Therefore I will not announce any route to M to my peers in some locations,
as I don't announce peers to other peers, and in others I will announce "C
M". Again, I do not make identical announcements to my peers, yet I have a
consistent policy.
Yep, policy filters run up against the policy of only announcing the
single, best route. I've been thinking with policy filters and variable
weighting, should it be changed to announcing the 'best' route that
meets policy, even if it is the second or third 'best' route you
know about.
Am I being unfair to my peers? Would they be justified in making a stronger
requirement than 'consistent' policy? What requirement would be reasonable?
[ note that, in the first example, the common policy of preferring customer
routes over peer routes will not change my announcements. ]
Fairness by what measure, and to which peers? My first concern is the
loss of information when the route to M isn't announced. This causes
unfairness when traffic ends up taking the 'long' route. Since we don't
have a full-mesh among peering partners, the unfairness of the long
route could be considered a normal part of today's Internet, like
asymetrical routing. More than likely your peer is doing the same
thing unto you.
The second effect of M's route not being announced happens when traffic
is blocked because no 'longer' path shows up anywhere else due to different
route weightings and policy filters across various combinations of ASs.
I consider this possibility the more serious problem. As the peering
mesh becomes sparser, expect more missing in action paths, even if
the physical connections exist the 'best' path may not be announced.