Hi Chris, Thanks for raising the issue and putting it on the I2RS wiki!
The current data model is aligned with the info model. Regarding the tunnel encap and decap, the info model is defined as is. Regarding GRE, NvGRE or VxLAN decapsulation, in my understanding, they are actually IP tunnels, and the current model has already support IPv4/IPv6 IP tunnel decapsulation. Or maybe I missed something? Best regards, Mach > From: Chris Bowers [mailto:[email protected]] > Sent: Thursday, November 12, 2015 11:28 AM > To: Nitin Bahadur; [email protected]; Mach Chen > Subject: RE: [i2rs] feedback on draft-ietf-i2rs-rib-data-model-03 > > Nitin and Mach, > > Thanks for your responses. Jeff Haas suggested to me that we keep track of > issues for this on the I2RS wiki at: > > http://trac.tools.ietf.org/wg/i2rs/trac/wiki/IssuesRibDataModel > > So far, I posted one issue that I think needs more discussion. I copied it > below. Please feel free to edit the Wiki as part of the discussion as well. > Issue 1: Should we define tunnel encapsulation and tunnel decapsulation as > next-hops in the RIB data model? > The RIB data model can model some types of encapsulation and decapsulation > by treating encapsulation and decapsulation as next-hops. For encapsulation, a > route is paired with a tunnel-encap-nexthop. For decapsulation, an initial > route > match condition is paired with a next-hop chain which consists of a > tunnel-decap-nexthop and another nexthop such as rib-name-nexthop or an > egress-interface-nexthop. > 1) It is not clear if this model for decapsulation supports all useful > encapsulation > types. For example, it is not clear that the route-match-types currently in > draft-ietf-i2rs-rib-data-model-03 can be used to select traffic for GRE, > NVGRE, > and VXLAN decapsulation. > One could consider extending the route-match-types > to include the header information needed to identify other encapsulation > types. > However, this may also be a sign that the basic approach should be > re-evaluated. > 2) Does treating tunnel-encap and tunnel-decap as next-hops result in a data > model that is easy to use for someone trying to program network forwarding > behavior? From the point-of-view of a user of the data model, modeling tunnels > as interfaces seems more useful. Treating tunnel decapsulation as a type of > ingress interface and tunnel encapsulation as a type of egress interface would > fit with the current RIB model (which already has the concept of an > interface-route and an interface-nexthop.) And it would reduce the amount of > next-hop chaining that is required to make tunnels work compared to the > current model. > Thanks, > Chris > > > From: Nitin Bahadur [mailto:[email protected]] > Sent: Monday, November 09, 2015 5:53 PM > To: Chris Bowers <[email protected]>; [email protected]; Mach Chen > <[email protected]> > Subject: Re: [i2rs] feedback on draft-ietf-i2rs-rib-data-model-03 > > Hi Chris, > > Thanks for spending time on the spec. Please see NB> below for some > of the issues you have raised. > > ------------------------ > The description of the nexthop-preference-def (see below) is confusing. > First, > I assume there is an error in the text since the example of downloading > primary/standby/tertiary nexthops to the FIB should presumably select three > nexthops, but the text refers to selecting the two resolved nexthops with the > highest preference . > > NB> That is a typo IMO. > > More fundamentally, this example seems to imply that only two next-hops > will get downloaded to the FIB, whereas one could imagine an > implementation that uses three, four, five or more nexthops of different > preferences. If hardware supports more than two next-hop preferences > being installed in the FIB, then what is the mechanism for the client to learn > how many preference values are supported? This should all be made clearer > in the text. > > typedef nexthop-preference-def { > type uint8 { > range "1..99"; > } > description > "Nexthop-preference is used for protection schemes. > It is an integer value between 1 and 99. A lower > value indicates higher preference. To download a > primary/standby/tertiary group to the FIB, the > nexthops that are resolved and have two highest > preferences are selected."; > } > > NB> Would something like this be preferable > "To download N nexthops to the FIB, the N nexthops with the lowest value > are selected". > > > ------------------------ > If I understand the yang syntax and semantics correctly, the "nh-add" RPC > creates a nexthop in a given RIB that is not associated with any match > condition on a route. I assume the intention is to create a nexthop with a > nexthop-id but not associated with any prefix that can then be referenced by > multiple other route match conditions. This seems like a reasonable thing to > do. However, I can see two possible issues with this. > > The first issue is that the structure of the data model doesn't seem to not > allow this. "grouping route" uses "grouping route-prefix" next to > "container next-hop". It appears to me that as currently written "container > match" in "grouping route-prefix" is a mandatory node based on section 3.1 > of RFC6020 , since the "mandatory" statements below choice/cases cascade > up to the container. So the current form of the "nh-add" RPC may not be > consistent with the data model as currently defined. > > The second issue is that creating a next-hop without an associated match > appears to differ from the RIB grammar defined in section 6 of > draft-ietf-i2rs-rib-info-model-08. In the RIB info model, it seems that the > only > way for a <nexthop> to appear is together with a <match>. > > <route> ::= <match> <nexthop> > [<route-attributes>] > [<route-vendor-attributes>] > > > NB> I'm not sure if I agree with the creation of nexthop discrepancy. A > nexthop > can be created independently and then in the <route>, you can reference the > relevant nexthop-id. > > <route> ::= <match> <nexthop> > = <match> <nexthop-base> > = <match> <NEXTHOP_ID> > > > ------------------------ > Treating tunnel-decap as a type of next-hop doesn't make sense to me. I > assume the desire to include tunnel-decap as well as tunnel-encap is to have a > usable stand-alone data model module which to deal with some use cases > without having to rely on another module that defines > tunnel-decap. However, the result doesn't make sense. I think the most > common scenario involving routers would be to install a route on router A for > prefix P whose nexthop is a tunnel-encap whose destination is router B. One > router B one would need to install a corresponding tunnel-decap whose source > is router A. The most common scenario is then that router B does a normal > route lookup on the decapsulated packet independent of the interface it > entered on. > > I don't see how this most common use case would be handled with the > tunnel-decap next-hop in this document. > > NB> On router B, <match> condition would be the incoming label and the > "action" to be taken on that would be "decap" the MPLS label. And you can > chain that with <RIB_NAME> to say continue the route lookup in say "inet.0". > The draft says, "RIB_NAME: A nexthop pointing to a RIB indicates that the > route > lookup needs to continue in the specified RIB." > > NB> Does that address your concern? > > > Section 7.2.5. of draft-ietf-i2rs-rib-info-model-08 gives an example usage for > tunnel-decap where the tunnel-decap nexthop is used to pop an MPLS label and > send the traffic out an egress interface next-hop. This example is not the > most common scenario. And if we want to accomplish this scenario > of decapsulating and sending to a particular nexthop, it makes more sense to > treat tunnel-decap as a route match condition similar to an interface-route in > the existing data model. However, I think the model should be able to handle > the more common scenario described above when traffic needs to be > decapsulated and routed based on a normal route lookup. > > Treating tunnel-decap as a next-hop type really makes no sense to me. I think > this aspect of the model should be changed. > > NB> See above comment. > > Thanks > Nitin _______________________________________________ i2rs mailing list [email protected] https://www.ietf.org/mailman/listinfo/i2rs
