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 <lsr-bounces@ietf.org> On Behalf Of Toerless Eckert
> Sent: Wednesday, November 14, 2018 6:29 PM
> To: lsr@ietf.org
> 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
> Lsr@ietf.org
> https://www.ietf.org/mailman/listinfo/lsr