Problems with removing NAT from a network

Matthew Kaufman matthew at
Sun Jan 9 00:46:47 CST 2011

On 1/8/2011 3:16 AM, Leen Besselink wrote:
> Hello Mr. Kaufman,
> In the upcoming years, we will have no IPv6 in some places and badly
> performing IPv4 (CGN, etc.) with working IPv6 in others.
Right. So we're discussing just how "badly performing" the IPv4 can be 
and still be acceptable as "access to the IPv4 Internet for your customers".

I am arguing that CGN (NAT44 to get additional IPv4 to dual-stack) 
doesn't break nearly as much as NAT64/DNS64 does, and that in fact 
NAT64/DNS64 breaks *so much* that you probably can't/shouldn't sell it 
to your customers as "access to the IPv4 Internet".

Note that for a *very* long time... much longer than there will be new 
IPv4 addresses available... there will be a whole lot of places that 
have good IPv4 and no IPv6. (As you note above)

> If I was Skype I would make really sure that all my relay nodes and
> login servers have IPv6 with enough bandwidth or can easily upgrade the
> bandwidth where neede. And make sure atleast IPv6-client and
> IPv6-servers communication works everywhere where there is IPv6.
Clearly that would be needed to serve the IPv6-only users well.
> For your customers it is really easy. When Skype does not work, people
> will jump ship where they can and maybe use Google Talk or whatever.
Ah. But you're taking the bet that when Skype does not work on *your* 
network that provides IPv4 access via NAT64 people won't "jump ship" to 
a provider that uses CGN or even has enough native IPv4 addresses left 
> I suggest making sure you include both IPv4 and IPv6 addresses in your
> protocol, maybe it needs to be extended. So that the client at the other
> end can choose what IP-version to use. Or can try both. Maybe the
> login-server can help to decide for the client. But those login servers
> will need to have good IPv6 connectivity to be able to do so.
But none of that solves the problem of talking from an IPv6 client that 
has broken IPv4 access (NAT64) to a an IPv4 client that has no IPv6 access.

> I'm sorry if it sounds a bit like fear mongering, but to me it sounds
> like common sense that if a business is not prepared when the
> environment that business operates in changes and that business does not
> adapt to the changes in time that business might suffer.
But that's true of ISPs when they choose how to deal with the lack of 
additional IPv4 space but continued customer demand to reach the IPv4 
Internet, too, isn't it?

Matthew Kaufman

More information about the NANOG mailing list