The Payment Card Industry Data Security Standard (PCI DSS) applies to a couple of servers we manage. In those standards is section 1.3.8. It reads
Implement IP masquerading to prevent internal addresses from being translated and revealed on the Internet, using RFC 1918 address space. Use network address translation (NAT) technologies—for example, port address translation (PAT).
With the testing procedure listed as:
For the sample of firewall and router components, verify that NAT or other technology using RFC 1918 address space is used to restrict broadcast of IP addresses from the internal network to the Internet (IP masquerading).
Which is sound practice, really. But we're running into an issue here that may become more of an issue once IPv6 gets deployed more widely. We're a University that received it's netblock back when they were still passing out Class B networks to the likes of us (188.8.131.52/16 in case you care). IPv4 address starvation is not something we experience. Because of this, NAT and IP-Masq have very little presence on our network.
We also believe in firewalls. Just because the address of my workstation is not in an RFC 1918 netblock, doesn't mean you can get uninvited packets to me. This is even more the case for the servers that handle credit-card data.It is my belief that the intent of this particular standard-line is to prevent scouting of internal networks in the aid of directed penetration attempts. Another line that should probably be in this standard to support this, would be something similar to:
Implement separate DNS servers for public Internet and Internal usage, and prevent public Internet access to the internal DNS servers.Because the same DNS servers we use internally are the same ones that are in our Name Server records for the WWU.EDU domain, you can do a lot of recon of our internal networks from home. We don't allow zone transfers, of course, but enough googling around our various sites and reverse-IP-lookups will reveal the general structure of our network, such as which subnets contain most of our servers and which are behind the innermost firewalls.
This is a long way of saying that our IPv4 network functions a lot like the network envisioned when IPv6 was first ratified. Because of this, we're running into some problems with the PCI standards that IPv6 will probably run into as well.
Take the requirement to have the PCI-subject servers on an RFC1918 IP number. RFC1918 only applies to IPv4. IPv6's version of that is RFC4193, so the standard will have to be modified to mandate IPv6 numbers be on RFC4193 numbers. Therefore, for strictest compliance no PCI servers can move to pure IPv6. Servers that have both IPv4 and v6 numbers on them are an interesting case, where the v4 number may be an RFC1918 number, but the v6 number is NOT private. To my knowledge, the standards are unclear on this topic.
We had to create NAT gateways for our PCI servers, and create RFC1918 addresses for them just for PCI compliance. The NAT gateway is behind the innermost firewall. These are our only servers behind a NAT gateway of any kind.
In the beginning, IPv6 expressly did NOT have NAT; it was designed to get rid of NAT. However, in recent years the case for IPv6 NAT has been pressed, and there is movement to get something like that working. In my opinion, a lot of that push was to allow NAT to continue as an obscuration-gateway (or low-cost stateless 'firewall') between internal resources and external hostile actors. I strongly suspect that when the PCI DSS standard gets it IPv6 update, they will continue to mandate some form of IP Masquerade.