the alleged evils of NAT, was Rate of growth on IPv6 not fast enough?

David Conrad drc at
Sat May 1 04:05:36 UTC 2010


On Apr 30, 2010, at 7:04 PM, Owen DeLong wrote:
> Ideally, in the vast majority of cases, resolv.conf is populated by dhcpv6 or it's successor.

:-).  I haven't been following the religious war against DHCPv6 -- is it now acceptable to get DNS information via DHCPv6? I note that MacOSX still doesn't appear to support DHCPv6. Does Win7?

> IPv6 also has the convenient concept of preferred and valid lifetimes on addresses facilitating a convenient overlap period while both prefixes still work, but, new flows should be universally originated from the specified prefix. 

I'm aware of this.  It would be interesting to see how many applications actually take advantage of this (rant about the socket API model deleted).

> There is a non-zero cost associated with renumbering.  However, it is much closer to zero than in IPv4.

I agree that it can or at least has the promise to be.

> There is also a non-zero cost to NAT.


> Unfortunately, the costs of NAT are more on the toxic polluter basis, where you must pay your own tab for renumbering. 

End users must pay the cost of renumbering in both cases.  With NAT, renumbering is done on the NAT box.  Without NAT, renumbering must be done within the entire network.  NAT can have an additional initial capital cost (although most CPE support NATv4 at no additional cost) and can have a potentially non-obvious additional opex cost associated with debugging network problems, application support, etc.  

In the end, it would be nice if it was a simple business decision.  In reality, I suspect most folks getting IPv6 prefixes from their ISP will follow the same model they use with IPv4 because that's what they know and it works for them.  Hopefully, we'll see.


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