Date: Wed, 29 Jul 2015 17:26:11 +0800 From: bycn82 <bycn82@gmail.com> To: Julian Elischer <julian@freebsd.org> Cc: freebsd-ipfw <freebsd-ipfw@freebsd.org> Subject: Re: keep-state and in-kernel NAT exposes local ip on external interface Message-ID: <CAC%2BJH2ybB_9W-okDbdvERRq=VE_9cAENj=rJDyky3OAAN--19Q@mail.gmail.com> In-Reply-To: <55B8833B.3030205@freebsd.org> References: <1435692039.18121.12.camel@yahoo.com> <5594395D.6050103@FreeBSD.org> <20150728150845.V17327@sola.nimnet.asn.au> <55B7DB52.7010504@FreeBSD.org> <55B8833B.3030205@freebsd.org>
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*Hi Julian,*
*So below are the rules in your example*
*5 skipto 10 from A to B*
*6 skipto 11 from any to any*
*10{action} from A to B keep-state*
*11{action} from C to D*
*If I remove the "skipto" rules they will become*
*10 {action} from A to B keep-state*
*11 {action} from C to D *
*Correct me if I was wrong, but in my opinion, the rule 5 and 10 are
almost the same, so I dont see the benefit by introducing the "skipto"
rulees. **IMHO, the "check-state" is to speed-up some selected packets, it
will slow-down all other unexpected packets at the same time.*
*Regards,*
*bycn82*
On 29 July 2015 at 15:39, Julian Elischer <julian@freebsd.org> wrote:
> On 7/29/15 3:43 AM, Lev Serebryakov wrote:
>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA512
>>
>> On 28.07.2015 08:30, Ian Smith wrote:
>>
>> I have global lack of any spare time (and all my FreeBSD activity is
>> only a hobby) for last ~2 months. I see the end of this unfortunate
>> state of affairs in near future and I remember about these examples.
>>
>>
>>> there are some simple examples of things this patch addresses..
> For example in the current code, the following (extemely simplified) set of
> rules will not do what you would think when you are working with a tcp
> session from A to B and another from C to D *which has previously been**
> **accepted with a keep-state at some other point in the ruleset*
>
>
> 10 {any action} from A to B keep-state
> 20 {any action} tcp from C to D
>
> because despite the fact that you are only triggering on a 'setup' packet
> for A to B, any rule
> that includes "keep-state" does a "check-state" implicitly.
> so the packet from C to D never gets past rule 10.
> the only way you can do this is to prefix rule 10 by something like
>
> 5 skipto 10 from A to B
> 6 skipto 11 from any to any
>
> to make sure packets that are not A to B do not hit the hidden
> 'check-state' .
>
> this is a very simple example and yes there are ways to get around it,
> but it complicates the ruleset and increases errors
>
> that reminds me I'd also like to be able to put a "not" at the
> front of the rule matching to negate the whole test but it doesn't seem to
> like that.
>
>
>
>
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