Groups > linux.debian.user > #200440

Re: Why does Debian allow all incoming traffic by default

From	Pascal Hambourg <pascal@plouf.fr.eu.org>
Newsgroups	linux.debian.user
Subject	Re: Why does Debian allow all incoming traffic by default
Date	2018-09-22 17:10 +0200
Message-ID	<wARHH-61D-1@gated-at.bofh.it> (permalink)
References	<wAjZo-39S-1@gated-at.bofh.it> <wABMB-57G-9@gated-at.bofh.it> <wAKGe-1MF-9@gated-at.bofh.it> <wALCh-2kl-1@gated-at.bofh.it> <wAO77-3Sp-5@gated-at.bofh.it>
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Le 22/09/2018 à 13:11, Joe a écrit :
> On Sat, 22 Sep 2018 10:38:52 +0200
> Pascal Hambourg <pascal@plouf.fr.eu.org> wrote:
> 
>> Le 22/09/2018 à 09:39, Joe a écrit :
>>>
>>> Two layers of NAT work just fine, for anything but IPSec.
>>
>> 1) Even one single layer of NAT can cause trouble with other
>> applications that IPSec : FTP, SIP...
> 
> Yes, but one can reasonably expect NAT hardware to also deal with
> tracking of multiple port/protocol communications. Pretty much the same
> basic code does both jobs, as well as stateful firewalling.

Each complex protocol requires specific handling by both NAT and 
connection tracking. You can always work around the lack of connection 
tracking support with static firewall rules (at the cost of weaker 
security), but you cannot always work around the lack of NAT support 
with static NAT rules.

>> 2) IPSec works through NAT, provided that you enable UDP
>> encapsulation aka NAT-T.
>>
> Yes, there's more to go wrong, though.

Like what ?

> IPSec is commonly used to
> provide pretty much fixed communication between organisations, so
> terminating it on the Internet interface rather than on an internal
> machine makes sense, as well as keeping it simple with just the public
> IP addresses.

IPSec is also commonly used by organisations for remote access by 
travelling employees.

> Other VPNs such as PPTP are more commonly used from
> internal workstations. PPTP will pass through two* layers of NAT at
> each end without special provision being made, apart from forwarding of
> course.

PPTP does require specific NAT support for the GRE protocol.
Use case : two clients of the same PPTP server share the same public IP 
address.
The server sends a GRE packet to the public IP address. How does the NAT 
device know which client the packet must be forwarded to ?

Thread

Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 05:10 +0200
  Re: Why does Debian allow all incoming traffic by default Roberto C. Sánchez <roberto@debian.org> - 2018-09-21 05:30 +0200
    Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 05:40 +0200
      Re: Why does Debian allow all incoming traffic by default Roberto C. Sánchez <roberto@debian.org> - 2018-09-21 05:50 +0200
        Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 07:10 +0200
        Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:40 +0200
      Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-21 19:10 +0200
        Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:40 +0200
          Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 20:00 +0200
            Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 20:10 +0200
              Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 21:40 +0200
          Re: Why does Debian allow all incoming traffic by default David Wright <deblis@lionunicorn.co.uk> - 2018-09-21 21:50 +0200
          Re: Why does Debian allow all incoming traffic by default mick crane <mick.crane@gmail.com> - 2018-09-23 01:10 +0200
            Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-23 20:00 +0200
              Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-23 23:00 +0200
                Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-24 00:00 +0200
        Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 09:40 +0200
          Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 11:20 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:00 +0200
              Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-22 13:40 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 17:00 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 20:20 +0200
                Re: Why does Debian allow all incoming traffic by default Richard Hector <richard@walnut.gen.nz> - 2018-09-24 05:20 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 05:30 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-24 09:10 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 11:00 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-24 11:40 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 14:20 +0200
                Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-22 20:30 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 22:20 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-22 22:40 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 23:20 +0200
                Re: Why does Debian allow all incoming traffic by default Simon Kengelbacher <simon.kengelbacher@mail.ch> - 2018-09-22 23:50 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-23 00:00 +0200
                Re: Why does Debian allow all incoming traffic by default Simon Kengelbacher <simon.kengelbacher@mail.ch> - 2018-09-23 00:20 +0200
                SSH X forwarding going awry (Was: Why does Debian allow all incoming  traffic by default) Étienne Mollier <etienne.mollier@mailoo.org> - 2018-09-23 11:40 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow all incoming traffic by default) Gene Heskett <gheskett@shentel.net> - 2018-09-23 16:10 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow  all incoming traffic by default) Joe <joe@jretrading.com> - 2018-09-23 23:00 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow all incoming traffic by default) Gene Heskett <gheskett@shentel.net> - 2018-09-24 04:50 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 21:00 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-23 00:00 +0200
            Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 21:00 +0200
              Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-24 21:30 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 15:50 +0200
                Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-26 17:10 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 19:30 +0200
          Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 15:50 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 16:50 +0200
        Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200
  Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-21 15:00 +0200
    Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 18:30 +0200
      Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 20:20 +0200
        Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 20:40 +0200
          Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 21:10 +0200
          Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 23:20 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 23:40 +0200
              Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 00:10 +0200
                Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 09:10 +0200
                Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 15:50 +0200
          Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 09:50 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 12:00 +0200
              Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:00 +0200
                Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 13:30 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-22 22:00 +0200
                Re: Why does Debian allow all incoming traffic by default Stefan Monnier <monnier@iro.umontreal.ca> - 2018-09-22 22:20 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 23:40 +0200
          Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-22 12:10 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 12:40 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:10 +0200
    netstat (was: Re: Why does Debian allow all incoming traffic by default) rhkramer@gmail.com - 2018-09-21 20:00 +0200
      Re: netstat Reco <recoverym4n@gmail.com> - 2018-09-21 20:20 +0200
        Re: netstat rhkramer@gmail.com - 2018-09-22 20:50 +0200
    Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200
      Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-24 21:30 +0200
        Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 15:50 +0200
  Re: Why does Debian allow all incoming traffic by default Pablo Álvarez Córdoba <pabloalvarezcordoba@protonmail.ch> - 2018-09-21 18:30 +0200
    Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:30 +0200
  Re: Why does Debian allow all incoming traffic by default songbird <songbird@anthive.com> - 2018-09-22 00:10 +0200
    Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-22 09:40 +0200
      Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 10:40 +0200
        Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-22 13:20 +0200
          Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 17:10 +0200
            Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-23 10:50 +0200
              Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-27 14:00 +0200
    Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200

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