netdev - Re: Query regarding IPV6 multipath (ECMP) routes in Linux

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Message-ID: <c025fe9d-bcf4-1683-40fe-baa2a7742dbb@gmail.com>
Date:   Mon, 15 Apr 2019 09:28:27 -0600
From:   David Ahern <dsahern@...il.com>
To:     Preethi Ramachandra <preethir@...iper.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Silambu Chelvan M <silambu@...iper.net>,
        Yogesh Ankolekar <ayogesh@...iper.net>
Subject: Re: Query regarding IPV6 multipath (ECMP) routes in Linux

On 4/15/19 3:32 AM, Preethi Ramachandra wrote:
> 
> In IPV4 a single route is added with multipath nexthops. However, in IPV6 , multipath routes are added as separate single routes with each multipath NH. I wanted to understand why is this behaviour change in Linux for IPV6 multipath routes. Why wasn’t same IPV4 approach followed in this case?

IPv4 support for multipath existed first. IPv6 is fairly new.

If you move forward a few kernel versions there is a bit more
consistency between IPv4 and IPv6, but still there are annoying
differences and limitations due to IPv6 code guessing whether to make
gateway routes multipath or not (see rt6_qualify_for_ecmp).