Subject: OSPF Applicability for LFAs

From: Alia Atlas <[email-masked]>
Date: Tue, 03 May 2005 12:56:36 -0400

Here is a first pass at the OSPF applicability statement in regards to 
LFAs.  Please let me know what you think of the clarity, wording, etc.

This goes after the list of potential issues in the OSPF Section.

"Due to these issues, there are certain applicability restrictions
that apply to OSPF networks where loop-free alternates can be safely
deployed.  These restrictions are as follows.

Loop-free alternates MUST NOT be used in the backbone area if there
are any virtual links configured unless, for each area that a virtual
link transits, there is a full mesh of virtual links between all ABRs
in that area.  Loop-free alternates MAY be used in non-backbone areas
regardless of whether there are virtual links configured.

Loop-free alternates MUST NOT be used in an area that contains more
than one alternate ABR.

Loop-free alternates MUST NOT be used for AS External routes or
ASBR routes in a non-backbone area of a network where there exists an
ABR that is announced as an ASBR in multiple non-backbone areas and
there exists another ABR that is in at least two of the same
non-backbone areas.

Loop-free alternates MUST NOT be used in a non-backbone area of a
network for AS External routes where an AS External prefix is
advertised with the same type of external metric by multiple ASBRs,
that are in different non-backbone areas, with a forwarding address of
0.0.0.0 or by one or more ASBRs with forwarding addresses in multiple
non-backbone areas when an ABR exists simultaneously in two or more of
those non-backbone areas."

Thanks,
Alia

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