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Date:      Wed, 13 Nov 2019 16:31:00 -0500
From:      Phil Staub <phil@staub.us>
To:        =?UTF-8?Q?Morgan_Wesstr=C3=B6m?= <freebsd-database@pp.dyndns.biz>
Cc:        freebsd-pf@freebsd.org
Subject:   Re: NAT for use with OpenVPN
Message-ID:  <CAMnCm8g8OHZdZnuC3qokQ643atK1VQ9DK4qKV_a2GN2Vw=ts=w@mail.gmail.com>
In-Reply-To: <5fce41df-37fb-fc8c-be80-f47dfd0d04ad@pp.dyndns.biz>
References:  <mailman.6.1573387200.62111.freebsd-pf@freebsd.org> <CAMnCm8gn3y7ai95%2BtkwdZs2qYndzQaNdpHev4ZdNLyd-bOY4iQ@mail.gmail.com> <0b13ae53-b211-ad2c-1447-225860f73d3a@pp.dyndns.biz> <CAMnCm8jZQi-UKm_-hF8WS0cofq0OWWP_d5No1AbOP8_KgQE5ZA@mail.gmail.com> <baa548e5-7dc3-05cf-0275-902d0193fc21@pp.dyndns.biz> <CAMnCm8iZ4iLJYOUFFpoTpF_=9xpG2=MN77xi%2BtGaSqumHeeqkQ@mail.gmail.com> <8ba7182d-8c4e-e10e-467b-6cf447490151@pp.dyndns.biz> <CAMnCm8gA_V1trdZtpidms54cmf4TL=R2BZ2MP52fJKrjndxtzA@mail.gmail.com> <fa9054ac-b22f-b873-0749-742b73100dba@pp.dyndns.biz> <CAMnCm8gN9aYgsJQYCuppGQ1M-YPwe1y7kaQCeEcDChrogsXj0w@mail.gmail.com> <b574e8e2-a921-99b8-2d2f-b3dc70341ce3@pp.dyndns.biz> <CAMnCm8gS40S27uOHYiKPp5E2hZhg=FknxTKxSsuH6vgOBD5Z9g@mail.gmail.com> <ef17181f-61b3-c2eb-9ebb-49e437ceea76@pp.dyndns.biz> <CAMnCm8hpTmww-pV%2BFbOcMJwk%2Bz1_bSs%2BcVJg5eu5zm84K8RPSA@mail.gmail.com> <cf52cc1b-c979-155c-604b-8918ac5fc2d6@pp.dyndns.biz> <CAMnCm8i46JOW-bGOutRyxUtJspeSkz4ZjfAQ=XGe_KtbeF387w@mail.gmail.com> <5fce41df-37fb-fc8c-be80-f47dfd0d04ad@pp.dyndns.biz>

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On Wed, Nov 13, 2019 at 4:13 PM Morgan Wesstr=C3=B6m <
freebsd-database@pp.dyndns.biz> wrote:

> > |iptables --table nat --append POSTROUTING --out-interface eth0 -j
> > MASQUERADE
>
> As I understand iptables, this is the normal/only way to provide NAT for
> any subnet.
>
> > ||One of the comments in another tutorial I was reading says that the
> > MASQUERADE rule is resource intensive, but if I understand it correctly=
,
> > the only alternative would be to put a specific rule in place for each
> > client. I don't think I want to do that
>
> I wonder what their reference was. When you're using iptables you only
> have MASQUERADE to chose from. Even my 20 year old Netgear RT-314 did
> NAT without problems...
>

See my follow up message. It's the SNAT directive. The tutorial I was
looking at was

https://www.karlrupp.net/en/computer/nat_tutorial

>
> > ||Comments?
>
> Well, I am concerned we couldn't identify what mechanism was responsible
> for the already working NAT for 192.168.1.0/24. We wouldn't want to end
> up with two competing mechanisms activated at the same time and the rule
> you added will provide NAT for 10.8.0.0/24 as well as 192.168.1.0/24 -
> the latter which was already working.
>

True enough.


> There should be init scripts on that router to start all services. Maybe
> they can give a clue on what's going on and how Netgear choses to
> activate their services.
>

This thing seems to have a very convoluted startup. Not at all like most
Linux systems I've seen. The file I found where they had added some rules
was definitely not where I expected it to be, and there are no MASQUERADE
commands in it.

>
> Whatever you do, just verify that the router's admin interface is not
> accessible from the Internet after you've added your rules!
>

Definitely. I assume the way to test that would be to attempt to access my
router from the outside the same way I would when I log in from the inside.

Phil


> /Morgan
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