Route Leak Detection and Filtering using Roles in Update and Open messages

[draft-ietf-idr-bgp-open-policy] defines a BGP OPEN capability and consequent route marking which enforces a valley-free peering relationship. This document defines an eOTC (external Only To Customer) transitive BGP attribute which propagates the specific marking to automatically detect route leaks. The goal is to allow a distant AS to determine a violation of valley-free peering.