interesting about OSX, NAT64 prefix discovery

Mikael Abrahamsson swmike at
Mon Oct 14 08:30:05 CEST 2013

Macbook running 10.8.5 with latest updates.

I am at the RIPE67 meeting, on their IPv6 only wifi. This has NAT64+DNS64 

I had an entry in my /etc/hosts with an IPv4 address only, and was SSHing 
to it. By some internal magic, OSX had discovered the NAT64 prefix and was 
using it by itself to connect to this "ipv4 only" host.

This caused great confiusion before I could figure out what was going on 
(didn't remember I had this hostname there), because when I was ssh:ing, 
it would first try the IPv4 address (using IPv4 LL, ie arp:ing directly on 
the link), and then it would try the IPv4 address mapped to the NAT64 
prefix, which I couldn't understand where it came from.

Well, I don't *know* this is what was happening, but I see no other 
mechanism that would explain the behaviour I was seeing. Anyone else seen 
this or know more?

Mikael Abrahamsson    email: swmike at

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