Also it might be important to align Admin checks for both LFA and rLFA by
pointing the below in RFC 5286. In other words, as it doesn't make sense to
use the nexthop, which is administratively not allowed for LFA to be used for
rLFA. Indication of this could be useful/important..
Page 16 - 5286
" 3. If H_h.link is administratively allowed to be used as an
alternate,
and the cost of H_h.link is less than the maximum,
and the reverse cost of H_h is less than the maximum,
and H_h.neighbor is not overloaded (for IS-IS),
and H_h.link is bidirectional,
then H_h can be considered as an alternate. Otherwise, skip it
and continue to the next candidate next-hop."
--
Uma C.
-----Original Message-----
From: rtgwg [mailto:[email protected]] On Behalf Of Stewart Bryant
Sent: Monday, February 03, 2014 10:06 AM
To: Bharath R; '[email protected]'; [email protected];
[email protected]; [email protected];
[email protected]; [email protected]; [email protected]
Subject: Re: FW: Regarding cost based algorithm for finding Extended P-Space.
Mike and I did some work on this this afternoon
We propose the following algorithm for calculating extend P space with avoids
stub node problem and also addresses a problem in the pseudocode that excluded
the use of a parallel link.
/////////////////////////////////////////////////////////////////
//
// Calculate extended P-space
//
// Note the strictly less than operator is needed to
// avoid ECMP issues.
Compute_Extended_P_Space(fail_intf)
foreach node y in network
y.in_extended_P_space = false
// Extend P-space to the P-spaces of all reachable
// neighbours
foreach interface intf in self
// Exclude failed interface, noting that
// the node reachable via that interface may be
// reachable via another interface (parallel path)
if (intf != fail_intf)
foreach neighbor n in intf.remote_node
// Apply RFC5286 Inequality 1
if ( D_opt(n, y) <
D_opt(n,self) + D_opt)(self, y)
y.in_extended_P_space = true
It might seem strange to run rlfa to a node via a parallel link, but it would
work and it seems strange to exclude it, particularly as some would like to use
only rlfa.
I have also extended the code to exclude the accidental selection of a
pseudonode as PQ and the use of a repair first hop that is reachable through a
pseudonode.
Note that RFC5286 does not seem to explicitly call out the case where the first
hop is a pseudonode.
Stewart
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