netdev - Re: [PATCH net-next v3] net: ipv4: add support for ECMP hash policy choice

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Date:   Tue, 14 Mar 2017 08:55:02 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        roopa@...ulusnetworks.com, dsa@...ulusnetworks.com,
        jkbs@...hat.com, edumazet@...gle.com, pch@...bogen.com
Subject: Re: [PATCH net-next v3] net: ipv4: add support for ECMP hash policy
 choice

On Tue, 14 Mar 2017 17:36:15 +0200
Nikolay Aleksandrov <nikolay@...ulusnetworks.com> wrote:

> This patch adds support for ECMP hash policy choice via a new sysctl
> called fib_multipath_hash_policy and also adds support for L4 hashes.
> The current values for fib_multipath_hash_policy are:
>  0 - layer 3 (default)
>  1 - layer 4
> If there's an skb hash already set and it matches the chosen policy then it
> will be used instead of being calculated (currently only for L4).
> In L3 mode we always calculate the hash due to the ICMP error special
> case, the flow dissector's field consistentification should handle the
> address order thus we can remove the address reversals.
> 
> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>

It is good to see ECMP come back from the grave.
Linux used to support it long ago but was abandoned after it was unstable
and removed from iproute2 in 2012.

The old API was through route attributes which makes more sense than
doing it with sysctl. It makes more sense to use netlink instead.
Therefore please go back and do something like the old API rather than doing it through
sysctl.