Aleksi Suhonen <Aleksi.Suhonen@tut.fi> Fri, 06 July 2012 07:41 UTC

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Date: Fri, 06 Jul 2012 10:41:30 +0300
From: Aleksi Suhonen <Aleksi.Suhonen@tut.fi>
Organization: Tampere University of Technology / Department of Communications Engineering
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Subject: draft-chen-v6ops-nat64-experience-02
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We've been running a NAT64/DNS64 setup at TREX Tampere Region Exchange 
for over a year now and I'd like to submit the following experience for 
your draft:

IPv6 Privacy Extensions are a big problem with stateless NAT64. A single 
device with priv exts enabled will use up several IPv4 addresses from 
the NAT64 pool. And since the IPv4 Internet is full of malware probing 
for vulnerabilities, the whole IPv4 address pool for the stateless NAT64 
will periodically get random traffic from the Internet.

Even if the priv ext addresses have expired, the network will generate 
an ICMPv6 unreachable message which will travel through the NAT64 device 
and thus refresh timers for the IPv4 mapping. Some firewalls will also 
generate TCP RST messages for such probes to non-existent IPv6 addresses.

In fact, our worst experience has been with an Apple iPad which was left 
alone in an IPv6 only WLAN which was using our DNS64 service. The iPad 
thought that the WLAN was broken because it only got an IPv6 address and 
no DHCPv4 response. It had time to send some packets using IPv6 through 
the NAT64 which created the mapping. Then it reset its WLAN and tried to 
associate with the same SSID again. Every time it created a new privacy 
extension based IPv6 address and a new mapping in the stateless NAT64 

Within an hour, all the IPv4 addresses in the pool for our NAT64 were 
registered to this one device.

It would be my recommendation that there was either a Router 
Advertisement Flags Option for "do not use privacy extensions here" and 
that this was used in all setups that use DNS64 name servers, or that 
all such setups should use Managed Address Configuration aka DHCPv6 
address configuration.

	Aleksi Suhonen, Researcher
	Department of Communications Engineering
	Tampere University of Technology