A routing protocol
computes repair paths for prefixes by implementing tiebreaking algorithms. The
end result of the computation is a set of prefixes with primary paths, where
some primary paths are associated with repair paths.
algorithm considers LFAs that satisfy certain conditions or have certain
attributes. When there is more than one LFA, configure the
command with the tie-break
keyword. If a rule eliminates all candidate LFAs, then the rule is skipped.
A primary path can
have multiple LFAs. A routing protocol is required to implement default
tiebreaking rules and to allow you to modify these rules. The objective of the
tiebreaking algorithm is to eliminate multiple candidate LFAs, select one LFA
per primary path per prefix, and distribute the traffic over multiple candidate
LFAs when the primary path fails.
cannot eliminate all candidates.
attributes are used for tiebreaking:
Downstream—Eliminates candidates whose metric to the protected
destination is lower than the metric of the protecting node to the destination.
Linecard-disjoint—Eliminates candidates sharing the same
linecard with the protected path.
Shared Risk Link
Group (SRLG)—Eliminates candidates that belong to one of the protected path
Load-sharing—Distributes remaining candidates among prefixes
sharing the protected path.
Lowest-repair-path-metric—Eliminates candidates whose metric to
the protected prefix is higher.
protecting—Eliminates candidates that are not node protected.
Primary-path—Eliminates candidates that are not ECMPs.
Secondary-path—Eliminates candidates that are ECMPs.