Subject: [NSIS] Policy-based forwarding

From: Bob Braden <[email-masked]>
Date: Thu, 21 Nov 2002 22:21:27 GMT

RE: policy-based forwarding.

To make path-coupled signaling work, you have to ensure that the
downstream signaling messages follow EXACTLY the path of the data,
whatever that takes.  If you are doing simple, standard IP forwarding
based on destination address, it just works is the signaling messages
carry the destination address of the data (as in RSVP Path messages).
If you do something fancier for routing, like source routing or load
balancing or policy-based routing, you have to do whatever it takes to
make the signaling messages follow the same path.

To the extent that forwarding depends only upon packet header fields
that can be made identical between the data packets and the signaling
packets, it will just work.  If the node is ISPS-capable, you just have
to ensure that the NF entity knows how to do the right thing in
forwarding the signaling packet.  For compatible operation through
non-ISPS-capable nodes, there will be combinations that just won't
work.  Your choices then are to (1) partially give up on path-coupled
signaling, or (2) stop doing whatever funny routing is being done for
those packets relevant to signaling, or (3) make all of your nodes
ISPS-capable.

Bob Braden
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