Hi Ahmed, Thanks for posting the update (and sorry for only getting to it now).
The two specific points I raised in my DISCUSS ballot are properly addressed, but before I go clear that I was hoping you could help me remember why the following text was removed when going from -13 to -14: [...] Because this document recognizes that miscofiguration and/or programming may result in false or conflicting label binding advertisements, thereby compromising traffic forwarding, the document recommends strict configuration/ programmability control as well as montoring the SID advertised and log/error messages by the operator to avoid or at least significantly minimize the possibility of such risk. I couldn't find anything in my email history that helped jog my memory. Thanks, Benjamin On Mon, Jul 16, 2018 at 02:10:37PM -0700, Ahmed Bashandy wrote: > Hi, > > I just posted version 14 > https://www.ietf.org/id/draft-ietf-spring-segment-routing-ldp-interop-14.txt > > Thanks > > Ahmed > > > > On 7/10/18 7:11 AM, Benjamin Kaduk wrote: > > Hi Bruno, > > > > Thanks for the additional clarifications in the suggested text -- it looks > > good to me, so you and Ahmed should please go ahead with it (once > > submissions open up again). > > > > -Benjamin > > > > On Tue, Jul 10, 2018 at 12:49:28PM +0000, [email protected] wrote: > >> Hi Benjamin, > >> > >> Thanks for the discussion. > >> Please see inline [Bruno2] > >> > >>> From: Benjamin Kaduk [mailto:[email protected]] > >> > Sent: Tuesday, July 10, 2018 12:53 AM > >> > On Mon, Jul 09, 2018 at 12:36:20PM +0000, [email protected] > >> wrote: > >> > > Hi Benjamin, > >> > > > >> > > Thanks for your comments. > >> > > Please see inline another addition to Ahmed's answer. [Bruno] > >> > > > >> > > > From: Ahmed Bashandy [mailto:[email protected]] > >> > > > Sent: Monday, July 09, 2018 2:30 AM > >> > > > > >> > > > Hi > >> > > > Thanks for the review > >> > > > > >> > > > See reply to the comment at #Ahmed > >> > > > > >> > > > Ahmed > >> > > > > >> > > > > >> > > > On 6/20/18 9:40 AM, Benjamin Kaduk wrote: > >> > > > > Benjamin Kaduk has entered the following ballot position for > >> > > > > draft-ietf-spring-segment-routing-ldp-interop-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-spring-segment-routing-ldp-interop/ > >> > > > > > >> > > > > > >> > > > > > >> > > > > > >> ---------------------------------------------------------------------- > >> > > > > DISCUSS: > >> > > > > > >> ---------------------------------------------------------------------- > >> > > > > > >> > > > > I may be missing something, but I don't see anything that says > >> whether the > >> > > > > preference field introduced in Section 3.2.3 uses larger values > >> or smaller > >> > > > > values for more-preferred SRMSes. > >> > > > #Ahmed: > >> > > > If I understand this statement correctly, the concern is about > >> which > >> > > > label(s) get assigned to which prefix(es). This concern is > >> addressed as > >> > > > follows > >> > > > > >> > > > From the MPLS architecture point of view, there is nothing wrong > >> in > >> > > > having multiple labels for the same prefix. Segment routing in > >> general > >> > > > and this document in particular did not introduce this behavior > >> nor did > >> > > > they prohibit/restrict/relax it. For example, an implementation > >> that > >> > > > allows the operator to locally assign multiple local labels to > >> the same > >> > > > prefix may continue to apply this behavior whether the platform > >> supports > >> > > > segment routing or not, in which case it is up to the > >> implementation > >> > > > and/or the configuration affecting the MPLS forwarding plane to > >> specify > >> > > > how to behave when multiple labels are assigned to the same > >> prefix. Such > >> > > > behavior is a general MPLS behavior that outside the scope of and > >> is not > >> > > > modified by segment routing. > >> > > > > >> > > > However the opposite, where the same label gets assigned to > >> multiple > >> > > > prefixes resulting in label collision is problematic. This > >> document > >> > > > prohibits label collision resulting from the use of SRMS (which is > >> > > > introduced by this document) in the first bullet starting at the > >> 3rd > >> > > > line of page 12: > >> > > > "- If there is an incoming label collision as specified in > >> > > > [I-D.ietf-spring-segment-routing-mpls] , apply the steps > >> specified > >> > > > in [I-D.ietf-spring-segment-routing-mpls] to resolve the > >> > > > collision."" > >> > > > > >> > > > > > >> > > > > > >> > > > > The introduction of the SRMS is also introducing a new way for > >> a protocol > >> > > > > participant to make claims about route prefixes directed at > >> "third parties" > >> > > > > (non-MS, non-MC routers). While routing protocols in general > >> do require high > >> > > > > levels of trust in all participants in order for proper routing > >> to occur, this > >> > > > > addition seems to create a "first among equals" situation that > >> could be called > >> > > > > out more clearly in the security considerations. (I do > >> appreciate that the > >> > > > > requirement for preferring SIDs advertised in prefix > >> reachability > >> > > > > advertisements over those advertised in mapping server > >> advertisements does help > >> > > > > alleviate some of the risk.) > >> > > > >> > > [Bruno] > >> > > 1) As the SID attached to the prefix reachability is more preferred > >> than the SID advertised by the > >> > SRMS, I would kind of argue that the SRMS is more "last among equals" > >> :-) > >> > > 2) I agree that routing protocols, especially Link State Internal > >> Routing Protocols, do require high > >> > levels of trusts among participants. In particular, please note that > >> any node can already advertise > >> > any IP prefix (with any attached SID), and with any metric/cost, hence > >> attracting the traffic. In this > >> > regards, I don't really see an increased risk in IGP routing. > >> > > >> > I don't really see an increased risk per se, either (since all routers > >> can > >> > break routing in all sorts of ways), but I do see a new mechanism by > >> which > >> > certain routers can cause routing breakage. So I was thinking "first > >> among > >> > equals" in terms of "more ways to break things", not "can break things > >> with > >> > a larger magnitude of breakage". You are right that the preference > >> order > >> > that Ahmed described does mean that this new "mechanism for breakage" > >> is > >> > only applicable when there are no explicit prefix-SID advertisements > >> > received via the IGP. So in that sense this new mechanism for > >> breakage is > >> > "last among equals", as you say, because it can only take effect if > >> the IGP > >> > leaves room for it. > >> > >> [Bruno2] Ack; I believe we are in sync. > >> > >> > > 3) I agree that SRMS allows for a "centralized" SID advertisement. I > >> personally don't feel that this > >> > is more risky than a "centralized" BGP Route Reflector. However, I'm > >> not against raising this in the > >> > security consideration section. > >> > > Please see below a proposed text. Please comment/propose text as > >> required. > >> > > > >> > > OLD: > >> > > This document introduces another form of label binding > >> > > advertisements. The security associated with these advertisement > >> is > >> > > part of the security applied to routing protocols such as IS-IS > >> > > [RFC5304] and OSPF [RFC5709] which both optionally make use of > >> > > cryptographic authentication mechanisms. This document also > >> > > specifies a mechanism by which the ill effects of advertising > >> > > conflicting label bindings can be mitigated. > >> > > > >> > > NEW: > >> > > This document introduces another form of label binding > >> > > advertisements. The security associated with these advertisements > >> is > >> > > part of the security applied to routing protocols such as IS-IS > >> > > [RFC5304] and OSPF [RFC5709] which both optionally make use of > >> > > cryptographic authentication mechanisms. > >> > > This form of advertisement is more centralized, on behalf of the > >> node advertising the IP > >> > reachability. > >> > > This document also > >> > > specifies a mechanism by which the ill effects of advertising > >> > > conflicting label bindings can be mitigated. In particular, > >> advertisements from the node > >> > advertsising the IP reachability is more preference than the > >> centralized one. > >> > > >> > I think that's enough to resolve my DISCUSS point. I would prefer if > >> there > >> > was a little bit more text, such as "more centralized, on behalf of the > >> > node advertising the IP reachability, which presents a different risk > >> > profile than existing mechanisms for distributing label bindings", but > >> your > >> > version does cover the key point. > >> > >> [Bruno2] ok. Proposed NEW2: > >> > >> This document introduces another form of label binding > >> advertisements. The security associated with these advertisements is > >> part of the security applied to routing protocols such as IS-IS > >> [RFC5304] and OSPF [RFC5709] which both optionally make use of > >> cryptographic authentication mechanisms. > >> This form of advertisement is more centralized, on behalf of the node > >> advertising the IP reachability, which presents a different risk profile. > >> This document also > >> specifies a mechanism by which the ill effects of advertising > >> conflicting label bindings can be mitigated. In particular, advertisements > >> from the node advertising the IP reachability is more preferred than the > >> centralized one. > >> > >> > >> > >> In short, I used your proposed text but removed " than existing mechanisms > >> for distributing label bindings" as this could be read as "LDP". We could > >> add more text to distinguish, but IMO the current text seems fine. > >> > >> > >> > (And to be clear, I am not trying to say > >> > that the centralized risk is better or worse in all cases; it's just > >> > different, so we should call that out to the reader and inform their > >> decision > >> > making.) > >> > >> [Bruno2] In sync. I agree with you that we should call that out to the > >> reader and inform their decision making. Thanks for bringing the comment. > >> I'll work with Ahmed, to have the draft reflect this, as he has the pen. > >> > >> Thanks, > >> Bruno > >> > >> > >> > Thanks, > >> > > >> > Benjamin > >> > > >> > > > >> > > Thanks, > >> > > --Bruno > >> > > > >> > > > #Ahmed: > >> > > > If I understand your comment, the concern is about > >> > > > "first-come-first-serve" behavior. I believe this concern is > >> addressed > >> > > > as follows > >> > > > (1) The sentence starting at the fourth line of the second > >> paragraph in > >> > > > page 10 says: > >> > > > For a given prefix, if an MC receives an SR mapping > >> advertisement > >> > > > from a mapping server and also has received a prefix-SID > >> > > > advertisement for that same prefix in a prefix reachability > >> > > > advertisement, then the MC MUST prefer the SID advertised in > >> the > >> > > > prefix reachability advertisement over the mapping server > >> > > > advertisement i.e., the mapping server advertisment MUST be > >> ignored > >> > > > for that prefix. > >> > > > > >> > > > (2) The last bullet at the bottom of page 11 says: > >> > > > - For any prefix for which it did not receive a prefix-SID > >> > > > advertisement, the MCC applies the SRMS mapping > >> advertisments with > >> > > > the highest preference. > >> > > > > >> > > > (3) The first bullet near the top pf page 12 says: > >> > > > - If there is an incoming label collision as specified in > >> > > > [I-D.ietf-spring-segment-routing-mpls] , apply the steps > >> specified > >> > > > in [I-D.ietf-spring-segment-routing-mpls] to resolve the > >> > > > collision. > >> > > > > >> > > > So for the same set of received advertisements (SRMS > >> advertisements, > >> > > > prefix-SID advertisements, or combination of both), the same set > >> of > >> > > > labels will be assigned to the same prefix. As mentioned in my > >> previous > >> > > > comments, if multiple labels get assigned to the same prefix, the > >> > > > behavior is not related to segment routing > >> > > > > >> > > > Regarding placing a comment in the security section, IMO a > >> specification > >> > > > of which advertisement(s) to use when receiving multiple > >> (conflicting or > >> > > > non-conflicting) advertisements has nothing to do with security. > >> It is > >> > > > an externally visible protocol(s) behavior that should be > >> specified in > >> > > > the sections covering the protocol(s) themselves rather than > >> security > >> > > > consideration of the protocol(s). > >> > > > > >> > > > But if you still think there is a need to mention something in the > >> > > > security section, a suggestion from your side will be greatly > >> appreciated . > >> > > > > > >> > > > > > >> > > > > > >> ---------------------------------------------------------------------- > >> > > > > COMMENT: > >> > > > > > >> ---------------------------------------------------------------------- > >> > > > > > >> > > > > I support Alissa's suggestion about the text covering > >> cryptographic authentication. > >> > > > #Ahmed: I modified the statement as Alissa suggested in version > >> 14 that > >> > > > will be published in the next 1-2 days > >> > > > > > >> > > > > "[100,300]" and "(100,200)" are each used as an example SRGB. > >> In > >> > > > > some contexts the round versus square brackets indicate a > >> > > > > distinction between "closed" (includes endpoints) and "open" > >> (does > >> > > > > not include endpoints) intervals. If there's no need to make > >> such a > >> > > > > distinction, I suggest standardizing one one format. > >> > > > #Ahmed: I changed both of them to use [] in version because we > >> mean > >> > > > inclusive > >> > > > > > >> > > > > As was mentioned in the secdir review, it would be good to > >> expand FEC and LFA on first > >> > usage. > >> > > > #Ahmed: Corrected in version 14 that will be published in the > >> next 1-2 days > >> > > > > > >> > > > > Section 1 > >> > > > > > >> > > > > Section 2 describes the co-existence of SR with other MPLS > >> Control > >> > > > > Plane. [...] > >> > > > > > >> > > > > nit: "other MPLS Control Plane" seems to be an incomplete > >> compound noun > >> > > > > -- is it other control plane technologies that are being > >> considered? > >> > > > #Ahmed: I added "protocols" in version 14 to clarify that > >> > > > > > >> > > > > Section 2 > >> > > > > > >> > > > > Note that this static label allocation capability of the > >> label > >> > > > > manager exists for many years across several vendors and > >> hence is not > >> > > > > new. Furthermore, note that the label-manager ability to > >> statically > >> > > > > allocate a range of labels to a specific application is not > >> new > >> > > > > either. [...] > >> > > > > > >> > > > > nits: "has existed", "label-manager's ability". > >> > > > #Ahmed: Corrected (thanks a lot) > >> > > > > > >> > > > > Section 2.1 > >> > > > > > >> > > > > MPLS2MPLS refers the forwarding behavior where a router > >> receives an > >> > > > > labeled packet and switches it out as a labeled packet. > >> Several > >> > > > > > >> > > > > nit: "refers to", "a labeled packet" > >> > > > #Ahmed: Corrected > >> > > > > > >> > > > > Section 3.2 > >> > > > > > >> > > > > This section defines the Segment Routing Mapping Server > >> (SRMS). The > >> > > > > SRMS is a IGP node advertising mapping between Segment > >> Identifiers > >> > > > > (SID) and prefixes advertised by other IGP nodes. The SRMS > >> uses a > >> > > > > dedicated IGP extension (IS-IS, OSPF and OSPFv3) which is > >> protocol > >> > > > > specific and defined in > >> [I-D.ietf-isis-segment-routing-extensions], > >> > > > > [I-D.ietf-ospf-segment-routing-extensions], and > >> > > > > [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. > >> > > > > > >> > > > > nit: Perhaps "IS-IS, OSPFv2, and OSPFv3 are currently > >> supported" is a > >> > > > > better parenthetical? > >> > > > #Ahmed: Corrected in the next version > >> > > > > > >> > > > > The example diagram depicted in Figure 3 assumes that the > >> operator > >> > > > > configures P5 to act as a Segment Routing Mapping Server > >> (SRMS) and > >> > > > > advertises the following mappings: (P7, 107), (P8, 108), > >> (PE3, 103) > >> > > > > and (PE4, 104). > >> > > > > > >> > > > > nit: I think this is Figure 2. > >> > > > #Ahmed: Corrected in the next version > >> > > > > > >> > > > > Section 3.2.1 > >> > > > > > >> > > > > [...] Examples > >> > > > > of explicit prefix-SID advertisment are the prefix-SID > >> sub-TLVs > >> > > > > defined in ([I-D.ietf-isis-segment-routing-extensions], > >> > > > > [I-D.ietf-ospf-segment-routing-extensions], and > >> > > > > [I-D.ietf-ospf-ospfv3-segment-routing-extensions]). > >> > > > > > >> > > > > Would draft-ietf-idr-bgp-prefix-sid (also on this week's > >> telechat) > >> > > > > be appropriate for inclusion in this list? > >> > > > > > >> > > > > for that prefix. Hence assigning a prefix-SID to a prefix > >> using the > >> > > > > SRMS functionality does not preclude assigning the same or > >> different > >> > > > > prefix-SID(s) to the same prefix using explict prefix-SID > >> > > > > advertisement such as the aforementioned prefix-SID sub-TLV. > >> > > > #Ahmed: The SRMS functionality is specific to IGPs as mentioned > >> in the > >> > > > second sentence of the second paragraph in Section 3.2 > >> > > > > > >> > > > > nit: I think the aforementioned things were a list, so > >> "sub-TLVs" plural > >> > > > > would be appropriate. > >> > > > > > >> > > > > Including the name for IS-IS TLV 135 might be helpful for the > >> > > > > reader. > >> > > > > > >> > > > #Ahmed: Corrected as suggested in the next version > >> > > > >> > > > >> > > > >> > > >> ________________________________________________________________________________ > >> > _________________________________________ > >> > > > >> > > Ce message et ses pieces jointes peuvent contenir des informations > >> confidentielles ou > >> > privilegiees et ne doivent donc > >> > > pas etre diffuses, exploites ou copies sans autorisation. 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