Subject: grow: a question about draft-grow-bounded-longest-match-00.txt

From: marcelo bagnulo <[email-masked]>
Date: 20 Jun 2003 19:19:16 +0200

Hi,

I have a question about draft-grow-bounded-longest-match-00.txt

I do not understand how this mechanism works in a different scenario
than the one included in the draft.

For instance consider the following alternative scenario:

                      (   )
             /-------( AS2 )---( AS6 )-----\
      (   ) /         (   )              ( R1   )       (   )
     ( AS1 )                            ( AS4  R2)-----( AS5 )
      (   ) \         (   )              ( R3   )       (   )
             \-------( AS3 )---------------/
                      (   )

   o    AS1 is advertising 192.168.1.0/24 to both AS2 and AS3.

   o    AS2 is advertising both 192.168.1.0/24 and 192.168.0.0/16 into
        AS6

   o    AS3 is advertising 192.168.1.0/24 into AS4

If i understand the proposed mechanism correctly, AS6 advertises only
192.168.0.0/16 to AS4. Is this correct?

If this is so, then AS4 will always prefer forwarding traffic through
AS3 and it won't forward traffic through AS6 if the path through AS3 is
available.

So if my understanding is correct, the proposed mechanisms forward
traffic through both links only if the third AS is common to both paths
(just like in the scenario depicted in the draft) if this is not the
case, the resulting behavior is that one path is only used as a backup.

Is this correct? am i missing something?

This could be solved if the AS6 does not uses the mechanism, but the
question then is does a AS knows when it has to apply it.

Perhaps an AS should only apply the mechanisms if it receives an two
advertisements of overlapping prefixes AND it also receives the longest
prefix from another AS...however, this would rise the same problems when
the end site is multi-homed to 3 providers.

Thanks, marcelo

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