Peter, How do we transition between algorithms in the approach that you suggest? Do all non-stub devices need to be upgraded to support the new algorithm before such time as we can use it? (I think so, because otherwise some non-stub device cannot be guaranteed to flood to its downstream stub devices - so we may end up isolating some devices if any device transitions before all nodes support it).
The advantage of having something advertised is that one can compute it centrally - and keep the per-node functionality simply obeying the advertised flooding graph. From an operational perspective, this means that one can introduce new experimental flooding topology computation approaches in a manner that is decoupled from needing to do software upgrades across the whole network. I can also implement non-standard flooding topology computations based on the network topology which could be only applicable to that particular network (consider if I wanted to do something like take into account shared-risk information in the algorithm to allow the most-SRLG disjoint flooding topology or so). This is in addition to the points Tony made. I think this centralised-computation-and-flooded approach is elegant. If the error handling behaviour for not being able to parse the flooding topology is to revert to flooding everywhere, then it seems non-destructive too. Cheers, r. On Fri, 6 Apr 2018 at 08:50 Peter Psenak <ppse...@cisco.com> wrote: > Hi Tony, > > if we start with a single standardized algorithm, that is easy to > implement and deploy. We can leave the door open for additional > algorithms to be defined later together with the selection mechanism. > > I have the feeling that the dependency of the "flooding topology" on the > flooded data is going to bring more complexity, than the selection of > the distributed algorithm to be used, if we ever need to support more > then one. > > thanks, > Peter > > > On 06/04/18 17:19 , tony...@tony.li wrote: > > > > Hi Peter, > > > > Thank you for your comments. > > > >> while I appreciate the flexibility associated with the centralized > >> computation of the flooding topology, it has some drawbacks as well: > >> > >> 1. "flooding topology" must be flooded. This makes the flooding > >> dependent on the flooded data itself. > > > > > > Absolutely true. If the computation of the topology is incorrect, that > > would certainly be a bug. > > > > > >> 2. The extra flooding of "flooding topology" adds some delay in the > >> convergence towards the new "flooding topology”. > > > > > > Since we distribute the flooding topology before there are topology > > failures, it would seem like the latency is not a significant concern. > > > > > >> Have you considered the distributed computation of "flooding topology" > >> using some standardized algorithm? > > > > > > Yes, Kireeti raised this in London as well. There are some practical > > issues with this. How do we ever converge on an algorithm? > > > > There are many perspectives on what an adequate flooding topology might > > be. Different administrations have different considerations and risk > > tolerances. > > > > Debugging is going to be more challenging, as inconsistencies between > > two nodes with different ideas of the topology will be difficult to > > detect until there is a catastrophic failure. > > > > I’m trying to do something practical, and it seems like doing this in a > > centralized fashion is the quickest, easiest, and most robust way > forward. > > > > > >> Eventually we can support multiple standardized algorithms. A node can > >> advertise support for several algorithms and the "active" algorithm is > >> selected based on some criteria that would guarantee that all nodes in > >> the flooding domain select the same one. > > > > > > Seems like that would also require some administrative input. > > > > So, I agree that that’s a technical possibility, but I think that > > there’s significant problems in making that work. I prefer to focus on > > something that we can implement more quickly. > > > > Tony > > > > > > _______________________________________________ > Lsr mailing list > Lsr@ietf.org > https://www.ietf.org/mailman/listinfo/lsr >
_______________________________________________ Lsr mailing list Lsr@ietf.org https://www.ietf.org/mailman/listinfo/lsr
