Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-03.txt

[Jeffrey Haas <[e-mail]>]

On Tue, Jul 04, 2017 at 12:48:40PM +0200, Job Snijders wrote:
> On Mon, Jul 03, 2017 at 06:20:28PM -0400, Jeffrey Haas wrote:
> > > On Jul 3, 2017, at 5:55 PM, Job Snijders <[e-mail]> wrote:
> > > 
> > > I'm not sure whether events will be packed together this neatly. 
> > > 
> > > Questions that remain: 
> > > 
> > > - is it absolutely necessary for the RS to be aware of the entire
> > > bfd session topology state?
> > 
> > The draft is written with the idea that some/many devices *won't* be
> > aware.  If the state is Unknown, things still work.
> 
> Like with today's RS? "This draft doesn't make it worse" is hardly an
> impressive statement ;-)

It's BGP.  You have to deal with what incremental deployment looks like.

[...]
> > Looked at a somewhat different way, choosing the backup paths is no
> > different than add-paths or diverse paths feature choosing the next
> > best path.  But since the RS and the client could have already
> > conveyed the possible set of nexthops for the view, there's no need
> > for stepwise discovery. Perhaps this point needs to be made clearer
> > in the draft.
> 
> But any churn in the possible set of nexthops, directly results in BGP
> churn, where as when the route server is not kept in the loop about who
> can reach who, there will not be any churn at the route server level
> when 2 RS participants cannot reach each other (temporarily).

I believe you are confused about the CPU work associated with providing
add-paths actually is.

Add-paths implementations already run N-best calculations.  They must
already include the work of running policy and BGP loop checks.  Adding an
additional exclusion list based on nexthop viability for the view isn't
significantly more work for a given round of route selection.

If you'd like to argue "send them 2, and if they both don't work, let god
and their backup paths sort it out", fine.  You're welcome to run your RS
that way - if you run a RS.  What I don't understand is why you object to
someone else doing something different.

-- Jeff