Date: Sat, 3 May 2014 19:19:24 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: bycn82 <bycn82@gmail.com> Cc: "freebsd-ipfw@freebsd.org" <freebsd-ipfw@freebsd.org>, Freddie Cash <fjwcash@gmail.com> Subject: Re: feature of `packet per second` Message-ID: <CA%2BhQ2%2BgXC9uNdtH1VCGa%2Bs1dPNWjErC9qfgXmEnfQ4SQ6Rnz_g@mail.gmail.com> In-Reply-To: <5364E097.9020106@gmail.com> References: <5360F1F4.9060808@gmail.com> <5361105C.1040203@freebsd.org> <53611738.8010103@gmail.com> <CAOjFWZ4zRUmcjG-r--OqoGEWcSZoWhtTykgAAHzCjoEWsMVS9g@mail.gmail.com> <53611EB1.4000406@gmail.com> <CA%2BhQ2%2BhjjS=AXVdnaEdFOKY1DqiLuX9iP0gy3wo6FbwnEdq_Qw@mail.gmail.com> <5364E097.9020106@gmail.com>
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On Sat, May 3, 2014 at 2:27 PM, bycn82 <bycn82@gmail.com> wrote:
> On 5/2/14 16:59, Luigi Rizzo wrote:
>
>
>
>
> On Wed, Apr 30, 2014 at 6:02 PM, bycn82 <bycn82@gmail.com> wrote:
>
>>
>>> fjwcash@gmail.com <mailto:fjwcash@gmail.com>
>>>
>> Thanks for your reply, and it is good to know the sysctl for ICMP.
>>
>> finally it works.I just added a new `action` in firewall and it is calle=
d
>> `pps`, that means it can be generic purpose while the
>> net.inet.icmp.icmplim is only for ICMP traffic.
>>
>> the usage will be like below
>>
>> root@F10:/usr/src/sbin/ipfw # .*/ipfw add pps 1 icmp from any to any*
>> 00100 pps 1 icmp from any to any
>> root@F10:/usr/src/sbin/ipfw # ./ipfw show
>> 00100 9 540 pps 1 icmp from any to any
>> 65535 13319 1958894 allow ip from any to any
>> root@F10:/usr/src/sbin/ipfw #
>>
>>
> =E2=80=8Bhi,
> as julian said it would be great if you would like to share your code
> so we can integrate it in future ipfw releases.
> Once again citing Julian, dummynet is a bit of a superset of pps but
> not exactly, so i see value in the additional feature.
>
> One thing =E2=80=8Bto keep in mind in the implementation:
>
> the burst size used for limiting is an important parameter that
> everyone forgets. 1 pps is basically "don't bother me".
> 1000 pps could be "1000 packets every fixed 1-sec interval"
> or "1 packet every ms" or (this is more difficult)
> "20 pkt in the last 50ms interval".
>
> If i were to implement the feature i would add two parameters
> (burst, I_max) with reasonable defaults and compute the internal
> interval and max_count as follows
>
> if (burst > max_pps * I_max)
> burst =3D max_pps * I_max; // make sure it is not too large
> else if (burst < max_pps / HZ)
> burst =3D max_pps * HZ; // nor too small
> max_count =3D max_pps / burst;
> interval =3D HZ * burst / max_pps;
> count =3D 0; // actual counter
>
> then add { max_count, interval, timestamp, count } to the rule
> descriptor.
> On incoming packets:
>
> if (ticks >=3D r->interval + r->timestamp) {
> r->timestamp =3D r->ticks;
> r->count =3D 1;
> return ACCEPT;
> }
> if (r->count > r->max_count)
> return DENY;
> r->count++;
> return ACCEPT;
>
> cheers
> luigi
>
> Hi Luigi,
> You are right, it will be more generic if provide two parameters as you
> described,
> But this PPS feature should not be used to control the traffic rate, the
> dummynet you provided is the correct way.
> So I am thinking in what kind of scenario, people need this PPS feature?
> in my opinion, people will use PPS only when they want to limit the
> connections/transactions numbers. ( already have limit command to limit t=
he
> connections)
> So I think provide a simple PPS feature is good enough, and we can improv=
e
> it if someone complaint on this.
>
=E2=80=8Bpps has a strong reason to exist because it is a lot cheaper
than a dummynet pipe, and given its pur=E2=80=8Bpose is to police
traffic (icmp, dns requests, etc) which should not even
get close to the limit which is set, I think it is
a completely reasonable feature to have.
Given that the above code is the complete implementation
with the two parameters (burst and interval) there is no
reason not to use them, at least internally.
Then you could choose not to expose them as part of the
user interface (though since you are implementing a new
option from scratch, it is completely trivial to
parse 1, 2 or 3 arguments and set defaults for the others).
cheers
luigi
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