On Sat, Sep 29, 2018 at 9:30 AM Dino Farinacci <[email protected]> wrote:
> Thanks Eric for your great comments. Like I said in previous emails, I’ll > address the simple things here and then handle all the security related > stuff separately next week. > > I will do the same with Benjamin’s comments as well. And in his reply, > send a diff with changes that reflect both Eric and Benjamin’s comments. > > > On Sep 27, 2018, at 5:16 AM, Eric Rescorla <[email protected]> wrote: > > > > Rich version of this review at: > > https://mozphab-ietf.devsvcdev.mozaws.net/D4115 > > > > > > IMPORTANT > > S 5.2. > >> s: This is the SMR-invoked bit. This bit is set to 1 when an xTR is > >> sending a Map-Request in response to a received SMR-based Map- > >> Request. > >> > >> m: This is the LISP mobile-node m-bit. This bit is set by xTRs that > >> operate as a mobile node as defined in [I-D.ietf-lisp-mn]. > > > > This would appear to create a normative reference to this document. To > > avoid that, you need to specify how I behave if I receive it but I > > don't implement lisp-mn. > > I am find making it a normative reference but need the lisp-chairs to > comment. I am not sure what the implications of that are. > Me neither. Seems like it could go either way. My only interest is that the protocol be unambiguous. > > S 5.5. > >> is being mapped from a multicast destination EID. > >> > >> 5.5. EID-to-RLOC UDP Map-Reply Message > >> > >> A Map-Reply returns an EID-Prefix with a prefix length that is less > >> than or equal to the EID being requested. The EID being requested > is > > > > How do I behave if I receive an EID-Prefix that is less than any of my > > mappings. So, I might have mappings for 10.1.0.0/16 and 10.2.0.0/16 > > and someone asks me for 10.0.0.0/8? I think I'm still unclear on this point. > Also, when you talk about prefix > > length, I assume you mean the length fo the mask? > > Yes, this is explained later in this section. Was that not helpful?? > I found it a bit confusing. It seems to me like there are two lengths involved here: - The length of the field (4 or 16) - The parts of the field that are significant (i.e., the mask) I had thought that "prefix length" referred to the former, but it seems like here it refers to the latter. > S 5.6. > >> Authentication Data: This is the message digest used from the > output > >> of the MAC algorithm. The entire Map-Register payload is > >> authenticated with this field preset to 0. After the MAC is > >> computed, it is placed in this field. Implementations of this > >> specification MUST include support for HMAC-SHA-1-96 [RFC2404], > >> and support for HMAC-SHA-256-128 [RFC4868] is RECOMMENDED. > > > > What prevents replay attacks here? I'm guessing it's the Map-Version- > > Number, but as I understand it, I can set this to 0. > > Well there are many. The nonce can change for each Map-Register sent. Same > for Map-Version number as well as the key-id. > I think you need to describe the precise process of replay prevention here. > > S 6.1. > >> receives an SMR-based Map-Request and the source is not in the > >> Locator-Set for the stored Map-Cache entry, then the responding Map- > >> Request MUST be sent with an EID destination to the mapping database > >> system. Since the mapping database system is a more secure way to > >> reach an authoritative ETR, it will deliver the Map-Request to the > >> authoritative source of the mapping data. > > > > If I'm understanding this correctly, this allows an ETR to prevent an > > ITR from learning that it is no longer the appropriate ETR for a > > prefix. The way this attack works is that before the topology shift, I > > send SMRs, thus causing Map-Requests, which, because my entry is > > cached, refresh the cache on the ITR past the topology shift. I can > > keep doing this indefinitely. Am I missing something > > Well if the ETR is being spoofed, then there is Map-Request load, but it > won’t corrupt the ITR’s map-cache. The ITR always sends a verifying > Map-Request to the mapping system to get the latest and authenticated > RLOC-set for the mapping. Rate-limiting is necessary so each SMR received > DOES NOT result in a Map-Requerst to the mapping system. > I'm probably just confused here: SMRs go through the mapping system, not directly? If so, I agree that this wont' work. > S 5. > >> \ | UDP Length | UDP Checksum > | > >> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > >> | > | > >> | LISP Message > | > >> | > | > >> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > > > What do these two diagrams correspond to? v4 and v6? This needs > > explanation. > > It is th entire IP packet sent as a LISP control-message. The header > before the diagrams indicate they are UDP packets. > A caption would probably help. > S 5.2. > >> P: This is the probe-bit, which indicates that a Map-Request SHOULD > >> be treated as a Locator reachability probe. The receiver SHOULD > >> respond with a Map-Reply with the probe-bit set, indicating that > >> the Map-Reply is a Locator reachability probe reply, with the > >> nonce copied from the Map-Request. See RLOC-Probing Section 7.1 > >> for more details. > > > > How am I supposed to handle this if I am a Map Server. > > It should be ignored. I will add text to reflect this point. Good point. > > > > > S 5.2. > >> receipt. > >> > >> 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. > > > > Is the xTR supposed to filter this on exiting the site. > > Nope. > Won't this cause problems on ingress to another site? > > S 5.3. > >> 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. > > > > This text here doesn't seem compatible with either of the two cases > > listed in "EID-prefix" above. > > I don’t understand the comment Eric. Maybe because I can’t find the exact > reference to EID-prefix where you think there is a conflict. Please cite > for me. Thanks. > > This does seem to have been assigned to the wrong text. I am referring to: " A Map-Reply returns an EID-Prefix with a prefix length that is less than or equal to the EID being requested. The EID being requested is 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 " versus " EID-Prefix: This prefix 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 length varies and for the LCAF AFI the format is defined in [RFC8060]. When a Map- " This is just the question of whether "prefix length" refers to the field or the significant bits of the field. > > > > S 5.4. > >> 'Nonce' field. > >> > >> Record TTL: This is the time in minutes the recipient of the Map- > >> Reply will store the mapping. If the TTL is 0, the entry MUST be > >> removed from the cache immediately. If the value is 0xffffffff, > >> the recipient can decide locally how long to store the mapping. > > > > Am I supposed to merge this with previous mappings? REmove them? > > No replace it. There is text that says this that is not in the packet > format description section. > OK. > S 8.3. > >> of the mapping database protocols. > >> > >> 8.3. Map-Server Processing > >> > >> Once a Map-Server has EID-Prefixes registered by its client ETRs, it > >> can accept and process Map-Requests for them. > > > > This section is confusing because the introduction says that this > > function is only performed by Map-Resolvers: > > ' > > "The LISP Mapping Service defines two new types of LISP-speaking > > devices: the Map-Resolver, which accepts Map-Requests from an > > Ingress > > Tunnel Router (ITR) and "resolves" the EID-to-RLOC mapping using a > > mapping database; and the Map-Server, which learns authoritative > > EID- > > to-RLOC mappings from an Egress Tunnel Router (ETR) and publishes > > them in a database.” > > The document does cover the operation of a Map-Resolver and a Map-Server. > Some functions are performed only by Map-Resolvers only and other different > functions are performed by Map-Servers only. > > I am not sure what you don’t understand. > Sure: As I understand it, Map Resolvers process Map Requests, and Map Servers do not (that's what the quoted text seems to say). However, this sentence talks about a Map Server processing a Map Request. That's where I am confused. -Ekr > Thanks, > Dino > >
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