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Date:      Sat, 3 Mar 2001 21:19:58 -0500
From:      Chris Johnson <cjohnson@palomine.net>
To:        Don Lewis <Don.Lewis@tsc.tdk.com>
Cc:        stable@FreeBSD.ORG
Subject:   Re: Did ipfw fwd just break?
Message-ID:  <20010303211958.A50525@palomine.net>
In-Reply-To: <200103040211.SAA24825@salsa.gv.tsc.tdk.com>; from Don.Lewis@tsc.tdk.com on Sat, Mar 03, 2001 at 06:11:58PM -0800
References:  <20010303203733.A49750@palomine.net> <200103040211.SAA24825@salsa.gv.tsc.tdk.com>

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On Sat, Mar 03, 2001 at 06:11:58PM -0800, Don Lewis wrote:
> On Mar 3,  8:37pm, Chris Johnson wrote:
> } Subject: Did ipfw fwd just break?
> }=20
> } --EeQfGwPcQSOJBaQU
> } Content-Type: text/plain; charset=3Dus-ascii
> } Content-Disposition: inline
> }=20
> } For a long time I've been running a transparent SMTP proxy on my firewa=
ll,
> } using this rule:
> }=20
> } ipfw fwd 127.0.0.1 tcp from any to any 25 in recv fxp0
> }=20
> } It's always worked just as I expected.
> }=20
> } I updated my system today (the previous update was on February 12), and=
 now,
> } even though "ipfw show" indicates that the above rule is matching, the
> } connection goes right through to its original destination (i.e. it's not
> } forwarded to 127.0.0.1) just as if the rule weren't there. Just prior to
> } rebooting the newly updated system, the SMTP connections were forwarded=
 to
> } 127.0.0.1, exactly according to plan.
>=20
> I can believe that it got broken by some changes to ip_input.c in the
> last few days that were intended to prevent outsiders from connecting
> to sockets bound to the loopback interface or an interface on the
> far side of the host that the administrator hoped were private.
>=20
> If you have rev 1.130.2.17 of ip_input.c, you should be able to disable
> this check by setting ths sysctl variable net.inet.ip.check_interface to
> 0.

Thanks! That's just the ticket.

Now, is it possible to protect myself from whatever evil check_interface is
supposed to protect me from, while still doing my transparent proxying? Or =
do I
have to choose one or the other?

Chris

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