Re: [v6ops] Flow Label Load Balancing
Tom Herbert <tom@herbertland.com> Tue, 24 November 2020 20:00 UTC
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From: Tom Herbert <tom@herbertland.com>
Date: Tue, 24 Nov 2020 12:59:46 -0700
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To: Brian E Carpenter <brian.e.carpenter@gmail.com>
Cc: Alexander Azimov <a.e.azimov@gmail.com>, Fernando Gont <fernando@gont.com.ar>, IPv6 Operations <v6ops@ietf.org>, tcpm <tcpm@ietf.org>
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Subject: Re: [v6ops] Flow Label Load Balancing
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On Tue, Nov 24, 2020 at 12:46 PM Brian E Carpenter <brian.e.carpenter@gmail.com> wrote: > > On 25-Nov-20 08:28, Alexander Azimov wrote: > > Hi Fernando, > > > > Stating that FL change during TCP session lifetime is a bug - is a bit harsh. > > It's a bug. It definitely breaks server load balancing, which in practice is more important than en route load balancing, because it will probably switch your session to a different server. (OK, I know that there are mechanisms sometimes for rescuing a session that has unexpectedly moved from one server to another, but in general it's a fail.) > Brian, IMO it's not that this breaks server load balancing, it's really that server load balancing and other stateful mechanisms break multipath, multihoming, and adaptive routing! In any case, I would agree that in the current Internet it is pragmatic in the current Internet to aim for consistent routing as the default. Tom > I assume you have read https://tools.ietf.org/html/rfc7098 > > Regards > Brian > > > > > It is a fantastic idea to change the FL value if RTO or SYN_RTO happens in a controlled environment. > > These are very specific TCP timeouts, that provide enough guarantee that there will be no out-of-order packets, though your packets will reach the destination even in case of an outage inside your network. Zero influence on your services in case of the network outage - doesn't sound like a bug for me. > > > > The problem is with the current Linux (though I haven't checked other OSes) defaults. Specifically, with the default behavior after RTO event. > > > > вт, 24 нояб. 2020 г. в 22:06, Fernando Gont <fernando@gont.com.ar <mailto:fernando@gont.com.ar>>: > > > > On 19/11/20 07:48, Alexander Azimov wrote: > > > Dear colleagues, > > > > > > I have added in the cc both v6op and tcpm for a reason and let me > > > explain why. > > > > > > It's clear that we are moving forward with load balancing that uses flow > > > label (FL). And the pressure will increase with SRv6 adoption. But at > > > the moment wide adoption of FL-based load-balancing may create > > > significant issues for TCP Anycast services. > > > > > > RFC6437 suggests putting hash from 5-tuple into FL value. And as far as > > > I know, there is no document that updates this behavior. This > > > description is perfectly fine, but what is implemented in the Linux > > > kernel is different: FL is carrying hash from 5-tuple with an additional > > > seed, and this seed is randomly changed after each RTO/SYN_RTO event. > > > > Changing the FL upon RTO is a bug. > > > > I guess/assume that when you say SYN-RTO, you really mean "user > > timeout", rather than RTO. If you don't, then that's also a bug. > > If you do, I fail to understand what's the reason for wanting the FL to > > change in that case, because as a result of port randomization, it 0s > > unlikely that the same four-tuple is employed for the next connection retry. > > > > > > > Here are related patches: > > > > > > * https://lore.kernel.org/netdev/alpine.DEB.2.02.1407012100290.20628@tomh.mtv.corp.google.com/ > > > * https://lore.kernel.org/netdev/1438124526-2129341-1-git-send-email-tom@herbertland.com/ > > > * https://lore.kernel.org/netdev/20160928020337.3057238-1-brakmo@fb.com/ > > > > > > > > > This is a great thing by the way because in the data center > > > environment with multiple equal paths it gives a way to have > > > pseudo-multipath TCP which jumps between paths in case of an outage. > > > There might be interest to writedown an informational document for this. > > > > That's a bad idea, since specs-wise the Flow-Label is not guaranteed to > > remain unchanged from source to destination. If you want to ahve > > multiple paths, then you should implement that in routing. > > > > > > > > > I wonder what you think is a proper solution: > > > > > > * Making FL related RTO change as knob instead of default behavior; > > > * Adding negotiation behavior in TCP; > > > * Something else? > > > > Just make the FL a function of the connection "identifier". And keeo it > > constant for the lifetime of that conenction. > > > > Thanks, > > -- > > Fernando Gont > > e-mail: fernando@gont.com.ar <mailto:fernando@gont.com.ar> || fgont@si6networks.com <mailto:fgont@si6networks.com> > > PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1 > > > > > > > > > > > > -- > > Best regards, > > Alexander Azimov > > > > _______________________________________________ > > v6ops mailing list > > v6ops@ietf.org > > https://www.ietf.org/mailman/listinfo/v6ops > > > > _______________________________________________ > v6ops mailing list > v6ops@ietf.org > https://www.ietf.org/mailman/listinfo/v6ops
- [v6ops] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Joel M. Halpern
- Re: [v6ops] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Joel M. Halpern
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] [tcpm] Flow Label Load Balancing Yuchung Cheng
- Re: [v6ops] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] Flow Label Load Balancing Mark Smith
- Re: [v6ops] Flow Label Load Balancing Joseph Touch
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] Flow Label Load Balancing Mark Smith
- Re: [v6ops] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] [tcpm] Flow Label Load Balancing Alexander Azimov
- Re: [v6ops] [tcpm] Flow Label Load Balancing Michael Tuexen
- Re: [v6ops] [tcpm] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] [tcpm] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] [tcpm] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] [tcpm] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] [tcpm] Flow Label Load Balancing Erik Kline
- Re: [v6ops] [tcpm] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] [tcpm] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] [tcpm] Flow Label Load Balancing Fernando Gont
- Re: [v6ops] [tcpm] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] [tcpm] Flow Label Load Balancing Brian E Carpenter
- Re: [v6ops] [tcpm] Flow Label Load Balancing Tom Herbert
- Re: [v6ops] [tcpm] Flow Label Load Balancing Fernando Gont