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Proposed Terminology section for IPFRR framework document

Subject: Proposed Terminology section for IPFRR framework document
From: mike shand
Date: Wed, 20 Oct 2004 14:09:02 +0100
Here is the proposed terminology section to be included in the framework document. Alia and I have had some discussion about this, and come up with the following. Note that we have changed from P to E for the primary next hop partly because there was some confusion with Provider routers and partly because we were both using "P" for different things. The equitable thing seemed be for neither of us to use P.
Alia's latest version of the basic draft uses this terminology, and we will
be re-spinning our draft to use this terminology where appropriate.
If anyone has any comments please let me have them by the end of the week.

        Mike

TERMINOLOGY

   This section defines words and acronyms used in this draft.

    S                    Used to denote a router that is the source of
                         a repair that is computed in anticipation of
                         the failure of a neighboring router denoted as
                         E, or of the link between S and E. It is the
                         viewpoint from which IP Fast-Reroute is
                         described.

    D                    Used to denote the destination router under
                         discussion.

    E                    Used to denote the router which is the primary
                         next-hop neighbor to get from S to the
                         destination D. Where there is an ECMP set for
                         the shortest path from S to D, these are
                         referred to as E_1, E_2, etc.

    N_i                  The ith neighbor of S.

    R_i_j                The jth neighbor of N_i.

    Distance_opt(A,B)    The distance of the shortest path from A to B.

    Link(A->B)           A link connecting router A to router B.

    Loop-Free            This is a neighbor N, that is not a primary
    Alternate            next-hop neighbor E, whose shortest path to
                         the destination D does not go back through the
                         router S.  The neighbor N must meet the
                         following condition:-

                         Distance_opt(N, D) < Distance_opt(N, S) +
                         Distance_opt(S, D)

    Downstream Path      This is a subset of the loop-free alternates
                         where the neighbor N meet the following
                         condition:-

                         Distance_opt(N, D) < Distance_opt(S,D)

    Upstream             This is a forwarding loop which involves a set
    Forwarding Loop      of routers, none of which are directly
                         connected to the link which has caused the
                         topology change that triggered a new SPF in
                         any of the routers.

    Primary Neighbor     One or more of the primary next-hops for S to
                         reach the destination D goes directly to this
                         neighbor.


    Loop-Free            A Neighbor N_i which is not the primary
    Neighbor             neighbor and whose shortest path to D does not
                         go through S.

    Loop-Free            This is a path via a Loop-Free Neighbor N_i
    Link-Protecting      which does not go through the particular link
    Alternate            of S which is being protected to reach the
                         destination D.

    Loop-Free            This is a path via a Loop-Free Neighbor N_i
    Node-Protecting      which does not go through the particular
    Alternate            primary neighbor of S which is being protected
                         to reach the destination D.

    FIB                  Forwarding Information Base. The database used
                         by the packet forwarder to determine what
                         actions to perform on a packet.

    IPFRR                IP fast re-route

    Routing              The process whereby routers converge on a new
    transition           topology. In conventional networks this
                         process frequently causes some disruption to
                         packet delivery.

    Micro-loop           A temporary forwarding loop which exists
                         during a routing transition as a result of
                         temporary inconsistencies between FIBs.

    RPF                  Reverse Path Forwarding. I.e. checking that a
                         packet is received over the interface which
                         would be used to send packets addressed to the
                         source address of the packet.

    SPF                  Shortest Path First, e.g. Dijkstra's
                         algorithm.

    SPT                  Shortest path tree


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