Joel, On Thu, Nov 7, 2013 at 11:15 AM, Joel M. Halpern <[email protected]>wrote:
> If I thought we could get away with not having protocol specific > information models, then trying to design a protocol independent topology > model for use with the network elements would seem applicable. > We certainly need protocol specific information included to help with resolving different data in LSDBs. We also need additional functionality for IGP IMs beyond the topology. But, as it stands, even if we had such a model, we would still need > protocol specific models, which would be having to manipulate many aspects > related to the common model. > Agreed - so can we have dependencies or reuse of the aspects in common? That seems desirable for accurately describing the IMs as well as the data-models. > The argument that an abstracted model is useful when you are northbound > from the topology manager is very understandable and attractive. But > northbound from the topology manager is not our working space. > I agree that it is not our workspace - but being able to combine the information from different device's into a network-wide model is important and I don't think it will be possible without careful initial thought and working in parallel. Regards, Alia > Yours, > Joel > > On 11/7/13 3:51 AM, Jan Medved (jmedved) wrote: > >> >> >> From: Alia Atlas <[email protected] <mailto:[email protected]>> >> >> Date: Wednesday, November 6, 2013 11:59 PM >> To: Nikolay Milovanov <[email protected] <mailto: >> [email protected]>> >> Cc: Russ White <[email protected] <mailto:[email protected]>>, "[email protected] >> <mailto:[email protected]>" <[email protected] <mailto:[email protected]>>, "Eric >> Osborne (eosborne)" <[email protected] <mailto:[email protected]>> >> >> Subject: Re: [i2rs] topology info model - what makes it a "network" >> model vs. a "device" model >> >> Hi, >> >> Yes - so what I'm really trying to do is elicit what the points of >> concern and different options are as far as modeling the topology >> information from a device. draft-medved-i2rs-topology-im has >> changed only minimally since last IETF - and in ways that don't seem >> to address any of the disagreements or concerns. >> >> We need to be sure to bite off the right-sized first chunk to do. >> >> If we have a device-centric model showing interfaces and so on, then >> there's not a good way to express the learned IGP topology. Would >> we then need a different IM - perhaps as part of an IGP-specific IM >> - to communicate the topology learned via the IGP? Would that be >> preferable? >> >> >> If we decide that topology learned via the IGP is indeed in scope WG to >> go, then the IGP-specific IMs are already defined >> in draft-medved-i2rs-topology-im. >> >> >> Given that the active IGP topology can be learned via BGP-LS, are we >> better off focusing on an interface-focused IM (whether that is a >> device model or an interfaces model or...)? >> >> >> The same topology I'm model would apply to BGP-LS and to IGPs. >> >> >> I'd really like to make significant progress in understanding the >> perspectives and thoughts of the WG on this. I understand that all >> these things may be useful but in our usual ocean-boiling-avoidance >> method, we've got to prioritize. >> >> >> IMHO, it is actually easier to define the base network topology IM than >> the device IMs from which a network topology can be 'stitched together'. >> The base network topology IM is simple: it's a directed graph with >> nodes, links and termination points. The base network topology IM can be >> easily augmented (extended) to cover L1-L3 networks, VPNs, etc. On the >> other hand, there is a variety of information (in devices and in other >> systems) that can (must be) be used to 'stitch' together a network >> topology: dynamically learned neighbor info (LLDP for example for L2, >> IGP neighbor info for L3, for example), statically configured neighbor >> info in device configurations, IGP LSDB, IGP configurations, inventory >> systems, interface data (interface type, speed, …), LAGs, etc. Trying to >> model all of this can turn out to be quite a chunk to bite off. >> >> >> I'm also not comfortable on having only one IM for basing all our >> requirements off of. >> >> >> I don't understand what you mean - can you please explain? >> >> >> So - more thoughts? >> >> >> The charter does not say anything about 'device-centric' or >> 'network-centric' IMs - it talks merely about 'topology information'. >> Can you define what 'device-centric' and 'network-centric' is? Would >> 'device-centric' be information that a client could get from a single >> routing system device, without a third party data aggregator, such as >> the Topology Manager or a Controller? Or would 'device-centric' be >> strictly information about the device, in which case an LSDB (or even >> neighbor info) would not be in scope? How would you define >> 'network-centric'? >> >> Could we also consider IM criteria such as useful/useless, >> easy-to-model/difficult-to-model, easy-to-use/difficult-to-use, >> easy-to-extract/difficult-to-extract? IOW, what kind of topology IM >> would be most useful to apps, relatively easy to model (and where an >> initial model could be expanded for different use cases), and relatively >> easy to obtain from the network? >> >> >> Alia >> >> >> Thanks, >> Jan >> >> >> On Thu, Nov 7, 2013 at 2:17 AM, Nikolay Milovanov >> <[email protected] <mailto:[email protected]>> wrote: >> >> Hi, >> >> I might be completely wrong but from a brief overview of >> the Topology API Use Cases my guess would be. >> >> The topology data model will be an undirected graph with nodes, >> edges with certain properties representing part of the network >> topology and the device centric model will be something >> hierarchical with a root object the network device its >> interfaces, their IPs, the protocols working on them and the >> neighbor devices learned dynamically by those protocols. >> >> Most likely the network-centric topology models coming from each >> of the devices will have to be merged by the network topology >> manager in order the rest of the applications to be able to >> benefit from a complete model of the entire network topology. >> >> In my opinion either of the models will be extremely useful for >> all kinds of OSS applications related to network service >> provisioning and fulfillment. Currently is quite difficult to >> build any of them by means such as CLI parsing and SNMP. Netconf >> is not bad but still an API will be much better :) >> >> BR, >> Nikolay Milovanov >> >> Network Engineer >> [email protected] <mailto:[email protected]> >> >> >> >> >> >> On Thu, Nov 7, 2013 at 8:16 AM, Russ White <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> > Are there really differences of opinion about what the >> difference is >> between >> > a network model and a device model? A network is a >> plurality of devices, >> > and a network model is something which deals with a system >> resulting from >> > the use of more than one device. (ok, yes, a network of >> one node is a >> corner >> > case blah blah handwave...). I don't see how there could >> be any real >> debate >> > around this, but if there is I'm quite interested in what >> it might be. >> >> Agreed--both seem necessary, but different beasts (see the >> discussion on >> sdnrg right now --same problem, different names). >> >> > It feels like the real question is whether i2rs should have >> network models >> in >> > scope. >> >> Right... >> >> I think network models at this point in the game might be >> useful to make >> certain we are getting all the information we need from the >> models at the >> protocol and device levels... In other words, there are >> things the network >> model cares about that a device model isn't going to care >> about. In other >> words, if we only look at protocol level use cases, we might >> miss some >> pieces of information we'll eventually need for building >> network topologies, >> or that sort of thing. >> >> > If Yes: ok, cool. But between link properties (that is, at >> least some >> kind of >> > topology view), counter dumps, debugs, routing, MPLS, and >> LAG member >> > rebalancing, show me what's *not* in scope. >> >> This is the problem on the other end, however... It's >> better, IMHO, to start >> with a single small set of problems and solve them in a way >> that >> specifically allows extensions to solve other problems. If >> we try to model >> every possible problem, to make certain we have accounted >> for every possible >> situation, well, we'll never actually do anything but >> describe problems. I'm >> pretty familiar with the "describing problems all the time" >> process, as I >> have kids... :-) (Oh, I'm glad they don't read this list, >> because they'd >> really be mad at me about now!). >> >> So I think it's valuable to describe these network models, >> and think about >> them. OTOH, I'm really concerned we're going to get bogged >> down in them, and >> take up a lot of time reading and accounting for them, which >> could well >> divert us (even more!) from picking a small set of >> well-defined problems and >> solving them in an extensible way. I think that's the point >> Joel was trying >> to make at the mic today, btw... >> >> :-) >> >> Russ >> >> >> >> _______________________________________________ >> i2rs mailing list >> [email protected] <mailto:[email protected]> >> >> https://www.ietf.org/mailman/listinfo/i2rs >> >> >> >> >> -- >> BR, >> >> Nikolay Milovanov >> Network Engineer >> Email: [email protected] <mailto:[email protected]> >> >> >> >> >> >> _______________________________________________ >> i2rs mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/i2rs >> >>
_______________________________________________ i2rs mailing list [email protected] https://www.ietf.org/mailman/listinfo/i2rs
