Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-mpls-elc-13: (with DISCUSS and COMMENT)
Benjamin Kaduk <kaduk@mit.edu> Thu, 21 May 2020 19:41 UTC
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Date: Thu, 21 May 2020 12:41:15 -0700
From: Benjamin Kaduk <kaduk@mit.edu>
To: Peter Psenak <ppsenak@cisco.com>
Cc: The IESG <iesg@ietf.org>, draft-ietf-ospf-mpls-elc@ietf.org, lsr-chairs@ietf.org, lsr@ietf.org, Acee Lindem <acee@cisco.com>, aretana.ietf@gmail.com
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Subject: Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-mpls-elc-13: (with DISCUSS and COMMENT)
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On Thu, May 21, 2020 at 12:16:44PM +0200, Peter Psenak wrote: > Hi Benjamin, > > thanks for review. > > Please see inline (##PP) two responses to OSPF specific comments. > > > On 20/05/2020 00:43, Benjamin Kaduk via Datatracker wrote: > > Benjamin Kaduk has entered the following ballot position for > > draft-ietf-ospf-mpls-elc-13: Discuss > > > > When responding, please keep the subject line intact and reply to all > > email addresses included in the To and CC lines. (Feel free to cut this > > introductory paragraph, however.) > > > > > > Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html > > for more information about IESG DISCUSS and COMMENT positions. > > > > > > The document, along with other ballot positions, can be found here: > > https://datatracker.ietf.org/doc/draft-ietf-ospf-mpls-elc/ > > > > > > > > ---------------------------------------------------------------------- > > DISCUSS: > > ---------------------------------------------------------------------- > > > > I have a question about the scope of some normative language, which may > > or may not be problematic but I'm too ignorant of OSPF details to be > > able to answer myself. In Section 3 we say that: > > > > When an OSPF Area Border Router (ABR) distributes information between > > connected areas it MUST preserve the ELC setting. > > > > My undesrtanding is that it's normal operation for an ABR to > > distribution information about prefixes and such between areas, and in > > particular that an ABR does not necessarily need to know the semantic > > details of every bit of information being distributed in that fashion. > > So, I am imagining a scenario where some routers in both areas > > advertise/understand the ELC flag but the ABR between them does not > > implement this spec. What would happen in such a scenario? If the ABR > > is still expected to distribute the ELC setting without change, isn't > > that just a core requirement from the respective OSPF specs, as opposed > > to a new requirement imposed by this spec (which, in this scenario, the > > ABR is not claiming to adhere to anyway)? > > > > There is perhaps a similar question about the ASBR guidance, though when > > doing cross-protocol signalling there is a more clear need for the ASBR > > to understand the semantics of the flags it is redistributing (and it's > > only a "SHOULD"). > > > > > > ---------------------------------------------------------------------- > > COMMENT: > > ---------------------------------------------------------------------- > > > > Section 1 > > > > The abstract is pretty explicit that "this draft defines" both ELC and > > ERLD signaling capabilities, but this section only has a clear statement > > for the ELC. Should we put something at the end of the last paragraph > > about "this document defines a mechanism to signal the ERLD using OSPFv2 > > and OSPFv3"? > > ##PP > this has been already addressed based on previous comments. Latest text > is as follows: > > "Multiprotocol Label Switching (MPLS) has defined a mechanism to > load-balance traffic flows using Entropy Labels (EL). An ingress Label > Switching Router (LSR) cannot insert ELs for packets going into a given > Label Switched Path (LSP) unless an egress LSR has indicated via > signaling that it has the capability to process ELs, referred to as the > Entropy Label Capability (ELC), on that LSP. In addition, it would be > useful for ingress LSRs to know each LSR's capability for reading the > maximum label stack depth and performing EL-based load-balancing, > referred to as Entropy Readable Label Depth (ERLD). This document > defines a mechanism to signal these two capabilities using OSPFv2 and > OSPFv3 and BGP-LS." Great; thanks! > > In cases where LSPs are used (e.g., SR-MPLS [RFC8660], it would be > > > > side note(?): I don't know that SR-MPLS is so popular so as to be > > privileged as the only example given for LSP usage. If we instead > > talked about using IGPs to signal labels, this selection would seem less > > surprising to me. > > > > Section 3 > > > > If the router supports ELs on all of its interfaces, it SHOULD > > advertise the ELC with every local host prefix it advertises in OSPF. > > > > Do we want to say anything about (not) advertising the ELC for other > > prefixes? > > > > Section 7 > > > > Should we say anything about considerations for redistributing ELC/ERLD > > information at the ASBR with respect to exposing "internal information" > > to external parties? > > > > This document specifies the ability to advertise additional node > > capabilities using OSPF and BGP-LS. As such, the security > > considerations as described in [RFC5340], [RFC7770], [RFC7752], > > [RFC7684], [RFC8476], [RFC8662], > > > > RFC 8662's security considerations have a pretty hard dependency on RFC > > 6790's security considerations; it might be worth mentioning 6790 > > directly in this list as well. > > > > [I-D.ietf-idr-bgp-ls-segment-routing-ext] and > > [I-D.ietf-idr-bgp-ls-segment-routing-msd] are applicable to this > > document. > > > > Could we also have a brief note that the (respective) OSPF security > > mechanisms serve to protect the ELC/ERLD information? > > > > Incorrectly setting the E flag during origination, propagation or > > redistribution may lead to black-holing of the traffic on the egress > > node. > > > > This is what happens when the E flag should not be set but is > > erroneously set. Should we also say what happens if we should set the E > > flag but erroneously clear it (e.g., that poor or no load-balancing may > > occur)? > > > > Section 8 > > > > I do see the note in the shepherd writeup about the sixth author (thank > > you!); if we're already breaking through the 5-author limit, did we > > consider making those who "should be considered as co-authors" listed as > > co-authors? > > > > Section 10.2 > > > > It's slightly surprising to see the core OSPF protocols only listed as > > informative, but I can see how they are to be considered "basic > > specifications" in the vein of > > https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/ > > ##PP > right, I can add it as normative, or remove completely, or keep as > informative. Whatever you like :) Keep it as-is seems simplest, then. But thanks :) -Ben
- [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf… Benjamin Kaduk via Datatracker
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Peter Psenak
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk