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

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Message-ID: <9fa3779b-7dba-3819-02d0-2009101a81fb@gmail.com>
Date:   Wed, 14 Feb 2018 15:56:25 -0700
From:   David Ahern <dsahern@...il.com>
To:     Or Gerlitz <gerlitz.or@...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 2/14/18 3:45 PM, Or Gerlitz wrote:
> On Tue, Feb 13, 2018 at 5:21 PM, David Ahern <dsahern@...il.com> wrote:
>> On 2/13/18 5:42 AM, Ido Schimmel wrote:
>>> On Tue, Feb 13, 2018 at 01:03:14PM +0200, Or Gerlitz wrote:
>>>> On Tue, Feb 13, 2018 at 2:05 AM, David Ahern <dsahern@...il.com> wrote:
>>>>> Hardware supports multipath selection using the standard L4 5-tuple
>>>>> instead of just L3 and the flow label. In addition, some network
>>>>> operators prefer IPv6 path selection to use the 5-tuple.
>>>>
>>>> The HW supports using flow label and AFAIK that is the preferred approach
>>>> by the community (?)
>>>>
>>>>> To that end, add support to IPv6 for multipath hash policy
>>>>
>>>> so a question comes up if/what are the disadvantaged
>>>> to support 5-tuple. E.g Tom was commenting that such DPI is problematic
>>>> when multiple IPv6 header extensions are used.
>>
>> Pros and cons to both approaches (L3 only or L4). We (Cumulus Networks)
>> use L4 5-tuple hash for both IPv4 and IPv6. When I asked around various
>> experts all of them gave me a puzzled look as to why I was asking the
>> question. Basically, the unanimous response was of course it is an L4 hash.
> 
> 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.