Hi Jeff, The situation when Control Plane does not understand what the Forwarding pane doing is a bug. Yes, RTO in TCP helps to find a work-around for this bug. And yes, Anycast is typically absent inside DC – it does not create the problem in the DC environment.
But the same LINUX is used outside DC. RTO Flow Label change here would create even more problems if Anycast would happen on the traffic path (not much predictable for client). Do we need separate LINUX distribution for DC and separate distribution for other environments? Or should we rely on the proper non-default configuration for different environments? (Admin should not forget to change) What if Anycast would become needed in DC? RTO flow label recalculation is mutually exclusive with Anycast on the traffic part. What is more valuable for the public? IMHO: It is better to fight the problem of such type of a bug with iOAM than to cancel Anycast. IMHO: It is better to have Flow Label recalculation on RTO as “off” by default. DC Admin has the higher qualification to activate it in a controlled environment than every client worldwide that should not forget to disable it. Eduard From: Jeff Tantsura [mailto:[email protected]] Sent: Monday, August 2, 2021 6:56 AM To: Vasilenko Eduard <[email protected]> Cc: [email protected]; routing WG <[email protected]> Subject: Re: Self-healing Networking with Flow Label Eduard, The issue is present not in link/device case, if well implemented - fast rehash takes care of updating forwarding within a number of ms. The problem is with “gray” failures, when the link in question is UP from routing/forwarding prospective but drops traffic (mostly occasionally and when a HW bug occurs has a distinct flow attributes). In many large DC fabrics, the majority of the traffic is east-west, between end-points that aren’t anycast. In such deployments - the solution solves issues rather elegantly and without any interventions from the operator. The issues/side effects are well understood and will be documented. The best way to receive RTGWG emails is well… to subscribe to RTGWG ;-) Cheers, Jeff On Aug 1, 2021, at 09:47, Vasilenko Eduard <[email protected]<mailto:[email protected]>> wrote: Hi Alexander, Have I understood your presentation right? The client SHOULD change IPv6 flow label after SYN RTO to have a chance to be moved to the working path inside DC fabric (if DC fabric supports flow label for hash calculation) But at the same time The client SHOULD NOT change the IPv6 flow label after SYN RTO to avoid being switched to a different TCP proxy engine. Looks like a deadlock, especially if both things should happen for the same traffic: it should reach DC fabric and it should be hash load-balanced between different TCP proxy engines (or applications) inside DC Fabric. I see one bad solution (“Disable Flow Label”): Routers up to TCP proxy engine SHOULD be configured not to use flow label (by the way these are all routers on the Internet), TCP flow engines SHOULD be outside of the DC Fabric (CLOS) – probably in front of it. Routers/Switches inside DC Fabric SHOULD use flow labels. I see another bad solution (“Disable Anycast”): Disable anycast on routers in principle, use only stateful LB. It has been commented in the chat that Anycast is not possible in principle for stateful connection. It is too general a statement. Anycast is just not compatible with Flow Label. It is not a problem for IPv4 anycast even if the connection is stateful (TCP) because 5-tuple for hash would not change. Hence, IPv6 anycast has become dead at the time when Flow Label change has been added in LINUX for active TCP session. Among 3 thins: - Anycast - Flow Label load balancing (basic Flow Label functionality) - Flow Label change on the active session for application to be more active in new path search You have to choose which one to kill – all 3 are not compatible with each other at the same. I vote to disable Flow Label change in LINUX. Then wait till the network would fix itself. We have so many fancy TE tools our days. A broken link or a broken node could be excluded from routing for 50ms. PS: I am not subscribed to the RTGWG alias, please keep me on a copy of this thread. <image001.png> Best Regards Eduard Vasilenko Senior Architect Europe Standardization & Industry Development Department Tel: +7(985) 910-1105, +7(916) 800-5506 _______________________________________________ rtgwg mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/rtgwg
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