netdev - Re: [PATCH net-next v3 0/4] net: ipv6: Improve user experience with multipath routes

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Message-ID: <7a363b93-bf14-9a13-d154-42a26ac06a06@cumulusnetworks.com>
Date:   Mon, 30 Jan 2017 16:53:44 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next v3 0/4] net: ipv6: Improve user experience with
 multipath routes

On 1/30/17 2:16 PM, Stephen Hemminger wrote:
> My fear is that routing daemons already adapt to the funny semantics of multi-path routing in IPv4 vs IPv6
> and therefore any change in semantics or flags risks breaking existing user space.

That is a possibility, but so far the 2 open source code bases I know of have problems with IPv6 mpath.

As I mentioned quagga does not work with IPv6 multipath as is today. 

I just looked at bird. IPv6 mpath support was added in Sept. 2016. It specifically hard codes not accepting RTA_MULTIPATH for IPv6 which I think is an odd choice and clearly coding to quirks as opposed to rtnetlink design. Having never looked at bird code I was able to get it working in < 1 hour. I will contact the patch author about that limitation. That said, the bird implementation needs work when you look at the add/delete/replace/append permutations, so the current code has its problems as well.