Hi Les, Thanks for the summary and citations.
To my understanding, although DSCP based steering could be used in multi-topology scenarios, such usage is not defined in IETF specifications. Actually there can be many ways of choosing which topology is used for the forwarding of a particular packet. Thus the relationship between DSCP and MT is not that tightly coupled. Best regards, Jie > -----Original Message----- > From: Lsr [mailto:[email protected]] On Behalf Of Les Ginsberg (ginsberg) > Sent: Thursday, November 15, 2018 12:41 PM > To: Toerless Eckert <[email protected]>; [email protected] > Subject: Re: [Lsr] LSR: Using DSCP for path/topology selection Q > > Toerless - > > It's pretty hard to understand the context for your email. > > What leads you to believe that any of the MT specifications you mention say > anything normative about DSCP and topologies?? > > RFC4915 does not mention DSCP at all - but does make the statement: > > https://tools.ietf.org/html/rfc4915#section-3.8 > "It is outside of the scope of this document to specify how the > information in various topology specific forwarding structures are > used during packet forwarding or how incoming packets are associated > with the corresponding topology." > > RFC 5120 does mention DSCP, but only as an example of something that "could" > be used to determine on what topology a packet should be forwarded. > > RFC 7722 also mentions DSCP as an example, but there is a statement in Section > 3: > > "It is assumed, but > outside the scope of this specification, that the network layer is > able to choose which topology to use for each packet" > > IGP WGs have never attempted to recommend (let alone normatively define) > any relationship between DSCP and MT. > > ??? > > Les > > > -----Original Message----- > > From: Lsr <[email protected]> On Behalf Of Toerless Eckert > > Sent: Wednesday, November 14, 2018 6:29 PM > > To: [email protected] > > Subject: [Lsr] LSR: Using DSCP for path/topology selection Q > > > > Whats the current best guidance on using DSCP for selection of path, > > specifically for selection of topology with MTR (RFCs 4915, 5120, 7722) ? > > > > My understanding from history is that this looked like a good idea to > > customers first, but when implementations became available, customers > > really did not want to implement it because of the overloading of DSCP > > between QoS and routing and the resulting management complexity. > > > > Has the idea of using DSCP for path selection been re-introduced in > > any later work like flex-Algos ? > > > > If there could be rough consensus that this is in general a bad idea, > > i wonder if it would be appropriate to have a short normative document > > from LSR defining that the use of DSCP for topology selection is > > historic and not recommended anymore and make this an update to above > > three RFCs, maybe also pointing out that there are other methods to > > select a topology and those remain viable: > > > > I specifically would not like to see the actual MTR RFCs to be changed > > in status, because MTR actually does work quite well and is supported > > in products and deployed with IP multicast, even with multiple > > topologies for IP multicast in live-live scenarios. > > > > Thanks! > > Toerless > > > > _______________________________________________ > > Lsr mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/lsr > > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr _______________________________________________ Lsr mailing list [email protected] https://www.ietf.org/mailman/listinfo/lsr
