[CFT] new tables for ipfw

[Luigi Rizzo]

On Thu, Aug 14, 2014 at 11:57 AM, Alexander V. Chernikov <
melifaro at yandex-team.ru> wrote:

>  On 14.08.2014 13:23, Luigi Rizzo wrote:
>
>
>
>
> On Wed, Aug 13, 2014 at 10:11 PM, Alexander V. Chernikov <
> melifaro at yandex-team.ru> wrote:
>
>> Hello list.
>>
>> I've been hacking ipfw for a while and It seems there is something ready
>> to test/review in projects/ipfw branch.
>>
>
>  ​this is a fantastic piece of work, thanks for doing it and for
> integrating the feedback.
>  ​
> I have some detailed feedback that will send you privately,
>  but just a curiosity:
>
>   ​...​
>>
>> Some examples (see ipfw(8) manual page for the description):
>>
>>
>> ​...
>>
>>
>>   ipfw table mi_test create type cidr algo "cidr:hash masks=/30,/64"
>>
>
>  ​why do we need to specify mask lengths in the above​ ?
>
> Well, since we're hashing IP we have to know mask to cut host bits in
> advance.
> (And the real reason is that I'm too lazy to implement hierarchical
> matching (check /32, then /31, then /30) like how, for example,
>

​oh well for that we should use cidr:radix

Research results have never shown a strong superiority of
hierarchical hash tables over good radix implementations,
and in those cases one usually adopts partial prefix
expansion so you only have, say, masks that are a
multiple of 2..8 bits so you only need a small number of
hash lookups.

​cheers
luigi​