Hi Sasha, thank you for your comments; much appreciated. Please find my notes below tagged GIM>>.
Regards, Greg On Mon, Jul 21, 2025 at 3:48 PM Alexander Vainshtein < [email protected]> wrote: > Hi all, > > I have asked the following question about the Applicability of Bidirectional > Forwarding Detection (BFD) for Multi-point Networks in Virtual Router > Redundancy Protocol (VRRP) draft > <https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-vrrp-p2mp-bfd-12> > during the RTGWG session in Madrid today: > > > > *Q1*: What happens if one of the VRRP routers on the LAN in > question does not support BFD for Multi-point network? > > My guess (FWIW) that such routers would receive P2MP BFD > packets at high rate and trap them to the CPU – and then to generate > > Destination Unreachable – Port Unreachable IGMP messages… > GIM>> AFAIK, routers are not expected to generate ICMP error message Port Unreachable. If that is the case, VRRP that does not support RFC 8562 would not be able to detect the failure of the Active Router and, likely, would not become the next Active Router. > > > *Q2*: What happens to the hosts on the LAN in question if the L2 > switches implementing this LAN flood multi-point BFD packets? > > My guess is that these hosts would experience high load receiving these > packets at presumably high rate. > GIM>> Would these L2 switches be flooding VRRP messages? If that is the case, would the hosts on the LAN segment be flooded by VRRP messages being transmistted at 1 decasecond interval without BFD being used for fast VRRP convergence? As proposed in draft-ietf-rtgwg-vrrp-p2mp-bfd <https://datatracker.ietf.org/doc/draft-ietf-rtgwg-vrrp-p2mp-bfd/>, BFD Control messages source MAC address follows rules set in Section 7.3 RFC 9568 <https://datatracker.ietf.org/doc/rfc9568/> and transmitted to "VRRP IPvX multicast group", as specified in Section 7.2 of RFC 9568. Am I missing something here? > > > I have also clarified that, to the best of my understanding, the purpose > of using BFD for detection of the Active router down is to replace fast > advertisement of VRRP Advertisement messages with something else. > GIM>> Indeed, that was our motivation. > With this understanding, using some form of 1-hop IP BFD (RFC 5881) looks > obviously preferable to using P2MP BFD flavors. > GIM>> We believe that using Asynchronous BFD (RFFC 5881) introduces significant overhead (number of BFD Control messages increases times 2 power of N, where N is number of Backup Routers in the given VR ID, and unnecessary control state on the Active Router per a Backup Router that monitors the state of the Active Router) compared with using the Demand BFD mode per RFC 8562. > > > Regards, > > Sasha > > > > > *Disclaimer* > > This e-mail together with any attachments may contain information of > Ribbon Communications Inc. and its Affiliates that is confidential and/or > proprietary for the sole use of the intended recipient. Any review, > disclosure, reliance or distribution by others or forwarding without > express permission is strictly prohibited. If you are not the intended > recipient, please notify the sender immediately and then delete all copies, > including any attachments. >
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