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

[adamv0025 at netconsultings.com]

Hi James,

> James Bensley
> Sent: Wednesday, December 21, 2016 10:06 AM
> 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.
> 
Hmmm, I'm not entirely convinced, as the LFA/rLFA is not a matter of a
simple iSPF calculation but rather: 
P-space; SPF rooted at S. 
Extended P-space; SPF rooted at neighbours of S. 
Q-space, rSPF rooted at E (for each protected prefix). 

So I'd assume that iSPF is used solely in case of primary path computation
not for LFA/rLFA selection.
But who knows...


adam


netconsultings.com
::carrier-class solutions for the telecommunications industry::