Hi, I reviewed this document as part of the Security Directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the Security Area Directors. Document authors, document editors, and WG chairs should treat these comments just like any other IETF Last Call comments. Please note also that my expertise in BGP is limited, so feel free to take these comments with a pitch of salt. Review Results: Has Nits Please find my comments below. Yours, Daniel Multicast VPN Fast Upstream Failover draft-ietf-bess-mvpn-fast-failover-11 Abstract This document defines multicast VPN extensions and procedures that allow fast failover for upstream failures, by allowing downstream PEs to take into account the status of Provider-Tunnels (P-tunnels) when selecting the Upstream PE for a VPN multicast flow, and extending BGP MVPN routing so that a C-multicast route can be advertised toward a Standby Upstream PE. Though it might be just a nit, if MVPN designates multicast VPN, it might be clarifying to specify the acronym in the first sentence. This would later make the correlation with BGP MVPN clearer. 1. Introduction In the context of multicast in BGP/MPLS VPNs, it is desirable to provide mechanisms allowing fast recovery of connectivity on different types of failures. This document addresses failures of elements in the provider network that are upstream of PEs connected to VPN sites with receivers. Well I am not familiar with neither BGP nor MPLS. It seems that BGP/MLPS IP VPNS and MPLS/BGP IP VPNs are both used. I am wondering if there is a distinction between the two and a preferred way to designate these VPNs. My understanding is that the VPN-IPv4 characterizes the VPN while MPLS is used by the backbone for the transport. Since the PE are connected to the backbone the VPN-IPv4 needs to be labeled. Section 3 describes local procedures allowing an egress PE (a PE connected to a receiver site) to take into account the status of P-tunnels to determine the Upstream Multicast Hop (UMH) for a given (C-S, C-G). This method does not provide a "fast failover" solution I understand the limitation is due to BGP convergence. when used alone, but can be used together with the mechanism described in Section 4 for a "fast failover" solution. Section 4 describes protocol extensions that can speed up failover by not requiring any multicast VPN routing message exchange at recovery time. Moreover, section 5 describes a "hot leaf standby" mechanism, that uses a combination of these two mechanisms. This approach has similarities with the solution described in [RFC7431] to improve failover times when PIM routing is used in a network given some topology and metric constraints. [...] 3.1.1. mVPN Tunnel Root Tracking A condition to consider that the status of a P-tunnel is up is that the root of the tunnel, as determined in the x-PMSI Tunnel attribute, is reachable through unicast routing tables. In this case, the downstream PE can immediately update its UMH when the reachability condition changes. That is similar to BGP next-hop tracking for VPN routes, except that the address considered is not the BGP next-hop address, but the root address in the x-PMSI Tunnel attribute. If BGP next-hop tracking is done for VPN routes and the root address of a given tunnel happens to be the same as the next-hop address in the BGP A-D Route advertising the tunnel, then checking, in unicast routing tables, whether the tunnel root is reachable, will be unnecessary duplication and thus will not bring any specific benefit. It seems to me that x-PMSI address designates a different interface than the one used by the Tunnel itself. If that is correct, such mechanisms seems to assume that one equipment up on one interface will be up on the other interfaces. I have the impression that a configuration change in a PE may end up in the P-tunnel being down, while the PE still being reachable though the x-PMSI Tunnel attribute. If that is a possible scenario, the current mechanisms may not provide more efficient mechanism than then those of the standard BGP. Similarly, it is assumed the tunnel is either up or down and the determination of not being up if being down. I am not convinced that the two only states. Typically services under DDoS may be down for a small amount of time. While this affects the network, there is not always a clear cut between the PE being up or down. [...] 3.1.6. BFD Discriminator Attribute P-tunnel status may be derived from the status of a multipoint BFD session [RFC8562] whose discriminator is advertised along with an x-PMSI A-D Route. This document defines the format and ways of using a new BGP attribute called the "BFD Discriminator". It is an optional transitive BGP attribute. In Section 7.2, IANA is requested to allocate the codepoint value (TBA2). The format of this attribute is shown in Figure 1. I feel that the sentence "In Section ... TBA2)." should be removed. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BFD Mode | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BFD Discriminator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Optional TLVs ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Format of the BFD Discriminator Attribute Where: BFD Mode field is the one octet long. This specification defines the P2MP BFD Session as value 1 Section 7.2. Reserved field is three octets long, and the value MUST be zeroed on transmission and ignored on receipt. BFD Discriminator field is four octets long. Morin, et al. Expires April 5, 2021 [Page 7] Internet-Draft mVPN Fast Upstream Failover October 2020 Optional TLVs is the optional variable-length field that MAY be used in the BFD Discriminator attribute for future extensions. TLVs MAY be included in a sequential or nested manner. To allow for TLV nesting, it is advised to define a new TLV as a variable- length object. Figure 2 presents the Optional TLV format TLV that consists of: * one octet-long field of TLV 's Type value (Section 7.3) * one octet-long field of the length of the Value field in octets * variable length Value field. The length of a TLV MUST be multiple of four octets. I am wondering why the constraint on the length is not mentioned in the paragraph associated to the field - as opposed to a separate paragraph. [..] 8. Security Considerations This document describes procedures based on [RFC6513] and [RFC6514] and hence shares the security considerations respectively represented in these specifications. This document uses p2mp BFD, as defined in [RFC8562], which, in turn, is based on [RFC5880]. Security considerations relevant to each protocol are discussed in the respective protocol specifications. An implementation that supports this specification MUST use a mechanism to control the maximum number of p2mp BFD sessions that can be active at the same time. At a high level view - or at least my interpretation of it - the document proposes a mechanism based on BFD to detect fault in the path. Upon a fault detection a fail-over operation is instructed using BGP. This rocedure is expected to perform a faster fail-over than traditional BGP convergence on maintaining routing tables. Once the fail over has been performed, BFD is confirms the new path is "legitimate" and works. It seems correct to me that the current protocol relies on BGP / BFD security. That said, having BFD authentication based on MD5 or SHA1 may suggest that stronger primitives be recommended. While this does not concerns the current document, it seems to me that the information might be relayed to routing ADs. What remains unclear to me - and I assume this might be due to my lake or expertise in routing area - is the impact associated to performing a fail-over both on 1) the data plane and 2) the standard BGP way to establish routing tables. Regarding the data plane, I am wondering if fail-over results in a lost of packets for example - I suppose for example that at least the packets in the process of being forwarded might be lost. I believe that providing details on this may be good. If there are any impacts I would like to understand also in which cases the decision to perform a failover operation may result in more harm than the event that has been over-interpreted. An hypothetical scenario could be that the non reception of a BFD packet is interpreted as a PE being down while it may not be correct and the PE might have been simply under stress. A "too fast" fail-over may over interpreted it and perform a fail-over. If such things could happen, an attacker could leverage a micro event to perform network operation that are not negligible. Another way to see that is that an attacker might not have direct access to the control plan, but could use the data plan to generate a stress and sort of control the fail over. It seems to me that some text might be welcome to prevent such cases to happen. This could be guidance for declaring a tunnel down for example. Similarly, it would be good to add some text regarding the interferences with the non-fast forwarding fail over when performed by the standard BGP. Typically, my impression is that the fast fail-over mechanism is a local decision versus the BGP convergence that is more global. As a result, even with more time this two mechanisms may come with different outcomes. One such example to illustrate my purpose could be the following. Note that this is only illustrative of my purpose, and I let you find and pick on ethat is more appropriated. I am thinking of a case where a standby PE is be shared among multiple PEs - supposing this situation could occur. Typically, if PE_1, PE_2 are shared by PE_a, ..., PE_z. In case PE_a and PE_b are down, we expect PE_a to switch to PE_1 and PE_b to switch to PE_2. It seems to me that BGP would end up in such situation while a local decision may end up in PE_a and PE_a to switch to PE_1.