[c-nsp] Incremental SFP (ISPF) - Provide any benefits "now"?

[CiscoNSP List]

Thanks James - Very Interesting re iSPF and FRR....Ill  try removing this under maintenance window, and see if fixes the issue.


The latest on the IP FRR rLFA is that TAC/Dev have asked me to "try" removing  fast-reroute keep-all-paths from OSPF  (Why? They think that this command is  the reason behind unused rLFA tunnel).....how? not entirely sure....Its nice for troubleshooting/debugging to see the list of candidate  repair paths that were considered)....but, Ill remove it, and see if it makes any difference.


Cheers


________________________________
From: cisco-nsp <cisco-nsp-bounces at puck.nether.net> on behalf of James Bensley <jwbensley at gmail.com>
Sent: Wednesday, 21 December 2016 9:06 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Incremental SFP (ISPF) - Provide any benefits "now"?

On 16 December 2016 at 14:01, CiscoNSP List <CiscoNSP_list at hotmail.com> wrote:
> Hey Adam - Have a TAC case open atm on ASR920 rLFA FRR (Tunnels being created, when they shouldnt, and not used)...anyway, from this case, MPLS, OSPF + ASR920 Dev teams have been working on it, and they have stated that "ISPF conf under router ospf is not recommended anymore. The command will soon be deprecated." - Its not related to the tac case, its was just a recommendation from them....I asked why is it being deprecated, and the reason they gave is that was introduced to improve convergence on slower processors, processors are fast now, so it is no longer needed.....somewhat strange, but I pressed them for more info, and that is all that they have provided so far...
>

In the case of IP FRR (r)LFA, iSPF is not a recommended setting under
OSPF. When there is a failure with FRR LFA enabled, my understanding
is that traffic will re-route via the backup LSP however the entire
OSPF DB needs to be crawled as a new backup tunnel(s) needs to be
calculated now, iSPF could hinder this process because not all
possible paths would be explored in the OSPF DB, instead the first
"suitable" match would be used. That is what Cisco had lead me to
believe although it was unclear at the time so happy to be corrected
here.

There is a note on the Cisco doc's that says something like "The
OSPF/ISIS configuration option "ispf" is not recommended although it
is supported" with no further explenation so that we may decide whats
best for us :s

Cheers,
James.
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