netdev - Re: [PATCH RFC net-next 0/7] net/ipv6: Add support for path selection using hash of 5-tuple

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Date:   Sun, 18 Feb 2018 12:40:27 +0200
From:   Or Gerlitz <gerlitz.or@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Ido Schimmel <idosch@...sch.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH RFC net-next 0/7] net/ipv6: Add support for path selection
 using hash of 5-tuple

On Thu, Feb 15, 2018 at 12:56 AM, David Ahern <dsahern@...il.com> wrote:
> On 2/14/18 3:45 PM, Or Gerlitz wrote:

>> how the various systems you are dealing with do with traffic that involves
>> ipv6 extension headers? what about environments with GRE? in ipv4 GRE
>> fabrics are just broken for ECMP, in ipv6 they can fly with flow label but
>> will crash again with L4 hash.

> If you like your ecmp hash algorithm, you can keep your ecmp hash algorithm.

> This gives users a choice; it is not a requirement to move from L3 only
> to L4. Further, this makes IPv6 on par with IPv4 with a choice between
> L3 and L4 and allows users to decide what works best for them.

Looking in the code for tunnels e.g in the vxlan xmit path (but I
believe this is the case for
other UDP tunnels as well), a call is made to generate the source udp
port as the hash of
the overlay tuple regardless if we are on v4/v6. Next, when it comes
to ipv6, the kernel
computes the  flow label which effectively takes into account the inner header.