[Asrg] For DNSBLs, embedded IPv4 in IPv6

[Daniel Feenberg]

On Mon, 4 Aug 2008, Frank Ellermann wrote:

> John Levine wrote:
>
>> Someone pointed out that in some popular dual stack systems,
>> connections from IPv4 addresses appear as IPv6 addresses
>> in :FFFF:0000:0000/96

Could someone explain why a DNSBL needs to return IPV6 addresses? Even 
assuming one wants to create a DNSBL that lists IPV6 addresses (which I 
don't think would be worthwhile*) the only place the V6 address appears is 
in the query hostname character string - the DNSBL reply only needs a 
handfull of values, which 127.0.0.X supplies without stress. The replies 
are never used as addresses. Are we worried that a DNSBL client 
nameservice library wouldn't support IPV4 addresses? That seems 
far-fetched. What am I missing?

Daniel Feenberg

>
> Yes, that is what I meant when I mentioned RFC 4408, (ab)using
> ::FFFF:127.0.0.2 as an "obvious" test entry.  Another proposal
> in the meeting was to use one of the IPv6 example addresses
> for this purpose.  But I can't remember the example addresses
> without my 4408 cheat sheet, an obvious entry would be better.
>
>> The immediate question is whether to add a sentence or two
>> to the DNSBL spec saying that if you have a DNSBL listing
>> both v4 and v6 addresses, and you list a v4 address, you
>> SHOULD or MUST also list the corresponding embedded v6
>
> No.  It is the job of the clients to get this right, they are
> supposed to ask for the IPv4 form of these addresses.  With
> ::FFFF:127.0.0.2 as a possible *exception* for test purposes.
>
> Frank
>
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