Jeff, Muthu and all, I concur with Jeff – MSD is not defined just by HW but also by SW. Same HW may yield different MSD values with SW defining different data paths thru it. And it may well be a matter of tradeoff where higher MSD could be achieved at the expense of some other parameters. This is exactly why MSD should be treated as a configurable attribute. Of course this does not preclude implementations when exactly one MSD value would be supported.
Regards, Sasha Office: +972-39266302 Cell: +972-549266302 Email: [email protected] From: spring [mailto:[email protected]] On Behalf Of Jeff Tantsura Sent: Wednesday, April 05, 2017 7:57 PM To: Muthu Arul Mozhi Perumal <[email protected]>; [email protected] Subject: Re: [spring] Is MSD really a configurable attribute? Hi Muthu, Thanks for your comments! MSD is a configurable attribute, it is not derived directly from HW capabilities, in fact no vendor today provides an API to query underlying HW for the MSD supported, there’s also dependency on SW support. That’s why we have introduced “Type” field, so more than a single MDS type could be signaled, as of now, we have only defined “Base” Type, that describes total number of SID’s supported. I’d expect vendors to provide clear guidance wrt MSD semantics, in disaggregated case, when HW and SW are coming from different vendors, I’d expect HW to be the limiting factor and HW vendors to provide an API to query for the MSD supported and auto-populate the value in IGPs. I have reached out to BCM and Barefoot, plan to discuss with more HW vendors. Per node vs per LC capability – even on a same generation NPU, depending on revision, MSD supported could vary drastically, routers with 3 generations of line cards are not an exception either, so MSD per adj/interface is a rather valuable information to a PCE if a tunnel could exit over different line cards. Per node MSD limits computation to the lowest value supported by the node. Hope this helps, Cheers, Jeff From: spring <[email protected]<mailto:[email protected]>> on behalf of Muthu Arul Mozhi Perumal <[email protected]<mailto:[email protected]>> Date: Wednesday, April 5, 2017 at 09:38 To: <[email protected]<mailto:[email protected]>> Subject: [spring] Is MSD really a configurable attribute? draft-ietf-spring-sr-yang seems to describe Maximum SID Depth (MSD) as a read-write attribute that is configurable on the node, but I really wonder how many vendors actually support changing the MSD on a node. Suppose a node is capable of pushing a maximum of K labels in h/w and the node MSD is configured as K, then a SR-TE tunnel on the node can specify up to K SIDs. This means the node will not be able to push a VPN label, so cannot do L3VPN/L2VPN. Given that a miss-configuration like would result in service failure, is there a real motivation for changing MSD on a node? Should MSD be a node capability instead, like the 'readable-label-stack-depth' defined in the yang draft? Regards, Muthu _______________________________________________ spring mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/spring ___________________________________________________________________________ This e-mail message is intended for the recipient only and contains information which is CONFIDENTIAL and which may be proprietary to ECI Telecom. If you have received this transmission in error, please inform us by e-mail, phone or fax, and then delete the original and all copies thereof. ___________________________________________________________________________
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