/96 prefix in ipv6/ipv4 mapping. The Why ?

Some one email me about the use of a /96 prefix in my ipv6v4 nat ( NAT 64 ) example. And here's the reason why, the  /96 prefix was created for the allowance of mapping  ipv4 32bit address into ipv6. If you think about it a /96 plus a /32 = 128 bits.

Here's the rfc  that explains some of this feature and mapping of ipv4 and ipv6 addres

http://www.ietf.org/rfc/rfc3056.txt

ipv6/ipv4 mapping becomes more of an issues as we start dealing with DNS64 and ipv6 enabled networks using name-lookup  resources to look up AAAA (  A   ) records, but having the return query massage with the direct ipv4-to-ipv6 mapping.

When ever we use NAT64, we need to be aware of the differences between the two;

-->

ipv4	ipv6
ttl	hop-limit
protocol field	next-header
dscp/tos	traffic  class
frag offset	frag-header

When  ever we map ipv4 to ipv6, the 32 bit address is always mapped with the lower 32bit  address embedded

e.g  ( using ipv4 address 10.0.0.1 and a 2001:179::/96 prefix )
10.0.0.1 =  A0:01 + /96 bit prefix    2001:179::10:0:0:1 or in hex format 2001:179::A0:01



 The above is  the proper way to map ipv4 to ipv6 address and using the /96 prefix

I hope this clears up  any confusion on way the /96 prefix.

Ken Felix
Freelance  Network & Security Engineer
kfelix at hyperfeed dot com