The MPLS WG Archive

[Tony Li <tony1@home.net>]

> All of it is correct and you are perfectly right that it is possible
> to do local constraint based routing between AS's but not over the AS.
> This is called stepwise or piecewise constraint based routing as
> opposed to hierarchical constraint based routing which requires that
> summarized constraint information cross AS boundaries.
>
> My own opinion, for what it is worth, is that we will probably have to
> start with piecewise routing since this is relatively easy to do.
> Then we can look at ways to make better gateway decisions based on
> constraints, possibly with more elaborate forms of inter AS feedback.
> We will have far more success getting something working reasonably
> well if we keep the solution simple and start with stepwise.
>
> My guess is the BGP guys will like this idea and the PNNI guys will
> prefer full hierarchy. Like I said though some simulations are
> probably in order here to help put things properly in perspective.

This BGP guy will simply point out that BGP does not and cannot
reasonably propagate anything like the number of possible paths
necessary to perform any reasonable type of inter-domain traffic
engineering, stepwise or global.  This is simply due to the path-vector
nature of the protocol.

We should be directing our efforts to the locations that will maximize
our return:
    - continued experience with intra-domain TE
    - expansion of this technology into the optical plane

Regards,
Tony