One of the topics discussed in https://datatracker.ietf.org/doc/draft-ginsberg-spring-conflict-resolution/ is how to handle inconsistent SRGB advertisements from a given node.
The draft defines one possible solution -from Section 2: " Each range is examined in the order it was advertised. If it does not overlap with any advertised range which preceded it the advertised range is used. If the range overlaps with any preceding range it MUST NOT be used and all ranges advertised after the first encountered overlapping range also MUST NOT be used." This is one instance of a class of solutions which attempt to make use of part of the advertisements even when there is some inconsistency (overlap) in the set of SRGB ranges received. A more complete discussion of this class of solutions can be seen in https://mailarchive.ietf.org/arch/attach/spring/txtk0n56G.txt - many thanx to Bruno for writing this. However, there is an alternative solution which was suggested (notably by Acee Lindem) after the draft was written. This alternative is to ignore the entire set of SRGB advertisements and treat the problematic router as if it were not SR MPLS capable. This alternative was discussed during the presentation in SPRING WG at IETF94 (see https://www.ietf.org/proceedings/94/slides/slides-94-spring-2.pdf slide #3<https://www.ietf.org/proceedings/94/slides/slides-94-spring-2.pdf%20slide%20#3>). It is also discussed in Bruno's post (https://mailarchive.ietf.org/arch/attach/spring/txtk0n56G.txt - see Section 2.2). The basis of the alternative solution is that a correct implementation should never allow inconsistent SRGB ranges to be successfully configured (let alone advertised). So this is not a case of a misconfiguration - it is a case of a defective implementation. It then seems appropriate to put the onus on the originating router to only send valid SRGB advertisements rather than forcing all the receivers to try to "correct" the invalid information in some consistent way. This has a number of advantages: 1. It is by far the simplest to implement 2. It isolates the router which is untrustworthy 3. As the problem can only occur as a result of a defective implementation the behavior of the originating router is unpredictable - it is therefore safer not to use the information It is worth noting that since the invalid advertisement is the result of some sort of defect in the originating router's implementation, it is not safe to assume that the source will actually be using the advertised SRGB in a manner consistent with the selective choice made by the receiving routers. I therefore propose that the above quoted text from https://datatracker.ietf.org/doc/draft-ginsberg-spring-conflict-resolution/ be replaced with the following: "The set of received ranges is examined . If there is overlap between any two of the advertised ranges the entire SRGB set is considered invalid and is ignored. The originating router is considered to be incapable of supporting the SR-MPLS forwarding plane. Routers which receive an SRGB advertisement with overlapping ranges SHOULD report the occurrence." Comments? Les
_______________________________________________ spring mailing list [email protected] https://www.ietf.org/mailman/listinfo/spring
