[OpenWrt-Devel] IPv6 firewall and Port Control Protocol (Was: Barrier Breaker 14.07-rc1)

Gui Iribarren gui at altermundi.net
Thu Jul 17 23:56:58 EDT 2014

On 17/07/14 21:59, Fernando Frediani wrote:
> Perfect and well said.
> Really don't see why people still think leaving firewalls opened is a
> good idea.

leaving *hosts* firewalls opened is a really bad idea. Agreed.

But openwrt doesn't run on hosts, it runs on network equipment
I.e. the building blocks of Internet.
Carriers don't block traffic,
ISP don't block traffic,
and back in the day, CPE equipment didn't block traffic either (think of
dialup, or dumb cablemodems which would simply act as a bridge)
"firewall" was a software installed in the computer connected to the

Then, with the ever increasing quantity of devices vs the evident
shortage of IPv4, people started to use NAT, or ISPs started to ship
CPEs that would do NAT, which made two-way transparent communication
I find it difficult to argue that NAT success was driven by a security
concern, rather than by IP scarcity. :P [1]

Fast-forward a few years, we have a new Internet Protocol being widely
deployed that solves the address scarcity, and thus makes NAT unnecessary.

Now CPEs can work again like transparent devices.

ps. RFCs that argue that NAT resulted in a *reduction in security*...

[0]: http://tools.ietf.org/rfc/rfc6092.txt , january/2011

  Security Considerations
   The IPv6 stateful filtering behavior described in this document is
   intended to be similar in function to the filtering behavior of
   commonly used IPv4/NAT gateways, which have been widely sold as a
   security tool for residential and small-office/home-office networks.
   As noted in the Security Considerations section of [RFC2993], the
   true impact of these tools may be a reduction in security.  It may be
   generally assumed that the impacts discussed in that document related
   to filtering (and not translation) are to be expected with the simple
   IPv6 security mechanisms described here.

   In particular, it is worth noting that stateful filters create the
   illusion of a security barrier, but without the managed intent of a
   firewall.  Appropriate security mechanisms implemented in the end
   nodes, in conjunction with the [RFC4864] local network protection
   methods, function without reliance on network layer hacks and
   transport filters that may change over time.  Also, defined security
   barriers assume that threats originate in the exterior, which may
   lead to practices that result in applications being fully exposed to
   interior attack and which therefore make breaches much easier.

[1]: http://tools.ietf.org/rfc/rfc2993.txt , november/2000,
      11. Summary
      NAT advantages - no item about security

> At the end it will bring more problems than solutions for those using
> OpenWRT and play against its good reputation.
> As mentioned before adjusting firewall for specific needs or using UPnP
> isn't the end of the world.
> Regards,
> Fernando
> On 18/07/2014 01:03, David Lang wrote:
>> I know that IPv6 designers pine for the "good old days" of the
>> Internet when no security was needed.
>> But the reality is that hackers and worms have shown that leaving
>> systems exposed to the Internet is just a Bad Idea.
>> As such, the idea that IPv6 would "restore" the "everyone can connect
>> to everyone on any port" of the early '80s was wishful thinking at best.
>> link-local addressing isn't a good idea, because the average home will
>> have three separate links (wired plus two bands of wireless), these
>> can get bridged together, but that causes problems as well.
>> There is no answer here that will satisfy everyone.
>> But do you really want to see the news stories about how anyone
>> running openwrt is vulnerable to $lastest_windows_exploit but people
>> running stock firmware aren't?
>> Yes, it would be ideal if every host was locked down so that it was
>> safe for them to be exposed.
>> But that's not the world we live in.
>> David Lang
>> On Wed, 16 Jul 2014, Lyme Marionette wrote:
>>> ----- Original Message -----
>>> On Wednesday, July 16, 2014 2:10:53 PM "Gui Iribarren"
>>> <gui at altermundi.net> wrote:
>>>> Benjamin is giving some great examples of real-world scenarios where
>>>> an
>>>> default-open firewall simplifies administration,
>>>> and where a default-closed firewall would be not only unnecessary
>>>> (provides no benefits), but would indeed complicate setting up
>>>> things.
>>> There have been many good arguments posted on this subject and to
>>> throw my opinion in, it a question of effort and expectations.
>>> I think everyone can agree that:
>>> -It takes equal effort to turn a firewall on, as it does to turn one
>>> off.
>>> -It takes equal effort to create a specific block list, as it does to
>>> create a specific allow list.
>>> -UPnP is not included by default for either the ipv4 or ipv6 stacks.
>>> I would also go further to suggest that:
>>> -Consistency is good, even if it consistent for superficial reasons.
>>> We know that, for NAT reasons, that the ipv4 stack by default blocks
>>> incoming connections:
>>> -Because it doesn't know by default where to route them.
>>> -ipv4 end-points have been traditionally insecure.
>>> The two ways to get around this (for gaming, etc):
>>> -Through setting firewall rules to route the traffic to an end-point.
>>> -Through the use of UPnP (which is used by most games to host, and
>>> gaming consoles).
>>> With the adoption of ipv6 there is the opportunity to change this
>>> behaviour such that instead of incoming traffic being restricted for
>>> technical reasons, that incoming traffic is routed to the correct
>>> end-point.
>>> However, that begs the questions:
>>> A) Is that consistent with what people would expect?
>>> B) Are ipv6 end-points secure by design?
>>> In regards to A, from the mindset of a non-technical user, would
>>> wager that the answer is 'no'. Even though there is a change in
>>> technology with ipv6, the ipv6 technology fulfills the same role as
>>> ipv4 and this could be seen as opposing direction between the two.
>>> This would likely catch many end-users by surprize unless they read
>>> the small print regarding this.
>>> As for B, given my view of software development, applications,
>>> networks, etc (I've been in the IT business for over 25 years now) I
>>> would wager that 80% of applications are secure, and that the 0ther
>>> 20% make the potential change in policy very risky.
>>> IMO, which others may disagree with, would be to include UPnP by
>>> default which would/should resolve most of the hosting issues.
>>> Thanks.
>>> _______________________________________________
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>>> https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-devel
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