netdev - Re: Per-flow IPv4 ECMP

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Message-ID: <20150929143532.7242b0ca@pch.odense.ordbogen.com>
Date:	Tue, 29 Sep 2015 14:35:32 +0200
From:	Peter Nørlund <pch@...bogen.com>
To:	roopa <roopa@...ulusnetworks.com>
Cc:	Matthew Dupre <Matthew.Dupre@...aswitch.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Per-flow IPv4 ECMP

On Mon, 28 Sep 2015 06:48:09 -0700
roopa <roopa@...ulusnetworks.com> wrote:

> On 9/28/15, 1:57 AM, Matthew Dupre wrote:
> > Hi,
> >
> > I'm interested in the Linux kernel's support for per-flow IPv4 ECMP
> > (i.e. consistent path selection based on a hash of the connection
> > tuple).  I'd been led to believe[1] that this depended on the route
> > cache, which was removed in 3.6.
> >
> > However, I tested a route with multiple next hops on a 3.10 and
> > 3.13 kernel, and ECMP was per-flow!  Obviously I'm pleased that
> > this was the case, but I'd like to understand why this is
> > supported, and whether I can rely on it in future.
> >
> > Could anyone give me a little clarification on whether this is now
> > supported by some means other than the route cache, and whether
> > that support is intended to be continued?
> >
> This is being worked on currently by Peter Nørlund
> https://lwn.net/Articles/657431/

Hi,

AFAIK if you create a socket on the machine having the multipath route,
each socket will seemingly be mapped to particular path, and it will
behave as per-flow. But if you use the machine as a router, each packet
is forwarded independently, potentially hitting different paths each
time.

Best Regards
  Peter Nørlund
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