RE: IPv4 flag day

[Gary Sparkes via NANOG <nanog () lists nanog org>]

I can't imagine any case in where the ability to arbitrarily punch through your firewall (as an attacker) once I have 
any kind of foothold is a good feature. 

It's explicitly one reason why I highly dislike 1:many NAT, having been party to cleanup of attacks where such 
technique was leveraged. 

-----Original Message-----
From: William Herrin via NANOG <nanog () lists nanog org> 
Sent: Thursday, June 18, 2026 5:06 AM
To: North American Network Operators Group <nanog () lists nanog org>
Cc: William Herrin <bill () herrin us>
Subject: Re: IPv4 flag day

On Wed, Jun 17, 2026 at 10:39 AM Douglas Fischer via NANOG <nanog () lists nanog org> wrote:
> NAT is cancer!
> NAT in IPv6 is spreading cancer cells to all the organs of a new, 
> healthy body.

Hi Douglas,

Hate on it all you want, 1:many NAT renders my internal network not just inaccessible from the Internet but 
inaddressible as well. That's a feature not a bug. It's a feature I want for some of my subnets.
When I get around to deploying IPv6 on those subnets it's a feature I will use. You don't have to like it. It's not 
your network.

Regards,
Bill Herrin

--
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