[Cake] de-natting & host fairness

[Sebastian Moeller]

Hi Jonathan,


On September 28, 2016 1:08:04 AM GMT+02:00, Jonathan Morton <chromatix99 at gmail.com> wrote:
>
>> On 26 Sep, 2016, at 06:20, Kevin Darbyshire-Bryant
><kevin at darbyshire-bryant.me.uk> wrote:
>> 
>> Another github user 'tegularius' presented some beautifully crafted
>code that did the lookups in a much neater way.  Originally it too had
>an 'ingress' lookup problem.  This was worked on and I hacked some
>conditional 'denat' options into cake & tc.
>> 
>> For your 'delight' a denat cake
>https://github.com/kdarbyshirebryant/sch_cake/tree/natoptions along
>with a matching tc
>https://github.com/kdarbyshirebryant/tc-adv/tree/denat
>
>As I’m now at the stage of trying to merge this, I’m going to make some
>executive design decisions:
>
>- De-NAT IPv4 packets only.  I think it’s safe to assume that IPv6 NAT
>will be rare, and in any case will typically preserve host
>distinctions.  This eliminates switch blocks in favour of simple if
>blocks.

      Famous last words.... I believe it is a bit premature to predict how IPv6 is going to be rolled out, you might be right, but I believe this to be one of the policy decisions (like ECN) that should be left to the users. Feel free to disagree...


>
>- Don’t bother with the distinction between src-NAT and dst-NAT
>lookups.  The full lookup has to be done anyway and then masked off,
>the use-case for the limited functionality is nebulous, and all we’re
>doing is adding a lot of nasty conditional branches to the fast path.
>
>This in turn reduces the configuration interface for the feature to a
>flag, which I’ll call “nat”.

       What about turning this around and make the option no-deNAT so the default is to do the right thing for most users. Also is there a way to detect, which features a given cake supports? That would be nice for sqm-scripts...


>
> - Jonathan Morton
>
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