Hi Robert, From: Robert Raszuk <rob...@raszuk.net> Date: Tuesday, October 12, 2021 at 4:27 PM To: Acee Lindem <a...@cisco.com> Cc: "Acee Lindem (acee)" <acee=40cisco....@dmarc.ietf.org>, "lsr@ietf.org" <lsr@ietf.org> Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and OSPF Extension for Event Notification"
Hi, > What are you worried about? Scaling? Yes if we were to establish BFD sessions between say 1000 PEs then each PE would need to handle such a number of BFD sessions (as long as at least one prefix comes with given PE's next hop). As you know those would be multihop BFD sessions running on REs/RPs which often are not hardware accelerated as p2p BFD with line card offloading. Ok – I think BFD should be implement in the data plane like it is for SDWAN tunnels (at least on the data center routers). But that is a different discussion. Then honestly it is not obvious if in such case BFD adds real value as compared to ICMP or UDP next hop periodic probing (as part of next hop periodic reachability validation). Usage of BFD with protocols is standard. Alternatives would work as well. You should put your BGP solution out there as well. Thanks, Acee Thx, Robert On Tue, Oct 12, 2021 at 10:15 PM Acee Lindem (acee) <a...@cisco.com<mailto:a...@cisco.com>> wrote: Speaking as WG member: Hi Robert, I think you are envisioning a use case beyond section 3 in https://datatracker.ietf.org/doc/draft-wang-lsr-prefix-unreachable-annoucement/ where the unreachable prefix is the loopback of PE. If not, I don’t see your concern with BFD between the PEs. What are you worried about? Scaling? In any case, we both agree that flooding this unreachability information to everyone in the IGP domain is possibly not the best way to solve the problem. Thanks, Acee From: Lsr <lsr-boun...@ietf.org<mailto:lsr-boun...@ietf.org>> on behalf of Robert Raszuk <rob...@raszuk.net<mailto:rob...@raszuk.net>> Date: Tuesday, October 12, 2021 at 3:52 PM To: "Acee Lindem (acee)" <acee=40cisco....@dmarc.ietf.org<mailto:40cisco....@dmarc.ietf.org>> Cc: "lsr@ietf.org<mailto:lsr@ietf.org>" <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and OSPF Extension for Event Notification" Hi Acee, I would like to make a comment on your point #1. You said: "Is this a problem that needs to be solved in the IGPs? The use case offered in both drafts is signaling unreachability of a BGP peer. Could this better solved with a different mechanism (e.g., BFD)..." That is not a very precise statement - simply due to the fact that to signal anything in any solution requires a peer to detect giben network event. In both cases such an event will likely be detected using BFD (if we are talking about unreachability of a BGP or IGP peer). Neither of the drafts mentioned here replaces local BFD detection. I do infer from your message that what was meant to be said was an alternative to support BFD sessions across areas/levels for example between PEs. Clearly that would get very ugly very quickly. However IMO the natural signalling in this case would be to use BGP itself. Here are the few reasons: * detection time will be the same for IGP or BGP * only those network elements which keep "interesting" state will be notified * speed of withdraw can be argued to be as fast as IGP flooding especially considering hierarchical IGP design * withdraws can be easily aggregated (when we loose PE single prefix can be used to remove all paths advertised by given PE) * withdraws can be injected as the next hop /32 or /128 prefixes and remote next hop validation can be set not to consider less specific routes to resolve next hops (in any case due to MPLS data plane host routes are used in many networks today to resolve BGP service routes to LSPs in spite of efforts to make this more scalable). Only when we prove that BGP based solutions are not sufficient we could/should explore moving such signalling to IGPs. Kind regards, R. On Tue, Oct 12, 2021 at 9:06 PM Acee Lindem (acee) <acee=40cisco....@dmarc.ietf.org<mailto:40cisco....@dmarc.ietf.org>> wrote: Speaking as WG Chairs: The authors of “Prefix Unreachable Announcement” have requested an adoption. The crux of the draft is to signal unreachability of a prefix across OSPF or IS-IS areas when area summarization is employed and prefix is summarised. We also have “IS-IS and OSPF Extension for Event Notification” which can be used to address the same use case. The drafts take radically different approaches to the problem and the authors of both drafts do not wish to converge on the other draft’s method so it is understandable that merging the drafts really isn’t an option. Before an adoption call for either draft, I’d like to ask the WG: 1. Is this a problem that needs to be solved in the IGPs? The use case offered in both drafts is signaling unreachability of a BGP peer. Could this better solved with a different mechanism (e.g., BFD) rather than flooding this negative reachability information across the entire IGP domain? 2. Assuming we do want to take on negative advertisement in the IGP, what are the technical merits and/or detriments of the two approaches? We’ll reserve any further discussion to “WG member” comments on the two approaches. Thanks, Acee and Chris _______________________________________________ Lsr mailing list Lsr@ietf.org<mailto:Lsr@ietf.org> https://www.ietf.org/mailman/listinfo/lsr
_______________________________________________ Lsr mailing list Lsr@ietf.org https://www.ietf.org/mailman/listinfo/lsr
