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Date:      Tue, 18 Jun 2019 12:56:01 -0500
From:      Karl Denninger <karl@denninger.net>
To:        freebsd-questions@freebsd.org
Subject:   Re: IPFW redirect to another port?
Message-ID:  <be7edcf3-2ab5-2e0c-7caa-d44cbfe9e04c@denninger.net>
In-Reply-To: <20190618165028.83C662015F9118@ary.qy>
References:  <20190618165028.83C662015F9118@ary.qy>

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On 6/18/2019 11:50 AM, John Levine wrote:
> I would like to use ipfw to redirect incoming port 53 requests from a
> few IP addresses to a different port, so I can use a custom DNS server
> to answer them.  I can figure out how to redirect their traffic to,
> say, port 5553, but the responses come from 5553 which of course
> doesn't work.
>
> Any suggestions about how to adjust the port numbers going both ways?  =
It's
> fine if they screw up other traffic to those IPs.  TIA.
The easiest way to do this is likely with an in-kernel NAT entry with a=20
"redirect_port" stanza; that will "twist" packets going in both=20
directions.=C2=A0 The most-common use for this is to take something on th=
e=20
external interface (e.g. 1.2.3.4:8080) and direct it at an internal host =

on port 80 (e.g. 10.1.1.1:80); the "redirect_port" stanza allows for=20
both TCP and UDP redirection with both sides being translated.
--=20
-- Karl Denninger
/The Market-Ticker/
S/MIME Email accepted and preferred

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