[Sidrops] draft-ietf-sidrops-aspa-verification-01: Handling unknowns

I believe the path verification algorithm works when all ASes in the as-path
make attestations. If some of the ASes make no attestations, then a more complete
algorithm is as follows:

For every sequence (A, B, C) of consecutive ASes in an AS-path:
If A attests that B is not a provider and C attests that B is not a provider,
then B leaked the route: B is transiting for free. The segment is invalid.
If either A or C attests that B is a provider, then the AS-path segment  (A, B, C) is valid.
If neither A nor C make an attestation, then the leak state is unknown. Even if B lists both A and C as providers, it is not necessarily a leak, because either A or C could consider B as a provider for some of their routes, even though they don't attest to it.

If all the path segments are valid, then the whole path is valid.
If any of the path segments is invalid, then the whole path is invalid.
Else, at least one path segment is unknown and one more rule must be applied: for any sequence of ASes (A, B1, ..., Bn, C), if A attests that B1 is not a provider and C attests that Bn is not a provider, then the AS-path is invalid. This is for any number of Bx greater than 1.

This algorithm breaks the AS-PATH into triples instead of pairs.
For example, the AS_PATH (A,B,C,D,E) is broken into the triples:
(A,B,C), (B,C,D), (C,D,E).
I find it easier to reason about it like that.
It can probably be re-worded into pairs.

An additional point:
If AS-SETs exist then complete sequences between the AS-SETs can be checked for invalidity.
The best such an AS-PATH can get is unknown, but it can also be verified invalid.

Regards,
Jakob.

-----Original Message-----
From: Sidrops <sidrops-bounces@ietf.org> On Behalf Of internet-drafts@ietf.org
Sent: Monday, July 8, 2019 1:24 PM
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Subject: [Sidrops] I-D Action: draft-ietf-sidrops-aspa-verification-01.txt

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the SIDR Operations WG of the IETF.

        Title           : Verification of AS_PATH Using the Resource Certificate Public Key Infrastructure and Autonomous System Provider Authorization
        Authors         : Alexander Azimov
                          Eugene Bogomazov
                          Keyur Patel
                          Job Snijders
	Filename        : draft-ietf-sidrops-aspa-verification-01.txt
	Pages           : 10
	Date            : 2019-07-08

Abstract:
   This document defines the semantics of an Autonomous System Provider
   Authorization object in the Resource Public Key Infrastructure to
   verify the AS_PATH attribute of routes advertised in the Border
   Gateway Protocol.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-sidrops-aspa-verification/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-sidrops-aspa-verification-01
https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-aspa-verification-01

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-sidrops-aspa-verification-01

Please note that it may take a couple of minutes from the time of submission
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Internet-Drafts are also available by anonymous FTP at:
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