Requirements for IPv6 Firewalls

Seth Mos seth.mos at
Fri Apr 18 07:15:59 UTC 2014

On 18-4-2014 8:57, Matt Palmer wrote:
> On Thu, Apr 17, 2014 at 09:05:17PM -0500, Timothy Morizot wrote:
>> On Apr 17, 2014 7:52 PM, "Matthew Kaufman" <matthew at> wrote:
>>> While you're at it, the document can explain to admins who have been
>> burned, often more than once, by the pain of re-numbering internal services
>> at static addresses how IPv6 without NAT will magically solve this problem.
>> If you're worried about that issue, either get your own end user
>> assignment(s) from ARIN or use ULA internally and employ NAT-PT (prefix
>> translation) at the perimeter. That's not even a hard question.
> Why use NAT-PT in that instance?  Since IPv6 interfaces are happy running
> with multiple addresses, the machines can have their publically-accessable
> address and also their ULA address, with internal services binding to (and
> referring to, via DNS, et al) the ULA address; when you change providers,
> the publically-accessable address changes (whoopee!), but the internal
> service address doesn't.

Sounds good in theory, I tried it but it got ugly really fast. Before
you know it you have a layers of obfuscation, and even more work to get
it to work right. That's really not a good argument for the general IPv6

Then there's the issue of making not just hosts do address selection but
bringing that down to making applications choose address selection. As a
admin I really don't want to go there. I just want a central point where
I can pass, block or redirect.

Just keep it as simple as possible, but not simpler. A host with a IPv4
and GLA IPv6 address is as complicated as you want it.

The only case I see for NPt is for cheap multi wan where you have the
primary prefix on your "LAN" and perform NPt for that prefix when it
goes out the "3G" stick. Note that you would still need the same
(delegated) prefix size on both connections (e.g. /64, /56 or /48)

What is also nice is that in the case of NPt the firewall rules for both
"WAN" and "3G" can be the same as the destination address (after
performing NPt) is still the same. "Manageable".

Kind regards,


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