
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 respinning 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 FastReroute is
described.
D Used to denote the destination router under
discussion.
E Used to denote the router which is the primary
nexthop 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.
LoopFree This is a neighbor N, that is not a primary
Alternate nexthop 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 loopfree 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 nexthops for S to
reach the destination D goes directly to this
neighbor.
LoopFree A Neighbor N_i which is not the primary
Neighbor neighbor and whose shortest path to D does not
go through S.
LoopFree This is a path via a LoopFree Neighbor N_i
LinkProtecting which does not go through the particular link
Alternate of S which is being protected to reach the
destination D.
LoopFree This is a path via a LoopFree Neighbor N_i
NodeProtecting 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 reroute
Routing The process whereby routers converge on a new
transition topology. In conventional networks this
process frequently causes some disruption to
packet delivery.
Microloop 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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