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Date:      Thu, 20 Jun 2019 11:55:54 +0200
From:      Jan Bramkamp <crest@rlwinm.de>
To:        freebsd-ipfw@freebsd.org
Subject:   Re: Look for an ipfw example using NPTv6
Message-ID:  <3629aeba-61ef-2cce-4971-c3a0ed973765@rlwinm.de>
In-Reply-To: <CAHu1Y72ezsU-f7WbYpH3h0Qcj1uttCsnQHqFue9F9xJmOtZd=w@mail.gmail.com>
References:  <CAHu1Y72ezsU-f7WbYpH3h0Qcj1uttCsnQHqFue9F9xJmOtZd=w@mail.gmail.com>

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On 18.06.19 22:00, Michael Sierchio wrote:
> I'm looking for a simple firewall example using nptv6 to translate
> link-local addresses to match the prefix assigned by my ISP.  I'll be using
> stateful rules and allowing only outbound traffic.
>
> If you have a snippet, I'l be grateful.  Thanks.
>
This sounds like you're trying to force IPv6 to behave like IPv4 with 
longer addresses and just replaced RFC1918 addresses with link local 
addresses. This isn't going to work because the differences are larger 
than just the addresses length. Link local addresses are just what the 
name says: they are local to the link. A link local address isn't even 
unique within a host e.g. you can have fe80::1234%em0 and fe80::1234%em1 
on the same host.

In theory you can get very close to NAT between global unicast addresses 
and private addresses by configuring NPTv6 between global unicast 
addresses and unique local addresses, but that would be a terrible 
choice. One of the great advantages of IPv6 it removes the address 
scarcity that forced NAT upon us. Each IPv6 device have as many global 
IPv6 unicast addresses as required.

Would you feel comfortable to describe the constrains shaping your 
design to us?




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