Possible Solutions
Solution #1 – Make sure E has the Y0 path
BGP Peers will need to advertise multiple paths
BGP will need a new Attribute that will allow a speaker to advertise multiple paths for the same prefix (draft coming soon)
A BGP speaker will then need to advertise a best path per “Neighbor AS” group IF that path came from an internal peer. This will force C and D to always advertise Y0 to D
Solution #2 – Eliminate “Y0 < Y1 < X < Y0” problem
Always comparing MEDs accomplishes this