an enquiry

[Yuko Murayama in Tokyo <[e-mail]>]

We have a working group of policy routing at WIDE Project, Japan, 
starting studying IDPR.

We have a small policy-routing problem which is termed 
"the Motonori Problem," because it was first defined 
clearly by Motonori Nakamura at Kyoto University.

The problem is: how can one enforce the preference of transits?
Suppose that we have two transit ADs, A and B between the source AD X
and the destination AD Y.  There are more than one interface (VG)
between A and B as follows:


Y1                    AS Y (destination)
|                  
---------------------
|                   |
|       AS B        |
|                   |
---B1----B2----B3----
   |     |     |
   |L1   |L2   |L3
   |     |     |
---A1----A2----A3----  
|                   |
|       AS A        |
|                   |
---------------------
                  |
                  X1  AS X (source)    

When one at AD X wants to send a message to someone at AD Y,
how can one say, "packets should go through AD A as much as possible,
and pass through B as less as possible due to some cost parameter" ?
Does a local route server at X have knowledge on locations of VGs, L1, L2, 
and L3, so that pakcets from X to Y would take L1?

Using BGP one could implement this policy to some extent, but not exactly
because, if my memory is correct, B has to
advertise each interface with different preference for the sake of A/X...which 
is not necessarily B's own policy.

Yuko