[lisp] Benjamin Kaduk's Discuss on draft-ietf-lisp-rfc6833bis-27: (with DISCUSS and COMMENT)
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Subject: [lisp] Benjamin Kaduk's Discuss on draft-ietf-lisp-rfc6833bis-27: (with DISCUSS and COMMENT)
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Benjamin Kaduk has entered the following ballot position for draft-ietf-lisp-rfc6833bis-27: 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-lisp-rfc6833bis/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- (1) The -27 brought back the "MUST" for HMAC-SHA256-128 in Section 5.6 per my ballot on the -26, but left unchanged section 9, so we still have a SHOULD vs. MUST inconsistency w.r.t. implementing HMAC-SHA256-128+HKDF-SHA256. (I would of course prefer the same resolution of the inconsistency that Roman does, but have forgotten to what extent we have to defer to the deployed reality.) (2) It looks like the update in Section 5.7 is attempting to address my point about only terminating Map-Notify retransmission when the authentication data of the Map-Notify-Ack validates, but the added text is either misplaced or malformed. Perhaps CURRENT: The Map-Notify-Ack message has the same contents as a Map-Notify message. It is used to acknowledge the receipt of a Map-Notify and for the sender to stop retransmitting a Map-Notify with the same nonce and the authentication data validates. [...] NEW: The Map-Notify-Ack message has the same contents as a Map-Notify message. It is used to acknowledge the receipt of a Map-Notify and, once the the authentication data is validated, allows for the Map-Notify sender to stop retransmitting a Map-Notify with the same nonce. [...] (3) I think that Eric Rescorla's concern about a misbehaving ETR being able to prevent an ITR from learning that the ETR is no longer the appropriate ETR for a given prefix remains unaddressed. I wrote up a longer description at https://mailarchive.ietf.org/arch/msg/lisp/O2ycn4CkWsPhFyqrZuB4ZJBNnl0/ but in short, we only require the ITR to send its Map-Request through the mapping system (vs. directly to the ETR) when SMR is sent from an address not in the current mapping data for that prefix -- if the SMR is sent from an address in the current mapping data, we allow sending Map-Request directly to the ETR, outside the mapping system. I don't see a mechanism that guarantees that such a "revocation" event is noticed by the ITR. (4) The specification of the MAC+KDF algorithms doesn't seem detailed enough to be implementable. RFC 4868 is attempted to be used as a reference for both HMAC-SHA256-128 (er, and the one-character-off HMAC-SHA-256-128) and HKDF-SHA2562 (note spurious final '2'), but I think it can only work as a reference for the MAC algorithm. Presumably we need RFC 5869 or such for the KDF part (5) This is probably my fault, but we're missing a step with how we describe the Map-Notify/Map-Notify-Ack per-message authentication. Specifically, while we do say that the authentication data needs to be recomputed each time, we don't clearly state that this is because the correct per-message key is different, because we are using a different 's' input to the KDF function for the different messages. In line with the "Map-Register Authentication" used for Map-Register, this would presumably be "Map-Notify Authentication" and "Map-Notify-Ack Authentication", but neither of those strings appear in this document. We might be able to localize the change to Section 5.6, akin to OLD: 4: The derived per-message key is computed as: per-msg- key=KDF(nonce+s+PSK[Key ID]). Where the nonce is the value in the Nonce field of the Map-Register and 's' is a string equal to "Map-Register Authentication". [...] NEW: 4: The derived per-message key is computed as: per-msg- key=KDF(nonce+s+PSK[Key ID]). Where the nonce is the value in the Nonce field of the Map-Register and 's' is a string that corresponds to the message type being authenticated. For Map-Register messages, it is equal to "Map-Register Authentication". Similarly, for Map-Notify and Map-Notify-Ack messages, it is "Map-Notify Authentication" and "Map-Notify-Ack Authentication", respectively. However, I think the rhetoric would be more robust if we also modified Section 5.7 to mention the existence of the different 's' values (or, rather, the different per-message key) when we say that the authentication data is recomputed. Perhaps, s/is recomputed/is recomputed using the corresponding per-message key/ (twice). ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- Abstract database designs. Since these devices implement the "edge" of the LISP Control-Plane infrastructure, connecting EID addressable nodes of a LISP site, their implementation and operational complexity reduces the overall cost and effort of deploying LISP. I think there might be a "simplifying" or "reducing" missing here (w.r.t. "their implementation and operational complexity"). Section 1 Conceptually, LISP Map-Servers share some of the same basic configuration and maintenance properties as Domain Name System (DNS) [RFC1035] servers; likewise, Map-Resolvers are conceptually similar I suggest adding "authoritative" to the DNS servers of the analogy. Section 3 Map-Resolver: A network infrastructure component that accepts LISP Encapsulated (ECM) Map-Requests, typically from an ITR, and determines whether or not the destination IP address is part of the EID namespace; if it is not, a Negative Map-Reply is returned. Otherwise, the Map-Resolver finds the appropriate EID-to-RLOC mapping by consulting a mapping database system. This could perhaps be misread as implying that the Map-Resolver returns the appropriate EID-to-RLOC mapping to the requestor directly, whereas IIRC the reply is sent directly from the ETR/Map-Server. Section 4 A Map-Server is a device that publishes EID-Prefixes in a LISP mapping database on behalf of a set of ETRs. When it receives a Map Request (typically from an ITR), it consults the mapping database to I feel like I said this already but forgot the answer; sorry for the duplication: the Map-Server is not getting the request directly from the ITR, but rather from the mapping system or a Map-Resolver. Do we want to say something like "originating from an ITR" to clarify? Section 5.2 A: This is an authoritative bit, which is set to 0 for UDP-based Map- Requests sent by an ITR. It is set to 1 when an ITR wants the destination site to return the Map-Reply rather than the mapping database system returning a Map-Reply. I'm not sure this paints a clear picture of when the bit is/isn't set. Are Map-Requests sent by an ITR that want the destination site to reply (rather than the mapping database) sent over some non-UDP-based scheme? Do ECM messages count as UDP-based? (I would make this a Discuss for lack of clarity but that would be double-jeopardy.) p: This is the PITR bit. This bit is set to 1 when a PITR sends a Map-Request. It might be worth saying something about what the recipient would do with the knowledge that the Map-Request was PITR-generated (rather than ITR-generated?). L: This is the local-xtr bit. It is used by an xTR in a LISP site to tell other xTRs in the same site that it is part of the RLOC-set for the LISP site. The L-bit is set to 1 when the RLOC is the sender's IP address. I'm not sure which RLOC is "the" RLOC -- the message format seems to allow multiple ITR-RLOC entries. D: This is the dont-map-reply bit. It is used in the SMR procedure described in Section 6.1. When an xTR sends an SMR Map-Request message, it doesn't need a Map-Reply returned. When this bit is Should this get s/SMR Map-Request message/SMR message/ as was done elsewhere in response to my comments on a previous version? EID-Prefix: This prefix address length is 4 octets for an IPv4 address family and 16 octets for an IPv6 address family when the EID-Prefix-AFI is 1 or 2, respectively. For other AFIs [AFI], the address length varies and for the LCAF AFI the format is defined in [RFC8060]. [...] Just to check: if I get a Map-Request that uses an AFI I don't recognize, I have to abort parsing the packet since I don't know how many bytes to skip? It seems like this might negatively affect the ability to introduce new AFIs. Map-Reply Record: When the M-bit is set, this field is the size of a single "Record" in the Map-Reply format. This Map-Reply record contains the EID-to-RLOC mapping entry associated with the Source EID. This allows the ETR that will receive this Map-Request to cache the data if it chooses to do so. We could perhaps mention something about whether the ETR believes the message is trustworthy, too, since it does not have the benefit of having gone through mapping system validation. Section 5.3 Map-Requests MUST be rate-limited to 1 per second per EID-prefix. After 10 retransmits without receiving the corresponding Map-Reply must wait 30 seconds. nit: incomplete sentence. a Map-Cache entry. If the ETR (when it is an xTR co-located as an ITR) has a Map-Cache entry that matches the "piggybacked" EID and the RLOC is in the Locator-Set for the cached entry, then it MAY send the "verifying Map-Request" directly to the originating Map-Request source. If the RLOC is not in the Locator-Set, then the ETR MUST send the "verifying Map-Request" to the "piggybacked" EID. Doing this forces the "verifying Map-Request" to go through the mapping database system to reach the authoritative source of information about that EID, guarding against RLOC-spoofing in the "piggybacked" mapping data. side note: Does it make much practical difference to send the Map-Request to the EID as the destination address vs. just consulting the mapping system to look up that EID? It seems like the former is strictly more work, and I'm not sure what additional benefit is gained from that additional work. I guess, reachability information for the EID in question. Section 5.4 P: This is the probe-bit, which indicates that the Map-Reply is in response to a Locator reachability probe Map-Request. The 'Nonce' field MUST contain a copy of the nonce value from the original Map-Request. [...] The description of the nonce field says that it's always copied from the Map-Request; is this MUST adding any additional requirements? Record Count: This is the number of records in this reply message. A record is comprised of that portion of the packet labeled 'Record' above and occurs the number of times equal to Record Count. We say earlier that the record count in a Map-Request is (artificially) limited to 1 for this document; we might note here that the reply count can be larger than the request count, e.g., when there's a need to return more-specifics that are carved out from the best match to the requested EID. Locator Count: This is the number of Locator entries in the given Record. A Locator entry comprises what is labeled above as 'Loc'. The Locator count can be 0, indicating that there are no Locators for the EID-Prefix. Do we want to say "also known as a negative Map-Reply"? (0) No-Action: The Map-Cache is kept alive, and no packet encapsulation occurs. (1) Natively-Forward: The packet is not encapsulated or dropped but natively forwarded. It might be worth a few words about how these two differ, as the "no encapsulation" part is superficially similar. A: The Authoritative bit MAY only be set to 1 by an ETR. A Map- Server generating Map-Reply messages as a proxy MUST NOT set the A-bit to 1 by an ETR, and not a Map-Server generating Map-Reply messages as a proxy. This bit indicates to requesting ITRs that nit: looks like a botched edit, with the "and not a Map-Server generating Map-Reply messages as a proxy" sticking around when it should have been removed. the Map-Reply was not originated by a LISP node managed at the site that owns the EID-Prefix. Please confirm that the "not" is correct, here. 12.5% of the traffic. If all Weights for a Locator-Set are equal, the receiver of the Map-Reply will decide how to load-split the traffic. See RLOC-hashing [I-D.ietf-lisp-rfc6830bis] for a "equal" or "equal to zero"? Just "equal" seems like it needlessly overloads the semantics for uniform balancing. (Similarly for the multicast weight.) R: This is set when the sender of a Map-Reply has a route to the Locator in the Locator data record. This receiver may find this useful to know if the Locator is up but not necessarily reachable from the receiver's point of view. See also EID-Reachability Section 7.1 for another way the R-bit may be used. I'm not finding mention of the R-bit in Section 7.1; am I missing something? The Record format, as defined here, is used both in the Map-Reply and Map-Register messages, this includes all the field definitions. (We also mentioend in the previous section that a single record in this format can be present in the Map-Request.) Section 5.5 either from the destination field of an IP header of a Data-Probe or the EID record of a Map-Request. The RLOCs in the Map-Reply are nit(?): "EID of a record of a Map-Request"? invoking the reply. The source address of the Map-Reply is one of the local IP addresses chosen, to allow Unicast Reverse Path Something seems amiss here. It might just be that the comma is misplaced (after chosen vs. before it), but that hinges on the nature of the choice in question. Section 5.6 E: This is the Map-Register EID-notify bit. This is used by a First- Hop-Router (FHR) which discovers a dynamic-EID. This EID-notify based Map-Register is sent by the FHR to the same site xTR that propogates the Map-Register to the mapping system. The site xTR nit(???): I think maybe s/the same site/a same-site/, though that nominally changes the meaning. 4: The derived per-message key is computed as: per-msg- key=KDF(nonce+s+PSK[Key ID]). Where the nonce is the value in There's some notational quirks to handle here, since a KDF() function is typically represented as taking two inputs, an input key material and a salt, and depending on context an output length as well. (Though resolving this may depend on how discuss point (4) is resolved.) We should probably also say that '+' is used to represent concatenation. Section 5.7 procedure defined in the previous section. For an unsolicited Map- Notify, the fields of a Map-Notify used for publish/subscribe are specified in [I-D.ietf-lisp-pubsub]. We probably want to tweak how we make this reference to avoid a perceived need to make pubsub a normative reference. Perhaps something like "the Map-Notify message can also used, outside the scope of this specification, in an unsolicited manner, such as is specified in [pubsub]". Also, there are other ways to get an unsolicited Map-Notify, right? This text doesn't really make that clear. A Map-Server sends an unsolicited Map-Notify message (one that is not used as an acknowledgment to a Map-Register message) in only nit: s/in only/only in/ (my fault, sorry) conformance the Congestion Control And Relability Guideline sections of [RFC8085]. A Map-Notify is retransmitted until a Map-Notify-Ack nit: s/conformance/conformance with/ Upon reception of Map-Register, Map-Notify or Map-Notifiy-Ack, the receiver verifies the authentication data. I suggest adding "If the authentication data fails to validate, the message is dropped without further processing". Section 5.8 LISP: Type 8 is defined to be a "LISP Encapsulated Control Message", and what follows is either an IPv4 or IPv6 header as encoded by the first 4 bits after the 'Reserved' field. [...] S: This is the Security bit. When set to 1, the field following the 'Reserved' field will have the following Authentication Data format and follow the procedures from [I-D.ietf-lisp-sec]. So is it the IP version or the authentication data that follows the Reserved field? Section 6.1 mapping data. Please note that this procedure does not result in cryptographic or strongly authenticated verification. "in the absence of [LISP-SEC]". When an ITR receives an SMR-based Map-Request for which it does not One more s/SMR-based Map-Request/SMR message/, I think (I missed it in my review of the -26). Section 7 4. An ITR may receive a Map-Reply from an ETR in response to a previously sent Map-Request. The RLOC source of the Map-Reply is likely up, since the ETR was able to send the Map-Reply to the ITR. I note that in the analogous text in 6830bis (Section 10), we have a furthe statement "Please note that in some scenarios the RLOC [from the outer header] can be an spoofable field." When ITRs receive ICMP Network Unreachable or Host Unreachable messages as a method to determine unreachability, they will refrain from using Locators that are described in Locator lists of Map- Replies. However, using this approach is unreliable because many network operators turn off generation of ICMP Destination Unreachable messages. I think there is also some level of unreliability in the other direction -- even when following draft-ietf-opsec-icmp-filtering and validating the echoed contents, the contents could in some cases be sufficiently predictable that an attacker could spoof them. Having random nonces/ports be in use helps, of course, but the ICMP message could be generated in response to arbitrary traffic, not all of which will necessarily have all of those. The ITR can test the reachability of the unreachable Locator by sending periodic Requests. Both Requests and Replies MUST be rate- nit: I think we haven't been using the bare forms of "Requests" and "Replies" (in favor of the "Map-" prefixed forms). Section 8.1 o A Negative Map-Reply, with action code of "Natively-Forward", from a Map-Server that is authoritative (within the LISP deployment Section 1.1) for an EID-Prefix that matches the requested EID but that does not have an actively registered, more-specific EID- prefix. In this case, the requested EID is said to match a "hole" Presumably the more-specific prefix still needs to match the requested EID? Section 9 3. LISP-SEC [I-D.ietf-lisp-sec] MUST be implemented. Network operartors should carefully weight how the LISP-SEC threat model nit: s/operartors/operators The Map-Request/Map-Reply message exchange to inject forged mappings directly in the ITR EID-to-RLOC map-cache. This can lead to traffic nit: the grammar's a bit off, maybe s/to inject/can inject/? attacks. In this case, attackers can claim to own an EID-prefix that is larger than the prefix owned by the ETR. Such attacks can be I'd consider adding ", since the Map-Reply is sent directly from ETR to ITR without a chance for validation by the mapping system". addressed by using LISP-SEC [I-D.ietf-lisp-sec]. The LISP-SEC protocol defines a mechanism for providing origin authentication, integrity, protection, and prevention of 'man-in-the-middle' and nit: s/integrity,/integrity/ (spurious comma) replay attacks by a man-in-the-middle. However, a compromised ETR can overclaim the prefix it owns and successfully register it on its corresponding Map-Server. To mitigate this and as noted in The "can overclaim" is a little weird since we go on to describe the mandatory mitigation against this attack. Maybe something with "could" or a more drastic rewording to "there is a potential attack where a compromised ETR could"? Section 11 [I did not attempt to double-check that the listed changes match the actual differences between RFC 6833 and this document, but do note that it looks like the authors did so at some point since my initial review.] o This document is incorporating the codepoint for the Map-Referral message from the LISP-DDT specification [RFC8111] to indicate that a Map-Server must send the final Map-Referral message when it participates in the LISP-DDT mapping system procedures. It's pretty hard to claim that RFC 8111 is only an informative reference in light of statements like this that a Map-Server needs to do something from it when a flag bit defined by this document is set. Section 12.3 New ACT values can be allocated through IETF review or IESG approval. Four values have already been allocated by [RFC6830], IANA is requested to replace the [RFC6830] reference for this registry with the RFC number assigned to this document and the [RFC6830]. Action nit: comma splice. values references with the RFC number assigned to this document. nit: incomplete sentence (lingering remnants of a previous edit that should just get removed?) Section 12.4 The IANA registry "LISP Canonical Address Format (LCAF) Types" is used for LCAF types. The registry for LCAF types use the Specification Required policy [RFC8126]. Initial values for the "Specification Required" includes review by designated experts. Do we want to give any guidance to the experts for reviewing new submissions? (Similarly for other registries; I note that the LISP Bit Flags section doesn't use the "Specification Required" keyword.) Section 13.1 We don't currently cite RFC 6347 in a way that requires a normative reference. Though I for one wouldn't mind if we made DTLS mandatory somewhere :) Section 13.2 We nominally have a "MUST" for behavior from RFC 1071, that would make it a normative reference, but this is pretty foundational so it seems a bit like overkill.
- [lisp] Benjamin Kaduk's Discuss on draft-ietf-lis… Benjamin Kaduk via Datatracker
- Re: [lisp] Benjamin Kaduk's Discuss on draft-ietf… Albert Cabellos
- Re: [lisp] Benjamin Kaduk's Discuss on draft-ietf… Benjamin Kaduk