Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt

[Nick Hilliard <[e-mail]>]

Robert Raszuk wrote:
> Let's observe that the ultimate objective of this draft (and in fact
> much more) can be achieved by assuring that clients receive more then
> one path to given bgp destinations at normal operation. 

This is a fundamental misunderstanding.  The aim of this draft is to
ensure that traffic isn't blackholed if there is a layer 2 incongruity
on the IXP which causes connectivity to be non commutative.

Given the following topology, A's connectivity to RS works fine, and B's
connectivity to RS works fine, but A cannot communicate with B:

>    +-----+    +-----+
>    |     +--> |     |
>    |  A  |    |  B  |
>    |     | <--+     |
>    +-----+    +-----+
>       |           |
>       | +------+  |
>       +-+      +--+
>         |  RS  |
>         |      |
>         +------+

What's needed is some protocol running between A and B to ensure that
they can still talk to each other, i.e. BFD.

No amount of alternative paths will save you in this situation because
the control plane (RS) has connectivity to both data plane routers.

Nick