The MPLS WG Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] [mpls] LDP P2MP Extensions : loops ?
Hi, Two recent drafts have recently been submitted and propose extensions to LDP to setup multipoint MPLS trees (P2MP and/or MP2MP). The question I have is about the impact of transient loops that may occur because of e.g. IGP inconsistencies, or because of the delay needed to update label switching tables. As you know, IP multicast forwarding implies systematically doing an RPF check against a packet source address, and dropping packets arriving on an interface different from the one that would be used to reach the source, thus effectively preventing exponential growth of the traffic on a loop (always only one upstream interface). With proposed LDP extensions for P2MP, its not hard to see how this RPF-check is "emulated" : impose a break-before-make procedure (labe withdraw THEN label map). But for MP2MP, it seems to me that nothing like this can be done : you'll have to accept traffic on many interfaces, and the label hides the packet source so no RPF-like check can be done, except by looking inside the labeled packet (!...). Thus, it looks to me that exponential-traffic loops can occur during IGP reconvergence in the MP2MP case. So I'd like to know if this problem was considered during the design of the MP2MP solution described in draft-wijnands-mpls-ldp-mcast-ext-00 ? -Thomas _______________________________________________ mpls mailing list mpls@lists.ietf.org https://www1.ietf.org/mailman/listinfo/mpls |
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