Re: [v6ops] Flow Label Load Balancing

Alexander Azimov <a.e.azimov@gmail.com> Tue, 24 November 2020 19:28 UTC

Return-Path: <a.e.azimov@gmail.com>
X-Original-To: v6ops@ietfa.amsl.com
Delivered-To: v6ops@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 2EC9B3A1836; Tue, 24 Nov 2020 11:28:41 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.097
X-Spam-Level:
X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EfVz3TBW_-Bq; Tue, 24 Nov 2020 11:28:39 -0800 (PST)
Received: from mail-ot1-x329.google.com (mail-ot1-x329.google.com [IPv6:2607:f8b0:4864:20::329]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 503FD3A0E2A; Tue, 24 Nov 2020 11:28:33 -0800 (PST)
Received: by mail-ot1-x329.google.com with SMTP id n11so20453734ota.2; Tue, 24 Nov 2020 11:28:33 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=d2Xk5BepEbljT/Z1DDKDV6TQTWWdAO2+ntkk96OgV6Q=; b=Ny9BF7iUIP3MYWQ1UBgx6UE4q4FXPMsuuVnlVV9p3l1+Mz1f0ySXLW4aeRLzUdjEpU WK/0/E6p61UvOIN8OrHq1My1YXyBVkV0hlztYZO8YsGishtE8XQnrfxY6pm83ZP98owO r9Sm5Cl1fnxR/cvuEktOvCS29S+ih/R/NLQJnVBe5Ae/SDYGMuJ+dHJ1GLf3IO2NX8kT Ly+ga4UhJEiAkiXW77nQrvC86UQvP8KJpA1lsL0kU9H3OsCgzgmXo3ydBHMV76bbBOVf mqgn3yH3KpLfp1yrsNs6MZSh5XIihkZYz9A/j4Rw3PaQyOF8aXmSV48U/dRwNtC5uu8E M0fQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=d2Xk5BepEbljT/Z1DDKDV6TQTWWdAO2+ntkk96OgV6Q=; b=hhzcYOFA8+wRpzuXEapTCOB5VKZB1oy8XQVcr8Pgt7gE89OJ0UJJG0cPa0H1YhWy4n 7OA5IWnbh9cv0I4CIl6cf6kbdUdiYCE7XU9wAZ7d0WV0uj+OJkQX6oOttQ7SIqgjfZa7 sWxDiMTeAZVKWkR9Jt8qhX5RJFZpuh0ys0z5Fh6wEuVHHYvJ9GNod25fx3gzpBwrZLEQ eEcZ1VTQU1bYxrRqlKe6Y/YurmX5p/2+XBRfJGCb1M6QFEzzPfeggX1rYVOtzVFbMdWM J7IvxPS+ahRBwzd/J5dBmgJMQSXW/NdFvhqNrntuKNz5bkf084U1z7aEibXi/39lrbTS eeVQ==
X-Gm-Message-State: AOAM531BzvcM+EREv9CF30SNTX05bT+V3NgjpIk5zNx8G1MrAsWHCOXG prDg3MFqQiMXnoHe8kJuwLcLM4Vwj/69XnuLlBioeLYlN+M=
X-Google-Smtp-Source: ABdhPJwpCkE7Wo9kQRbR/wp1Wr+ihnnRJ5+6pRxlD+/U08o7Gwg896MomdUurN34kHYD2hWwb2a6bX/kH9pay7nM5Ug=
X-Received: by 2002:a9d:4c92:: with SMTP id m18mr108833otf.248.1606246112526; Tue, 24 Nov 2020 11:28:32 -0800 (PST)
MIME-Version: 1.0
References: <CAEGSd=DY8t8Skor+b6LSopzecoUUzUZhti9s0kdooLZGxPEt+w@mail.gmail.com> <d29042a7-742b-a445-cf60-2773e5515ae5@gont.com.ar>
In-Reply-To: <d29042a7-742b-a445-cf60-2773e5515ae5@gont.com.ar>
From: Alexander Azimov <a.e.azimov@gmail.com>
Date: Tue, 24 Nov 2020 22:28:21 +0300
Message-ID: <CAEGSd=AB5DMopq5Hc0ydZwP+xQuwxNBHuFSpCPcZvnaZbJfRoQ@mail.gmail.com>
To: Fernando Gont <fernando@gont.com.ar>
Cc: tcpm <tcpm@ietf.org>, IPv6 Operations <v6ops@ietf.org>
Content-Type: multipart/alternative; boundary="000000000000f5860905b4df50ad"
Archived-At: <https://mailarchive.ietf.org/arch/msg/v6ops/jEAHF56MdKz9kd9aczWNS_vzqnk>
Subject: Re: [v6ops] Flow Label Load Balancing
X-BeenThere: v6ops@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: v6ops discussion list <v6ops.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/v6ops>, <mailto:v6ops-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/v6ops/>
List-Post: <mailto:v6ops@ietf.org>
List-Help: <mailto:v6ops-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/v6ops>, <mailto:v6ops-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 24 Nov 2020 19:28:41 -0000

Hi Fernando,

Stating that FL change during TCP session lifetime is a bug - is a bit
harsh.

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>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 || fgont@si6networks.com
> PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
>
>
>
>

-- 
Best regards,
Alexander Azimov