I-D ACTION:draft-martin-isis-local-protect-cap-00.txt

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	Title		: ISIS Extensions for Signaling Local Protection 
                          Capabilities
	Author(s)	: A. Atlas
	Filename	: draft-martin-isis-local-protect-cap-00.txt
	Pages		: 6
	Date		: 2004-2-9
	
This document specifies additional information that can inserted in
IS-IS LSPs to convey link capabilities that may be useful in certain
applications.  In particular, an IS may indicate that zero or more of
its links may be used by an upstream IS as an alternate, SPT-disjoint
path to an arbitrary destination D.  Additionally, an IS may convey
that zero or more of its links are capable of breaking a U-turn, which
may be described as a single-hop forwarding loop between two IS's.
This means that a router can detect the presence of a forwarding loop
by recognizing that traffic to a destination is being received from a
neighbor to which it has forwarding state pointing back to the same
neighbor for that destination.  In such a situation, it will switch to
a loop-free node-protecting alternate until new primary forwarding
state has been installed, thus breaking the U-turn.  Therefore, the
immediate applicability for these two link capabilities is in support
of local protection in the event of a link and/or node failure while
the IS-IS area is reconverging onto a new topology.

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