.0.0/8}
 * 
 * ripe-81++ says pp 27-28 in ascii version:
 * 
 *    If the global policy mentions more routes than the local policy
 *    then local preferences for these routes are assumed to be equal for
 *    all links.
 * 
 * My interpretation is as follows:
 * 	as-in:      AS2 100 AS100 OR {10.0.0.0/8}
 * mentions more routes than
 * 	interas-in: AS2 as1nap1 as2nap1 AS100.
 * I.e. it mentions {10.0.0.0/8} extra.
 * Hence,
 * "local preferences for {10.0.0.0/8} are assumed to be equal for all
 * links".
 * 
 * All links include "as1nap1 as2nap1" Hence, AS1 accepts {10.0.0.0/8} on
 * nap1 as well.

OK, to say what we actually mean, the paragraph in ripe-181 should say:

"If the global policy mentions more routes than the *combined local
policies* then local preferences for these routes are assumed to be
equal for all links."

This is what I understood this means.

 * Marten Terpstra (Marten.Terpstra at ripe.net) on September 20:
 * > aut-num:    AS1
 * > as-in:      AS2 100 AS100 OR {10.0.0.0/8}
 * > interas-in: AS2 as1nap3 as2nap3 {10.0.0.0/8}
 * 
 * This will make AS1 accept {10.0.0.0/8} on nap1 and nap2 as well.
 * Since policies on those naps will be the one in as-in.

Yes and no, interpretation again. If you take my (modified) paragraph
of above you can also say that *only* the surplus routes mentioned in
as-in will be assumed equal for all links. Ie, only AS100 (which is not
explicitly used in any interas-in rule) is assumed to be accepted
equally on all links. There's an exception trule for 10/8 so that one
should never be accepted on the other interas policies. Then again, if
the other two interas rules are not there, how can you even generate a
config for these two...

 * Perhaps, with the current ripe181 document, there is no correct
 * solution. If this is the case, Laurant owes me a beer.

There is a solution, the problem we all have is the different
interpretations of the as-in and interas-in combination. If you all
agree with what I said above, we should try and rewrite that paragraph
to more clearly explain what the interaction is. If we can find a
common interpretation, I am sure an algorithm can be made.

-Marten





-------- Logged at  Tue Sep 20 23:04:04 MET DST 1994  ---------