[prev in list] [next in list] [prev in thread] [next in thread]
List: ms-ospf
Subject: Re: [Lsr] Temporary addition of links to flooding topology in dynamic flooding
From: Peter Psenak <ppsenak () cisco ! com>
Date: 2019-03-12 11:09:45
Message-ID: 0e8b3753-7263-900d-7d6c-e103c25b5689 () cisco ! com
[Download RAW message or body]
Robert,
On 12/03/2019 10:42 , Robert Raszuk wrote:
> Jeff & Les,
>
> The suggested use of "LFA" was completely unrelated to ECMP or to data
> plane. I realize that some people may just think of LFA in its original
> meaning :).
>
> It was just a hint how an edge node can determine which links are
> "towards" the disconnected nodes and which of his local links would be
> going in the opposite direction just by running SPF virtually putting as
> initial node your adjacent FT nodes. No more no less.
>
> Per section 6.7.9 it seems that implementation is already mandated ot
> find such links towards the disconnected part of the network, but it
> does not seems to indicate how. Maybe it is just a matter of local smart
> implementation.
>
> Peter,
>
> If I am reading your reply and section 6.7.5 it seems to indicate that
> you would not start adding any link to FT as long as you have at least
> one there still being alive. You just advertise new LSA/LSP over still
> active flooding link indicating change in topology and sit and wait till
> you get a new FT ?
>
> Well perhaps wrong, but my understanding was that if you have two active
> FT links you start adding new ones (and request your peer over that link
> to do so too) just after you loose one as a temporary patch till you get
> a new graph.
>
> So what happens when you loose one link and you do not get a new FT for
> time t. How long do you wait ?
when the local link that is on FT is lost, the FT is recalculated,
either locally, or centrally and flooded. That should provide
bi-connectivity again, if available.
Temporary flooding is only triggered when node itself or its neighbor
becomes isolated.
thanks,
Peter
>
> Many thx,
> R.
>
>
>
> On Tue, Mar 12, 2019 at 7:45 AM Peter Psenak <ppsenak@cisco.com
> <mailto:ppsenak@cisco.com>> wrote:
>
> Hi Robert,
>
> On 11/03/2019 22:28 , Robert Raszuk wrote:
> > Hi,
> >
> > As of now at the event of failure of any of the FT enabled link
> > additional links are being added in more or less random fashion by
> nodes
> > directly connected to the failed links.
>
> above statement is incorrect. It is absolutely NOT TRUE that "at the
> event of failure of any of the FT enabled link additional links are
> being added".
>
> Temporary additions of the links to the FT has its strict rules:
>
> 6.7.5. Failures of Link On the Flooding Topology
>
> "If the failed local link represented the only connection to the
> flooding topology on the node where the link failed, the node MUST
> enable temporary flooding on a subset of its local links."
>
> 6.7.9. Treatment of Disconnected Adjacent Nodes
>
> Every time there is a change in the flooding topology a node MUST
> check if there are any adjacent nodes that are disconnected from the
> current flooding topology. Temporary flooding MUST be enabled
> towards a subset of the disconnected nodes.
>
>
> So we are only performing temporary flooding if either we or one of our
> neighbors got isolated from the FT, which given the bi-connectivity of
> the FT itself is an unlikely event.
>
> thanks,
> Peter
>
> >
> > In the event of 100s of links on such nodes and advisable rate
> limiting
> > addition of those links it seems that repair of FT may take some time.
> >
> > In order to reduce such time interval better then random addition of
> > remaining links seems recommended. How about we hint participating
> nodes
> > to execute purely in control plane of FT an LFA algorithm for possible
> > future event of active link failure and use results of the LFA
> > computation to prioritize links which will be first temporary
> additions
> > upon active flooding links failures ?
> >
> > Such optimization is local and optional and does not require any
> changes
> > to proposed protocol signalling.
> >
> > _Therefor how about just one sentence addition to section 6.7.1
> > of draft-ietf-lsr-dynamic-flooding:_
> >
> > /Temporary additions of links to flooding topology could be more
> > educated if given node runs a pure control plane LFA ahead of any FT
> > failure on active FT links completely detached from potential LFA runs
> > for data plane topology. /
> >
> > Kind regards,
> > R.
> > /
> > /
> >
> >
> > _______________________________________________
> > Lsr mailing list
> > Lsr@ietf.org <mailto:Lsr@ietf.org>
> > https://www.ietf.org/mailman/listinfo/lsr
> >
>
_______________________________________________
Lsr mailing list
Lsr@ietf.org
https://www.ietf.org/mailman/listinfo/lsr
[prev in list] [next in list] [prev in thread] [next in thread]
Configure |
About |
News |
Add a list |
Sponsored by KoreLogic